Handbook of Stable Isotope Analytical Techniques [Vol II] 978-0-444-51115-7

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H ANDBOOK OF S TABLE I SOTOPE A NALYTICAL T ECHNIQUES

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H ANDBOOK OF S TABLE I SOTOPE A NALYTICAL T ECHNIQUES VOLUME 2

PIER A. DE GROOT Editor Delta Isotopes Consultancy, Pastoor Moorkensstraat 16, 2400 Mol-Achterbos, Belgium ( present address)

Amsterdam • Boston • Heidelberg • London • New York • Oxford Paris • San Diego • San Francisco • Singapore • Sydney • Tokyo

Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, The Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK First edition 2009 Copyright  2009 Elsevier B.V. All rights reserved No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the publisher Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone (+44) (0) 1865 843830; fax (+44) (0) 1865 853333; email: [email protected]. Alternatively you can submit your request online by visiting the Elsevier web site at http://elsevier.com/locate/permissions, and selecting Obtaining permission to use Elsevier material Notice No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. Because of rapid advances in the medical sciences, in particular, independent verification of diagnoses and drug dosages should be made British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress For information on all Elsevier publications visit our web site at books.elsevier.com Printed and bound in the Hungary 08 09 10 10 9 8 7 6 5 4 3 2 1 ISBN: 978-0-444-51115-7

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CONTENTS

VOLUME II (author: Pier A. de Groot1)

Descriptions and Diagrams of Stable Isotope Analytical Techniques – An Encyclopedic Overview

ix

PART 3 1

Hydrogen 1-0 1-1 1-2 1-3 1-4 1-5

1 1 2 25 166 213 214

2

Lithium

225

3

Boron

227

4

Carbon

229

4-1 4-2 4-3 4-4 4-5

229 270 271 272

4-6 4-7 4-8

5

1

Introduction Water-Sampling Techniques Waters from Different Sources – Analytical Methods Organic Compounds Hydrogen Absorbed in Metal Labeled Water Methods

Organic Materials Gas Compounds Compounds from Water Compounds in Rock and Minerals Carbon (13C/12C) and Oxygen (18O/16O) Isotopes in Carbonate Rock and Minerals Graphite and Diamond Cyanides SiC (Moissanite) and TiC

273 323 327 328

Nitrogen

331

5-1 5-2 5-3

331 342 404

Nitrate, Nitrite, Ammonium and Cyanide Organic Materials Gaseous Compounds

Guest co-authorship of a section in Chapter 4-5: H. Le Q. Stuart-Williams & Pier A. de Groot; Guest authorship of Section 12-0.2.4.1 by Frank J. Stadermann. Guest authorship of Section 12-0.2.5.1 by Isaac B. Brenner. Guest co-authorship in a section in Chapter 17 by Mayer, Krouse & De Groot.

vi

6

7 8

Contents

Oxygen

405

6-1 6-2 6-3 6-4 6-5 6-6 6-7 6-8 6-9

405 453 516 570 580 581 582 587 589

Silicate Minerals, Oxides and Rock Samples Waters From Different Sources Organic Materials Sulfates Phosphates Carbonate Rock and Minerals Nitrates Metal Oxides 17 O – A Review on D17O Determination Methods S.S. Assonov & Pier A. de Groot

Silicium

619

Sulfur

621

8-0 8-1 8-2 8-3 8-4 8-5 8-6

Introduction Sulfides Elemental Sulfur Sulfates Complex Organic Materials and Organic Compounds Sulfur in Metals D33S and D36S: Mass Independent Fractionation

621 625 667 671 695 712 717

9

Chlorine

721

10

Selenium

723

11

Bromine

741

12

Mg, K, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn, Ga, Ge

743

12-0 12-1 12-2 12-3 12-4 12-5 12-6 12-7 12-8 12-9 12-10 12-11 12-12

743 764 774 780 814 819 820 826 845 849 859 875 877

Introduction Magnesium (Mg) Potassium (K) Calcium (Ca) Titanium (Ti) Vanadium (V) Chromium (Cr) Iron (Fe) Nickel (Ni) Copper (Cu) Zinc (Zn) Gallium (Ga) Germanium (Ge)

vii

Contents

13

14

Whole Rock, Soil and Sediment Analytical Techniques and Stepped Heating Methods

881

13-1 13-2 13-3

881 905 928

Whole Rock Analytical Techniques Soil and Sediment Analytical Techniques Stepped Heating Methods

Fluids and Gases from Inclusions or Dissolved in Rocks or Glasses (H, C, N, O Isotopes)

929

15

Compounds in Water Reservoirs

935

16

Atmospheric – Tropospheric – Stratospheric Compounds

957

17

Non-Atmospheric Natural Gases

989

18

Absolute Stable Isotope Measurement

1003

19

Mass Spectrometer Correction and Calibration Procedures

1007

20

Isotope Separation Methods

1025

Appendix A

List of Stable Isotopes and their Relative Abundance in Nature

1033

Chemicals Commonly used for Stable Isotope Analytical Preparations

1035

Appendix C

Vacuum Technology and Related Matters

1043

Appendix D

List of Theses Including Stable Isotope Studies

1087

Appendix E

Handbooks on Stable Isotope Matters

1105

Appendix B

Corrections and Additions to Volume I

1113

References

1123

Subject Index

1323

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D ESCRIPTIONS AND D IAGRAMS OF S TABLE I SOTOPE A NALYTICAL T ECHNIQUES – A N E NCYCLOPEDIC O VERVIEW

Pier A. de Groot Delta Isotopes Consultancy, Pastoor Moorkensstraat 16, 2400 Mol, Belgium e-mail: [email protected] with: H. Le Q. Stuart-Williams & P.A. de Groot contributing with section: ‘‘Discussion on properties of the phosphoric acid and its reaction with carbonates’’ – part of Chapter 4-5.1.5 with S. Assonov & P.A. de Groot, authors of Chapter 6-9: ‘‘A review on D17O determination methods’’ with: F.J. Stadermann contributing with section: ‘‘NanoSIMS – A brief description’’ – Chapter 12-0.2.4.1 with: I. B. Brenner contributing with section: ‘‘Inductively coupled plasma mass spectrometry (ICP-MS), Collision cells’’ – Chapter 12-0.2.5.1 with B. Mayer & H.R. Krouse contributing to section: ‘‘Sampling of H2S from natural gas’’ – part of Chapter 17

INTRODUCTION The honor for the creation of this two-volume book series on stable isotope analytical techniques must be given to James O’Neill. At the very start of this project, I did not realize that he, together with Zachary Sharp, had begun writing a book on a very similar subject. Originally, James O’Neill and Zachary Sharp were among the first authors I invited to write a chapter for my book series. It was in this way that I discovered about their own book project, which already had been in progress for some time. It was Zachary Sharp in particular who convinced and motivated me, supported by James O’Neill, to continue my project, after he recognized that the books I had in mind had a different approach and aimed at a far larger range of elements (isotopes) than their own. The prospective publication by James O’Neil and Zachary Sharp will have the form of a textbook and is concentrated more on a purely geochemical field. I am grateful for their ‘open-minded attitude’. At the start, the aim of these books was to concentrate on stable isotope analytical methods of purely geochemical interest, but very soon it became clear that it was not easy to draw a line between purely geochemical methods with geological applications and methods used in other fields of science. Considering the interest isotope chemists working in other ix

x

Descriptions and Diagrams of Stable Isotope Analytical Techniques – An Encyclopedic Overview

disciplines could have in a handbook in analytical techniques, I decided to extend the contents of these books, and to include a wide range of other disciplines, where stable isotope analysis is used for different purposes. Disciplines of interest besides geochemistry are anthropology, archaeology, agronomy, atmospheric science, biology, bio(geo)chemistry, climatology, drug detection methodology, ecology, environmentology, food science or alimentology (e.g. detection of adulteration), forensic science, hydrology, marine science, medical science, metallurgy, meteoritic science, metrology nutrition studies, palaeontology, petrochemistry, pharmacology, planetary science and toxicology. The range of elements chosen is purely arbitrary but dependent on the choice of the invited authors. Because new methods were actually developed for Br isotope analysis, by analogy with Cl isotope methods, I decided the element of Br to be the upper limit for these books. This also considerably extended the range of basic techniques. For instance, stable isotope analysis of elements such as Li, B, Mg, Si, K, Ca, Ti, Cr, Fe, Ni, Cu, Zn, Ga, Ge and to some extent Se concentrated historically more on solid source mass spectrometry (MS) rather than gas source MS. Other tools for isotope measurement cross this classical boundary between ‘solid source MS and gas source MS’, such as secondary ionization MS (SIMS), inductively coupled plasma MS (ICP-MS), laser-related MS systems, fast atom bombardment MS (FAB-MS) or nuclear activation analysis (NAA) techniques. Far less common techniques for stable isotope analysis, such as glow discharge MS (GDMS), accelerator MS (AMS) and some forms of optical spectrometry, are developed and some already are commonly used, while others are at different stages of development. For example, optical analytical method was developed for gas samples as a faster but less precise method, parallel with the MS technique. Stable isotope analytical methods were developed soon after the discovery of the existence of isotopes. For example, in 1934 there was the discovery of deuterium by Harold Urey, for which he received the Nobel prize. Early techniques were based on the determination of isotopic ratios by densimetric gravity, electric resistivity and pycnometry. The development of a usable mass spectrometer, by Nier, and improved by McKinney and coworkers in the late 1940s to early 1950s, gave an important impulse for the use of stable isotope techniques in scientific studies. These early methods were generally complicated, time-consuming procedures and had relatively low precision and accuracy. First improvements were on precision of methods, and soon attempts were made to simplify preparation procedures. In early methods sample size was comparatively large, in the order of a few to 10s or 100s of milligrams. Decrease of sample size was another aim, while improving analytical methods. Accuracy of methods is controlled by certified standard or reference materials. Standardization of techniques and correct calibration methods are an important concern and need continuous attention to avoid comparision of isotopic values based on different or badly calibrated scales. Reduction of sample size was made possible first by use of so-called ‘static mass spectrometer’ with a single inlet, thus avoiding the continuous pumping of samples while not being actively measured and basically reducing the needed gas volume by half. This technique is still in use at present, for example in stepped heating procedures or in fluid inclusion analysis techniques in geological, geochemical, meteoritic or planetary studies. The development of secondary ionization mass spectrometry (SIMS) and laser techniques introduced the possibility of analyzing in situ for specific type of samples. The firstgeneration SIMS was limited in the elements on which stable isotopes could be measured

Descriptions and Diagrams of Stable Isotope Analytical Techniques – An Encyclopedic Overview

xi

using low mass resolution characteristics and precision was comparatively low. Highresolution SIMS has recently been developed (e.g. most recently the NanoSIMS), increasing the type of materials (including organic materials) and the number of isotopes which can be measured, and with improved precision compared with the first-generation machines. The introduction of laser technology, after the pioneering work by Ian Franchi, Douglas Rumble and Zachary Sharp for stable isotope measurements, decreased the sample size considerably. Techniques for analyzing powered or grain size samples or analyzing on a microscopic scale in an in situ mode are available with their own specific characteristics and limitations. Single grain or spot analysis inside grains is made possible with the laser of the SIMS techniques. First laser types used were infrared (IR) Nd:YAG and Co2 lasers. Newer developments are with ultraviolet (UV) laser such as excimer lasers, quadrpoled Nd-YAG lasers, Ar-F or KR-F2-Ne or Xe-Cl gas mixture lasers and double-frequency Cu vapor lasers. The development for measuring organic, fluid or solid samples is moving in a different way, into on-line systems [originally a converted elemental analyser (EA) was used] with oxidizing, reducing or pyrolyses reactors, eventually in a combined order depending on the sample material and the gas of interest for isotopic measurement, and with application of a carrier gas (generally He, seldomly H2 or N2 are considered; Ar may introduce problems in the ion source of a MS by sputtering effects) in a so-called continuous flow (CF) system to transport reaction gases through the system. The carrier gas may contain O2 for oxidation purpose in combustion (oxidizing) systems. Addition of gas chromatographs (GC’s) for separation or purification of sample materials and/or for purification of effluent gases after reaction in the EA section of these on-line systems became a common feature. The advantage of such techniques is the very small sample size needed, the high number of samples that can be analyzed in short time periods compared with classical methods, the possibility of automation of these systems, reducing labor intensity (and thus costs) for analyzing and the option to combine the measurement of different effluent gases for different isotopic ratios in consecutive way. Moreover, with application of CF-IRMS techniques there is no need for vacuum conditions, as was the case in precursory techniques. Increasingly, specially designed EA’s are used in on-line systems for analysis of organic materials and fluids. New developments also include inorganic materials such as phosphates, sulphates and nitrates for oxygen, sulphur and/or nitrogen isotopes. Few years ago, also a LC-IRMS was in which introduced, also organic compounds are oxidized while being dissolved in water. The oxidation products (e.g. CO2) are separated from the solvent, dried and carried by a He flow into a mass spectrometer for isotopic measurement. Automation, as mentioned earlier, is another trend in analytical techniques. A large group of materials are suitable for such automated systems (e.g. organic materials, carbonates, water or fluid samples) while other materials are not suitable (e.g. rock or mineral samples for O and H isotope analysis, including fluorination systems). Another trend is to combine measurement of several isotopes in a sample in an on-line system. Organic matter is suitable for such an approach, and combinations of some of H, O, C, S and N isotopes can be applied. This places some constraints on the MS side in such systems, where an MS must be able to jump from one m/z ratio to another quickly and to handle the measured peaks for samples and references, including background and other corrections by advanced computer automation.

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Descriptions and Diagrams of Stable Isotope Analytical Techniques – An Encyclopedic Overview

In the fast development of laser technology, (tunable) diode lasers must be mentioned for possible application on a number of materials by optical spectroscopic methods as a highly probable technique in the future. Actually there are a small number of specialized optical spectrometers available on the market for stable isotope analysis, and development of other optical spectrometers in (near?) future is expected. Other analytical techniques and tools have been developed, but details of all these developments are not given here in this introduction. As presented in the foregoing sections, the modern tendency is to analyze smaller samples (including in situ analysis), preferably for a major part automated, and faster analysis per sample. Analysis of a number of different isotopic ratios on the same sample, generally in a sequential way, are applied either on separated phases in effluent gases produced from samples in reactors, or by sequential analysis of separated sample compounds, or by subsequent handling of the same sample with different treatments (e.g. gas equilibration methods). This handbook consists of two volumes. The first, edited volume contains two parts: Part 1 includes contributions presenting ‘subjective’ reviews on analytical techniques for specific stable isotopes or materials, reviews on stable isotope analysis by selected machines and descriptions of specialized and novel methods in stable isotope analytical techniques. Readers are guided to modern analytical techniques and are advised which techniques are the best to use of specific materials or conditions. Part 2 includes matters that are not strictly confined to analytical techniques themselves but related to analysis of stable isotopes, such as views on the development of mass spectrometers and ion source stability, matters concerning isotopic scales, standards and reference materials, calibration and correction matters, a review on experimental isotopic fractionation determination and directives for setting up a laboratory. Appendices present the Internet-based stable isotope discussion list named ‘isogeochem list’, the Internet-based stable isotope fractionation calculator and information on suppliers of stable isotope reference materials. The second volume, consisting of Part 3, aims to present an encyclopedic overview of stable isotope analytical techniques in an ‘objective’ way. The chapters in this volume are intended to be complementary to the chapters in the first volume. In the second volume, analytical techniques from historical times up to the most recent developments are presented as a classical order of elements. Short descriptions of methods and diagrams of analytical devices are presented. Many classical techniques, of which several were never used in an operational form or became obsolete or forgotten, are included. They also may improve the understanding of the development of analytical techniques which are used in preference today. Much of the experience from the old technology can be useful in applying to or in constructing modern analytical systems. The complete Handbook, including Volume I and Volume II, is dedicated to Simon M.F. Sheppard. A dedication is included in the introduction section of Volume I, at pages vii–ix.

Introduction to Volume II, Part 3 This Volume II, Part 3 presents as many different techniques for stable isotope analysis as traceable in literature, supplemented by personal experience and communications, and by information supplied in discussions on Isogeochem list (see Volume I, Part 2, Appendix A) on

Descriptions and Diagrams of Stable Isotope Analytical Techniques – An Encyclopedic Overview

xiii

the Internet. The book volumes are limited to analytical techniques for stable isotopes of the first 35 elements in the periodic table, excluding noble gases (He, Ne, Ar) and elements with one stable isotope (Be, F, Na, Al, P, Sc, V, Mn, Co, As). The aim is to provide a guide to historical and modern laboratory procedures for the stable isotope analysts. The descriptions basically are short, while references for further reading are given where appropriate. Diagrams of devices, such as vacuum systems and directly related equipment, are given with the descriptions supporting a visual explanation of the methods. The diagrams can be used directly to build stable isotope extraction devices or may form a base for own designs. Nobody ever can claim to give an absolute complete review of all techniques that are presented for the stable isotope analysis, mainly during the last 70 years. This presentation is an attempt to reach a high percentage coverage of these techniques, and if any technique is overlooked, I like to apologize to anybody involved with that specific technique not presented here. Unfortunately, in this edition of my books, I have to compromise with the contents. Some chapters are completed at a more advanced stage than others. The author reasoned that it is more important to present this overview and the collected material at this stage to the stable isotope community, rather than wait longer for a more complete presentation. I made the decision to carry on this project after publication of these books, by adding material I still was not able to include or which is newly published. The question how to present such upgrades to the stable isotope analytical community is not yet settled, but hopefully can be done in a second edition of this handbook in future. In different laboratories, I have experienced different philosophies for approach of stable isotope analytical techniques. The two main philosophies basically are 1. In an analytical extraction system, all procedures eventually causing fractionation should be avoided, or at least controlled if unavoidable, even if not causing detectable fractionation, and 2. Only a procedure or operating step leading to detectable fractionation should be avoided or controlled; if no fractionation is detected, the procedure or operating step can be followed. Although both philosophies have a valid reasoning, I prefer philosophy (1), in avoiding all possible steps which might cause fractionation, even if very small and apparently undetectable. Accumulation of very small fractionations may cause deviation of the correct value (lowering of accuracy) in the end and may affect reproducibility (decrease in precision). This also can be seen as a ‘playing safe’ approach. The statement made some years ago by J. Horita on the Isogeochem list, supported by B. Fifer: ‘Consistency in any analytical procedure for stable isotope analysis is important. Any change should be referenced by standard measurements’, is an important consideration on accuracy and precision (repeatability) in procedures for stable isotope analytical systems. Many, if not all, of the isotope chemists and technicians will support this statement. I remember this rule was strongly stressed by my tutor Simon Sheppard, to whom these books are dedicated (see Introduction part of Volume I ), to assure a correct operation of the analytical devices – not without success. Wright & Hoering (1989) gave three important requirements for proper stable isotope analysis, in their case for geological materials, but valid in a more general sense too: 1. All steps in a preparation procedure must be quantitative to avoid isotope fractionation due to incomplete yield, or else a reproducible fractionation must be corrected for in the result;

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Descriptions and Diagrams of Stable Isotope Analytical Techniques – An Encyclopedic Overview

2. There must be no addition of external material, by contamination, memory effects or isotopic exchange, to the specific element of interest during the analytical procedure; 3. The final product to be measured on the mass spectrometer must be free of spectral contaminations. I take the opportunity here to ask stable isotope scientists and technicians from any discipline to sent me new material, or material not included in this book, considering analytical devices or procedures (to be) published in magazines, in books or in reports. If sometime there will be an upgrade of this book, it will be very convenient for me if I am well informed about new developments. Additionally, I like to invite everybody to inform me about any ‘shortcomings’ detected in my books, and to fill the ‘gap’ by sending me the appropriate material. Although I dislike to give a disclaimer type of statement, I state here that I do not take responsibility for accidents or damage caused by use or misuse of the presented material in this Part 3 of my books in any possible form. Care is taken to present devices and procedures in the safest and most controlled way. Review of material presented in the book hopefully improve prevention from mistakes or wrongly presented concepts, but nevertheless mistakes cannot be excluded completely. Any calamities in laboratories, caused by uncontrolled use, inexperienced use, negligence or mistakes, should be carefully avoided, and external factors, such as electric power failure, instability of electric currents, cooling water supply discontinuity and other sorts of ‘uncontrollable’ processes, should be prepared for, for instance by application of uninterrupted power supply for electricity or closed water cooling systems that are not dependent on the main water supply; the latter is more ‘environmental friendly’ by using less water. UCP applications also can be used in combination of electric supply stabilization, which forms another major consideration, especially if tools strongly sensitive to such a factor, like mass spectrometers, are involved. I like to conclude this introduction by quoting a statement by Etienne Roth (in his review publication, 1997): It may be surprising that, in view of the many areas where decisive contributions have been made by employing stable isotope techniques, these are still principally tools in the hands of specialists. And it is not patent that the fact that stable isotope work is a key that opens doors that remain closed to radioactive tracer applications is well recognized.

Trademarks – In this Volume II, Part 3, trademarks and registered names or products are not marked with the common symbols  and  in the text. No preference is given in this Volume II, Part 3 to any company or specific product such as are named in the text. Naming a company or product only relates to those as given in the reference given in that specific publication or document, and does not imply that no other brands or products can be used. Often, such a given name relates to the experience of a specific laboratory and nothing else. Figures and Tables – In this Volume II of the handbook, a large number of figures and tables is included. Most of these figures and tables were redrawn or redesigned after the original versions as they were published in literature. In a few cases figures were scanned and reworked. I have carefully included reference to all original sources, i.e. to the authors of this material and to the publisher (magazine or book) in question. In no case I tried to show these figures and tables as if they were my own or were my property. Hereby I like to thank all authors and publishers for their understanding.

Descriptions and Diagrams of Stable Isotope Analytical Techniques – An Encyclopedic Overview

xv

Acknowledgment My gratitude goes to, in alphabetic order, Anne-Marie Aucour, Damian Axente, Evgeni Barkan, Roland Bol, Robert Clayton, Tyler Coplen, Stephen Crowley, John de Laeter, Paul Dijkstra, Irving Friedman, Brian Fry, Jean-Pierre Girard, Andrea Grottoli, Stanislaw Halas, Chris Harris, Thomas Johnson, Pieter Kleingeld, Stephen Macko, Bernhard Mayer, Franck Poitrasson, Kinga Re´ve´sz, Olivier Rouxel, Akira Sasaki, Arndt Schimmelmann, Dale Schoeller, Alex Sessions, Siep Talma, Mark Thiemens, Leonard Wassenaar, Roland Werner and Klaas Westerterp for their careful review of different parts of Volume II. Their corrections, comments and suggestions improved the contents of Volume II considerably. All others who were helpful during the preparation of my books are thanked here too. Mentioning everybody personally would give a too long list, and I apologize to all of them for not being mentioned in person. Moreover, I do not want to make any difference between those who did a lot to support me and others who might have added a small fraction. All were very useful to me and were highly appreciated.

