IUPAC/CITAC Webinar “Metrology, quality assurance and chemometrics—Correlation of test results and mass balance influence on conformity assessment”

Since the biannual IUPAC/Cooperation on International Traceability in Analytical Chemistry (CITAC) Workshop on metrology, quality and chemometrics scheduled for January 2021 in conjunction with Isranalytica, Israel, was postponed to Jan 2022 because of COVID-19 a Webinar was organized as a Zoom meeting on 21 January 2021, hosted by NRC, Canada.

The webinar started with the opening remarks and welcoming by Zoltan Mester, NRC, IUPAC ACD President, and CITAC Vice-Chair. Then, participants heard a CITAC update—a foreword given by Bernd Güttler, PTB, Germany, CITAC Chair. Michela Sega,INRIM, Italy, and CITAC Past Chair,spoke about CITAC as a stakeholder of the IUPAC project on mass balance influence on conformity assessment. After her welcoming, Sega continued in the role of the Webinar moderator. Four overview lectures were provided.

Ilyav Kuselman

Ilyav Kuselman, Independent Consultant on Metrology, Israel, (https://orcid.org/0000-0002-5813-9051), gave a lecture on IUPAC/CITAC Guide: Evaluation of risks of false decisions in conformity assessment of a multicomponent material or object due to measurement uncertainty and correlation of test results. The Guide was developed by the IUPAC project task group consisting of Francesca R. Pennecchi, INRIM, Italy; Ricardo J.N.B. da Silva, University of Lisbon, Portugal; and D. Brynn Hibbert, UNSW Sidney, Australia; and chaired by Kuselman (https://iupac.org/project/2018-004-1-500). The work was supported by CITAC. In this Guide, risks of a false decision on conformity of the chemical composition of a multicomponent material or object due to measurement uncertainty are defined using the Bayesian approach. Even if the conformity assessment for each particular component of a material is successful, the total probability of a false decision (total consumer’s risk or producer’s risk) concerning the material as a whole might still be significant. This is related to the specific batch, lot, sample, environmental compartment, or other item of material or object (specific consumer’s and producer’s risks), or to a population of these items (global consumer’s and producer’s risks). When the actual values of the components’ concentrations or contents, as well as the measured values, are correlated, they are modelled by multivariate distributions. The effect of correlation on the risks is not easily predictable. Examples of the evaluation of risks are provided in the Guide for conformity assessment of denatured alcohols, total suspended particulate matter in ambient air, a cold/flu medication, and a PtRh alloy.

Francesca R. Pennecchi

Francesca R. Pennecchi, INRIM, Italy, (https://orcid.org/0000-0003-1328-3858), discussed in her lecture the influence of a mass balance constraint on risks in conformity assessment of substances and materials. She said that the IUPAC/CITAC Guide Evaluation of risks of false decisions in conformity assessment of a multicomponent material or object due to measurement uncertainty offers a general Bayesian approach for evaluating the risks of false decisions in conformity assessment of multicomponent materials or objects. When components of such substances are linked by a mass balance constraint (i.e., the sum of their mass fractions, molar fractions or any other positive quantity ratios is 100 % or 1), test results of the components’ contents are named “compositional data.” These data are always correlated, because of the constraint. Such correlations, being named “spurious”, may influence measurement uncertainty of test results as well as risks of false decisions in conformity assessment of a substance or material. That is important in testing geological and environmental objects, products of metallurgical and food industries, etc. A special case is the evaluation of purity of substances by an indirect method based on a mass balance, and development of corresponding (pure) certified reference materials. IUPAC project 2019-012-1-500 is under development now with the aim of studying how to deal with mass balance constraint in conformity assessment. A Bayesian multivariate approach is applied to different scenarios of the data modelling, based on a Monte Carlo method that includes the mass balance constraint.

Angelique Botha

Angelique Botha, NMISA, South Africa, (https://orcid.org/0000-0003-3987-359X), gave an overview of development of the ISO/REMCO guidance, and in particular for the production of high purity reference materials. The ISO Committee for Reference Materials (ISO/REMCO) has actively been updating its guidance documents over the past eight years. Since the conversion of the third edition of ISO Guide 34 to the international standard ISO 17034 to address the conformity assessment of reference material producers, the work of the committee has focused on the revision of ISO Guide 35 and the development of up-to-date guidance for the users of reference materials. In 2014, a guidance document, ISO Guide 80, for the in-house preparation of quality control materials was published by the committee. The third edition of ISO Guide 33 Reference materials—Good practice in using reference materials was published early in 2015. While the previous edition focused on the use of certified reference materials, the new one relates to all types of reference materials and their uses. The prospects for the future work of the committee include the development of more field specific guidance. At the beginning of 2018 a proposal was approved for the development of a guidance document for the production of qualitative reference materials (ISO Guide 85). Two new proposals (ISO Guide 86 and ISO Guide 87) were also approved for the development of harmonized guidance for the preparation of high purity reference materials for small organic molecules as well as metals and metalloids, respectively.

D. Brynn Hibbert

The lecture of D. Brynn Hibbert, School of Chemistry, UNSW Sydney, Australia, (https://orcid.org/0000-0001-9210-2941), was on metrology and the law: presenting chemical measurements to the courts. In Australia, an expert is bound to help the court no matter who is paying. Expert conferences are encouraged so that complex science can be presented to allow the “trier of fact” to make a properly informed decision. In particular, for example, the issue is often one of conformity assessment—is the driver over the legal limit for alcohol? Three examples from the author’s case book will show how reliable measurements have been crucial to providing justice. First, a racing horse is not allowed to have more than 100 ng/mL of cobalt in its urine. In a landmark case the court accepted a statistical distribution of cobalt mass concentrations that allowed calculation of the probability of an ‘ordinary horse’ having a mass concentration greater than the legal threshold. Second, illegal ‘meth labs’ are found in most countries. While the identity of the product (‘ice’ or N-methylamphetamine hydrochloride) is often not in dispute, the amount of drug synthesised determines the length of the custodial sentence. Measurement of purities, and thus mass of drug, requires proof that the sample analysed was representative of the item seized. Estimation of potential yields from seized precursors also has a bearing on indictable amounts. Finally, in a recent cold-case murder, the author successfully argued against the admissibility of lead isotope analysis results that matched bullets in a body to bullets in a box of bullets in the possession of one of the accused. Was the method properly validated? And does the chemical match actually prove the body bullets came from the box?

The number of the participants from different countries and continents varied during the Webinar from about 130 to 200. They had a possibility for questions, and the interaction with the lecturers was interesting. The Zoom event was recorded and published on YouTube, https://www.youtube.com/watch?v=3mZMv6hwDMY. Corresponding links are available on IUPAC webpage https://iupac.org/event/metrology-quality-and-chemometrics/ and CITAC website www.citac.cc (Conferences & Workshops).

Reprint from CITAC News April 2021, p. 72, https://iupac.org/event/metrology-quality-and-chemometrics/