Abstract
The weighted least squares method to build an analysis function described in ISO 6143, Gas analysis—Comparison methods for determining and checking the composition of calibration gas mixtures, is modified to take into account the typically small number of instrumental readings that are obtained for each primary standard gas mixture used in calibration. The theoretical basis for this modification is explained, and its superior performance is illustrated in a simulation study built around a concrete example, using real data. The corresponding uncertainty assessment is obtained by application of a Monte Carlo method consistent with the guidance in the Supplement 1 to the Guide to the expression of uncertainty in measurement, which avoids the need for two successive applications of the linearizing approximation of the conventional method for uncertainty propagation. The three main steps that NIST currently uses to certify a reference gas mixture (homogeneity study, calibration, and assignment of value and uncertainty assessment), are described and illustrated using data pertaining to an actual standard reference material.
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Acknowledgements
The authors are particularly grateful to their NIST colleagues Andrew Rukhin, Blaza Toman, and David Duewer, who kindly provided detailed reviews of a draft, and offered useful comments and suggestions. However, we may not have incorporated all of their suggestions, or heeded all of their advice, hence there is no implication that they subscribe to the current version of the contribution. The same applies to other colleagues including Hung-kung Liu and Stefan Leigh, who have given us suggestions, comments, and references, on several occasions.
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Guenther, F.R., Possolo, A. Calibration and uncertainty assessment for certified reference gas mixtures. Anal Bioanal Chem 399, 489–500 (2011). https://doi.org/10.1007/s00216-010-4379-z
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DOI: https://doi.org/10.1007/s00216-010-4379-z