Extension of the JCGM 106:2012 - Conformity assessment of multicomponent items and finite statistical samples

The JCGM 106:2012 document provides guidelines on how to perform conformity assessment of a (scalar) property of interest of a single item (a product, material, object, etc.). In particular, based on a Bayesian approach, it indicates how to model and calculate specific and global risks of the consumer and the producer. In the present work, the JCGM 106 approach is generalized to items that are multicomponent materials (each component having its own property that should undergo conformity assessment with respect to its own requirements), and to a set of N items drawn from a common population (the probability of having a certain number of conforming items within this sample needs to be calculated)

IUPAC/CITAC Guide: Selection and use of proficiency testing schemes for a limited number of participants-chemical analytical laboratories (IUPAC Technical Report)*

Abstract: A metrological background for implementation of proficiency testing (PT) schemes for a limited number of participating laboratories (fewer than 30) is discussed. Such schemes should be based on the use of certified reference materials (CRMs) with traceable property values to serve as PT items whose composition is unknown to the participants. It is shown that achieving quality of PT results in the framework of the concept "tested once, accepted everywhere" requires both metrological comparability and compatibility of these results. The possibility of assessing collective/group performance of PT participants by comparison of the PT consensus value (mean or median of the PT results) with the certified value of the test items is analyzed. Tabulated criteria for this assessment are proposed. Practical examples are described for illustration of the issues discussed

IUPAC/CITAC Guide: Selection and use of proficiency testing schemes for a limited number of participants-chemical analytical laboratories (IUPAC Technical Report)*

Abstract: A metrological background for implementation of proficiency testing (PT) schemes for a limited number of participating laboratories (fewer than 30) is discussed. Such schemes should be based on the use of certified reference materials (CRMs) with traceable property values to serve as PT items whose composition is unknown to the participants. It is shown that achieving quality of PT results in the framework of the concept "tested once, accepted everywhere" requires both metrological comparability and compatibility of these results. The possibility of assessing collective/group performance of PT participants by comparison of the PT consensus value (mean or median of the PT results) with the certified value of the test items is analyzed. Tabulated criteria for this assessment are proposed. Practical examples are described for illustration of the issues discussed

Международный семинар. Качество результатов испытаний для оценки соответствия химического состава нормам – что такое хорошо и что такое плохо?

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Acids Extraction from Vegetable Oils for Acid Value pH-metric Determination without Titration

Theoretical and experimental analysis of free fatty acids extraction from vegetable oils into a reagent containing triethanolamine for pH-metric acid value determination without titration was carried out. Practically complete extraction of the free fatty acids in the form of triethanolammonium salts was demonstrated. The obtained results allow to understand more possibilities of the pH-metric and other methods for acid value determination in different oils

Correlation of test results and influence of a mass balance constraint on risks in conformity assessment of a substance or material

When components of a substance or material are subject to a mass balance constraint, test results of the components’ contents are intrinsically correlated because of the constraint. This so-called ‘spurious’ correlation is observed in addition to possible metrologically-related correlation of test results, and natural and/or technological correlation of the components’ contents. Such correlations may influence understanding of test results and evaluation of risks of false decisions, due to measurement uncertainty, in conformity assessment of the substance or material. The objective of the present paper is the development of a technique for appropriate evaluation of the risks. A Bayesian multivariate approach to evaluate the conformance probability of materials or objects and relevant risks is discussed for different scenarios of the data modelling, taking into account all observed correlations. A Monte Carlo method, including the mass balance constraint, written in the R programming environment, is provided for the necessary calculations

Interlaboratory comparison of the intensity of drinking water odor and taste by two-way ordinal analysis of variation without replication

A case study of ordinal data from human organoleptic examination (sensory analysis) of drinking water obtained in an interlaboratory comparison of 49 ecological laboratories is described. The recently developed two-way ordinal analysis of variation (ORDANOVA) is applied for the first time for the treatment of responses on the intensity of chlorine and sulfurous odor of water at 20 and 60 degrees C, which is classified into the six categories from 'imperceptible' to 'very strong'. The one-way ORDANOVA is used for the analysis of the 'salty taste' intensity of the water. A decomposition of the total variation of the ordinal data and simulation of the multinomial distribution of the data-relative frequencies in different categories allowed the determination of the statistical significance of the difference between laboratories in classifying chlorine or sulfurous odor intensity by categories, while the effect of temperature was not significant. No statistical difference was found between laboratories on salty taste intensity. The capabilities of experts to identify different categories of the intensity of the odor and taste are also evaluated. A comparison of the results obtained with ORDANOVA and ANOVA showed that ORDANOVA is a more useful and reliable tool for understanding categorical data such as the intensity of drinking water odor and taste