G ENERAL D EFINITIONS AND E QUATIONS Isotopic values are usually presented in the delta notation and fractionations or separation factors in the alpha notation: A ¼



 RA  1  103 Rstd

and

AB ¼

RA RB

[I.1]

with  in per mil (‰), A and B for different phases and std for standard. R is the ratio of different isotopes of a specific element: e.g. D/H, 7Li/6Li, 11B/10B, 13C/12C, 18O/16O, 34 32 S/ S, 37Cl/35Cl, and  is the fractionation factor between phase A and B. Craig (1957) noticed that the isotopic ratio R is used both for isotope ratios (e.g. 18 O/16O) and for molecular mass ratios as measured in the MS, giving the example of oxygen: 18O16O/16O16O ratio. A similar reasoning is valid for HD/H2 ratios. Relationship between  and  can be expressed as 103 ln AB  DAB ¼ A  B

or

AB ¼

A  103 B  103

[I.2]

If 17O is considered in terrestrial or extraterrestrial samples, a terrestrial fractionation line can be defined as (see: Clayton et al., 1991) 17 O ¼ 0:5218 O while for meteoritic samples, the excess in

17

[I.3]

O can be defined as

D17 O ¼ 17 O  0:5218 O

[I.4]

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Descriptions and Diagrams of Stable Isotope Analytical Techniques – An Encyclopedic Overview

No unique way exists to assign an excess or deficiency to any particular isotope; it may be useful to calculate a 16O excess, defined by the equation (Clayton & Mayeda, 1983; Clayton et al., 1991) 0:52 18 1  O 17 O [I.5] 1  0:52 1  0:52 In Chapter 6-9 this matter is discussed in detail. Recently, the IUPAC Commission advised (publication under review) to omit ‘x 1000’ from the delta equation [I.1], because this is the mathematical correct notation and conform the notation as is followed by SI (Syste`me International, or International System). This leads in a mathematical notation in the form of: 0.00x instead of x‰, while both represent ‘per mil’ values. The equation [I.1] transfers into A ¼

RA 1 Rstd

[I.6]

Note that values obtained with this equation [I.6] are not followed by the usual ‰ sign! A very clear relation between the equations [I.1] and [I.6] is given in Coplen et al. (2002). In studies on atmospheric, tropospheric or stratospheric (trace) gases, a very high ‘precision’ is required for a significant interpretation of the isotopic values. In such studies, the term per meg can be used (e.g. Abe & Yoshida, 2003; Barkan & Luz, 2003), where 1 per meg ¼ 1=1000‰

[I.7]

For elements showing small isotopic fractionation (e.g. transition metals), an ‘e’ notation was introduced (e.g. Belshaw et al. 2000; Graham et al., 2004; Matthews et al., 2004). The e is defined by the equation  x y  ð M= M Þ sample x " M¼ x y  1  104 [I.8] ð M= M Þ standard where M is an element (generally a metal) and x and y are the mass numbers of a specific isotope of element M, with x 6¼ y. Recently the the IUPAC Commission advised (publication under review) the use of  instead of ". Other ways of reporting isotopic signatures are in atom% (= abundance), mostly used for tracer study results, or atom% excess (APE), generally used by clinical researchers. The atom% is an absolute measurement of the atoms of a specific isotope in 100 atoms of the element, as can be expressed for 13C (Barrie et al., 1989): 13

Cabundance ¼ 100ð13 CÞ=ð12 C þ 13 C þ 14 CÞðatom% 13 CÞ

[I.9]

The atom% excess or APE measures the abundance of a specific isotope above a specified background level. For example, in medical applications of stable isotopes, a sample is collected from a patient before the tracer is administered. Its atom% value is then subtracted from those of the enriched (tracer involved) samples to give APE (Barrie et al., 1989). Isotope effect is the name given to any change of physical or chemical property induced by the substitution of one isotope for another, but leaving out differences in nuclear properties. Effects can be equilibrium, kinetic or ‘vital’ (= bio-mediated; metabolic effects) (after Roth, 1997).

Descriptions and Diagrams of Stable Isotope Analytical Techniques – An Encyclopedic Overview

xvii

Delta per mil values and atom percent Relative delta () values (in ‰ or per mil) are used for the relatively low natural levels and very small variations in heavy stable isotopes (e.g. D, 13C, 15N, 18O and 34S). If the heavy isotopes are strongly enriched, it is more convenient to express the heavy isotope content in atom percent (or atom%), following the definition (Wong & Klein, 1986): atom percent ðatom%Þ ¼ fractional abundance  100

[I.10]

The fractional abundance (F) for D is calculated from the  value as follows: F¼ R¼



R ð1 þ RÞ

[I.11]



[I.12]

 1000 þ 1

 RV- SMOW

where R is the D/H ratio of the sample,  is the normalized D value of the sample and RV-SMOW is the D/H ratio of V-SMOW (value of 155.95  106; de Wit et al., 1980). Rittenberg (1946) presented similar equations on 15N expressed in atom percent, in the form: Atom% 15 N ¼ number 15 N atoms  100=ðnumber 14 N atoms þ number 15 N atomsÞ [I.13] or Atom% 15 N ¼

ð14 N14 NÞ þ 2ð15 N15 NÞ  100 2½ð14 N14 NÞ þ ð14 N15 NÞ þ ð15 N15 NÞ

[I.14]

Hauck (1982) presented simple equations for atom% 15N, for m/e 28 and m/e 29 measured (i.e. 14N2/14N15N), without measurement of m/e 30 (15N concentrations 10,000 fwhm) and relatively low costs. Sensitivity of the method for peptides is in the subpicomolar range. Protein molecules were imbedded in a matrix solution [5 mg/mL -cyano-4-hydroxycinnamic acid in a solution of acetonitrile, ethanol and 0.1% trifluoroacetic acid (ratio 1/1/1) with pH 2.5 by Mandell et al., 1998; 15 mg/mL sinapinic acid (trans-3, 5-dimethoxy-4-hydroxycinnamic acid] and 5 mg/mL diammonium hydrogen citrate in a mixture of D2O and ethanol (ratio 9:1), with HCl added to adjust pD at 2.7, by Buijs et al. (1999) typically in equal volumes of 5 mL, loaded on a (silica or methylated silica: Buijs et al., 1999) slide and were dried. A laser (nitrogen laser, emitting 337 nm with pulse length of 3 ns: Buijs et al., 1999) ‘desorps’ and ionized the solids from the slide. Ions were measured [see Buijs et al. (1999) for details on TOF MS settings] for mass, comparing deuterated amides with similar protonated ones to obtain information on the deuterium levels in the protein molecules. Double-focusing analyzer spectrometry on doublets and triplets of gases – Nakabushi et al. (1970) used double-focusing (electrostatic analyzer, magnetic analyzer) spectrometry for comparing molecular masses (and for determination of systematic errors in this system) of doublets (C2H4-CO, C2H4-N2, N2-CO in the triplet system: C2H4-N2-CO and C2H4-C2D2 in the doublet system (all phases with ‘mass 28’). No information was given on the ionization method of the device. See Mattauch et al. (1965) for comparable measurements. Gas chromatograph – Mass spectrometer deuterated tracer method – Jenden et al. (1973) presented a method for simultaneously measuring endogenous and deuterated (tracer labeled) organic materials (choline, acetylcholine) at sub-picomole quantities by a combined gas chromatography–MS system. This rather was a method using deuterium in form of a label to determine quantitatively ratios of organic materials in mixtures rather then a method to obtain isotopic compositions.

1-3.3.

C ELLULOSE AND CELLULOSE N ITRATE PREPARATION

A general review on preparation and analysis of -cellulose materials is given in Volume I, Part 1, Chapter 24, while in Volume I, Part 1, Chapter 23 a specialized discussion of analytical technique (named ‘pyrolysis’) for O-isotope determination is presented. The colloquial expression ‘cellulose nitrate’ is a chemical misnomer that does not reflect the nitric acid ester character (Schimmelmann, personal communication). Besides the non-exchangeable C–H bonded hydrogen (70%), two types of cellulose O–H groups with exchangeable hydrogen can be distinguished: regular hydrogen bonded in an ordered, crystalline manner (relatively slower hydrogen exchange; 15%) and irregular hydrogen-bonded in a disordered, amorphous manner (relatively faster hydrogen exchange; 15%) (Mann, 1971; Grinsted & Wilson, 1979). Hydrogen exchange in O-H

201

Hydrogen

groups seldom reaches complete replacement (Grinsted & Wilson, 1979), and Schimmelmann et al. (1993) stated that: ‘‘However, there appears to be a widespread overly optimistic and complacent view on the accuracy of the method’’ and ‘‘Some problems associated with the nitration of cellulose, namely that hydrogen stable isotope data show systematic differences among various nitration techniques, and that celluloses from woody plants require special precaution to avoid ‘contamination’ [DeNiro, 1981], may be due to insufficient elimination of O-H’’.

Methods for wood cellulose extraction were described by Green (1963). Epstein et al. (1976), Yapp & Epstein (1977), DeNiro (1981) and Gray & Song (1984) used an esterification technique on wood powder (40 mesh) to obtain cellulose from plant materials. This was done by solvent extraction (lipids, resins, hydrocarbons) with 1:1 benzene/ methanol (24 h) and washing with acetone (24 h). Leavitt & Danzer (1993) applied a second extraction. Nitration of the cellulose (100–800 mg) was done, after rinsing samples with distilled water and drying in vacuo, by using a mixture of nitric–phosphoric acid (64% HNO3–26% H3PO4–10% P2O5; at 0–5C) (method after Goring & Timmell, 1960 and Alexander & Mitchell, 1949). Sternberg et al. (1984a, b) air-dried plant samples (stem and leaf material) at 50C for several days, and further desiccated them in a freeze dryer before grinding to a fine powder. Figure 1-3.28 shows the essential steps in the extraction method by Epstein et al. (1976). Timmell (1957, reference in Yapp & Epstein, 1977) showed that the measured yield of cellulose nitrate is an indication of the -cellulose content of a wood sample. DeNiro (1981) reviewed methods for cellulose nitrate preparation. He concluded that cellulose nitrate prepared after the method by Epstein et al. (1976) is contaminated and that the contaminant can have a different D/H ratio from that of the non-exchangeable hydrogen of cellulose. A difference as large as 15‰ (or larger) but probably on average closer to 6–8‰ in applying the Epstein et al. (1976) method must be considered (DeNiro, 1981). DeNiro (1981) discussed the influence of hemicellulose as contaminating side-product in the preparation steps for cellulose nitration. It was concluded that, even if present after preparation was completed, no significant isotopic deviations were caused.

Soluble

Raw wood –156‰ A –128‰ B

Lipids, resins –255‰ A –256‰ B Cellulose nitrate –106‰ A –107‰ B

Benzene–methanol extraction Insoluble

Cellulose, lignin, hemicellulose –94‰ A –95‰ B

Nitrate acetone extraction

Figure 1-3.28 Flow chart of the essential steps for the extraction of cellulose nitrate from plant materials (after Epstein et al., 1976). The D values given below the respective steps are example values from Bristlecone Pine samples A and B.

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Yapp & Epstein (1982) also reviewed the method of preparation of cellulose nitrate. In the first method (Epstein et al., 1976), in which solvent extracted wood directly was nitrated, a mixture of nitrated cellulose, hemicellulose and lignin was produced. The separation of the cellulose nitrate from the other components was accomplished by dissolution of the cellulose nitrate in acetone, centrifugation of the insoluble nitrated lignin and hemicelluloses, decantation of the supernatant solution and precipitation of the cellulose nitrate from the acetone solution by rapid addition of distilled water. DeNiro (1981; see above) found deviating D values for some of these cellulose nitrate samples. Therefore, he used a chlorite delignification technique using a NaClO and NaOH solution (Epstein et al., 1977; after Wise, 1944). The purified -cellulose was nitrated to obtain cellulose nitrate. Nitration reagents: nitric–phosphoric acid or nitric acid–acetic anhydride, was tried (e.g see Bennett & Timmell, 1955), but no difference in result was found between the use of them (DeNiro, 1981; Yapp & Epstein, 1982). DeNiro (1981) also found that double nitration with the method of Epstein et al. (1976) was leading to D values of cellulose nitrate comparable with the D values from the delignified cellulose nitrate. Although a second nitration did not significantly reduce the variability in D (+4‰: DeNiro, 1981). Yapp & Epstein (1982) presented a preparation procedure for cellulose nitrate as shown in Figure 1-3.29. Gray & Song (1984) prepared their cellulose nitrate in two ways: by direct nitration of wood samples followed by extraction of cellulose nitrate and by extraction of -cellulose first, followed by nitration to cellulose nitrate. Removal of hemicellulose from the holocellulose was applied by stirring holocellulose in 50 mL of 17% NaOH solution (room temperature) for 40 min, dissolving the hemicellulose and leaving behind the -cellulose. Sternberg (1989) reviewed methods for preparation of cellulose and cellulose nitrate. After a method described by Wise (1944), plant material (2–4 g) was dried at 50–70C and ground. It was then delipified by using organic solvents such as benzene, methanol or acetone [see also Dunbar & Wilson (1983) for holocellulose preparation], especially important for tree trunks because they may contain considerable quantities of resins (depleted in deuterium). The material was then boiled for 2 h in 200 mL distilled water and cooled to 70C. Under a wellvented hood, 1 g (1.5 g: Mullane et al., 1988) of NaCl and 1 mL of acetic acid were added to this mixture (still at 70C) for 1 h. NaCl and acetic acid were added each hour over a 5 h period, until cellulose appears thoroughly bleached. The fuming solution was cooled and cellulose was settling at the bottom of the beaker. The supernatant solution was decanted and the residual cellulose was washed at least three times with distilled water [Mullane et al. (1988) first soaked the cellulose at 90C with 10% NaCl solution for 45 min]. Cellulose was soaked in a 17% NaOH solution for 45 min (room temperature), solubilizing and thus removing hemicellulose. The solution was decanted and the cellulose was washed several times with distilled water. The cellulose was placed for 15 min in a 10% acetic acid solution, washed thoroughly and freeze-dried or dried in an oven at 50–60C. Cellulose may be further purified by dissolving in concentrated phosphoric acid and re-precipitation with distilled water. Mullane et al. (1988) filtered and washed the cellulose successively with 17% NaOH solution, water, 1% HCl solution and several portions of water. The -cellulose was air-dried. Cellulose was subjected to decomposition at higher temperatures (typically at 180– 250C; Yang & Freemen, 1993). Changes at hydrogen isotopic level during thermal treatment of cellulose molecules was discussed by Krishnamurthy & Machavaram (1998).

203

Hydrogen

Insoluble

{

Raw wood powder Soluble

Benzene–methanol Acetone Hot water extractions Discarded

Cellulose, lignin, hemicelluloses Nitration

Dissolved, re-precipitated

{

Cellulose nitrate Nitrated lignin Nitrated hemicelluloses (methanol wash) Insoluble

Acetone extraction Cellulose nitrate + ?

Discarded

Re-nitration

Dissolved, re-precipitated

{

Cellulose nitrate + ? (methanol wash) Insoluble

Acetone extraction Cellulose nitrate

Discarded

Figure 1-3.29 Flow diagram for preparation of cellulose nitrate by the nitration method (after Yapp & Epstein, 1982).

Leavitt & Danzer (1993) placed air-dried, ground (30–40 mesh) plant matter (0.1–0.2 g) in individual glass-fiber filter paper pouches, tied with plastic tags. Compounds such as oils, waxes and resins were removed via Soxhlet extraction using a 2:1 (v:v) toluene/ethanol mixture for 16–18 h. After cooling and drying, samples were again Soxhlet-extracted with 100% ethanol for 16–18 h. Samples were removed from the Soxhlet, dried for 1–2 hours and boiled in deionized water for 6 h. Some inorganic salts and low-molecular-weight polysaccharides (e.g. gums and starches) are soluble in hot water. The pouches with samples were then transferred to a flask with 700 mL of deionized water with NaClO3 (6–8 g) and glacial acetic acid (1 mL) added. The flask was loosely closed and heated at 70C overnight.

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Handbook of Stable Isotope Analytical Techniques

Next day, three more additions of NaClO3 and glacial acetic acid were made at 2-h intervals and reaction was carried on for a second night. Samples were rinsed after decanting the fluid and addition of deionized water. After allowing to sit for 0.5–1 h the process was repeated unless the conductivity of the supernatant was decomposed molecule Nano-size samples monitoring biological or chemical processes

1-3.2.7

150–200 0C for cellulose

Diverse

Rare Old method Modern method; specialized

Modern method; specialized Very rare/experimental Rare; questionable, if applicable Modern; specialized method; high potential for clinical, bio(chem), pharmaceutical, or forensic studies (Continued ) 211

212

Synopsis of methods as reported in Chapter 1-3 Section 1-3.2.13

Method

(Continued ) Analyte

Organic material

1-3.4

Chitin–collagen compounds

Biological samples

1-3.5

Petroleum/coal

1-3.2.14 1-3.3

Deuterated or labeled organic material Wood and plant materials

Comments Spectroscope (e.g. methane) Generally quantative method; use of D tracer Compare with H equilibration method [1-3.2.8] laborious technology Nitration method as cellulose procedure; difficulties with complete replacement exchangeable of hydrogen during hydrolysis preparation

Status Very rare on organic compound Rare for precise isotope ratio determination Standard

Modern method

Overview of methods

Handbook of Stable Isotope Analytical Techniques

Optical methods (IR spectrometry) Methods on D-enriched materials (diverse methods reported) Cellulose/cellulose nitrate methods

T(C)

213

Hydrogen

1-4.

H YDROGEN A BSORBED IN M ETAL

1-4.1.

ABSORPTION AND DIFFUSION OF H YDROGEN IN M ETALS

Diffusion (where absorption forms part of the process) of hydrogen (H, D) in metals or alloys was tested as a method for phase separation of hydrogen from other gases, e.g. in on-line He flow systems, to avoid the trailing of the 4He peak in the D detector of the MS (see Chapter 1-2.26.2). Diffusion of hydrogen through Ni walls of a reaction tube is used for the elimination of hydrogen gas from CO2 (+ other gases) in pyrolysis of organic compounds for O isotope determination (see Chapter 6-2.5). An alternative to the latter method is for the hydrogen gas to be collected for hydrogen isotope determination (organic materials: pyrolysis: water analysis: reduction with carbon) (see Chapter 1-2.16). Lewis (1967) published a book devoted to the Pd–H2 system. Wicke et al. (1978) presented an extensive review on hydrogen in Pd and Pd alloys. In a set of edited books, Alefeld & Vo¨lkl (1978a, b) discussed basic and application-oriented properties of hydrogen in metals.

1-4.2.

G LOW DISCHARGE MASS SPECTROMETRY

Donohue & Petek (1991) presented a study on hydrogen isotope measurement by glow discharge mass spectrometry (GDMS), to show possible isotopic fractionation in Pd metal as a result of electrolysis in a D2O medium. For an extensive description of the GDMS technique, see Volume I, Part I, Chapter 35.

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Handbook of Stable Isotope Analytical Techniques

1-5.

L ABELED W ATER M ETHODS

1-5.1.

CALCULATION M ETHODS FOR T OTAL BODY W ATER

Early documentation of the use of hydrogen isotopes for calculation of body water volume in humans (or animals) can be found in Hevesy & Hofer (1934a, b) and Moore (1946, 1948). Literature on the TBW method can be found in London & Rittenberg (1950), Solomon et al. (1950), Hurst et al. (1952), Lifson et al. (1955), Faller et al. (1955), Lilienfield et al. (1955), Stansell & Mojica (1968), Mendez et al. (1970), Houseman et al. (1973), Wang et al. (1973), Blake et al. (1975), Culebras & Moore (1977), Culebras et al. (1977), Halliday & Miller (1977), Kirchgessner et al. (1977), Schoeller et al. (1980, 1982, 2000), Lukaski & Johnson (1985), Whyte et al. (1985), Davies et al. (1988, 1990), Johnson & Farrell (1988), Wong et al. (1988), DeLany et al. (1989), McMillan et al. (1989), Villalpando et al. (1992), Andrews et al. (1997), Bowen & Iverson (1998), Jennings et al. (1999), Visser et al. (2000), Gonzalez et al. (2002), Raman et al. (2004), Mendley et al. (2005), Morgenstern et al. (2005), Spanel et al. (2005) and Slater & Preston (2005). Reilly & Fedak (1990) and Arnould et al. (1996) measured body composition by hydrogen isotope dilution methods while MacLennan et al. (1983) used D2O for isotope dilution to measure water metabolism in neonatals. Whyte et al. (1985) stated ‘The only practical methods for measuring body water in vivo are those in which the dilution space of a substance (or ‘‘tracer’’) is assumed to approximate the space assumed by the body water’. Deuterium can be considered a nearly ideal tracer. The small tracer quantities are below toxic levels, it is distributed uniformly throughout all the body water compartments without transformation and it can be measured accurately for the enrichment levels in question. The detection space, however, is 4‰ larger than body water due to exchange with non-aqueous hydrogen (note by D.A. Schoeller). When using urine or blood serum for the isotopic tracer studies, it must be realized that these reservoirs are normally enriched in D and 18O compared with local drinking water, and that body water compositions generally fall to the right of the (MWL: see Sheppard, 1986) (Halliday & Miller, 1977; Schoeller et al., 1986b). Slopes of linear regression of D and 18O equations generally are less than eight, the common slope for precipitation waters (Schoeller et al., 1986b). Schloerb et al. (1950) presented a method for body water determination based on the falling drop and on the Zn reduction/MS method. An equation for calculating the body water volume by using a D2O tracer and assuming complete equilibration in the human body is given by Schloerb et al. (1951): C1 V1 C2

[1-5.1a]

C1 V1  Cu Vu C2

[1-5.1b]

V2 ¼

V2 ¼

215

Hydrogen

where C1 is the concentration of the injected D2O tracer, V1 the volume of D2O injected, corrected to 37C, Cu the concentration of D2O in water excreted prior to equilibration, Vu the volume of excreted water prior to equilibrium, C2 the serum (sample!) D2O concentration at equilibrium and V2 the volume of water into which injected D2O diffuses at equilibrium (=TBN). Wentzel et al. (1958) presented a method for calculation of TBW based on direct measurement of the masses 18 and 19 on water vapor in a MS. Stansell & Mojica (1968) included temperature of the fluids in their calculation procedure: VðmLÞ ¼

WðgÞ  ð% of D2 O in administered sampleÞ Density of D2 O at t ðCÞ

[1-5.2]

where V is volume of administered pure D2O, W is weight of D2O administered and t is temperature (in C). From this the TBW is calculated as TBW ¼

Volume D2 O administered  volume D2 O excreted 10 ðconcentration of D2 O in serum water in volumes per 100 mLÞ

[1-5.3]

The volume of D2O excreted includes both insensible loss and urinary excretion. Nielsen et al. (1971) reported a simple calculation method, using hydrogen measurement of body fluids with use of a hydrogen tracer, by the formula gD2 O administered gD2 O administered 1000 g=L ¼ TBWðLÞ ¼ Extrapolated D2 O serum concentration D2 O serum concentrationð%Þ  10 ðgD2 O=g waterÞ [1-5.4] Similar calculation methods were presented by Solomon et al. (1950) and in a slightly simpler form by Mendez et al. (1970). A method to calculate TBW based on 18O tracer methods was presented by Schoeller et al. (1980, 1982). Assuming that the TBW is equal to the H218O dilution space (dilution space might be 1–2% larger than the TBW), the TBW (in kg) can be calculated: TBW ¼

d APE f   18:02  kg MW 100 RPDB  DPDB18 O

[1-5.5]

18 where d is the dose of H18 2 O in g, MW is the molecular weight of the H2 O, APE is the 18 atom percent excess O, f is the oxygen isotopic fractionation between CO2 and H2O (1.041 at 25C), RPDB is the ratio of 18O to 16O in the PDB standard and DPDB18O is the arithmetic difference between the per mil enrichments of the pre- and post-isotope administration fluid samples.

