Standard atomic weights of the elements 2021 (IUPAC Technical Report)

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The present Table of Standard Atomic Weights (TSAW) of the elements is perhaps one of the most familiar data sets in science. Unlike most parameters in physical science whose values and uncertainties are evaluated using the “Guide to the Expression of Uncertainty in Measurement” (GUM), the majority of standard atomic‐weight values and their uncertainties are consensus values, not GUM‐evaluated values. The Commission on Isotopic Abundances and Atomic Weights of the International Union of Pure and Applied Chemistry (IUPAC) regularly evaluates the literature for new isotopic‐abundance measurements that can lead to revised standard atomic‐weight values, Ar°(E) for element E. The Commission strives to provide utmost clarity in products it disseminates, namely the TSAW and the Table of Isotopic Compositions of the Elements (TICE). In 2016, the Commission recognized that a guideline recommending the expression of uncertainty listed in parentheses following the standard atomic‐weight value, for example, Ar°(Se) = 78.971(8), did not agree with the GUM, which suggests that this parenthetic notation be reserved to express standard uncertainty, not the expanded uncertainty used in the TSAW and TICE. In 2017, to eliminate this noncompliance with the GUM, a new format was adopted in which the uncertainty value is specified by the “±” symbol, for example, Ar°(Se) = 78.971 ± 0.008. To clarify the definition of uncertainty, a new footnote has been added to the TSAW. This footnote emphasizes that an atomic‐weight uncertainty is a consensus (decisional) uncertainty. Not only has the Commission shielded users of the TSAW and TICE from unreliable measurements that appear in the literature as a result of unduly small uncertainties, but the aim of IUPAC has been fulfilled by which any scientist, taking any natural sample from commerce or research, can expect the sample atomic weight to lie within Ar°(E) ± its uncertainty almost all of the time.

Section: A Tsaw Of the Elementsmentioning

confidence: 73%

Section: A Tsaw Of the Elementsmentioning

confidence: 99%

Section: The Process Of Revising a Standard Atomic Weightmentioning

confidence: 99%

Section: A New Column and Footnote For Standard Atomic-weight Uncerta...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Table of Standard Atomic Weights—An exercise in consensus

Coplen

Holden

Ding

et al. 2022

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Machine learning approach for the prediction of the number of sulphur atoms in peptides using the theoretical aggregated isotope distribution

Agten¹,

Claesen

Burzykowski

et al. 2023

Rationale:The observed isotope distribution is an important attribute for the identification of peptides and proteins in mass spectrometry-based proteomics.Sulphur atoms have a very distinctive elemental isotope definition, and therefore, the presence of sulphur atoms has a substantial effect on the isotope distribution of biomolecules. Hence, knowledge of the number of sulphur atoms can improve the identification of peptides and proteins.Methods: In this paper, we conducted a theoretical investigation on the isotope properties of sulphur-containing peptides. We proposed a gradient boosting approach to predict the number of sulphur atoms based on the aggregated isotope distribution. We compared prediction accuracy and assessed the predictive power of the features using the mass and isotope abundance information from the first three, five and eight aggregated isotope peaks.Results: Mass features alone are not sufficient to accurately predict the number of sulphur atoms. However, we reach near-perfect prediction when we include isotope abundance features. The abundance ratios of the eighth and the seventh, the fifth and the fourth, and the third and the second aggregated isotope peaks are the most important abundance features. The mass difference between the eighth, the fifth or the third aggregated isotope peaks and the monoisotopic peak are the most predictive mass features.Conclusions: Based on the validation analysis it can be concluded that the prediction of the number of sulphur atoms based on the isotope profile fails, because the isotope ratios are not measured accurately. These results indicate that it is valuable

Perspective: Hidden biases in isotope delta results and the need for comprehensive reporting

Dunn,

Skrzypek

2023

Measurements of stable‐isotope composition on an isotope‐delta scale can be subject to bias between laboratories or over time within a single laboratory. This bias can arise not just from differences in method protocol but also from changes in reporting guidelines, or even to the isotope‐delta scales themselves. Without a clear description of method protocols, including all sample preparation steps, instrumental parameters and settings, data processing including calibration of results and estimation of measurement uncertainty, the traceability and comparability of isotope‐delta values cannot be assured as bias(es) may remain hidden. To address this need, there are now clear guidelines published by IUPAC for reporting isotope‐delta values for the “light” elements hydrogen, carbon, nitrogen, oxygen and sulfur.1 We recommend that authors and reviewers adhere to those guidelines when preparing and reviewing future publications.