Risks in Conformity Assessment of a PtRh Alloy due to Measurement Uncertainty

Ilya Kuselman, Independent Consultant On Metrology, Modiin, Israel (ilya.kuselman@gmail.com)
Francesca R. Pennecchi, Istituto Nazionale Di Ricerca Metrologica, Turin, Italy
Ricardo J.N. Bettencourt da Silva, Faculdade De Ciencias Da Universidade De Lisboa, Lisbon, Portugal
D. Brynn Hibbert, School of Chemistry, University of New South Wales (UNSW), Sydney, Australia
Elena Anchutina, JSC Ekaterinburg Non-ferrous Metal Processing Plant, Ekaterinburg, Russia

A dataset of test results of 100 batches of PtRh alloy produced at the same plant is studied when contents of four components of the alloy composition are under control. There are specification limits for contents of 1) Pt and 2) Rh; 3) three precious impurities, and 4) eight impurities, both precious and non-precious. Testing was performed at the plant laboratory using X-ray fluorescence and optical atomic emission spectrometry methods. Measurement uncertainties of the test results are evaluated summarizing data of validation reports of the measurement procedures for the different analytes. These test results are correlated because of the natural chemical origin of the raw materials used in the alloy production and because of mass balance constraints. Correlations between test results for two pairs of the components (Pt vs. Rh, and the three vs. the eight impurities) are strong. To assess the correlation effects on the total risk of false decision in conformity assessment of an alloy batch, the study was performed for two scenarios considering 1) correlated test results for all four components, and 2) practically uncorrelated test results for two components only - Rh and the eight impurities. A multiparametric Bayesian approach was applied for total risk evaluation, where the observed correlations were taken into account within the experimental correlation matrix. It was shown that simplification of the testing by reducing the number of components under control leads to a significant increase of the probability of a false decision on conformity of an alloy batch.

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Short Biography of Presenting Author

Ilya Kuselman has received his Ph.D. in inorganic chemistry from Kalinin State University, and D.Sc. in analytical chemistry – from R&D Institute for Rare Metal Industry, Moscow, Russia. Since 1971 to 1990 Ilya has been researcher and then Head of Metrology in Chemistry Division of All-Union R&D Institute of Non-ferrous Secondary Metals, Donetsk, Ukraine, USSR. Since 1991 to 2014 he was a co-worker and further Director of the National Physical Laboratory of Israel. Now Ilya is Independent Consultant on Metrology. He has published above 200 papers on metrology and quality in analytical chemistry. Ilya is a member of CITAC, ISO/REMCO and IUPAC Analytical Chemistry Division, Chair of the IUPAC Interdivisional Working Party on Harmonization of Metrology and Quality Guidelines.