1-5.1.1.

Comparisons and alternatives

Wong et al. (1987c) measured plasma, urine, saliva, breath water vapor and breath carbon dioxide (last obviously only for 18O) and compared results between D and 18O ‘dilution spaces’ for TBW estimation. Urine, saliva, breath water vapor and CO2 samples all were

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within 0.2 + 0.7 kg (mean difference + SD, n = 80) of the plasma samples. D dilution spaces obtained from plasma, urine and saliva samples were consistently larger than those obtained with 18O. Breath water vapor estimates by D gave systematic deviations. Vache et al. (1995) promoted the use of 18O-enriched water as a low-cost alternative to D labeling.17 Instead of 18O, 17O could also be considered to serve as oxygen tracer for TBW determination. However, 17O tracers are by far more expensive than 18O tracers and therefore not attractive for routine usage (see Schoeller et al., 1995). Crum et al. (1985) used a tritium label instead of deuterium in order to predict TBW in partridges.

1-5.2.

DOUBLY L ABELED WATER M ETHOD FOR ENERGY BUDGET D ETERMINATION

The doubly labeled water (DLW) method was developed by Lifson & McClintock (1966), after the finding by Nathan Lifson that 18O in body water is in isotopic equilibrium with oxygen in respiratory CO2 (Lifson et al., 1949; Speakman, 1998; Horvitz & Schoeller, 2001). In essence, the method is recording the metabolic turnover of water in the human body. After a loading of water labeled with D and 18O, the D washes out of the body as water and the 18O washes out as water and carbon dioxide. Under steady-state conditions, single-compartment kinetics, the difference between the two elimination rates is a measure of carbon dioxide output. Energy expenditure is then calculated from carbon dioxide production using standard equations for direct calorimetry. The advantage of the method is that it is not necessary to collect the expired carbon dioxide, but simply collect periodically urine specimens to determine the amount of stable isotope left in the body (Schoeller, 1983, 1999; Schoeller et al., 1995). A simple representation of this isotopic balance was given by Schoeller (1999): Deuterium elimination: rH2 O ¼ TBW kH O elimination: rH2 O þ 2 rCO2 ¼ TBW kO Arithmetic difference: rCO2 ¼ TBW ðkO  kH Þ=2 18

[1-5.6a] [1-5.6b] [1-5.6c]

where r is the rate of water output (rH2O) or carbon dioxide output (rCO2), respectively. TBW is the total body water, and kO and kH are the oxygen and the hydrogen elimination rates, respectively. Modest corrections were required for differences in isotope dilution spaces and isotopic fractionation. However, it must be considered that these methods use tracers that are enriched in the heavy isotopes (D and 18O), and samples collected from subjects are not in the natural range of isotopic compositions (e.g. Wong et al., 1993). This may raise problems in linearity or 17

Actually 18O-enriched water is considerably higher in costs than D-enriched water. This is caused by technological advances in the other areas, such as positron emission tomography, which generated a large demand for 18 O with an increased price as a result (e.g. Speakman, 2005).

Hydrogen

217

scale calibration (needed stretching or shrinking of the scale) for water samples, as is usually applied on the SLAP–SMOW scale. This scale is based on standards with negative delta values considering both D and 18O isotopes. No comparable certified reference material exist for the positive delta values (Wong et al., 1993). The DLW method is an objective means to determine energy expenditure in human subjects, with a ‘proven’ accuracy of better than 2% and a precision of 2–10% (Schoeller et al., 1986b). Coward & Prentice (1985; including a reply by Schoeller) demanded for validation studies of the doubly labeled tracer method for estimation of energy expenditure (breath CO2 volume). Validation studies considering this method are included in the reference list following directly below. Reports on the application of the DLW method, including descriptions of/reference to analytical methods, can be found in Lifson et al. (1955, 1975), McClintock & Lifson (1958a, b), Lifson & Lee (1961), LeFebvre (1964), Lifson & McClintock (1966), Mullen (1973), Utter & LeFebvre (1973), King & Hadley (1979), Nagy (1980), Schoeller et al. (1980, 1983, 1986a–d, 1990, 1995, 2000), Schoeller & van Santen (1982), Bryant & Westerterp (1983), Schoeller & Webb (1984), Schoeller (1983, 1984, 1987, 1988, 1999), Westerterp et al. (1984, 1986, 1988, 1991, 1995), Westerterp & Bryant (1984), Williams & Nagy (1984a b), Barrie & Coward (1985), Williams (1985), Black et al. (1986, 1996, 1997, 2000), Fancy et al. (1986), Prentice et al. (1986, 1990, 1996), Roberts et al. (1986, 1988, 1991), Tatner & Bryant (1986, 1989), Jones et al. (1987b, 1988, 2000), Schoeller & Taylor (1987), Speakman (1987, 1993, 1995, 1997), Speakman & Racey (1987, 1988, 1989), Stein et al. (1987, 1996, 1999), Van Loan & Maylin (1987), Wong et al. (1987c, 1988, 1990), Coward (1988, 1990, 1998), Haggerty et al. (1988, 1991, 1994, 1998), Masman et al. (1988), DeLany et al. (1989, 1995, 2006), ForbesEwan et al. (1989), Gales (1989), Huss-Ashmore et al. (1989), Midwood et al. (1989, 1993, 1994), Riumallo et al. (1989), Roberts (1989), Schulz et al. (1989), Seale et al. (1989, 1990, 1993, 2002), Webster & Weathers (1989), Coward & Cole (1990), Goran et al. (1990, 1992, 1994), Livingstone et al. (1990, 1992), Prentice (1990), Tatner (1990), Welle (1990), Williams & Winnel (1990), Hoyt et al. (1991, 1994), Ravussin et al. (1991), Speakman et al. (1991, 1993, 1994, 2001), Calazel et al. (1993), Jones & Leitch (1993), Jones et al. (1993), Lavelady et al. (1993), Poppitt et al. (1993), Pullicino et al. (1993), Stroud et al. (1993), Ballevre et al. (1994), Broemeling & Wolfe (1994), Clark et al. (1994), Coward et al. (1994a, b), Racette et al. (1994, 1995), Ritz et al. (1994, 1996a, b), Thomas et al. (1994), Bevan et al. (1995), Black et al. (1995), Boyd et al. (1995), Brenna & Yeager (1995), Buhl et al. (1995), Dolnikowski (1995), Goran (1995), Jones (1995), Kashiwazaki et al. (1995, 1998), Kashiwazaki (1999), Maffeis et al. (1995), Matthews & Gilker (1995), Roberts et al. (1995), Sawaya et al. (1995, 1996), Seale (1995), Speakman & Roberts (1995), Begley & Scrimgeour (1996), Martin et al. (1996a), Schoeller & Hnilicka (1996), Wolf et al. (1996), Dykstra et al. (1997), Gretebeck et al. (1997), Gotaas et al. (1997), Junghans et al. (1997), Mudambo et al. (1997), Poehlman et al. (1997), Seale & Rumpler (1997), Trappe et al. (1997), Westerterp & Bouten (1997), Williams et al. (1997), Champagne et al. (1998), Gardner & Poehlman (1998), Johnson et al. (1998), Rothenberg et al. (1998), Starling et al. (1998a, b, 1999), Thielecke et al. (1998), Wells et al. (1998), Corp et al. (1999), Kroke et al. (1999), Philippaerts et al. (1999), Scrimgeour et al. (1999), Stunkard et al. (1999), Toerien et al. (1999), Visser & Schekkerman (1999), Bertheaux (2000), Black & Cole (2000), Blanc et al. (2000, 2002), Dvorak et al. (2000), Ebine et al. (2000, 2002), Kaczkowski

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et al. (2000), Persson et al. (2000), Visser et al. (2000), Doherty et al. (2001), Horvitz & Schoeller (2001), Leenders et al. (2001, 2006), O’Connor et al. (2001), Staten et al. (2001), Trabulski & Schoeller (2001), van Trigt et al. (2001, 2002b), Weathers et al. (2001), Conway et al. (2002a, b), Fournier et al. (2002), Henen (2002), Hise et al. (2002), Rafamantanantsoa et al. (2002, 2003), Vander Haegen & DeGraaf (2002), Gibney et al. (2003), Sjoberg et al. (2003), Yao et al. (2003), Butler et al. (2004), Isenring et al. (2004), Lopez-Alarcon et al. (2004), Maˆsse et al. (2004), Richelle et al. (2004), Arvidsson et al. (2005), Koebnick et al. (2005), Levine (2005), Liu et al. (2005), Montgomery et al. (2005), Paul et al. (2005), Ramirez-Marrero et al. (2005), Voigt et al. (2005), Bederman et al. (2006), Clusella Trullas et al. (2006), Jodice et al. (2006), Mahabir et al. (2006a b), Mann et al. (2006), Fuller et al. (2007), Ishikawa-Takata et al. (2007), Okubo et al. (2007), and Sasaki (2007). Speakman (1998) published a review on the history and theory of the DLW technique. Availability (and therefore price) of tracer preparates and the influence of technique development were discussed by Speakman (2005). Improvement by lowering costs and precision (e.g. by including monitoring of changing isotopic values of background) of the DLW method by application of stable isotope ratio infrared spectrometry (SIRIS) was reported by Speakman (2005) as a potential solution to make the DLW method a feasible clinical application. Validation of the DLW method by SIRIS methods was published by van Trigt et al. (2002b). Tatner (1988) discussed natural abundance of H and O isotopes in animal body waters. The relative dilution spaces for D and 18O in human subjects were calculated by the plateau method by Racette et al. (1994). Loss of D or 18O by the urine was calculated by the equation (Racette et al., 1994)

D or

18

Ourine loss ðgÞ ¼

ðV  APEbw Þ ðAPEA  MWbw =MWA Þ

[1-5.7]

where V is the volume of overnight urine collected (in mL) between the time of dose administration and the morning urine sample used for the TBW determination, APE is atom percent excess of D or 18O in body water (bw) and the dose water (A) and MW is the molecular weight of the body or dose water. Overnight urinary loss averaged 3.0 + 1.5% of the dose administered (Racette et al., 1994). Added to this is the loss in breath 18O during the same overnight period to adjust the balance of 18O. TBW was calculated by methods given above in Section 1-5.1. An early calculation, of CO2 production per unit body mass based on Lifson & McClintock (1966), was given by Nagy (1980) by the equation   mL CO2 produced 29:93W ln O 1 H 2 =O 1 H 2 ¼ gh Mt

[1-5.8]

where W is body water volume (mL), M is body mass (g), O 1 and O 2 are initial and final specific activities (background-corrected) of O isotopes in body water, H 1 and H 2 are the same for H isotopes, t is time elapsed (days) and ln is natural logarithm.

219

Hydrogen

The mean daily CO2 production (rCO2 in moles/day) can be calculated by Lifson & McClintock (1966) and Schoeller et al. (1986a): rCO2 ¼

N ðkO  kH Þ 2:08  0:015NkH

[1-5.9]

or by (Schoeller, 1983; Schoeller et al., 1986a) rCO2 ¼

N f2  f 1 rG ðkO  kH Þ  2f3 2f3

ðmol=dayÞ

or by Schoeller & Webb (1984):   0 TBW 0 ðkO  kH Þ  0:015  TBW  k2 22:41 QCO2 ¼ 2:08

ðmol=dayÞ

[1-5.10]

[1-5.11]

or by Schoeller (1980): rCO2 ¼

1 ðNO kO  NH kH Þ  0:0246 : 1:05ðNO kO  NH kH Þ ðL=dayÞ [1-5.12] 2:076

or by (DeLany et al., 1989; Speakman et al., 1993: if the mean dilution space ratio for a group is significantly deviating from 1.0427): rCO2 ¼

N ð1:01 kO  1:04 kH Þ  0:0246 rH2 O f 2:078

ðmol=dayÞ

[1-5.13]

and (Speakman et al., 1993: two options if the mean dilution space ratio for a group is similar to 1.0427):   N  ð1:01 kO  1:0531 kD Þ  0:0246 rGf ðmol=dayÞ rCO2 ¼ 2:078 with [1-5.14a] NO ND þ N¼ 1:01 1:0531 or with rCO2 ¼

N  ðKO  1:0427 KD Þ 2:196

with N¼

½NO þ ðND =1:0427Þ 2

[1-5.14b]

or by (Stunkard et al., 1999) rCO2 ¼ TBW ð1:007 kO  1:042 kH Þ=2:076  0:0246 rH2 O f

ðmol=dayÞ

[1-5.15]

where N is the average of the beginning and end period total body water, TBW is the total body water, TBW0 is the corrected total body water for water excreted overnight (TBW0 = TBW - ‘overnight’), rH2O f is the rate of fractionated evaporative water loss, kH and kO are the isotope elimination rates for hydrogen and oxygen, respectively. f1 and f2 are

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Handbook of Stable Isotope Analytical Techniques

the fractionation factors for the evaporative water losses of D and 18O, respectively, and f3 is the fractionation factor for 18O between CO2 and H2O. Conway et al. (2002) expressed this relationship as follows: " # TBW rCO2 ¼  ½ð1:01  kO Þ  ð1:04  kh Þ  f1  ½1:05   ð f 2  f 1 Þg L=d ð2  f3 Þ [1-5.16a] where ‘constant isotopic fractionation factors’ f1 = 0.941, f2 = 0.992 and f3 = 1.039, ko and kh are the isotopic clearance rates for oxygen and hydrogen, respectively (in L/day). Conway et al. (2002a) also included an equation for the daily production rate of water: rH 2 O ¼

TBW  kh ð1  fð1f 2 Þ  ½ð2:3  rCO2 Þ=ðTBW  kH ÞgÞL=d

[1-5.16b]

In an appendix, Schoeller et al. (1986a) discussed different cases, including different equations, for calculation of ‘rCO2’ by using the DLW method. See also the discussion on ‘rCO2’ equations, representing energy expenditure estimates, in the review by Speakman (1998). The D and 18O isotope elimination rates (kH and kO) for each period were calculated by a two-point method, using the isotopic enrichment relative to the ‘day 1’ baseline isotopic abundance and the time difference between collection of the initial and final samples: ln APEf  ln APEi [1-5.17] t where APE is atomic excess percentage, subscripts i and f are standing for initial and final, and t is a time factor. Welle (1990) and Cole & Coward (1992) discussed the two-point versus multipoint sample collection methods to estimate the CO2 production in humans. For the multipoint method, assumption was made that the two isotopes (D and 18O) have constant exponential disappearance rates, so that (Cole & Coward, 1992): k¼

EDi ¼ ID expð  kD ti Þ þ error term

[1-5.18a]

EOi ¼ IO expð  kO ti Þ þ error term

[1-5.18b]

where i = 1, . . ., n, subscripts D and O indicate deuterium and oxygen isotopes, respectively, Ei is the isotope enrichment net of background expressed as a fraction of dose/mol of body water, ti is the time (days), I is the enrichment at time zero and k is the (positive) flux rate. Cole & Coward (1992) included an extensive discussion on precision and accuracy levels for both methods. It was concluded that the multipoint method has greater precision, but is less accurate than the two point method (Schoeller & Coward, 1990; Welle, 1990; Cole & Coward, 1992). Welle (1990) concluded that . . . an advantage of the multipoint method is that it minimizes the impact of an imprecise analysis. However, simply increasing the number of replicate analyses of an initial and final sample is more effective in reducing the effect of analytical error than is performing single analyses of more time points’. Further he concluded that ‘. . . the two point and multipoint methods will generally give the same results when the DLW technique is used to calculate mean energy expenditure in groups of human subjects.

221

Hydrogen

The two-point method was considered better for individual cases. Livingstone et al. (1992) used the multipoint method to calculate CO2 production rates. Speakman & Racey (1988) stressed the importance for strict 24 h interval sampling periods and reported large errors if deviating 1 h or more from the 24 h period. Goran et al. (1992) presented a correction equation for non-aqueous exchangeable hydrogen in the body (other then breath, urine or transpiratory excretion from the human body) using constants from Culebras & Moore (1977): ðfat  0:0035Þ þ ðprotein  0:0149Þ þ ðcarbohydrate  0:0185Þ  100 TBW  0:1111

[1-5.19]

where TBW is the total body water. Fat, protein and carbohydrates in the body were measured in kg. Carbohydrate mass in the body was considered negligible by Goran et al. (1992). Schoeller et al. (1986c) reasoned that the agreement between DLW and intake-balance in human subjects suggests that de novo synthesis did not occur to significant extents. Typical isotopic elimination rates for 18O and D from the human body in temperate climates are in the order of 0.095 and 0.07 per day, respectively (Schoeller et al., 1995). Considering as subject for error both the baseline and final abundance measurements, the precision of the isotope abundance measurements themselves must be 0.11‰ and 0.9‰ for 18 O and D, respectively (Schoeller et al., 1995). Effects of change in baseline during the testing period, including modified equations, were discussed by Gretebeck et al. (1997). Schoeller (1983) presented diagrams, for different age groups of humans, of theoretical precision against metabolic period for determination of the correct tracer amount that can be used to obtain a sufficiently precise result [within 3% (adults) to 5% (infants)]. Ravussin et al. (1991) tested if the DLW method was valid in the determination of the energy expenditure in both lean or obese subjects. A relationship in underestimation of energy expenditure and percent body fat (BF) and fat mass was found; the fatter the subject, the larger the underestimate in energy expenditure by the DLW method. Schoeller & Webb (1984), however, did not find this relationship, which was explained by Ravussin et al. (1991) either by the small sample size or by the narrow range of body fatness in the study by Schoeller & Webb (1984). Contamination of small samples (£ 20 mL) by humidity from air can be seriously (10 mL air at 25C with 50% relative humidity contains 0.13 mg of water). Memory occurs, to different extent, in the sample preparation system or in the inlet system of the MS (Schoeller et al., 1995).

1-5.2.1.

Single, homogeneous and dual water pools

Ballevre et al. (1994), by applying the DLW method, calculated the CO2 production in a subject as the difference in the disappearance rate between 18O (loss in H2O and CO2) and D (loss in H2O only). In this study by Ballevre et al. (1994), models with a single homogeneous water pool and with a dual water pool were considered. The model with a single water pool (generally used in small animal studies; after Lifson & McClintock, 1966) used the oxygen dilution space as an estimate of the water pool, expressed by the equation rCO2 ðmol=dayÞ ¼ ðNO =2:08ÞðkO  kd Þ  0:015ðNO kd Þ

[1-5.20]

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Handbook of Stable Isotope Analytical Techniques

with N standing for the water space and k for the water rate constant, and subscripts ‘o’ and ‘d’ standing for oxygen and hydrogen reservoirs, respectively. The dual water pool [generally used for large animals and humans; after Schoeller & Coward, (1990) reference in Ballevre et al., 1994] considers both, the D and 18O dilution space, and is expressed by rCO2 ðmol=dayÞ ¼ ð1=2:08ÞðNO kd  Nd kd Þ  0:0258ðNO kO  Nd kd Þ

[1-5.21]

To convert to energy expenditure, the respiratory quotient must be known. In a state of energy balance, it can be reasonably assumed that the food quotient equals the respiratory quotient. The energy expenditure is calculated as follows:   3:70 þ 1:326  4:184 [1-5.22] EEðkJ=dayÞ ¼ rCO2  22:4 cFQ where EE is energy expenditure and cFQ is the food quotient.

1-5.2.2.

Comparison of results for enriched D and from different laboratories

18

O samples

Wong et al. (1993) published the results of a ‘round-test’ for a number of D- and 18 O-enriched water samples, prepared by the IAEA, and distributed to a group of ‘test’ laboratories. From these results, it was clear that a reasonable part of the laboratories involved was outside the 95% confidence level of the accepted means of the D and O isotopic values. Because different analytical techniques were involved, part of the bias can be accredited to this factor, but certainly does not explain all of the ‘deviative values’.

1-5.2.3.

Comparison between deuterium and tritium tracer methods

Comparison between D and T tracer methods for determination of human TBW levels was published by Stansell & Mojica (1968). No significant difference in precision or sensitivity between the two methods was found. This clearly gives the deuterium method the advantage, because low levels of deuterium used as tracer are below any toxic level, while radiogenic tracers always carry the risk of radiation introduced in the human body.

1-5.2.4.

Tritium or Tritium-18O combined studies

Radiogenic tritium, instead of stable deuterium, was used in combination with 18O as tracer in the form of HT18O. References for discussion of this method are Prentice et al. (1952), Richmond et al. (1962), Kaplan & Boyer (1969), Buscarlet et al. (1978), Congdon et al. (1978), Nagy (1980, 1983), Nagy & Costa (1980), Weathers & Nagy (1980), Cooper (1983), and Gettinger (1983). Pace et al. (1947), Reid et al. (1958), Foy & Schneiden (1960), Kay et al. (1966), Carnegie & Tulloch (1968), Gordon et al. (1971), Holleman & Dietrich (1973, 1975), Smith & Sykes (1974), Tsivipat et al. (1974), Meissner (1976), Meissner et al. (1980), Degen et al. (1981), Johnson & Farrell (1988) and Lydersen et al. (1992) applied tritiated water for determination of body water space and turnover in animals or humans.

