Project Details Evaluation of isotopic abundance variations in selected heavier elements

Project No.: 
Start Date: 
01 September 2008
End Date: 
01 June 2013


The purpose of this project is to evaluate isotopic abundance variations of selected elements, including Ca, Ti, Cr, Fe, Ni, Cu, Zn, Se, Mo, and Cd in a range of materials, based on peer-reviewed measurements, to make graphical plots of these data and to provide CIAAW with information to update the Table of Standard Atomic Weights.


Recent developments in inorganic mass spectrometry enable isotope ratio measurement of heavy elements at unprecedented precision. A steadily growing body of measurements shows mass-dependent isotope abundance variations for the heavy elements such as Ca, Ti, Cr, Fe, Ni, Cu, Zn, Se, Mo, Cd. This raises the question of how far current IUPAC recommendations for the standard atomic weights of these elements and their respective uncertainties incorporate any natural variations in isotope abundances.

In July 2009, task group members will convene in Glasgow, prior to the IUPAC General Assembly, to evaluate published information and its possible impact on current recommendations for the Standard Atomic Weight and its uncertainty. Detailed discussions and calculations will be carried out in agreement with the concepts of data evaluation established by SIAM and CIAAW over recent decades. Particular attention will be paid to possible sources of systematic bias in the measurement uncertainty, the selection of materials for analysis, and the variability of measured isotope ratios in these materials. Graphical plots of these data with atomic weight axes, delta scale axes, and mole fraction axes, presented for various types of chemicals and substances, in a manner similar to previous SNIF diagrams.

Recommendations will be incorporated into those generated by the Subcommittee on Isotope Abundance Measurements (SIAM) and they will be sent to CIAAW for approval. Approved changes will be incorporated into the next CIAAW Table of Isotopic Composition of the Elements (TICE) and Table of Standard Atomic Weights (TSAW).

The technical report will complement the earlier IUPAC (SNIF) report “Isotope-Abundance Variations of selected elements” (Pure Appl. Chem. 74:1987-2017, 2002) in which the heavier elements could not be comprehensively covered because of paucity of data.


May 2013 – Atomic weights of the elements 2011 (IUPAC Technical Report) published in Pure Appl. Chem., 2013, Vol. 85, No. 5, pp. 1047-1078;

project completed

Last updated 7 June 2013