Project Details Guidelines for mass spectrometric isotope ratio measurements

Project No.: 
Start Date: 
01 January 2002
End Date: 
31 October 2011


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 > [provisional recommendations ../../reports/provisional/abstract08/coplen_310508.html]

September 2009 – IUPAC Technical Report titled ‘Atomic weights of the elements 2007’ has been published (Pure Appl. Chem. 2009, doi:10.1351/PAC-REP-09-08-03) and this report also includes recommendations for the inclusion of
systematic errors in the publication of mass spectrometric
isotope-ratio measurements.

June 2010 – IUPAC Technical Report titled ‘Correction for the 17O interference in δ(13C) measurements when analyzing CO2 with stable isotope mass spectrometry’ is published in Pure Appl. Chem., Vol. 82, No. 8, pp. 1719–1733, 2010; doi:10.1351/PAC-REP-09-01-05 

August 2011 – Project Completed – The report titled ‘Guidelines and recommended terms for expression of stable-isotope-ratio and gas-ratio measurement results’ has been published. These guidelines:

  • Are based on publications of the Commission on Isotopic Abundances and Atomic Weights, with input from more than 30 subject-matter experts.
  • Provide examples of stable isotope measurement results consistent with the Système International d’Unités, the SI (known in English as the International System of Units), and the third edition of the International Vocabulary of Basic and General Terms in Metrology (VIM, 3rd edition).
  • Encourage the use of and provide examples of stable-isotope-delta definition equations that are coherent quantity equations, where the extraneous factors 100, 1000, and 1000 000 have been removed.
  • Recommend and provide examples for expression of stable isotope and gas-ratio measurements using the symbols for dimensionless quantities, per mil (‰), part per million (ppm), and per meg (one part in a million parts).
  • Provide examples of column headings and axis labels for stable isotope and gas-ratio measurements consistent with quantity calculus.

Published in Rapid Commun. Mass Spectrom. 2011, 25, 2538–2560, doi:10.1002/rcm.5129 (first online 19 August 2011)


Last update 20110831