223

Hydrogen

Tritium used as tracer in milk intake measurements on sucklings was described in MacFarlane et al. (1969), Lowenstein et al. (1975), Romero et al. (1975), Lakshmanan & Veech (1977) and Rath & Thenen (1979). Further studies including tritium tracer were presented by Enns & Chinard (1956), Sepall & Mason (1960), Siri & Evers (1962), Panaretto (1963, 1968), Panaretto & Till (1963), Jungas (1968), Szeluga et al. (1984), Viljoen et al. (1988) and Gales (1989).

1-5.3.

D-NMR METHOD

A method to measure deuterium for TBW estimates by NMR (2H NMR) was presented by Abu Khaled et al. (1987). A comparison was made with standard IR absorption procedures. A tracer dose of +10 g D2O for each human subject was used. Precision and accuracy for both methods were very similar. A 300-MHz multinuclear NMR spectrometer was operated at a frequency of 46.06 MHz and at a probe temperature of 24C. The D spectra were obtained with a pulse width of 24 ms for a 90 magnetization vector with a delay time of 500 ms and without any proton de-coupling. Total spectral acquisition time was 4–5 min. A 99.8% deuterated benzene (C6D6) was selected for use as an external standard. About 0.5 mL of 0.1% C6D6 solution was pipetted into a 5-mm NMR tube and placed coaxially inside a 10-mm NMR tube containing 1.5 mL of the sample to be analyzed. The advantages of the 2H NMR method over other presently available techniques based on D2O dilution are as follows: it is fast, accurate, needs only small dose of D2O, can be done using any body fluid and, most importantly, does not require any sample preparation. Moreover, a NMR machine is relatively expensive, but the analytical costs are relatively low (in the order of a few US$/measurement). For more general discussion on D-NMR on water samples, see Chapter 1-2.24.1. D-NMR in organic materials is discussed in Volume I, Part 1, Chapter 5.

1-5.4.

OTHER APPLICATIONS OF ‘HEAVY WATER ’

Other applications of ‘heavy water’ used as tracer were described. D-enriched water can be used as carcinolytic agent, and in neutron radiography (Blake et al., 1975). Stansell & Mojica (1968) and Seale et al. (1990) presented a method, TBW determination, for estimation of lean body mass (LBM) and BF in the human body. Because water constitutes, on average, 73% of the body fraction after subtracting fat, the following relationships can be given: LBM ¼

TBW 0:73

[1-5.23]

and BF ¼ 100  LBM

[1-5.24]

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Handbook of Stable Isotope Analytical Techniques

The possibility of hydration of BF may result in a variation of +6.5% in TBW volume. Therefore, it was advised by Stansell & Mojica (1968) to be cautious in application of this method. Similar methods were applied by Blanc et al. (2005). D-enriched water was used for measuring de novo fatty acid synthesis in humans or animals (Javitt & Javitt, 1989; Hellerstein et al., 1991a, b; Leitch & Jones, 1993; Ballevre et al., 1994; Lee et al., 1994; Hellerstein, 1996; Jones, 1996; Yang et al., 1996c; Diraison et al., 1997; Konrad et al., 1998; Scrimgeour et al., 1999; Guo et al., 2000). Discussion on de novo fat synthesis in dietary tests were published by Riumallo et al. (1989). Serum cholesterol and triglyceride synthesis were measured by D-labeling (Taylor et al., 1966; Jones et al., 1988; Jones & Schoeller, 1990; Leitch & Jones, 1991). Plasma and fat tissue were extracted for total lipids and oxidized, and the water from this reaction was converted into H2 gas by methods as reported in Chapter 1-2. Preparation of plasma, adipose tissue, fatty acids and cholesterol and conversion into water and other compounds are reported in Chapter 1-3. Klein et al. (1990) used D-labeling (D-enriched water) for the determination of cholesterol synthesis in vivo in human subjects, and Diraison et al. (1996) applied the same in rats. Mass isotopomer analysis on synthesis of organic molecules was reported by Lee et al. (1990, 1992) and Katz & Lee (1991). Chen et al. (2005) used DLW to estimate eventual imbalance between triacylglycerol synthesis and breakdown as occurs in case of obesity. DLW was used for the measurement of triglyceride synthesis for estimation of slow turnover of lipids by Turner et al. (2003) and turnover of adipose tissue components (lipids and cells) in humans by Strawford et al. (2004). Enriched (D and 18O) tracer methods to study milk intakes were described by Coward et al. (1982), Schoeller & Fjeld (1986), Butte et al. (1983, 1988) and Fjeld et al. (1988). Livingstone et al. (1992) used the DLW method in combination with heart-rate monitoring to estimate active energy expenditure in humans. Urine was sampled for the measurement of the D and 18O isotopes in their tracer experiments.

C H A P T E R

2

L ITHIUM

2-0.

I NTRODUCTION

The element lithium has two stable isotopes: 6Li and 7Li. Their atomic abundances in natural sources are approximately 7.59% and 92.41%, respectively (Qi et al., 1997). The cosmic abundance of lithium isotopes reflects primordial nucleosynthesis, galactic cosmic-ray spallation and destruction processes (Olive & Schramm, 1992). On Earth, the two isotopes are susceptible to separation in geological processes, due to their relatively large difference in mass. Lithium isotopic compositions of natural material therefore have important geochemical and cosmochemical implications. Lithium isotopes are also of interest to nuclear and biomedical sciences. One nuclear application is the use of 6Li as shielding material in nuclear reactors. In medical science, lithium is a therapeutic drug for manic depression. Despite considerable interest in lithium isotopes, applications in earth science and other disciplines have been seriously hampered by the intrinsic difficulty of precise measurement of low-mass isotopes. The relative mass difference between the two isotopes of lithium is about 16%, which is among the highest of thermally ionized elements. Isotopic fractionation during mass spectrometric and other instrumental analyses is severe and, in the absence of a third isotope, the effect of mass discrimination cannot be internally corrected. For several decades, many investigators have studied the isotopic composition of lithium in an effort to determine the natural variation of its isotopic abundance. The results of research prior to the early 1980s display a wide range of isotopic ratios in geological samples and meteorites (see reviews of Heier & Billings, 1972, and Chan, 1987). In addition to natural fractionation, this large measured variation is also attributable to isotopic separation during chemical preparation and instrumental analysis. In the last two decades, considerable progress has been made to minimize mass fractionation in mass spectrometric analysis. As a result, the isotopic compositions of the major lithium reservoirs are becoming known. This chapter is devoted to the review of recent advances in mass spectrometric techniques for lithium isotope measurements. The intent is not to provide an exhaustive coverage of all recent developments, but to describe chemical and instrumental procedures that have proven useful for lithium isotope analysis in geological material. The emphasis will be on thermal ionization mass spectrometry (TIMS) and the relatively new method of inductively coupled plasma mass spectrometry (ICPMS). The merits and shortcomings of the various methods for geological applications will be evaluated. Finally, the state of knowledge of the terrestrial variation of lithium isotope composition and examples of geological applications will be presented. Ion microprobe technique will be briefly mentioned here but will be discussed in detail inVolume I, Part 1,Chapter 30. A review on Li isotope analytical methods is given inVolume I, Part 1,Chapter 6. 225

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C H A P T E R

3

B ORON

3-0.

INTRODUCTION

Boron is a quintessential crustal element that is widely distributed in surface rocks and aqueous fluids on Earth (Leeman & Sisson, 1996; Anovitz & Grew, 1996). It has two natural stable isotopes, 10B and 11B, with an average abundance of approximately 19.9% and 80.1% respectively. The unique geochemical characteristics of B, which include high solubility in aqueous fluids, high magmatic incompatibility and large relative mass difference between two isotopes, make B and 11B useful tracers of deep earth fluids and the recycling of subducted materials in convergent margins (Kotaka, 1973; Kakihana et al., 1977; Palmer, 1991; Ishikawa & Nakamura, 1994; Palmer & Swihart, 1996; You et al., 1996b). For instance, the boron isotopic compositions in natural waters (such as seawater, hydrothermal fluids, groundwater and spring water) vary approximately 80‰ (Barth, 1993; You et al., 1994) and show distinctive isotopic compositions in each hydrological reservoir. The 11B distribution in aqueous solutions, therefore, serves as a diagnostic proxy for tracing water sources in hydrological processes or possible water/rock interactions (Heumann et al., 1995; Barth, 1997, 1998). Throughout this chapter, the boron isotopic composition (11B) is expressed as per mil (‰) deviation from NIST SRM 951. " # ð11 B=10 BÞsample 11  B ¼ 11 10 [3.1]  1  103 ð B= BÞSRM 951 where SRM 951 is the NIST boric acid standard, prepared from a Searles Lake borax, and has a certified 11B/10B ratio of 4.0437 – 0.0033 (Cantanzaro et al., 1970). Boron is an underused tracer in earth sciences, in particular, when compared with the wellestablished H, O and C stable isotopes. This mainly is a result of lacking proper analytical technique for B isotopic analysis. The first boron isotopic measurement, in fact, was made more than 30 years ago (Thode et al., 1948; McMullen et al., 1961; Shima, 1962; Agyei & McMullen, 1968; Schwarcz et al., 1969). Since then the progress in this field has been extremely slow because of problems associated with mass spectrometric analysis. Not until the last decade did a rapid increase in the number of studies of the stable boron isotope composition in natural samples start to be seen in the related literature (Spivack & Edmond, 1986; Klo¨tzli, 1992; Barth, 1993; Palmer & Swihart, 1996). During this period, a variety of instrumental analytical methods with varying degrees of accuracy and precision were proposed and subsequently have been evaluated by researchers in different fields (Aggarwal & Palmer, 1995; Heumann et al., 1995). These techniques include inductively coupled plasma mass spectrometry, ion microprobe, 227

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Handbook of Stable Isotope Analytical Techniques

glow discharge mass spectrometry and thermal ionization mass spectrometry (TIMS) (see Swihart, 1996). Below I will focus attention to discuss two techniques, namely alkaliborates positive ion (e.g., Cs2BO2þ) TIMS and BO2 negative ion TIMS. Other more detailed information on the analytical procedures, including chemical separation, other instrumental techniques and relevant geological implications are referred to in recent review articles by Swihart (1996), Palmer & Swihart (1996), Aggarwal & Palmer (1995), Heumann et al. (1995) and Barth (1993). A review on B isotope analytical methods is given in Volume I, Part 1, Chapter 7.

C H A P T E R

4

C ARBON

4-1.

O RGANIC M ATERIALS

4-1.0.

INTRODUCTION AND P REPARATION OF SAMPLES

Analytical methods for quantitative determination of carbon in specific organic components were presented for longer time in literature. Some of the combustion devices as described in quantitative methods were, generally in modified form, adopted for stable isotope analytical techniques. To name a few examples: Pregl combustion by an O2 flow for the determination of hydrogen and carbon (Belcher & Ingram, 1950a) and combustion with Pt gauze for heat capacity with oxidation by water vapor oxygen (Van Hall et al., 1963).

4-1.1. 4-1.1.1.

COMBUSTION METHODS

Combustion with O2 circulation

Leavitt & Danzer (1993) combusted holocellulose samples placed in a combustion furnace (800C) in a ‘recirculation micro combustion’ device in the presence of excess of O2. CO2 produced by the combustion was cryogenically trapped and purified and used for isotopic measurements.

4-1.1.2.

Empty tube combustion (Pregl combustion) with O2 flow

Ingram (1948) applied Pregl type combustion, where organic materials were combusted in a rapid stream of O2 (50 mL/min) in an empty tube at a temperature of 800C (Figure 4-1.1). Both combustion and sweeping out of the reaction gases were accomplished by the same O2 stream. Combustion of a sample took 10 min by this method. Raising of the furnace temperature to 950C did not affect the combustion process. The method was presented for quantitative determination of C and H isotopic compositions of organic materials, but basically can be adopted for isotopic determination too, depending on complete yields of CO2 and H2O after combustion of the organic material. Epstein et al. (1976) and Yapp & Epstein (1977) combusted cellulose nitrate with an excess of O2. CO2 was separated from the other effluent gases, H2O (trapped cryogenically) and nitrogen oxides (eliminated over Cu at 450C), and was used for C isotope measurement. For more details on the combustion method, see Chapter 1-3.2.2. 229

230

Handbook of Stable Isotope Analytical Techniques

Furnace O2 Flow Quartz wool Ag gauze roll

Figure 4-1.1

4-1.1.3.

Empty tube combustion of organic materials in an O2 flow (after Ingram, 1948).

Combustion with O2 – Pt catalyzed

Naughton & Frodyma (1950) described a combustion system of organic material for quantitative purpose. A sample was combusted in a furnace with Pt catalyzer in an O2 atmosphere. CO2 and H2O can be collected for C and H isotopic analysis, respectively. St-Jean (2003), in an overview of the two major methods of organic matter conversion into CO2, made a division on low (650C) and high (800–950C) temperature combustion. Organic matter is combusted in an atmosphere of O2 with Pt coated either on alumina beads or on quartz wool or on crushed quartz (depends on temperature of process and application) as a primary catalyst. A total carbon (TC) value can be obtained by a nondispersive infrared (NDIR) detector. Advantage of this (classical) method is that refractory compounds, such as humic or vulvic acids, oxidize better and faster. Disadvantage is the relatively larger volume of sample material needed by this technique. Total organic carbon (TOC) is determined by difference , according to [4-1.1]

TOC ¼ TC  TIC with TIC is total inorganic carbon.

4-1.1.4.

Combustion with CuO and O2 flow

Rittenberg (1946) described a technique for combustion of organic materials by combustion on CuO with a stream of O2 (Figure 4-1.2). Organic materials (1–5 mg) were combusted in a stream of O2 (swept through a trap with concentrated H2SO4 for removal of water and used as bubbler to adjust the gas flow) and through a furnace filled with CuO (at 800C). Combustion time was 4–5 min. The CO2 released from the combustion was trapped in a centrifuge tube Sample boat

Furnace Rubber hose

Plug

CuO wire O2

Concentrated H2SO4

15-cc centrifuge tube Ba(OH)2 solution

Figure 4-1.2 Device for combustion of organic materials on CuO in a stream of O2 (after Rittenberg, 1946). CO2 is trapped in a Ba(OH)2 solution as BaCO3.

231

Carbon

(at room temperature), filled with 5cc of a saturated solution of Ba(OH)2, as BaCO3. BaCO3 was washed three times with water by centrifugation. The carbon could be released as CO2 from the carbonate by acid treatment, and the CO2 was measured on a MS (direct CO2 measurement in a MS was another option). Anderson et al. (1952) presented a device for combustion of organic matter by CuO and O2 (Figure 4-1.3). The device was flushed for 15 min with O2 before combustion of samples was started. The O2 (from a commercial cylinder) was cleaned through a trap with anhydrone (MgClO4) and ascardite (NaOH on an asbestos bearer) separated by glass wool and by a water trap cooled by a dry ice acetone slush bath. If the sample contained hydrogen, it was collected as water in a special connected trap WT (Figure 4-1.4a); the water could be used for analysis of the H isotope composition of the organic compound (see Chapter 1-2). Nitrogen, present as

Two-liquid manometer Oil Hg m

Pre-heater Furnace with reaction tube

m

CO2 collection

O2

Vacuum Bypass place for WT H2O trap CO2 trap

Figure 4-1.3 Device for combustion of organic matter with CuO and O2 (after Anderson et al., 1952). Hydrogen (as water) and nitrogen (as N2) can also be collected for isotopic measurement with the device. (a)

(b) Water trap

Fitting at bypass in Figure 4-1.4

Figure 4-1.4 reducer.

Cu

N2O Reducer

Water trap and N2O reducer (after Anderson et al., 1952). (a) water trap; (b) N2O

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Handbook of Stable Isotope Analytical Techniques

nitrogen oxide, was reduced in a furnace containing Cu gauze (Figure 4-1.4b). The conversion of N2O was needed because it has similar physical behavior as CO2 and therefore is hard to separate from CO2. The N2 can be used for isotopic measurement or was pumped away. A sample was loaded in a Pt boat in the reaction tube in the combustion furnace. This tube contained 0.5 cm wad of compressed asbestos, 1 cm wad of Ag wire, 18 cm of CuO wire, 1 cm wad of Ag wire and 2 cm roll of Pt screen fitting into the reaction tube nicely and holding the reagents in place. The furnace was heated at 750–800C for the reagent part of the tube, and at 750C for the sample boat part. The furnace was movable over the reaction tube. CO2 was purified cryogenically in a set of traps (Figure 4-1.4), collected and measured in a MS. Yields were measured in a two-liquid manometer, as is shown in Figure 4-1.3. The liquids in the manometer are Hg and dibutoxytetraethylene glycol. The manometer was carefully evacuated and outgassed; the oil was outgassed by gentle heating and freezing cycles. Craig (1953) presented a vacuum device for C isotope analysis on organic matter by combustion of a sample mixed with CuO and an O2 gas flow (Figure 4-1.5). Included in the device was an extension for C and O isotope analyses on carbonates (see Chapter 4-5). A silica glass combustion tube was partly filled with CuO (half of the part positioned in the furnace) and with a sample (sufficient to provide 10–15 mL CO2; CO2 volumes as small as 1 mL can be measured) in an alundum boat. Tank O2, purified in a CuO furnace at 700C, was added to the system at a pressure of 15 cmHg. Combustion took place at 900–950C. A Toepler pump circulated the gases through the furnace. CO2 was condensed in a liquid nitrogen trap, and all CO or other C compounds were converted into CO2. After complete conversion, the CO2 was purified cryogenically and measured on a MS. Christman et al. (1955) presented a device for combustion of microsamples (oil samples) mixed with CuO and followed by oxidation with O2 (Figure 4-1.6) following the method Pumps

O2

CuO furnace

Carbonate acid digestion

Sample tube Hg Column

Combustion furnace

Figure 4-1.5 Combustion system for C isotope analysis on organic matter including a carbonate analytical extension (after Craig, 1953).

233

Carbon

Pressure regulator O2 O2 To purifying system

From purifying system O2

CO2 take off V1

H2SO4

V2 m Vacuum

Combustion tube H2O trap

4 2 1

3

CO2 trap

MnO2 trap

Figure 4-1.6 Device for dry combustion of organic matter for O isotope measurement (after Christman et al., 1955). 1 = coarse glass frit; 2 = MnO2; 3 = glass wool; 4 = anhydrone. For the two-liquid manometer connected to m, see Figure 4 -1.4.

comparable with the one described by Kirsten (1953). A small sample (mixed with 200–500 mg CuO) was loaded into a Pt thimble brought into the silica glass reaction tube of the device and heated to 930–970C by a furnace. The products of the pyrolysis were oxidized by a stream of O2 (dried by passing through a trap with H2SO4; flow 30 mL/min). Ni foil act as catalyzer for the oxidation – the Ni was heated in concentrated sulfuric acid at –130C for 30 min before analyses were started. Ag wire in balls was pre-treated by heating them at 400C in porcelain boats in a silica glass tube for 1 h in a hydrogen atmosphere and 1 h in an oxygen atmosphere. Normally about 10 min were taken to push the Pt thimble with sample with an electromagnet into the furnace. The total combustion time was 30–40 min. H2O was removed from the resulting gas mixture by a cold trap. Nitrogen oxides, eventually formed during combustion, were removed by reduction over hot Cu (e.g. Anderson et al., 1952) or by absorption on MnO2 at room temperature (e.g. Belcher & Ingram, 1950b). The MnO2 trap consisted of a coarse fritted glass seal at the bottom of the inner tube as is shown in Figure 4-1.6, with 2.5 g 10–20 mesh MnO2 on top of the frit and covered by a glass wool plug and anhydrone and a glass wool plug again. The trap was placed in the combustion device between an acetone–dry ice trap (H2O trap) and a liquid nitrogen trap (CO2 trap). MnO2 was regenerated at 120C under vacuum. Biggs et al. (1952) under a flow of O2 ‘pyrolyzed/combusted’ organic compounds, and passed the products over hot CuO. CO2 from the combustion (here by absorption) and water (labeled with tritium) were collected separately for analysis and measurement. See Chapter 1-3.2.2 for more details on the combustion procedure. Schiegl & Vogel (1970) presented a combustion system where organic compounds were heated under a flow of O2 and send through a furnace filled with CuO. CO2, formed during combustion, was separated from H2O cryogenically and was directly measured for C-isotopes (Chapter 1-3.2.2). At the isotope laboratory of the Institute of Earth Sciences at the University of Utrecht, a device for combustion of solid and fluid organic compounds mixed with CuO and under an O2 atmosphere was used (Figure 4-1.7). Samples, mixed with CuO, were loaded

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Circulation pump

Flow

CuO + sample

Teflon tube

Whitey valve

Magnet

Teflon tube Furnace (800°C)

Cold traps

Quartz wool

Silica glass SS spiral

Sample O 2 boat

Sample boat

Vacuum

Sample tube Cold trap

Pressure sensor Yield-measuring tube

Cold traps

Figure 4-1.7 Device for combustion of organic compounds with CuO þ O2 by O2 circulation. Detail of the sample boat is shown in the right upper corner (unpublished; Institute of Earth Sciences, University of Utrecht).

in silica glass ‘boats’ (see detail in Figure 4-1.7) and covered by quartz wool. Sample boats were introduced in the system under O2 flow to refuse air flushing into the system. Combustion was applied at 800C for about 15–20 min under a flow (circulation) of O2 at 180–210 mbar pressure to avoid condensing of O2 in the liquid nitrogen trap. H2O was removed in a slush at –100C and CO2 was collected in a liquid nitrogen trap. O2 left over after combustion and other non-condensable gases (NCGs) were pumped away. CO2, after eventual yield measurement in a calibrated volume by pressure sensor, was used for O isotope measurement in a mass spectrometer (MS). Fry et al. (1992) presented a system for simultaneous measurement of C and N isotopes in an elemental analyzer-isotopic ratio mass spectrometer (EA-IRMS) system with He þ ’ portion of O2’ flow on the same organic material sample. The sample was placed in a Sn boat and flash combusted (1800C) in a furnace with CuO kept at 1000C. A He-flow, doped with a portion of O2 when the sample dropped into the furnace, transported the effluent gases through a Cu furnace at 600C for reducing any N oxides into N2 and for removal of excess O2, and further to a cold trap where H2O and CO2 were collected and N2 passed through. After N2 procedures, the CO2 was cryogenically separated from the H2O and measured for its C isotopic composition. A more detailed description of the procedure can be found in Chapter 5-2.5.1.

