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Inorganic Chemistry Division


Number: 2001-019-2-200

Title: Guidelines for mass spectrometric isotope ratio measurements

Task Group
Thomas Walczyk

Members: Michael Berglund, John Karl Böhlke, Tyler B. Coplen, Klaus G. Heumann, and Philip D.P. Taylor

Best measurement practice of isotope ratio measurements by the mass spectrometric community.

Isotope ratio measurements by mass spectrometric techniques are required in basic and applied research e.g. geology, environmental sciences, biomedicine and human nutrition research. The advent of new mass spectrometric techniques, the improvement of existing techniques and the broadening of applications have result in a tremendous increase in reported data over recent years. As no guidelines exist to date on how to perform high quality isotope ratio measurements, the evaluation of published data becomes increasingly difficult. This project will define recommendations to improve the quality and comparability of isotope ratio measurements. Because of the diversity of available techniques, instrumentation and element specific characteristics this project will be limited to the definition of generally applicable guidelines. Sources of bias in sample preparation, ion generation, ion separation and ion detection will be outlined. Protocols for bias control for the most commonly used techniques in isotope ratio mass spectrometry, i.e. thermal ionization mass spectrometry (TIMS), inductively coupled plasma mass spectrometry (ICPMS) and gas isotope ratio mass spectrometry (GIRMS), will be defined. As a consequence, evaluation of published data will be facilitated.

June 2004 update - Recent activities indicate that even a basic consensus amongst the different user groups is difficult to achieve. Quality control issues, especially in the field of multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS), are subject to often emotional discussions. Based on these observations it has been decided to move away from a publication of guidelines to a publication that discusses the various sources of systematic bias in isotope ratio measurements and the various strategies how to control underlying effects. By creating the awareness for these effects and providing a choice of practical approaches for their control, quality standards in isotopic analysis are expected to be further improved, which is the final aim of the project.

> Publication of a paper on perspectives of inorganic mass spectrometry Walczyk T (2004) TIMS versus multicollector ICP-MS: coexistence or struggle for survival? Anal. Bioanal. Chem. 378, 229-231 [doi: 10.1007/s00216-003-2053-4]

June 2005 update - Over the past two years it became clear that it is not possible to come-up with a consensus within the community as the basis for the acceptance of generally applicable guidelines. However, the primary reasoning for the Commission of Isotopic Abundances and Atomic Weights (CIAAW) to pursue on this project was to facilitate evaluation of published isotope ratio measurements by CIAAW in the future. Through these evaluations, CIAAW identifies if currently valid recommendations for the Standard Atomic Weight of the elements and their natural isotopic abundances need to be modified. Essentially, either an incomplete consideration of systematic sources of bias or the lack of sufficient details in the publication makes it often difficult to assess their impact on measurement accuracy in practice. For this reason it is proposed to modify the title as well as the intended primary outcome of the project from "Guidelines for mass spectrometric isotope ratio measurements" to "Guidelines for reporting mass spectrometric isotope ratio measurements".

Jan 2007 update - A draft of the document will be submitted to PAC within the next 12 months for publication.

Jan 2008 - A draft titled 'Explanatory Glossary of Terms Used in Expression of Relative Isotope Ratios and Gas Ratios' is submitted to public review comments until 31 May 2008 > see provisional recommendations

Last Update: 24 January 2008

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Page last modified 24 January 2008.
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