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International Union of Pure and Applied Chemistry

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Project: Evaluated published isotope ratio data (2005-2007)

Objective

Evaluate isotope ratio publications between 2005 and early 2007, to determine "best isotope ratio measurements" for compilation and publication in a 2009 TICE, recommend "new" standard atomic weights, and publish "Atomic Weights of the Elements 2007" in Pure and Applied Chemistry, which will also include a table of relative atomic masses and half-lives of selected radionuclides.

Description

The aim of the task group is to evaluate isotope ratio publications between early-2005 and early 2007. The evaluated data will be incorporated into the CIAAW* Table of Isotopic Composition of the elements (TICE) and Table of Standard Atomic Weights. This project is an interim step in the evaluation of isotopic data production for the next proposed publication of TICE in 2009.

> *see CIAAW actvities

The Subcommittee on Isotopic Abundance Measurements (SIAM) recognizes that there are a number of elements that need particular attention and for which significant publications are expected. These include Zn, Ca, Mg, and Si: for which two, significantly different, high precision publications have recently been assessed by IUPAC, is in the process of being resolved and will require evaluation.

The task group will evaluate recently published isotope ratios and resulting atomic-weights. Detailed discussions and calculations will be carried out on any chemical element for which new isotope ratio information exists. Particular attention will be paid to authors' evaluations of uncertainty, the selection of materials for analysis, and the variability of isotope ratio measurements in these materials. The task group will than present their recommendations for adoption of best isotopic ratios and new standard atomic weights to the Commission on Isotopic Abundances and Atomic Weights at the General Assembly in Torino.

Subsequently, a publication titled "Atomic Weights of the Elements 2007" will be prepared for Pure and Applied Chemistry. Subsequently, publication in J. Phys. Chem. Ref. Data is anticipated.

Progress
August 2007 - The task group evaluated isotope ratio data for 13 elements (Ar, Br, C, Cl, Cd, Lu, Mo, Ni, O, Si, Ti, Zn, Yb) in 16 publications reported between mid-2005 and mid 2007. Particular attention was paid to evaluations of uncertainties, the types of materials analysed, and the variability of isotope ratio measurements reported.

Of equally importance to the approval of the new data was the attention paid by the task group to high precision isotopic ratio measurements reported for elements such as Cd, Ti, and Ni for which changes to best measurements were not made. This highlighted the need for specialist analysts to be called on to address issues related to specific analytical techniques.

Final uncertainty calculation and expansions were performed using the principles and procedures proposed by IUPAC project number 2003-031-2-200 (RICEII) using full GUM procedures. For the elements requiring changes, appropriate uncertainty expansion factors were used to ensure compatibility with current CIAAW accepted evaluation procedures. A full implementation of RICEII proposals in this type of work awaits CIAAW approval.

At the 24-27 July 2007 Pisa meeting of the Subcommittee on Isotopic Abundance Measurements the new "best isotope ratio" data for Ar, Lu, Mo, Yb and Zn were recommended to CIAAW for inclusion in the next (2009) CIAAW Table of Isotopic Composition of the elements (TICE). In addition, new Standard Atomic Weights were also recommended for Lu, Mo, Ni, Yb and Zn to be published in "Atomic Weights of the Elements 2007" prepared for Pure and Applied Chemistry. A subsequent, publication in J. Phys. Chem. Ref. Data is also anticipated. Details of the evaluations and the recommendations are shown in the attached minutes of the SIAM meeting.