4-1.1.5.

Combustion with O2 + metallic Cu

Kirsten (1954) presented a method for combustion of organic materials in an atmosphere of O2 and with addition of Cu in a sealed tube (Figure 4-1.8). Sample was brought in the closed end of a combustion tube (silica glass). Cu metal was placed at the other side of a constriction in the tube, O2 (10–30 mmHg pressure) was introduced and the combustion tube was sealed by a torch. Cu was added to trap excess of O2 to avoid reaction of N2 into oxides. Combustion gases were H2O, CO2 and N2. Besides C isotope determination

235

Carbon

Sample

Restrictions

O2

Cu Sealed tube

Figure 4-1.8 Sealed combustion tube with O2 þ Cu for organic materials for H, C and N isotope measurements (after Kirsten, 1954).

(on CO2), H and N isotopes from the same sample were measured on H2 (produced from H2O by reduction) and N2, respectively.

4-1.1.6.

Combustion with Ag-based catalyst + O2

A method for C isotope analysis of organic matter, based on Ag-based catalyzed O2 combustion at 800C, was presented in a sales folder by VG (now Micromass) (Figure 4-1.9). A reduction furnace with metallic Cu (250C) was included after the oxidation furnace to convert nitrogen oxides into N2 and to remove excess oxygen. The carbon isotopic composition of the CO2, produced in the oxidation furnace, was not effected by this reduction furnace. A Mg perchlorate-colorcarb finally removed water from the effluent gas. He was used to flush the combustion effluent gases through the system. A liquid nitrogen trap collected the CO2 while He was flushed to air. Back diffusion of air was prevented by a silica gel trap.

4-1.1.7.

Laser combustion in an O2 atmosphere

A laser device (Nd-YAG IR laser), described in Chapter 4-5.3.2 for the carbonate ablation method by Smalley et al. (1989), can also be used for O isotope analysis on organic material. Combustion took place in an O2 atmosphere (pressure 500–750 mbar). In the same system, CO2 was purified and measured on-line in a MS. Liu et al. (2000) described a laser (Nd:YAG laser) combustion system for organic C isotope determination (Figure 4-1.10). Graphite rod, graphite–silica mixture discs and natural shale slab samples were tested in their system by in situ C isotope analysis. Combustion in both O2 atmosphere and O2-free atmosphere (last not for graphite rod obviously) was applied. CO Reduction furnace Sample pusher Oxidation furnace High heat

O2

He

To atmosphere

H2O trap

Anti-diffusion trap To atmosphere

Collection tube Gas scrubbers

Figure 4-1.9 Combustion line for carbon isotope determination on organic matter: ISOPREP 13 (after sales folder byVG).

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Video camera

Monitor

Microscope

Nd:YAG laser sample chamber

O2 tank Turning mirror To MS

X–Y adjustable stage

To vc. Cold Acetone Acetone liquid Pentane finger slush Pt wire slush nitrogen slush –94°C –131°C 850°C –94°C

Figure 4-1.10 Diagram showing the Nd:YAG laser combustion system for C isotope analysis in graphite and in organic compounds in rock samples (after Liu et al., 2000).

was converted in a Pt-wire furnace at 850C (Figure 4-1.10). SO2 and CO2 were separated cryogenically, if needed. Claimed reproducibilities for the tested materials were between 0.1 and 0.3‰.

4-1.1.8.

Flash combustion with O2 in He atmosphere

Dugan & Aluise (1969) presented a system for simultaneous quantitative determination of C with H, N, O and S in organic compounds by combustion with O2 in a He atmosphere. Effluent ˚ columns. Total gases were collected and partly separated in carbowax and molecular sieve 5 A separation can be obtained by cryogenic distillation. See Chapter 1-3.2.2 for more details.

4-1.1.9.

Flash combustion with WO3 on Al2O3 + O2

Pichlmayer & Blochberger (1988) described an EA flash combustion system for determination of C isotopes in organic compounds. A system combining the determination of C, N and S isotopes was presented. Combustion occurred, with a sample contained in a Sn capsule, on WO3 on Al2O3 and with a quantity of O2. Precision, for samples between 50 and 1000 mg C, was better than –0.1–0.2‰.

4-1.1.10.

Combustion with O2 + Pt wire–CuO-electrodeposited Ag crystal catalyzer

Naughton & Frodyma (1950) described a combustion system of organic material for quantitative purpose. They found best results for combustion with a catalyzer (Pt wire), CuO and electrodeposited Ag crystals.

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4-1.2. 4-1.2.1.

O XIDATION METHODS

Oxidation with CuO

Wilzbach & Sykes (1954) presented a method for sealed tube combustion of organic compounds (Figure 4-1.11). The CO2 produced by the combustion was isolated cryogenically in a vacuum system. Yields were reproducible within 1%. A sample could be prepared within 30 min. Added to the system, as shown in Figure 4-1.11, was a detection system for 14C. An organic compound sample (1–10 mg) was mixed with 0.75 g/60-mesh CuO and 0.25 g/60-mesh reduced Cu in a glass ampoule, which was evacuated, degassed and sealed. The ampoule was heated at 640 – 10C for 30 min. After cooling the ampoule was loaded into a larger glass tube and, after being evacuated, broken and the CO2 was purified by cryogenic distillation in a vacuum system. Frazer (1962) and Frazer & Crawford (1963) described a method for combustion of organic compounds with CuO and Cu gauze in evacuated, sealed vycor or silica glass ampoules at 900–950C for 1 h (at temperatures >950C Cu fuses with the silica of the glass) for quantitative determination of H, C and N. CO2 was separated cryogenically and could be analyzed for its C isotopic composition. High sulfur contents caused the need of slow cooling, with formation of CuSO4 while preventing any SO2 formation. In a modified system, halogens produced by the reaction of the organic compounds were removed by a Cu–Hg amalgam trap. Uranium turnings were used for reducing NO to N2 – temperature of reduction of NO depends on surface to volume ratio of the packing of uranium. MnO2 (135C) was used for SO2 removal. Stuermer et al. (1978) used CuO and Ag for oxidation (at 900C) of humic substances (after a method by Stump & Frazer, 1973). CO2, N2 and water (methods described in Chapter 1-2) were collected, were measured volumetrically and were used for C, N and H isotopic analysis, respectively. Sofer (1980) described a combustion method for reaction of organic compounds with CuO wire in an ampoule. CuO wire was purified by firing in a furnace at 900C for 1 h. Borosilicate glass tubes (20 cm  9 mm) were cleaned from contaminants by heating at 550C for 1 h. CuO wire (2 g) was loaded in the bottom of a glass tube with the organic compound (1–2 mg) on top of it. Loading method depended on the quality of the sample: gas was introduced by a Toepler pump, liquids by a capillary tube (high-viscous liquids were heated to decrease viscosity)

Pumps

14C

detector Sample + CuO + Cu

Cold traps Tube with ampoule

Manometer

Figure 4-1.11 Combustion device for organic compounds (after Wilzbach & Sykes, 1954).

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Handbook of Stable Isotope Analytical Techniques

and solids were weighted and dropped onto the CuO wire or first dissolved in an appropriate solvent (most of the solution was absorbed by the CuO) and placed in a heated sandbath to evaporate the solvent under a flow of dry N2. Prepared tubes were evacuated (2  103 Torr) and sealed with a torch, about 16–17 cm from the bottom end. If the sample had a high vapor pressure, the tube was cooled by liquid nitrogen during evacuation. The sealed tubes were loaded horizontally on a rack and placed in a thermostated furnace that was preheated at 550C (slow heating may caused charring of the organic compound) and were combusted for 1 h (methane was combusted for 5 h). Important for a complete combustion was the evenly spreading of the CuO on the floor of the tube. After completion of the reaction, the tubes stayed in the furnace, which was turned off, for a night to cool down slowly. The tubes were cracked at a vacuum system (see Appendix C5), and CO2 from the reaction was purified from other gases cryogenically in the vacuum system, and was measured on a MS. Nitrogen or sulfur from the organic compound formed no problem: NO2 was reduced to N2 during combustion and SO2 reacted during combustion with excess Cu into solid CuSO4. Comparison with the ‘dynamic’ method of Craig (1953) shows a 2‰ difference with the ampoule method, for which an explanation was not found. Borosilicate glass was used at reduced reaction temperature to save costs. Mu¨hle et al. (1981) presented a combustion furnace with CuO (þAg wool) for the determination of isotopic compositions on organic compounds (Figure 4-1.12). No details were available1 for further description. Schoell et al. (1983) compared closed CuO oxidation (1–2 mg sample þ 500 mg CuO as fine powder; in sealed silica glass tubes; evacuated to 4‰ in 80Se/76Se ratio; this problem can be overcome using the double-spike method; see Section 10-4.2,3 and Volume I, Part 1, Chapter 29). SeH2 was formed by hydride generation [3 w% solution of NaBH4 (Figure 10-1.1)], and H2Se was stripped out of N2 Peristaltic pump

Droplet separator

Teflon tubing NaBH4 solution HNO3 Stripping vessel

Sample + spike

Absorption tube Sintered glass plugs Stirrer

Figure 10-1.1 Diagram showing the system for hydride generation of SeH2 and subsequent absorption in HNO3 (afterTanzer & Heumann, 1991; see also Heumann & Ra«dlein, 1989).

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Selenium

the solution by a N2 carrier gas in a liquid–gas separator and was passed to a fluoropolymer tube containing concentrated HNO3 where it was absorbed into solution. HNO3 was taken to dryness with Se recovery of 85% (Rouxel et al., 2002; Ellis et al., 2003) or an average of 48% (Johnson et al., 1999), with major losses occurring through incomplete reaction and flow of unreacted Se out of the liquid–gas separator. Johnson et al. (1999) removed ferric iron via cation exchange resin to avoid interference with the Se reduction process. Ellis et al. (2003) described a continuous flow hydride generation system (Figure 10-1.2; see also Figures 10-5.2 and 10-6.2 and Rouxel et al., 2002) for purification of large-volume samples of Se for TIMS analytical purpose. All Se was converted to Se(IV). The sample dissolved in a 3–6 M HCl matrix was pumped at 8 mL/min and mixed with 1% NaBH4 solution pumped at 1 mL/min. Organic compounds were removed by oxidation with several additions of 100 mL concentrated HNO3 and 50 mL, 30% H2O2 to the dried samples, each followed by evaporation to dryness (Rouxel et al., 2002; Ellis et al., 2003). Heating to 120C (samples in closed PTFE containers) followed by overnight evaporation to dryness at 70C was applied by Rouxel et al. (2002). Temperature must stay below 80C to prevent Se loss during evaporation. Separate extraction of Se(IV) and Se(VI) by anion exchange methods was applied by Ellis et al. (2003) on sediment samples. Selenium redox change – Isotopic fractionation induced by reduction of Se(IV) to Se(0) was variable (between 19 and 10‰) and depended on the reaction mechanism and rate. Krouse & Thode (1962) and Rashid & Krouse (1985) reduced Se(IV) (5 g Na-selenite dissolved in 50 mL water) with dilute hydroxylamine hydrochloride (excess quantity) to form elemental Se (slow precipitation) following the reaction

H2Se + N2 to concentrated nitric acid trap

H2Se + N2 + solution

Frit

Drain

NaBH4 (1% w/v) (1 mL/min)

Sample (1–4 M HCl) (8 mL/min) 3–6 M HCl matrix

N2 Peristaltic pump

Figure 10-1.2 Schematic diagram of the continuous flow hydride generation system developed for purification of Se before TIMS analysis (after Ellis et al., 2003).The frit is a 4 - to 5.5-mm fine-glass frit.

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Handbook of Stable Isotope Analytical Techniques

2Hþ þ 2NH2 OH þ SeO2 3 ! Se # þN2 O " þ4H2 O

[10-1.1]

Rashid & Krouse (1985) determined the isotopic fractionation in this system for 80Se/ 76Se and 82Se/76Se. Selenate (Se[VI]) was reduced to selenite (Se[IV]) by HCl (1 M) following the reaction (Rees & Thode, 1966) SeO42 þ 8Cl þ 8Hþ ! SeCl62 þ Cl2 þ 4H2 O

[10-1.2]

Rees & Thode (1966: 82Se/76Se) studied isotopic fractionations in the system of equation [10-1.2]. Rees & Thode (1966: 82Se/76Se) reduced Na-selenite (in solution) with ascorbic acid (C6H8O6) following the reactions SeO32 þ 2Hþ ¼ H2 SeO3

[10-1.3]

H2 SO3 þ 2C6 H8 O6 ¼ Seþ2C6 H6 O6 þ 3H2 O

[10-1.4]

and studied the Se isotopic fractionations in this system. Rashid & Krouse (1985) reduced SeO32 to H2Se with a mixture of HI–H3PO2–HCl and studied the isotopic fractionations, and compared these with fractionations in other reduction methods given above. They concluded that Se(IV) reduction was a multi-step process and the relative rates of the steps determined the amount of isotopic fractionation involved. Rees and Thode (1966) found a fractionation of around 18‰ for Se(VI) to Se(IV) reduction by strong HCl at 25C. Johnson et al. (1999) measured a much smaller fractionation (8.3 ‰) at 70C. Brimmer et al. (1987) described a quantitative method for reduction of selenate into selenite. Johnson et al. (1999) used 6 N HCl with heating at 100C for 20 min. See also Janghorbani & Ting (1989) and Ting et al. (1989). Water samples – Water samples were filtered (0.45-mm cellulose nitrate filter; polycarbonate filter) and any material passing the filter was considered to be dissolved. A procedure for Se extraction from water samples for isotopic measurement (by N-TIMS), mostly based on reductive reactions is given in Figure 10-1.3. Heumann & Grosser (1989) separated selenite and selenate from water solutions by a weakly basic DEAE (diethylaminoethyl; 2 g) cellulose exchange column. Formic acid (1 mol/L) was added first and then the sample solution. Selenite is eluted with 1 mol/L formic acid and selenate with 0.1 mol/L HNO3. Tanzer & Heumann (1991) separated compounds from water samples by GC and used HNO3/HClO4 reaction for extraction of Se from the thus separated organic compounds. For details of the acid reaction, see the next section and Figure 10-1.4 [Tanzer & Heumann (1991) used different ratios of acid mixture and heating procedures]. Organic or biological samples – For enriched Se isotope tracer studies, Se can be derivatized in the form of 5-nitropiazselenol (NPD) from organic or biological samples by digestion with HNO3, H3PO4 and H2O2 (rapid reaction: 10–20 min to get clear solution: Reamer & Veillon, 1983) followed by reaction of the acid solution with (4-nitro-)o-phenylenediamine (purification/preparation procedure described by Reamer & Veillon, 1981, 1983 and Aggarwal et al., 1992b). The remaining HNO3, which will react with the chelating agent, was removed by the addition of formic acid (Reamer & Veillon, 1983; Swanson

729

Selenium

Weighing sample (~200 mL) Addition 82SeO32– tracer (~1 g)

Bring at pH 11–12 with 2 M KOH solution Evaporate to near dryness

Reduction of SeO42– to SeO32– with 10 mL 5 M HCl; cover heat ~30 min at 90–100°C

Reduction of SeO32– to Se0 with ascorbic acid (5 g; 200 mg/g solution)

Elementary Se (colored red) filtered off (filter with 1–2 mL methanol and drops of water Dissolve in concentrated HNO3/HCl Evaporate to dryness Dissolve in 20 μL water

Figure 10-1.3 Diagram for preparation of Se from water samples for N-TIMS measurement (after Grosser & Heumann, 1988).

et al., 1991; Aggarwal et al., 1992b; Moser-Veillon et al., 1992), and the undigested lipids were, after addition of 10 mL deionized H2O (pH of solution is 0.5–1.5), removed with 5 mL of chloroform (Reamer & Veillon, 1983). Se–NPD was extracted into chloroform (2 mL 15 min in mechanical shaker: Reamer & Veillon, 1983) for injection in a GC-MS device (Reamer & Veillon, 1981; Patterson et al., 1989; Veillon et al., 1990; Aggarwal et al., 1992b). The above described methods were not meant for high-precision Se isotope determinations, but to detect enrichment of Se isotopes in tracer experiments or tests. Ting et al. (1989) used a mixture of HNO3–H2O2 (plasma, red blood cells, faeces, food) or a mixture of HNO3–HClO4 (urine) as an oxidant for wet-ashing samples. This was followed by boiling for 10 min with HCl to reduce Se into selenite form for analysis by hydride generation – ICP-MS. Buckley et al. (1992) added Mg(NO3)2 (20 mL = 23 g Mg/L concentrated HNO3) as an ashing aid to orchardgrass hay (1.0 g) or bovine serum (1.0 mL). Ashing was applied in covered beakers at 105C for 30 min, followed by 185C for 2 h; then, uncovered, the solutions were heated at 275C until the beakers were dry at the bottom. The cover was replaced and the beakers were heated at 500C in a muffle furnace for 4 h. Ash was dissolved in HCl (3.8 M in 20 mL). Use of 4-trifluoromethyl-o-phenylenediamine (TFMPD) (Veillon et al., 1990; Aggarwal et al., 1992b) or 3,5-dibromo-o-phenylenediamine (DBPD) (Aggarwal et al., 1992b) as

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Handbook of Stable Isotope Analytical Techniques

Weighed sample (0.3–2 g) Addition 82Se-enriched spike Exact weight; pH ≈ 1

Decomposition of sample + 5 mL bidest. H2O + 6 mL of concentrated HNO3 /HClO4 (10:1) Heating at 100°C for 30 min + 140°C for 20 min (= step 1)

Adding 6 mL HNO3/HClO4 (2:1); Heating at 180°C for 45 min + 200°C for 5 min (= step 2)

Concentration of solution (200°C) ± complete evaporation (Risk: HClO4 may form explosive compounds)

Reduction of Se(VI) to Se(IV) with 15 mL 5 mol/L HCl Heating at 130°C for 30 min

Formation of SeH2 with NaBH4 (3% solution) Selective distillation

Absorption of SeH2 in concentrated HNO3 evaporated to dryness

Figure 10-1.4 Diagram for preparation of Se from food samples for N-TIMS measurement (after Heumann & Ra«dlein, 1989).

a chelating agent, instead of 4-nitro-o-phenylenediamine (NPD), was reported and tested for GC behavior (memory; precision and accuracy of isotopic ratio measurement). – Blood samples (serum – red blood cells) were collected into 12- or 25-mL disposable, trace-metalfree syringes containing acid citrate dextrose and were centrifuged (2000 = g for 15 min), and plasma was drawn off with a disposable pipette and aliquots were placed in cryotubes and frozen quickly within 45 min after collection and stored at 20C (Janghorbani et al., 1982a: without citrate dextrose in syringe; Patterson et al., 1989). Samples were further treated by acid digestion followed by derivatization as is reported above.

Selenium

731

– Urine samples (100 mL) were placed in plastic bottles and stored at 20C until analysis (Janghorbani et al., 1982a; Patterson et al., 1989). Samples were further treated by acid digestion followed by derivatization as is reported above. – Fecal samples were collected in polystyrene containers and, in the laboratory, homogenized in a colloid mill using deionized water. Weighed samples were lyophilized for 6 days and stored frozen at 20C (Janghorbani et al., 1982a; Patterson et al., 1989). Samples were further treated by acid digestion followed by derivatization as is reported above. – Food contains, commonly, Se in the form of selenomethionine (Veillon et al., 1990; Swanson et al., 1991). Food samples were decomposed with a HNO3/HClO4 mixture and eventually a spike solution was added (Heumann & Ra¨dlein, 1989). Se was recovered by hydride formation (SeH2) and the hydride was trapped in a HNO3 solution and evaporated to dryness (see procedure in Figure 10-1.2). – Oil products from refineries, waste streams were processed either by ferric iron coprecipitation methods or by hydride generation (see above; Johnson et al., 2000). – Plant material (0.2 Mg) was dried, ground and digested at 40C with concentrated HNO3 (10 mL) and periodic additions of 200 mL of 30% H2O2 was done over a period of 5 days. The solution was taken to dryness and dissolved with 6 M HCl (Herbel et al., 2002). Marin et al. (2003) derived concentrated selenium from lichens and plants using matrix separation and pre-concentration of samples with thiol cotton (see also below). Thereafter, samples were digested with HNO3–H2O2–HF and analyzed for Se content by graphite furnace atomic absorption spectrometry (GFAAS). Column separation techniques Al2O3 column separation of Se(IV)–Se(VI): Acidic (1–8 M HCl) Al2O3 has been found to be an effective and selective ion exchanger for Se(IV) and Se(VI) (Knab & Gladney, 1980). Phosphate added to the preconditioning solution of the column precludes adsorption of Se(VI) without affecting Se(IV) adsorption. For complete Se collection on the column, Se(VI) must be reduced in HCl (which is temperature and pH dependent: 6 M HCl and 20 min boiling are required for complete reduction; see Knab & Gladney, 1980 for details). Herbel et al. (2002) applied a ferric hydroxide co-precipitation technique to separate Se(VI), which did not adsorb strongly when sulfate was present, from other dissolved Se species which did adsorb strongly. Anion-exchange chromatography: Johnson et al. (2000) collected Se on an anion-exchange resin [Se(IV) and Se(VI)] (but only a small part of organic Se) or, after conversion of Se(VI) and organic Se into Se(IV), by co-precipitation with hydrous ferric oxide. Herbel et al. (2000) used anion chromatography for separation of Se(IV) and Se(VI) if they coexisted in the samples after a method as was given in Ornemark & Olin (1994). Ellis et al. (2003) applied a similar anion chromatography Se separation technique. Se extraction by TCF (thiol cotton fiber): TCF, cotton to which thiol groups had been attached by reaction with thioglycollic acid, quantitatively absorbed elements such as Se, Te, As and Sb, depending on their various oxidation states, and were used for separation of Se from the sample solution (Yu et al., 1983; Xiao-Quan & Kai-Jing, 1985; Rouxel et al., 2002, 2004; Marin et al., 2003). This method enabled rapid sample preparation, as Se was extracted from solutions with a single step and was then released from the TCF via oxidation by nitric acid. Separation of Se from Ge (an isobaric interferent) was complete, but separation from As was not.

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Handbook of Stable Isotope Analytical Techniques

10-2.

