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The Table of Standard Atomic Weights-An exercise in consensus
Tyler B Coplen1, Norman E Holden2, Tiping Ding3
1U.S. Geological Survey, Reston, Virginia, USA.
Rapid Communications in Mass Spectrometry : RCM
|June 20, 2020
Summary
The International Union of Pure and Applied Chemistry (IUPAC) updated its standard atomic weight (SAW) uncertainty reporting. New guidelines align with the Guide to the Expression of Uncertainty in Measurement (GUM) for clearer scientific data.
Area of Science:
- Chemistry
- Metrology
- Physical Science
Background:
- The Table of Standard Atomic Weights (TSAW) is a key scientific dataset.
- Atomic weight uncertainties were previously consensus values, not evaluated by the Guide to the Expression of Uncertainty in Measurement (GUM).
- Discrepancies existed between TSAW uncertainty notation and GUM recommendations.
Purpose of the Study:
- To clarify the expression of uncertainty in standard atomic weight values.
- To ensure compliance with the Guide to the Expression of Uncertainty in Measurement (GUM).
- To enhance the reliability and clarity of the Table of Standard Atomic Weights (TSAW) and Table of Isotopic Compositions of the Elements (TICE).
Main Methods:
- The Commission on Isotopic Abundances and Atomic Weights (CIAAW) regularly reviews isotopic abundance measurements.
- A new format using the "±" symbol was adopted in 2017 to report uncertainties.
- A footnote was added to the TSAW to define atomic weight uncertainty as a consensus (decisional) uncertainty.
Main Results:
- The new format aligns uncertainty reporting with GUM standards.
- Users are protected from unreliable literature values with unduly small uncertainties.
- The revised reporting ensures atomic weights are within the stated uncertainty for most natural samples.
Conclusions:
- The updated uncertainty reporting enhances the clarity and reliability of standard atomic weights.
- The changes ensure consistency with international metrology standards (GUM).
- This benefits scientists by providing more dependable atomic weight data for research and commerce.
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