F LUORINATION M ETHOD

Elemental Se was fluorinated into SeF6 by Krouse & Thode (1962), basically following fluorination methods such as those described for sulfur isotope analysis (Chapters 8-1.7 and 8-1.8.2 and Volume I, Part 1, Chapter 20.4.5). Krouse & Thode (1962) used Monel steel for their sample-handling system and avoided any contact with grease or Hg in their system. Se isotopes (82Se/76Se ratio) were measured on the most abundant ion species: SeFþ 5 (masses 171 and 177). Rees & Thode (1966) and Rashid & Krouse (1985) described methods to prepare elemental Se from selenite and selenate. Doctoral theses by Krouse (1960) and Rashid et al. (1978) included studies of fluorination of Se. A repeatability for 82/76Se analysis in natural samples between –0.1 and 1‰ was reported by Krouse & Thode (1962).

10-3.

GC-MS M ETHOD

A GC-MS (quadrupole) equipment was used, with stable isotope dilution [added: Se (= stable) and 75Se (= radiogenic); see Volume I, Part 1, Chapter 37 for explanation of isotope dilution techniques], for quantitative measurement of Se (Reamer & Veillon, 1981; Patterson et al., 1989; Veillon et al., 1990). Because isotopes are involved in the method, it is included in this review. From isotope ratio measurements in the Se-NPDþ parent ion cluster, the amount of ‘Se-tracer’ [74Se, 75Se (= radiogenic), 76Se, and 82Se were reported], the un-enriched natural Se and total Se can be quantitated. 82 Se/74Se, 82Se/76Se and 82Se/80Se ratios were determined by Veillon et al. (1990). Solutions were injected (1 mL; at 175C) into a column (1.2 m  2 mm i.d. silanized glass column packed with 1% SP2401 on 100/120 mesh Chromosorb 750; at 160C). A He carrier gas flow (20 mL/min) was applied (Reamer & Veillon, 1981). Aggarwal et al. (1992b) brought forward that the key problem in GC-MS methods is the lack of chelating agents without appreciable memory problem at nanogram levels. Other studies using GC-MS can be found in Mangels et al. (1990, following the method by Reamer & Veillon (1983); tracers: 74Se in selenomethionine and 76Se in sodium selenite], Swanson et al. (1991), Moser-Veillon et al. (1992; tracers: 74Se in selenomethionine and 76Se in sodium selenite) and Van Dael et al., (2002: 76Se-selenate and 74Se-selenite in a milk-based infant formula). Boza et al. (1995) analyzed Se isotopes in a comparative intrinsic and extrinsic 78Se and 82 Se and radiogenic (75Se) tracer study. Rat feces and yeast (Saccharomydes cerevisiae) were dried, ground and well mixed and isotopically spiked. These preparates were digested with equal volumes of HNO3 (14 mol/L) and HClO4 (70%) at 180C for 36 h. Selenate was reduced to selenite by the addition of HCl (6 mol/L) and neutralized with NH4OH (7 mol/L). Se was derivatized with 4-nitro-o-phenylene-diamine, extracted with chloroform and dried under an atmosphere of N2 and measured for its isotopic composition by GC-MS. Wolf & Zainal (2002) analyzed the five Se isotopes in selenomethionine and methylselenocystine in food materials by GC-MS with 74Se-enriched selenomethionone as the tracer. 82

733

Selenium

An overall repeatability of about 1% in a day and of about 3% day-to-day was reported. Note that many of these studies concern enriched tracer methods, where repeatability is less of a concern.

10-4. 10-4.1.

TIMS M ETHOD

Negative ion TIMS

Dual filament approach – Heumann et al. (1985), Grosser & Heumann (1988), Wachsmann & Heumann (1989, 1992) and Heumann & Wachsmann (1989) described a negative TIMS (N-TIMS) method for measuring Se isotopes. They used a double-Re-filament ion source with distance between the filaments of 2 mm for optimal performance. Se (0.5–15 mg) was loaded as H2SeO3 or BaSeO3 solution and evaporated to dryness, and 10 mL silica gel suspension was added dropwise and also evaporated to dryness (causes enhancement of the Se current by a factor of 40; ion current >1011 A). Wachsmann & Heumann (1989) and Heumann & Wachsmann (1989) first mixed the silica gel and dried selenium sample to load on the filament. After reaching a vacuum of 106 Torr, the ionization filament is heated to 1.4 A at a rate of 0.15 A/min, after which the rate was decreased to about 0.04 A/min. At a temperature between 850C and 900C, the first Se ions were observed. Now, the heating rate is 0.01 A/min until the signal stops growing and becomes almost stable (at 930–960C). In some cases, the evaporation filament needs to be heated to 0.5–1 A (e.g. if Se is loaded as BaSeO3 or Na2SeO4 or if Se was separated from the matrix by ion exchange chromatography, introducing an additional retarding effect of organic material originating from the resin). In earlier stages, techniques for Se isotope measurement with Ba(OH)2 loaded on the ionization filament without additions to the Se salt loaded on the evaporation filament were applied (e.g. Grosser & Heumann, 1988), but with the disadvantage that relatively large sample amounts are necessary to generate sufficiently high ion currents (>1012 A). In this method, SeO and SeO 2 were also produced as minor abundance ions. Further, the dependence of the Se ions on filament temperature is similar to the above described method. Ba(OH)2 was continued to be loaded on the ionization filament with the Se sample prepared with silica gel on the evaporation filament (e.g. Heumann & Wachsmann, 1989). Grosser & Heumann (1988) reported a factor 4 higher Se beam when selenious acid instead of barium selenite or sodium selenate is loaded on the filament. A maximum ion intensity was reached at temperatures between 970C and 1000C (1.8 A) of the ionization filament. Se isotope ratios can be determined with this negative TIMS method with a relative standard deviation in the order of 0.3–0.6% (Grosser & Heumann, 1988), improved to 0.1–0.3% by application of the silica gel technique (Wachsmann & Heumann, 1989). Wachsmann & Heumann (1989) also applied loading of samples in a resin bead, where better results were obtained then with the ‘Ba(OH)2-only-technique’ used before. However, the silica gel method gave results better (more thermal Se ions

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Handbook of Stable Isotope Analytical Techniques

produced) than those of the resin-bead method and this method was not followed up for that reason. It was noted that a smaller sample amount is necessary with negative TIMS compared with positive TIMS (0.5 mg versus 10 mg). IUPAC (1991) considered results by the negative TIMS method by Wachsmann & Heumann (1992) as ‘best results’ for Se isotopes. Single-filament approach – Johnson et al. (1999) developed a single-filament N-TIMS method for Se isotopic measurement. Ba(OH)2 (1 mL saturated solution = 24 mg Ba) was added to the Re filament to enhance ionization (see above) and the filament was dried. Volatility of the Se was reduced by adding graphite to the Se sample (100–500 ng Se as selenious acid þ 20.2 mg colloidal graphite). This mixture was loaded on top of the Ba(OH)2 and gently evaporated to dryness. The filament was heated for 5 min at 900C to remove interfering contaminations. Ion beams of 1011 A 80Se are yielded with this technique. Maximum signal intensity for Se occurs between 950C and 1000C, although data were collected at a lower temperature to minimize drift in instrumental discrimination. Ratios 82Se/80Se, 78Se/80Se, 77Se/80Se, 76Se/80Se and 74Se/80Se were determined, some in steps (caused by detector configuration limitations). A similar technique was applied by Ellis et al. (2003).

10-4.2.

Isotope dilution TIMS

The N-TIMS technique, in combination with IDMS, has been applied successfully (e.g. Heumann et al., 1985) in determination of Se and Se species in aquatic samples with very low concentrations (range of 10–100 pg/g) (Grosser & Heumann, 1988). Johnson et al. (1999) used ‘double spike (74Se, 80Se) TIMS’ (IDMS) methods for measuring Se (quantitatively) on shale samples. Johnson et al. (2000) used the same technique for water, oil refinery waste water and sediment samples, Herbel et al. (2000) for samples related to bacterial respiratory reduction processes and Herbel et al. (2002) for sediment cores and pore waters, plants, algae and shallow ground waters in a study on an agricultural drainage management system.

10-4.3.

Double-spike TIMS

Currently, high-precision Se isotope ratio data (better than 1‰ precision) can only be obtained by TIMS if a double isotope spike approach is employed. Double-spike TIMS techniques are discussed in Volume I, Part 1, Chapter 29. Briefly, two stable spike isotopes (e.g., 74Se and 82Se) are mixed to form a double spike solution, which is then added to the sample prior to sample preparation. The two spike isotopes are analyzed along with the target natural ratio isotopes (e.g. 76Se and 80Se), and their ratio is used to determine the mass bias of the instrument and correct it. Johnson et al. (1999) used double-spike TIMS methods for measuring 80Se/76Se to a precision of 0.2‰. Johnson et al. (2000b) used the same technique for water, oil refinery waste water and sediment samples, Herbel et al. (2000) for samples related to bacterial respiratory reduction processes and Herbel et al. (2002) for sediment cores and pore waters, plants, algae and shallow ground waters in a study on an agricultural drainage management system.

735

Selenium

10-5.

ICP-MS

All Se isotopes suffer polyatomic interferences (e.g. 37Cl2 þ, 40Ar36Arþ, Ar37Clþ, Ar Arþ, 40Ar2 þ; see Table 10-4.1) (Lyon et al., 1988; using ICP-QMS). Results on 82Se are anomalously high, indicating that there must be an unidentified interference at this mass number (although a possible interfering molecule was reported by Crews et al., 1994; see Table 10-5.1). To decrease interferences of other ions with Se ions, collision cells or dynamic reaction cells can be applied (see Chapter 12-0.2.5.1). The use of a hexapole collision cell with hydrogen as the collision gas for measuring Se isotopes was reported by Palacz et al., (2001). Layton-Matthews et al. (2006) presented a continuous-hydride-generation 40

38

Table 10-4.1 List of possible common mass interferences encountered in an ICP-MS analysis of Se isotopes Isotope

Potential interference

Reference

74

Se

40

Ar34S, 58Ni16O, 37Cl2, 36Ar38Ar, Ge, 39K35Cl, 42Ca16O2, 152Sm2þ, 154 Gd2þ

Lyon et al. (1988), Crews et al. (1994), Rouxel et al. (2002), Elwaer & Hintelmann (2007)

Se

36

Ar40Ar, 38Ar38Ar, 40Ar36S, 60Ni16O, AsH, 76Ge, 58Fe18O, 39K37Cl, 40 Ca18O2, 154Sm2þ, 154Gd2þ

Lyon et al. (1988), Buckley et al. (1992), Crews et al. (1994), Boulyga & Becker (2001), Palacz et al. (2001), Rouxel et al. (2002), Elwaer & Hintelmann (2007)

Se

40

Ar37Cl, 36Ar41K, 76SeH, 61Ni16O, K37Cl, 40Ar36ArH, 38ArH, 59Co18O, 155 Gd2þ

Lyon et al. (1988), Buckley et al. (1989), Crews et al. (1994), Palacz et al. (2001), Rouxel et al. (2002), Chatterjee et al. (2003), Elwaer & Hintelmann (2007)

Se

38

Ar40Ar, 77SeH, 62Ni16O, 41K37Cl, Ar36ArH2, 38Ar40Ca, 156Dy2þ, 156 Gd2þ

Lyon et al. (1988), Buckley et al. (1989), Crews et al. (1994), Palacz et al. (2001), Rouxel et al. (2002), Elwaer & Hintelmann (2007)

Se

40

Lyon et al. (1988), Buckley et al. (1989), Crews et al. (1994), Boulyga & Becker (2001), Palacz et al. (2001), Patterson & Veillon (2001), Rouxel et al. (2002), Elwaer & Hintelmann (2007)

Se

40

76

77

78

80

82

74

75

40

40

Ar2, 40Ar40Ca, 40Ar36ArH2, Ar40K, 64Ni16O, 32S16O3, 48 Ca16O2, 158Dy2þ, 158Gd2þ 40

80

Kr,

Ar42Ca, 34S16O3, 40Ar40ArH2, 82Kr BrH, 36Ar46Ti, 66Zn16O, 164Er2þ, 164 Gd2þ 81

Crews et al. (1994), Palacz et al. (2001), Chatterjee et al. (2003), Elwaer & Hintelmann (2007)

[It must be noted that this list is not exhaustive and many optional other interferences are possible.]

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Handbook of Stable Isotope Analytical Techniques

dynamic-reaction-cell ICP-MS technique, where mass interference was strongly reduced and a precision for 82/76Se of – 0.84‰ was obtained. Janghorbani & Ting (1989) used two ways of sample introduction: (1) a pneumatic nebulizer (PN), and (2) a hydride generator (HG). For the PN system the sample material was introduced into an Ar plasma via a peristaltic pump (sample solution flow rate 0.96 mL/min). For the HG system, a peristaltic pump was used to introduce the reagent (solution of 10 g NaBH4 and 2.5 g NaOH diluted with H2O to 1 L) and sample solution into the mixing chamber of the HG (Figure 10-5.1). Ting et al., (1989) also used ‘on-line’ hydride generation by reacting selenite sample solution (formed by boiling and reducing the oxidized selenium compound with HCl) with NaBH4. A two-channel peristaltic pump pumping both analyte and reagent (NaBH4) into the mixing chamber of the hydride generator was used. The output of the mixing chamber was send through a liquid–gas separator before introduction (H2Se) into the Ar plasma. Isotope dilution with 82Se was applied and 82Se/77Se and 74Se/77Se ratios were measured. For details of machine settings, see Ting et al. (1989). Minor influences by matrix interferences and over-all memory effects (pneumatic nebulizer) were discussed by Ting et al. (1989). Similar methods were used by Buckley et al. (1992: biological materials, measuring on enriched 76Se, 77Se, 82Se, and using 78Se as reference isotope). Addition of 0.2 M NaI to the NaBH4 solution during hydride generation suppressed interference of Cu2þ. Finley (1999) applied Se tracer methods (74Se, 82Se) for the study of retention and distribution of Se by humans consuming Se-labeled selenite, selenate or broccoli. Se extracted from urine, blood plasma, selenite, selenate and plant material was measured by HG-ICP-MS.

Torch Spray chamber

2-channel pump Analyte (10% HCl) Mixer NaBH4

Flow meter

Waste

Carrier gas Separator Hydride generator

Figure 10-5.1

Schematic diagram of the hydride generator (after Janghorbani & Ting, 1989).

737

Selenium

Fox et al. (2005) studied absorption of Se by humans from wheat, garlic and cod, which were intrinsically labeled with 77Se and 82Se isotopes. All Se was converted into Se(IV), as this is the valence state of Se that can efficiently generate a hydride for HG-ICP-MS stable isotope analysis. Boulyga & Becker (2001; discussing analysis of Se, Ca and Fe) brought forward the fact that the use of a double focusing ICP-MS in high-resolution mode reduces drastically ion interferences, but involves a significant loss of ion intensity and therefore increased detection limits. Boulyga & Becker (2001) used a hexapole collision cell (see Chapter 12-0.2.5) in an ICP-QMS to depress molecular ion interferences. All of the above studies’ measured isotope ratios have precisions of about 1‰ or worse because single collector mass spectrometers were applied. High-precision isotope ratio measurements were obtained by Rouxel et al. (2002, 2004) by use of a continuous-flow hydride generator (Figure 10-5.2) coupled to an MC-ICP-MS device. The reducing agent used for the hydride generation was NaBH4 (1%) in NaOH (0.05%) solution, which was pumped with the sample or standard solution through a mixing coil for reaction. Liquid was separated from the analyte hydride gas, which was transported by Ar (carrier gas) to the torch for isotopic analysis in the MC-ICP-MS. All Se isotopes were measured by the array of nine Faraday cups of the MC-ICP-MS. Calibration was carried out by the ‘matching standard’ procedure as is also used for Fe or Cu isotopes (Belshaw et al., 2000; Zhu et al., 2000a). Minimum amount of Se for determination of 76Se/82Se ratios is 10 ng, while routine analysis was performed on amounts of 50 ng Se or more. Overall external analytical precision for the ratios 82Se/ 76Se, 82Se/78Se and 82Se/77Se was estimated to be 0.25‰ (95% confidence level). For details on the analytical procedure and settings of the analytical device, see Rouxel et al. (2002).

Autosampler

Sample/standard in HCl 1.7 N Pump

Ar1

Stripping and carrier Ar Ar2

Mixing coil To MC-ICP-MS torch

NaBH4 (1%) in NaOH (0.05%)

PTFE aerosol filter Gas–liquid separator (at 4°C)

Drain

Figure 10-5.2 Schematic diagram of the continuous-flow hydride generator coupled to a MCICP-MS device (after Rouxel et al., 2002).

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Handbook of Stable Isotope Analytical Techniques

The use of ICP-MS technique for Se isotope analysis is briefly discussed in Volume I, Part 1, Chapter 20.4.5.

10-6.

N EUTRON ACTIVATION M ETHOD

The Se metabolic pathway was studied on feces, plasma, red blood cells and urine for Se absorption, turnover and excretion budgets by neutron activation methods (Janghorbani et al., 1981b,1982a). Subjects took an oral dose of 74Se (74SeO2 3 ) for tracer purpose. It is possible to measure five isotopes of Se by neutron activation: 74

Se Se 78 Se 80 Se 82 Se 76

(n,g: 120 d, 265 keV) 75Se (n,g: 117.6 s, 160 keV) 77mSe (n,g: 3.9 m, 96 keV) 79mSe (n,g: 57.0 m, 103 keV) 81mSe (n,g: 23.0 m, 356 keV) 83Se

Precision of the method is relatively low, in the order of 10%, which is sufficient in most of this type of tracer studies, but can be too large for other purposes. A procedure for measurement of isotopes 74Se, 76Se and 80Se is given in Figure 10-6.1. See also Chapter 12-0.2.6 for general discussion on NAA methods and Table 12-0.4 for some Se activation reactions [given for fecal samples, after Janghorbani & Young (1980)]. Environmental samples were studied for Se contents by NAA techniques using the 74 Se(n,g)75Se reaction by Knab & Gladney (1980). Irradiated samples (7 h; thermal neutron flux: 1  1013 n/cm3.s) were dissolved in acid (5 M HCl–1 M H3PO4 solution) and 75Se was adsorbed on Al2O3 (chromatographic grade, 60 mesh) in an ion exchange column (0.7 cm i.d.  19 cm tubes with tapered tip; 100-mL reservoir on top). The adsorbed 75Se was measured by 4 large (60–80 cm3) Ge(Li) g detectors at 265 and 280 keV peaks or the more sensitive 136 keV peak for low-level samples. Measurements first were carried out at least 3 weeks after irradiation (to reduce personal exposure to radiation and to lower interferences by other radio nuclides with shorter half-lifes). Krivan et al. (1981) used the 74Se(n,g)75Se reaction for (quantitative) Se determination in bovine liver, blood plasma and erythrocytes.

Selenium

739

Figure 10-6.1 Schematic of the neutron activation procedure for measurement of 74Se, 76Se and 80 Se in human feces, plasma, red blood cells (RBC) and urine (after Janghorbani et al., 1981b).

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C H A P T E R

1 1

B ROMINE

11-0.

INTRODUCTION

During the past 80 years, many attempts have been made to measure natural variations in the stable isotope compositions of Cl and Br. These variations are quite small; variations in the Cl isotope compositions of natural samples were first measured in 1982, and natural variations in Br isotope compositions were first measured in 1997. In this chapter, several methods are described that have been applied over the past 80 years both to separate Cl and Br from natural materials and to measure their isotope ratios by mass spectrometry. Only very few studies are known in which the (geo)chemistry of Br isotope variations are described. Although it has long been known already that Br has two stable isotopes (79Br and 81Br, Aston, 1920), no large natural isotope variations were expected due to the small relative mass difference between these two isotopes. Early studies by Cameron & Lippert (1955) showed no Br isotope variations beyond their analytical precision. In later years, however, fractionation due to diffusion was shown in molten lead bromide (Cameron et al., 1956) and zinc bromide (Lunde´n & Lodding, 1960). Willey & Taylor (1978) showed that it was possible to measure the Br isotope composition with a method comparable with the method for Cl isotopes using bromomethane. Xiao et al. (1993) described a method to measure the Br isotope composition using positive ion thermal ionization mass spectrometry, which is analogous to the method for measuring Cl isotopes. Eggenkamp & Coleman (2000) described a method to measure Br isotopes in natural samples, which includes a method to separate Br and Cl from samples which contain only (very) small Br concentrations. Bromine isotope analytical techniques are reviewed in Volume I, Part 1, Chapter 28.

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C H A P T E R

1 2

Mg, K, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn, Ga, Ge

12-0.

I NTRODUCTION

Interest in stable isotope abundance of the ‘alkali’ and ‘transition’ metals, also named ‘heavy stable isotopes’ (Johnson, 2001), has increased in recent times, Mass-dependent isotope fractionation in these ‘heavy’ elements (heavier than S), including elements such as Ca, Fe, Cu, Se, Mo Cr, Zn and even Hg were described as ‘new frontiers’ (Johnson, 2001). Disciplines where there is interest in differences in the ratios of these isotopes are mostly geochemistry, meteoritics, planetary sciences nutritional and food sciences and clinical sciences. For the first three disciplines, samples are present in solid form, and the metals of interest for isotopic measurement must either be extracted for analytical techniques where pure compounds are desirable or they are analyzed in the original form, with generally the need for matrix corrections. Samples in nutritional and food sciences normally are solids and less commonly fluids. Samples in clinical studies comprise both fluids (urine, blood, plasma) and solids (dried form of feces, urine and blood, and foods). Samples can be stored or shipped in freezedried form (e.g. Crews et al., 1994). Increasingly, metals such as Cu and Zn are used as tracers to elucidate metabolic pathways in biological systems (Soltani-Neshan et al., 1988). Others elements of biological importance, included in this chapter, are Mg, K, Ca, Cr and Fe. Overviews, valid up to the date of their publication of course, of the use of stable isotopes in human mineral nutrition research, including historical overviews, were published by Turnlund & Johnson (1984), Hachey et al. (1987), Turnlund (1989), Abrams (1999) and Patterson & Veillon (2001). In a recent book, Abrams & Wong (2003) presented an overview of methods where stable isotopes are applied for clinical purpose.

12-0.1.

PREPARATION P ROCEDURES

No losses of the elements discussed in this chapter were found during oven drying (Crews et al., 1994). Organic samples, placed in Pt or silica crucibles, often are prepared by wet (in open vessels or in closed system under pressure; with acid mixtures in concentrated form: HNO3–H2O2, HNO3–H2SO4–HClO4, HNO3–HClO4) or dry (e.g. in muffle furnace) ashing at 500–550C, in presence of oxidizing agents (O2 in air!). Closed system ashing or digestion procedures are preferred to avoid fuming of acids and corrosive reagents, 743

744

Handbook of Stable Isotope Analytical Techniques

and eventually risk of volatile sample loss. The use of a microwave to decompose biological materials with HNO3 placed in a closed bomb (takes 1–20 min) has become a popular technique. Following the acid digestion, typically a procedure of reaction with chelating reagents, such as -diketones, dithiocarbamates, tetraphenylporphyrins, o-phenylenediamines, 8-hydroxyquinoline, pentane-2,4-di-one [acetylacetone (ACAC)] or fluorinated analogues: trifluoroacetylacetone (TFA) or hexafluoroacetylacetone, are applied (Crews et al., 1994). A table of chelating agents after Crews et al. (1994) is given in Table 12-0.1. Aggarwal et al. (1991) described preparation procedures of some chelating agents, and Buckley et al. (1982) included description of a metal chelating procedure. Some examples of metal extractions by chelating procedures are given in Delves et al. (1971), Hachey et al. (1980), Sturgeon et al. (1980) and Drasch et al. (1982). Disadvantage of chelates is their susceptibility to metal exchange (i.e. in the ion source), cross-contamination and memory (retention of chelates in the ion source) effects (see Crews et al., 1994 for a more detailed discussion on these effects). A special procedure for digestion of meat samples is in vitro gastrointestinal enzymolysis at pH 6 (Owen et al., 1992) (Figure 12-0.1). Ion exchange columns are used for extraction of elements from a solution. General information on ion exchange resins, their application and how to produce them, can be found in the handbook by Korkisch (1990) and on adsorption of metals in an hydrochloric acid solution by Kraus et al. (1954). Zmijewska et al. (1984) described batch-mode anion exchange separation of trace elements from a water matrix.

Table 12-0.1 Chelating agents for isotope measurement by EIMS or GC–MS on trace ‘metals’ in organic compounds (after Crews et al., 1994) Chelating agent

Trace element

Precision of isotopic ratio [RSD (%)]

-Diketones and related compounds

Ca (1,2) Cr (1,3,4) Cu (1, 5,6) Fe (1,7,8)

8-Hydroxyquinoline

Cu, Fe, Zn (15,16) Cu (5) Cu (5)

0.07–6.25 (1); 0.1–2.7 (2) 0.12–1.2 (1); 0.7–2.1 (4) 0.2 (1); 1.6 (6) 0.05–0.9 (1); 0.1–1.7 (7); 0.03–0.67 (8) 0.08–1.8 (1); 0.5–18 (9) 0.1–3.3 (1) 0.9–3.4 (4); 1.2–1.9 (10) 1–1.9 (4); 1–5 (11) 1.0–3.8 (4); 1.2–7.2 (12) 0.3–2.8 (1); 1.2–3.4 (4); 1–5 (11) 1.9–38 (15,16) 1.1 (5) No data available

o-Phenylenediamines

Se (17,18,19,20,21)

1–7 (20)

Dithiocarbamates and N,N-disubstituted carbamates Tetraphenylporphyrins

Mg (1,9) Ni (1) Cr (4,10) Cu (1,4,6,11) Ni (4,12,13) Zn (1,4,11,14)

1 – Hachey et al. (1980); 2 – Kowatski et al. (1980); 3 – Anderson et al. (1993); 4 – Aggarwal et al. (1989a); 5 – Buckley et al. (1982); 6 – Aggarwal et al. (1991); 7 – Shaw et al. (1984); 8 – Miller & van Kampen (1979); 9 - Schwartz (1984); 10 – Aggarwal et al. (1990); 11 – Soltani-Neshan et al. (1988); 12 – Aggarwal et al. (1989b); 13 – Aggarwal et al. (1992a); 14 – Christie et al. (1984); 15 – Johnson (1982); 16 – Johnson (1984); 17 – Reamer & Veillon (1981); 18 – Reamer & Veillon (1983); 19 – Wolf et al. (1988); 20 – Aggarwal et al. (1992b); 21 – Ducros & Favier (1992).

745

Mg, K, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn, Ga, Ge

Sample (chicken meat) (10 g)

20 mL Incubate at 37°C for 4 h in a water bath with shaking

Gastric juice (1% pepsin in Milli-Q water + HCl, pH 1.8) After incubation for 1 h HCl added dropwise to maintain a pH of 1.8

Adjust to pH 6.0 with NaHCO3 20 mL Incubate at 37°C for 4 h in a water bath with shaking Ultracentrifuge for 3 h at 20,000 rpm (4°C) and filter (0.22 μm)

Intestinal juice (equal volumes of 3% pancreatin, 1.5 g/L bile salts in Milli-Q water)

Gastrointestinal supernatants

Figure 12-0.1 1992).

Flowchart of procedure for enzymolysis of meat samples (after Owen et al.,

12-0.2. 12-0.2.1.

G ENERAL D ESCRIPTION OF MAJOR ANALYTICAL T ECHNIQUES U SED

Electron ionization mass spectrometry

Organic compounds are treated to form volatile chelates for elements such as Ca, Cr, Cu, Fe, Mg, Ni, Se and Zn (Crews et al., 1994). In electron ionization mass (EIMS) samples are vaporized under spectrometry vacuum and then bombarded by electrons (e), generated by resistance heating of a W or Re filament (Figure 12-0.2). Sample particles are accelerated to an average translational energy of 70 eV. This results in removal of an electron from the particle (molecule) M to form a radical cation: M þ e ! Mþ þ 2e

[12-0.1]

Low abundance of multiple charged and negative ions are also produced. Mass spectrometers with both magnetic sector and with a quadrupole are used with ‘EI’ for ion mass separation. The magnetic sector instruments have a high mass resolution (M/DM) and quadrupole instruments have low mass resolution (Crews et al., 1994).

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Handbook of Stable Isotope Analytical Techniques

Filament Ionizing electrons

Ion beam Ion repeller plate

Sample vapor in

To mass spectrometer ion optics Electron trap

Figure 12-0.2 Schematic diagram showing an electron ionization source for an EI ^ MS device (after Crews et al., 1994).

Combined with the EIMS system, a GC can be used for separation of different compounds before being introduced directly into the ion source of the MS. Combined GC–MS is very sensitive: high-resolution spectra can be obtained on picomolar to nanomolar amounts of analyte (Crews et al., 1994). Crews et al. (1994) discussed the use of a selected ion recording (SIR) or selected ion monitoring (SIM) technique, where only a part of a complete isotopic spectrum of a chelated compound is observed, thus increasing sensitivity and lowering detection limits. Crews et al. (1994) noted that molecular ion clusters formed by chelates also include heavy isotopes of H, C, N and O, which must be corrected. Typical relative standard deviations for the method are in the order of 5%, but in rare instances better values have been found (as low as 0.1%) (Crews et al., 1994). Most important advantage of (GC-)EIMS is the wide availability of devices, also in the form of compact bench-top models. The relatively short analysis time (excluding sample preparation time), of typically 15–20 min is another advantageous factor. Preparation of samples, however, might take far longer, and in case of chelating procedures, reagents sometimes have to be prepared too. Crews et al. (1994) stated: ‘‘. . . a small number of laboratories have demonstrated the ability to generate good stable isotope ratio data by EIMS and/or GC-MS of chelated minerals and trace elements, success has not been widespread, and these techniques appear to be too problematic to be recommended for general use, mainly because of relatively poor precision, metal exchange, memory effects, and other problems. . .’’

12-0.2.2.

Thermal ionization mass spectrometry (TIMS)

TIMS is the most precise method for stable isotope measurement for the elements as discussed in this chapter. The most significant drawback is the meticulous sample purification necessary prior to mass spectrometric measurement (Eagles et al., 1989b). Sample throughput is very low and time consuming with this method (Johnson, 2001). The use of

747

Mg, K, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn, Ga, Ge

Triple filament

Double filament

Single filament

Figure 12-0.3

Schematic diagram of filament configurations inTIMS (after Crews et al., 1994).

double-spike methods (see Volume I, Part 1, Chapter 39) introduces a very precise procedure, where precision on the order of 0.2‰ or better can be reached (e.g. for 44Ca/40Ca, 57 Fe/54Fe: Johnson, 2001). Different filament setups (1, 2, or 3 filaments) are commonly used (Figure 12-0.3). Single filament procedures are optimal for the transition elements, and double filament techniques for Ca, Mg and negative ion mode Se. Optimum filament temperatures for most elements are in the range of 800–2000C, and therefore high melting point filaments, such as Re, Ta and W are essential for this technique. Only singly charged ions are formed during the thermal ionization process because of the high ionization energy of the elements relative to the filament temperature. If the ionization energies are greater than 7 eV for a specific element (e.g. Fe, Cu, Zn, Se, Mo), special techniques, such as addition of ion enhancers to the filament, are required (Crews et al., 1994). Measurement on positive and negative ions can be applied (P-TIMS and N-TIMS, respectively). Elements preferably measured by P-TIMS include Li, Mg, Si, K, Ca, Ti, Fe, Ni, Cu, Zn and Ga, and those preferably measured by N-TIMS include B, C, N, Cl, Se and Br. For the elements S, Cr and Ge there is no preference for P-TIMS or N-TIMS (see Heumann et al., 1995 for discussion). A special design for ion source was presented by Duan et al. (1997a), named highefficiency thermal ionization source. The source consisted of a W crucible with a deep cavity holding the sample. The W crucible was heated by high-energy electron bombardment from a Ta filament surrounding the crucible. Sample particles evaporated inside the crucible and interact with the crucible walls producing positive ions through surface

748

Handbook of Stable Isotope Analytical Techniques

ionization. The ions were extracted from the crucible through a small opening at the end of the crucible, and analyzed for isotope composition (e.g. by quadrupole MS or magnet sector MS). By regulation of the electron emission, the energy and power applied to the crucible can be controlled, and therefore the temperature. According to Duan et al. (1997a), ionization efficiency was 10–100 times higher than with conventional TIMS. Application of the TIMS technique is exemplified by the more specialized cases of Se, Fe and Cr isotopes in Volume I, Part 1, Chapter 29.

12-0.2.3.

Fast atom bombardment mass spectrometry

The main strength of fast atom bombardment mass spectrometry (FAB-MS) is the availability of instruments. However, the throughput is low at between five and eight samples/ day, while samples must be introduced manually, placing the analyte on a probe tip (Crews et al., 1994). Measurement demand a skillful operator and a careful monitoring is needed. Added to these facts is the technical problem of interference at some masses, e.g. by metalhydride formation (see Eagles et al., 1989b; Miller et al., 1989). FAB-MS is an alternative to IRMS and can be retrofitted to virtually any MS at low cost (e.g. Caprioli, 1990; Flory et al., 1993). It was suggested that the acronym FAB-MS had to be SIMS (secondary ion mass spectrometry), and when a liquid matrix is analyzed the term liquid SIMS or LSIMS should be used (Crews et al., 1994). Martin et al. (1982c) stated that: The relationship between FAB-MS and SIMS rests in the fact that in both techniques the sample is bombarded with particle beams moving with approximately the same kinetic energy and sample ions are produced as a result of the interaction of the beam with the sample. In FAB-MS the particle beam is neutral whereas in SIMS the beam is charged.

A flowchart showing sample preparation procedures for FAB-MS is presented in Figure 12-0.4. Samples are bombarded with a stream of Xe atoms (average translational energy: 6–8 kV). Ions are sputtered from the probe into the gas phase, where they are separated and detected by a conventional mass analyzer (Figure 12-0.5). FAB-MS was developed for non-volatile, polar molecules of organic compounds, such as peptides, polysaccharides, glycosides and glycoconjugates (dissolved in a low boiling, viscous solvent, e.g. glycerol). Inorganic samples are analyzed without the use of a liquid matrix (dry inorganic salts yield a continuous, stable ion beam, unlike solid organic compounds which produce only weak, transient beams) (Crews et al., 1994). Requirement of medium to high-resolution measurements (resolving power of 3500 – 10,000) on, for instance, stable isotopes in organic compounds made application of double focusing (magnetic sector preceding the electrostatic sector) MS necessary, instead of lower resolution quadrupole or magnet sector MS. Measured isotope ratios must be corrected to compensate for factors that cause a systematic bias, where measured ratios differ from true ratios depending on factors depending on the MS that is used (isotopic fractionation caused by the MS is typical for each machine). One of the major fractionation processes occurs because the light atoms are more easily desorbed from a surface than heavier atoms. Different forms of correction needed for different operating settings were discussed by Crews et al. (1994). Crews et al. (1994)

749

Mg, K, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn, Ga, Ge

Dry sample Dissolve in matrix compatible solvent (for glycerol e.g. H2O, MeOH, DMSO) Add Matrix at least 50% (v/v) (e.g. glycerol, thioglycerol, 2,4-ditert-amylphenol) Lyophilize Concentrate (Speed vac concentrator®)

HPLC

Sep Pak®

Apply 0.3 μL to tip Record (+/–) FAB-MS

Dominated by salts

Add acid (+) FAB base (–) FAB

Evaluate data Weak spectrum

Add shift reagent Molecular weight?

FINAL RESULT

Figure 12-0.4 Flowchart showing procedures for preparation of samples for FAB-MS analysis (after Martin et al., 1982c).

Gun

Fast atoms/ions Probe

Figure 12-0.5

To analyzer Sample in viscous matrix Source (e.g. glycerol) ion optics

Schematic diagram of a FAB-MS ion source (after Crews et al., 1994).

presented a table with precisions of several isotope ratios that could be reached, reproduced here in Table 12-0.2.

12-0.2.4.

Secondary ion mass spectrometry

Description of the SIMS technique is given in Volume I, Part 1, Chapter 30. No further details are given here.

750

Handbook of Stable Isotope Analytical Techniques

Table 12-0.2 Precision of stable isotope ratios of metals from organic compounds (nutrient minerals) analyzed by FAB–MS technique Isotope ratio

Precision (%)

References

26

Mg/ Mg

Liu et al. (1987)

42

Ca/40Ca,

No figures given 0.2–0.5

48

Ca/40Ca Fe/56Fe

54

25

44

Ca/40Ca

58

Zn/67Zn

12-0.2.4.1.

0.5

Fennessey et al. (1991) Eagles et al. (1989a, b)

1.9–14 1.3–4.5

Fe/56Fe 63 Cu/65Cu 64 Zn/67Zn, 64Zn/68Zn, 64 Zn/70Zn 64

0.5 1.1 0.8 0.5–3

Smith (1983), Smith et al. (1985), Jiang & Smith (1987), Self et al. (1987) Pratt et al. (1987), Self et al. (1987) Eagles et al. (1985), Gharaibeh et al. (1985), Self et al. (1985) Lehmann et al. (1988) Eagles et al. (1985), Gharaibeh et al. (1985) Miller et al. (1989) Pratt et al. (1987), Miller et al. (1989),

NanoSIMS – A brief description1

The NanoSIMS (Cameca ‘NanoSIMS 50’ ion microprobe) is a new type of ion microprobe that can be used for elemental and isotopic studies on a sub-micrometer scale. The instrument is based on a design concept by G. Slodzian (Universite´ de Paris-Sud) who was also responsible for the development of the very successful CAMECA ims3f-7f series, as well as the ims1270/1280. The NanoSIMS 50 was built by CAMECA in France and the first instrument of this type was delivered to Washington University in St. Louis (MO, USA) in December 2000. By now there are more than ten NanoSIMS instruments installed worldwide with applications ranging from cosmochemistry to biology and material sciences. The most significant innovation in the ion optical design of the NanoSIMS (Figure 12-0.6) is the normal primary ion incidence and a normal coaxial secondary ion extraction. This makes it possible to reduce the distance between the sample and the immersion lens to 400 mm, which results in a much smaller spot size than in other SIMS instruments at a given probe current. The diameter of the primary ion beam at the sample defines the smallest area whose chemical or isotopic composition can be determined without interference from neighboring regions. Obviously, a smaller spot size allows the analysis of smaller particles and gives more detailed information about the internal composition of a given sample of heterogeneous composition. In imaging mode, the primary beam diameter defines the lateral resolution of a secondary ion image. The typical Csþ primary beam diameter of a CAMECA f-series ion microprobe is on the order of 1–3 mm although slightly smaller spot sizes can be achieved through careful tune-up and with significant loss of intensity. The NanoSIMS, in contrast, offers a routine Csþ primary beam diameter of 100 nm (hence the instrument’s name), but beam diameters as low as 30 nm have been achieved. In negative (O) primary beam mode the best achievable probe diameter is around 150 nm. 1

Section 12-0.2.4.1 is contributed by F. J. Stadermann: Laboratory for Science, Physics Deppartment, CB 1105, Washington University, Saint Louis, MO 63130-4862. E-mail: [email protected]

751

Mg, K, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn, Ga, Ge

Faraday cup FC Electron multiplier EM Large detector LD Scintillator Sc Photo multiplier PM Total Ion current EM TIC eGun Electron source Dduo Be, Bext Magnetic field Lduo ES Entrance slit AS Aperture slit EnS Energy slit DØ ExS Exit slit eGun

CCD Camera LF6(x) LF7(y) L4 B3

FCo Sample x

EØP D1 eGunBe EØW EØS

y

C5 C6

SS3Ø Oct-45 B1 L3 B2 P1 P4Oct-9Ø

eGunBext Sc PMse

Vertical plane

CS6Ø

EM4 PdLD ExSLD

WF coil CWF CØ

Cs source z y

LØ x L1 C1 L2 Cx FCp

Hx Hy

LF3(y)

P3 LF2 (x)

C2 Hex ES AS

p al

SS10Ø

C4 LF5(x)

FCq

x

Q

ExSFc ExS4 FCs PdFC

TIC

C3 EnS LF4(y)

ne

nt

izo

r Ho

5X

Cduo

la

z

EMLD

Cy

P2

Duoplasmatron

Vertical plane

L,EØ Circular lens LF Slit lens C, Pd deflector B Scanning plate P Main deviating plate D Diaphragm Oct Octupole Hex Hexapole Q Quadrupole lens SS Spherical sector CS Cylindrical sector WF Wien filter

y z

Pd4 B field Magnet

Figure 12-0.6 Schematic of NanoSIMS ion optics (Figure by F. J. Stadermann). See text of Section 12- 0.2.4 1 for a brief explanation of the working of the NanoSIMS and for comparison with other SIMS designs.

Due to the coaxial ion optical design of the NanoSIMS, the primary and secondary ion beams must be of opposite polarity and thus the instrument is used either with a duoplasmatron and an O primary beam for electropositive elements or with a Cs microbeam source and a Csþ primary beam for electronegative elements. Typical primary beam currents in the NanoSIMS are in the pA range, but due to a very efficient secondary ion collection and a high secondary transmission, even at high mass resolution, large secondary ion count rates are received at the detectors. The mass spectrometer has a modified Mattauch–Herzog geometry that achieves double focusing and high mass resolution at all positions along the focal plane which ranges from a magnet curving radius of 130–550 mm. The NanoSIMS 50 is equipped with seven detectors for secondary ion detection: four moveable miniature electron multipliers (EM), two EMs at fixed positions (a miniature EM and a large EM) and one moveable Faraday cup (FC). These detectors can be used in multi-collection mode for the simultaneous measurement of different elements and/or isotopes. It is possible to measure several species simultaneously (e.g. 12C, 13C, 28Si, 29Si, 30Si or 16O, 17O, 18O, 12C14N, 12 15 C N).

752

Handbook of Stable Isotope Analytical Techniques

The laminated magnet can be controlled alternatively with a Hall probe or an NMR device which makes measurements in both peak switching and multidetection mode possible. It is also possible to combine magnet switching and multidetection in a single measurement to analyze a larger number of masses. This combined mode is also required, e.g. for the analysis of all Ti isotopes, whose locations in the focal plane are otherwise too close to one another to fit into adjacent miniature EMs which have a minimum separation distance of 8 mm. Thus, the odd (47Ti, 49Ti) and the even (46Ti, 48Ti, 50Ti) numbered isotopes of Ti can be measured with the same detectors in an automated two-step cycle. The imaging capabilities of the NanoSIMS are based on rastering of the primary ion beam on the sample and thus the lateral resolution will depend on the primary beam diameter on the sample surface. The raster size is adjustable over a wide range (up to 200  200 mm2). It is possible to use all secondary ion detectors in parallel for image acquisition, which can, e.g. be used for isotope ratio imaging. Several factors contribute to the sensitivity of the NanoSIMS. One is the increased collection efficiency of secondary ions, achieved through the small working distance of the immersion lens. Another factor is the large turning radius of the ions going through the magnet. A third factor is the secondary ion optical design that squeezes the ion beam into a thin line at the entrance slit of the mass spectrometer. Finally, the normal incidence of the primary beam results in a sputter rate smaller than that of a beam with oblique incidence. This means that the concentration of the primary ion species (Cs or O) implanted into the analyzed sample is higher, giving rise to a higher ionization efficiency. Most isotopic systems (e.g., C, N, O, Si) require measurement at high mass resolution to eliminate molecular interferences. In conventional double-focusing SIMS instruments, high mass resolution is achieved by closing the entrance and exit slits of the mass spectrometer, which has the unwanted side effect of severely reducing the measurement sensitivity. Due to the unique design of the NanoSIMS it is possible to reach high mass resolution without a significant loss of transmission. At the typical mass resolutions required for negative secondary ion isotopic analysis (3000 for C, 3500 for Si and 4800 for O), the NanoSIMS is more than 40 times as sensitive as a ims3f instrument. Among the additional features of the NanoSIMS are total secondary ion detection, secondary electron detection, and normal incidence electron gun charge compensation.

12-0.2.5.

Inductively coupled plasma mass spectrometry

Different designs of ICP-MS machines, used for stable isotope measurement, were described in literature. Houk & Thompson (1982) and Houk (1994) gave an overview on development of the ICP-MS analytical technique. After the ICP technique was established, this led from classical ICP-quadrupole (Q)MS, through double focusing magnet sector ICP-MS, also named high-resolution (HR-)ICP-MS, to multiple collector magnet sector (MC-)ICP-MS (reviewed in Volume I, Part 1, Chapter 31). ICP-MS has the advantage of fast sample throughput and a relatively simple sample preparation (Eagles et al., 1989b; Crews et al., 1994), if any (depending on the quality of the sample of interest: solid, fluid, solution, etc.). The disadvantage is the possible interference of ions other then the ion of interest, with similar masses (e.g. Lyon et al., 1988; Eagles et al., 1989b; Crews et al., 1994). Sometimes, by using a high detection resolution, these ion peaks can be separated from the peak of the isotope to be measured. However, increase

Mg, K, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn, Ga, Ge

753

in resolution decreases the precision of the measurement (eventually leading to rounding of peak shapes: e.g. Mason et al., 2004a). The most acceptable level between these two factors must be determined. If measuring isotopes with an ICP-QMS, special condition are required, such as operation in a cool plasma mode at low power and with a high carrier gas flow, to reduce interference from background species, molecular ions and doubly charged ions (Tanner, 1995; Patterson et al., 1999; Duan et al., 2001). However, cool plasma mode reduces detection sensitivities for most elements and isotopes by at least two orders of magnitude (Jiang et al., 1988; Tanner, 1995; Patterson et al., 1999; Duan et al., 2001) and the sample matrix needs to be removed prior to analysis (Niu & Houk, 1996; Patterson et al., 1999). Most common background plasma ions under ‘cold plasma’ conditions are þ þ NOþ, Oþ 2 and H3O , and H3O is considered a strong indication for a ‘cool plasma’ (Tanner, 1995). The use of double-focusing magnet sector (combination of a magnet sector and an electrostatic sectors, also named high resolution) devices cures many of these above mentioned problems and produces good isotopic measurements (Vanhaecke et al., 1996, 1997; Stu¨rup et al., 1997; Becker & Dietze, 1998; Duan et al., 2001), but is also a more expensive solution. Samples analyzed by ICP-MS techniques have a wide range of matrix compositions. Common materials of interest for isotopic analysis include organic or biological materials. These materials are generally digested or diluted by acids (e.g. HNO3, H2SO4, HClO4, HCl, sometimes together with H2O2), eventually aided by wet or dry ashing. Chemical separation of elements can eliminate potential interferences from matrix components. Selective extraction, precipitation, ion exchange, chromatography (e.g. HPLC: Owen et al., 1992), hydride generation (‘on- or off-line’), and electrothermal vaporization are techniques that have been used to isolate isotopes of interest. The most common sample introduction technique for stable isotope analysis is direct injection of solution by way of nebulizer (a large number of different types exist) and spray chamber (Crews et al., 1994). Alternative methods for sample introduction to the ICP-MS that are used include laser ablation, electrothermal vaporization and flow injection (e.g. Dean et al., 1988). Studies by ICP-MS, where instrument settings and sample preparations were discussed for a group of elements, were reported in Ting & Janghorbani (1988: Li, Fe, Cu, Zn), Vanhoe et al. (1989: Fe, Cu, Zn, Co, Rb) and Owen et al. (1992: Fe, Co, Cu, Zn, Sr, Cd, I, Ba, Pb). Based on general IDMS procedures (see Volume I, Part 1, Chapter 37), a ‘matching’ of the blend of a spiked sample with an equivalent blend of a spiked natural standard, involving an iterative approach to achieve a ‘perfect match’, was described by Catterick et al. (1998) for measuring of Li, Mg and Fe isotopes. ICP-QMS and double focusing magnet sector ICP-MS machines were applied. Vogl et al. (2000) used a correction in ICP-MS caused by isobaric overlap of element a by element b, expressed in the equation: tot I cor a1 ¼ Ia1  Ib2  Rb1b2

[12-0.2]

where a1 represents the interfered isotope of the element a and b1 represents the interfering isotope of element b. Rb1b2 represents the measured isotope amount ratio b1/b2, where b2 is a non-interfered isotope of element b.

754

Handbook of Stable Isotope Analytical Techniques

Isobaric interferences are an important concern in ICP-MS analyzing techniques. Many interferences are reported in literature, and a summary of the most common interferences are given in Table 12-0.3. However, it must be realized that far more Table 12-0.3 A compilation of reported common isobaric interferences encountered in ICPMS stable isotope measurements of Mg, K, Ca, V, Cr, Fe, Ni, Cu, Zn, Ge and Br Isotope

Potential interference

24

12

25

24

26

12

39

38

41

40

40

40

42

40

43

26

44

12

46

14

48

32 16

46

46

47

14

Mg Mg Mg K K Ca

Ca Ca Ca

Ca Ca Ti Ti

48

Ti

49

Ti

50

Ti

50

V V

51

C2, 23NaH, 48Ca2þ, 48Ti2þ MgH, C2H,

V ,

2þ

Cr

12

C2H2,

Ar, 23Na16OH, 24Mg16O

ArH2, 40ArD, 84Sr2þ, 26Mg16O, 25 Mg16OH Mg16OH, 86Sr2þ,

27

Al16O

88 2þ C16O2, 28Si16O, 14N16 Sr , 2 O, 26 Mg16OH2

N16O2, 32S14N, S O,

34 14

S N,

Ca, 14N16O2,

48

Ti

48

Ti, 36Ar12C

32 14 N16 S N, 2 O,

15

N16O2H, 15N16O2, 12C35Cl, 32S15N, 30 16 Si OH 14 16 18 N O O, 14N17O2, 32S16O, 12C4, 36 Ar12C 14 17 N O2H, 14N35Cl, 32S16OH, 36Ar13C, 36 Ar12CH 50 Cr, 50V, 36Ar14N, 14N35ClH, 32S18O, 32 17 S OH, 34S15NH 50 Ti, 50Cr, 36Ar14N 36 Ar14NH, 35Cl16O, 34S16OH, 32S18OH

40

53

36

54

40

Cr

Ti ,

2þ 50

ArH, 25Mg16O, 40Ca42Ca2þ

52

Cr

2þ 50

ArH

50

Cr

50

C14N, 25MgH, 24MgH2, 12 13 C CH, 52Cr2þ

50

Cr

Reference

V, 50Ti, 36Ar14N, 32S18O Ar12C, 38Ar14N,

36

Ar16O, 35Cl16OH

Ar16OH, 37Cl16O Ar14N,

37

Cl16OH, 54Fe

Ramseyser et al. (1984), Crews et al. (1994), Reed et al. (1994), Galy et al. (2001) Ramseyser et al. (1984), Reed et al. (1994), Galy et al. (2001) Ramseyser et al. (1984), Crews et al. (1994), Reed et al. (1994), Becker & Dietze (1998), Galy et al. (2001) Reed et al. (1994), Sakata & Kawabata (1994), Tanner (1995), Becker & Dietze (1998) Reed (1989), Tanner (1995), Becker & Dietze (1998) Crews et al. (1994), Tanner (1995), Patterson et al. (1999), Boulyga & Becker (2001), Becker & Dietze (1998), Amari et al. (2000), Duan et al. (2001), Palacz et al. (2001), Stu¨rup (2002), Fietzke et al. (2004) Crews et al. (1994), Stu¨rup et al. (1997), Patterson et al. (1999), Amari et al. (2000), Duan et al. (2001), Stu¨rup (2002), Fietzke et al. (2004) Patterson et al. (1999), Amari et al. (2000), Duan et al. (2001), Stu¨rup (2002), Fietzke et al. (2004) Crews et al. (1994), Reed et al. (1994), Sakata & Kawabata (1994), Stu¨rup et al. (1997), Patterson et al. (1999), Amari et al. (2000), Duan et al. (2001), Stu¨rup (2002), Fietzke et al. (2004) Dever et al. (1989), Crews et al. (1994), Patterson et al. (1999), Stu¨rup (2002) Crews et al. (1994), Patterson et al. (1999), Amari et al. (2000), Stu¨rup (2002) Dever et al. (1989), Reed et al. (1994), Amari et al. (2000) Reed et al. (1994) Reed et al. (1994), Amari et al. (2000) Reed et al. (1994) Dever et al. (1989), Reed et al. (1994), Amari et al. (2000) Dever et al. (1989), Reed et al. (1994) Lyon et al. (1988), Dever et al. (1989), Reed et al. (1994) Dever et al. (1989), Crews et al. (1994), Reed et al. (1994), Veillon et al. (1994b), Amari et al. (2000) Lyon et al. (1988), Dever et al. (1989), Crews et al. (1994), Reed et al. (1994), Veillon et al. (1994b) Lyon et al. (1988), Dever et al. (1989), Crews et al. (1994), Reed et al. (1994), Veillon et al. (1994b) Dever et al. (1989), Crews et al. (1994), Reed et al. (1994), Veillon et al. (1994b)

755

Mg, K, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn, Ga, Ge

Table 12-0.3

(Continued )

Isotope

Potential interference

54

54

56

40

57

40

58

58

58

58

60

23

Fe

Fe

Fe

Fe

Ni Ni

61

Ni Ni

62 64

Ni

63

Cu

40

14

38

16

Reference 36

18

Cr, Ar N, Ar O, Ar O 36 Ar17OH, 38Ar15NH, 37Cl16OH 37 17 Cl O, 36S18O, 36S17OH, 40Ca14N

Ar16O, 38Ar18O, 38Ar17OH, 40Ca16O, 40 Ar15NH, 42Ca14N, 44Ca12C, 43Ca13C, 37 18 Cl OH

Ar17O, 40Ar16OH, 38Ar18OH, 40Ca17O, 40 Ca16OH, 42Ca15N, 44Ca13C, 56FeH

Ni, 40Ar18O, 57FeH

Fe, 40Ar18O, 29Si2, 23Na35Cl

Na37Cl, 44Ca16O, 40Ar20Ne,120Sn2þ, 120 Te2þ 40 Ar21Ne, 45Sc16O, 122Sb2þ, 122Te2þ 40 46 16 Ar22Ne, 23Na16 Ti O, 124Sn2þ, 2 O, 124 Te2þ, 124Xe2þ, 31P2 64 Zn, 32S2, 32S16O2, 40Ar24Mg, 40Ar12C2, 48 16 48 16 Ca16O, H14 Ti O, 128Te2þ, 2 N O3, 128 Xe2þ 40 Ar23Na, 36Ar12C14NH, 31P16O2, 23 23 28 35 Na16 Na17 Si Cl, 48Ca15N, 2 OH, 2 O, 46 Ca17O, 46Ca16OH, 14N12C37Cl, 16 12 35 O C Cl, 47Ti16O, 126Te2þ, 126Xe2þ

Ting & Janghorbani (1986, 1987), Lyon et al. (1988), Dever et al. (1989), Vanhoe et al. (1989), Whittaker et al. (1989), Crews et al. (1994), Reed et al. (1994), Tanner (1995), Beard et al. (1999,2003a), Belshaw et al. (2000), Boulyga & Becker (2001), Skulan et al. (2002), Beard & Johnson (2003, 2004a), Johnson et al. (2003a, 2005), Roe et al. (2003), Rouxel et al. (2003, 2004), Welch et al. (2003), Anbar (2004), Graham et al. (2004), Tondeur et al. (2004), Teutsch et al. (2005), Poitrasson & Freydier (2005), Walczyk & von Blanckenburg (2005), Dideriksen et al. (2006) Ting & Janghorbani (1986, 1987), Lyon et al. (1988), Dever et al. (1989), Vanhoe et al. (1989), Whittaker et al. (1989), Lam & Horlick (1990), Crews et al. (1994), Sakata & Kawabata (1994), Tanner (1995), Beard et al. (1999, 2003a), Boulyga & Becker (2001), Patterson & Veillon (2001), Yu et al. (2001), Skulan et al. (2002), Beard & Johnson (2003, 2004a), Johnson et al. (2003a, 2005), Rouxel et al. (2003, 2004), Roe et al. (2003), Welch et al. (2003), Anbar (2004), Graham et al. (2004), Poitrasson & Freydier (2005), Teutsch et al. (2005), Walczyk & von Blanckenburg (2005), Dideriksen et al. (2006) Ting & Janghorbani (1986, 1987), Vanhoe et al. (1989), Stuhne-Sekalec et al. (1992), Crews et al. (1994), Reed et al. (1994), Belshaw et al. (2000), Palacz et al. (2001), Skulan et al. (2002), Beard et al. (2003a), Johnson et al. (2003a, 2005), Rouxel et al. (2003, 2004), Welch et al. (2003), Anbar (2004), Beard & Johnson (2004a), Graham et al. (2004), Severmann et al. (2004), Poitrasson & Freydier (2005), Walczyk & von Blanckenburg (2005), Dideriksen et al. (2006) Ting & Janghorbani (1986, 1987), Dever et al. (1989), Crews et al. (1994), Beard et al. (2003a), Johnson et al. (2003a), Rouxel et al. (2003), Anbar (2004), Beard & Johnson (2004a), Tondeur et al. (2004), Walczyk & von Blanckenburg (2005), Dideriksen et al. (2006) Lyon et al. (1988), Dever et al. (1989),Reed et al. (1994) Reed et al. (1994), Mason et al. (2004a) Mason et al. (2004a) Mason et al. (2004a) Reed et al. (1994), Mason et al. (2004a) Lyon et al. (1988), Vanhoe et al. (1989), Lyon & Fell (1990), Crews et al. (1994), Reed et al. (1994), Vanhaecke et al. (1997), Zhu et al. (2000a), Patterson & Veillon (2001), Mason et al. (2004a)

(Continued )

756

Handbook of Stable Isotope Analytical Techniques

Table 12-0.3

(Continued )

Isotope

Potential interference

65

33 16

Cu

64

Zn

66

Zn

67

Zn

68

Zn

70

Zn

69

Ga

71

Ga Ge

70

72

Ge

73

Ge Ge 76 Ge 79 Br 81 Br 74

32 33

32 16

Reference 17

32 16

S O2, S S, S O O, S O2H, 25 Mg40Ar, 30Si35Cl, 28Si37Cl, 23Na19 2 F, 37 14 Cl N2,48Ca17O, 48Ca16OH, 36 Ar14N2H, 40Ar12C13C 49Ti16O, 48 16 Ti OH, 130Te2þ, 130Xe2þ, 130Ba2þ H31P16O2, 32S16O2, 32S2, 64Ni, 40Ar24Mg, 40 Ar12C2, 38Ar12CH, 36Ar12C16O, 36 46 Ar14N2, 23Na18 Ca18O, 48Ca16O, 2 O, 46 16 128 Ca17OH, 16O4, H14 Te2þ, 2 N O3, 128 Xe2þ 34 16 S O2, 34S32S, 32S16O18O, 32S17O2, 33 16 17 S O O, 33S2, 40Ar26Mg, 38Ar14N2, 40 Ar12C14N, 36Ar16O14N, 48Ca18O, 28 35 16 18 Si ClH, 29Si35Cl, H14 2 N O2 O 48 16 Ti O, 48Ca17OH, , 49Ti16OH 50 16 Ti O, 35Cl14N16OH, 35Cl12C18OH, 37 15 12 Cl N C, 37Cl12C16OH, 50Cr16O, 50 16 V O, 132Ba2þ, 132Xe2þ 35 16 Cl O2, 37Cl14N16O, 32S35Cl, 33S34S, 34 16 S O2H, 36Ar14N16OH, 40Ar27Al, 50 16 Ti OH, 50Cr16OH, 51V16O, 50 16 V OH, 134Ba2þ, 134Xe2þ 40 Ar14N2, 40Ar28Si, 38Ar14N16O, 40 Ar12C16O, 36Ar32S, 36Ar16O2, 36S16O2, 32 36 S S, 52Cr16O, 35Cl16O2H, 52Cr16O, 51 16 V OH, 135Ba2þ, 136Ba2þ, 137Ba2þ, 136 Ce2þ, 136Xe2þ 40 Ar14N16O, 40Ar14N16N, 38Ar16O2, 40 Ar30Si, 35Cl2, 70Ge, 37Cl16O2, 54Cr16O, 53 Cr16OH, 54Fe16O, 139La2þ, 140Ce2þ, 141 2þ Pr 37 16 Cl O2, 34S16O18O, 36Ar35S, 36Ar16O2H, 40 Ar29Si, 53Cr16O, 52Cr16OH, 137Ba2þ, 138 Ba2þ, 138Ce2þ, 138La2þ 40 Ar15N16O, H35Cl2 70 Zn, 35Cl2, 40Ar14N16O, 38Ar14N18O, 37 16 Cl O2H, 35Cl2, 23Na33S14N, 40Ar30Si, 54 Cr16O, 53Cr16OH, 54Fe16O, 139La2þ, 140 Ce2þ 35 37 Cl Cl, 40Ar16O2, 40Ar32S, 38Ar34S, 36Ar2, 36 Ar36S, 36S2 H35Cl37Cl, 40Ar16O2H, 40Ar33S 37 Cl2, 40Ar34S, 38Ar36S, 36Ar38Ar, 58Ni16O 36 Ar40Ar, 38Ar2, 40Ar36S, 60Ni16O 38 Ar40ArH 40 Ar2H

Lyon et al. (1988), Vanhoe et al. (1989), Crews et al. (1994), Reed et al. (1994), Vanhaecke et al. (1997), Zhu et al. (2000a), Mason et al. (2004a) Vanhoe et al. (1989), Lyon et al. (1988), Crews et al. (1994), Reed et al. (1994), Stu¨rup (2000a, b), Mason et al. (2004a) Vanhoe et al. (1989), Lyon et al. (1988), Crews et al. (1994), Reed et al. (1994), Stu¨rup (2000b), Mason et al. (2004a)

Crews et al. (1994), Reed et al. (1994), Stu¨rup (2000b), Mason et al. (2004a) Ting & Janghorbani (1987), Amarasiriwardena et al. (1992), Crews et al. (1994), Reed et al. (1994), Stu¨rup (2000b), Mason et al. (2004a) Amarasiriwardena et al. (1992), Crews et al. (1994), Reed et al. (1994), Stu¨rup (2000b), Mason et al. (2004a) Reed et al. (1994), Mason et al. (2004a) Reed et al. (1994) Lyon et al. (1988), Reed et al. (1994), Hirata (1997), Mason et al. (2004a) Lyon et al. (1988), Reed et al. (1994), Hirata (1997) Reed et al. (1994), Hirata (1997) Lyon et al. (1988), Reed et al. (1994), Hirata (1997) Reed et al. (1994), Hirata (1997) Crews et al. (1994) Crews et al. (1994)

Note that the existence of interfering compounds depends on the matrix composition, on quality of plasma conditions and eventual contaminations in the system. The reported interfering compounds were reported or tested in studies on isotopic compositions of materials of interest in this handbook. Many more possible interferences, not included in this table, certainly will exist

interferences are possible and certainly will exist, also depending on the quality of the sample and its matrix. A review on MC-ICP-MS techniques is given in Volume I, Part 1, Chapter 31. Comparison of performance between different types of ICP-MS machines is presented in

757

Mg, K, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn, Ga, Ge

Application of isotope analysis

Isotopic ratio measurements

Tracer experiments

Isotope dilution

of Stable isotopes

Unstable isotopes

Isotopic variation in nature

Using enriched stable isotopes

• Radioactive waste • Clinical and biol. Determination of research • Environmental concentrations monitoring

Geochronology 6 7 e.g. Li/ Li 10B/ 11B

e.g. 87Rb

β–

87Sr

147Sm α 143Nd 187Re

β

187Os

e.g. 236U/ 238U 240Pu/ 239Pu

e.g. 41K / 39K 44Ca/ 42Ca 25Mg/ 26Mg

Figure 12-0.7 Diagram showing applications of ICP-MS in isotope analysis for different purposes (after Becker & DietZe, 1998).

Volume I, Part 1, Chapter 32. Comparison between a ‘conventional’ ICP-MS and a hexapole ICP-MS (collision cell type machine) was reported in Xie & Kerrich (2002) and between MC-ICP-MS machines equipped with an electrostatic filter and with a hexapole collision cell was reported by Mason et al. (2004a). Application of ICP-MS in isotopic analysis for different fields of research are given in Figure 12-0.7.

12-0.2.5.1.

Collision cells2

Introduction – The application of ion molecule chemistry, in radio frequency (RF) multipole reaction and collision cells, pressurized with reactive gases, results in attenuation of polyatomic ions that interfere with sensitive isotopes used for analysis. In 1989 Rowan & Houk (1989) published their data on processes prevailing in pressurized multipole cells for ICP-MS applications. The instrument used by Rowan & Houk (1989) consisted of two quadrupoles – the first in the RF mode operating synchronously with a mass filter quadrupole via capacitive coupling. The d.c potential of the quadrupole rod offsets were independently adjustable so that certain interferences were suppressed without suppressing analyte signals. Of note was the formation of new interfering ions in the collision cell, formed by reaction with the cell gas. Rowan & Houk (1989) also showed that ions could be discriminated by setting the d.c rod offset of the collision cell more negative than that of the mass filter. As a result, cell ions had lower kinetic energies than analyte ions derived from the plasma, and were consequently prevented from entering the mass filter.

2

Section 12-0.2.5.1 is contributed by Isaac B. Brenner. 9 Dishon Street, Malkha, Jerusalem, 96956, Israel. E-mail: [email protected]

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Handbook of Stable Isotope Analytical Techniques

Koppenaal et al. (1994) ascribed the absence of argide polyatomic ions to charge transfer reactions of these ions with entrained water molecules. Subsequent work by the same group showed effective application of ion–molecule chemistry with other gases (H2O and CH3). Subsequently, H2 was added to the trap to promote reactions with Ar resulting in six orders of magnitude reduction of the expected Ar ion signals and only a small loss of non-interfered analyte ions Instruments and mode of operation Differences in collision and reaction cells – In initial reports, classical hexapole or octopole collision cells were used to promote ion fragmentation, energy focusing and enhance ion transmission by collisional focusing. Subsequently, it became clear that near-thermal ion– molecule chemistry also occurs in ‘collision cells’ as defined in reaction cells; i.e. reactions governed by thermochemical properties of the ions and the reaction gas. Indeed, with chemically reactive gases such as hydrogen, methane and ammonia the same kind of reactions occur in both types of cells. Thus, the big difference between commercial reaction and collision cells is that the former operates in a mass filtering mode to remove unwanted polyatomic ions formed in the cell. Contrary to the DRC, where new ions formed in the cell are rejected by RF filtering, in collision cells, ions are rejected by setting the d.c pole bias of the subsequent quad more positive than the d.c pole bias of the collision cell. According to Tanner et al. (2002), the gas density in a DRC is greater than that in a collision cell. Therefore the extent of polyatomic ion rejection in the DRC exceeds that of collision cells. Perkin Elmer-SCIEX (ELAN DRC) – Various generations of the Perkin-Elmer SCIEX ELAN DRC (Dynamic Reaction Cell) use a high-precision quadrupole cell that can be pressurized. There are two principal modes of operation; (a) conventional ICP-MS, in which the reaction cell is operated at low pressure (