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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.14, #3)

What is our best measurand when measuring “something” in “something”? by Paul De Bièvre (pp. 121-122).

Reproducibility estimates from single-laboratory ruggedness tests compared with those derived from collaborative trials of six microbiological measurement methods by Keith Jewell; Heather Leach; Christopher Baylis (pp. 123-137).

This work investigated the feasibility of single-laboratory ruggedness experiments to estimate between-laboratory reproducibility. Six microbiological measurement methods that had already been subject to multi-laboratory validation were studied. Ruggedness experiments were designed and executed to determine sensitivity coefficients for factors judged likely to vary between laboratories. These were combined with estimates of factor variation to give reproducibility estimates. The single-laboratory estimates of reproducibility were generally not similar to those generated from multi-laboratory work. The experimental plans were difficult to design and execute, and were only partially successful in producing useful sensitivity coefficients. The authors conclude that ruggedness tests do not offer a single-laboratory alternative to multi-laboratory method validation or a practical approach to the evaluation of measurement uncertainty for microbiological methods.

Keywords: Single-laboratory validation; Sensitivity coefficient; Measurement uncertainty

Long-term equilibrium potential and electrochemical impedance study of Ag/AgCl electrodes used in Harned Cell measurements of pH by Richard J. C. Brown; Paul J. Brewer; Dan J. L. Brett (pp. 139-145).

A long term study of the voltage and electrochemical impedance characteristics of Ag/AgCl electrodes used in Harned Cell measurement of pH is presented. By all the measures investigated the electrodes are shown to degrade only slowly until approximately 200 days after manufacture, after which time the rate of degradation and critical failure of the electrodes increases. The absolute voltage drift of the electrodes may not be easily measured, so parameters determined directed or indirectly by electrochemical impedance spectroscopy have been assessed as a method to produce an alternative indication of electrode integrity. In this respect, resistance to charge transfer has been shown to be a very sensitive measure of changes in the characteristics of the electrodes, and the most closely related to the observed changes in voltage. Evidence is presented to support the hypothesis that the majority of electrode degradation (excluding critical failure) comes from the increased blocking of the microporous structure of the electrodes.

Keywords: pH; Ag/AgCl electrodes; Harned Cell; Electrochemical impedance; Long-term degradation

Examples of the ‘characteristic’ function applied to instrumental precision in chemical measurement by Michael Thompson; Barry J. Coles (pp. 147-150).

The ‘characteristic function’ $$ sigma = sqrt {alpha^{2} + left( {eta c} ight)^{2} } ,$$ with two empirically determined parameters α and β, is proposed as a general purpose function to describe the variation of precision (in terms of standard deviation σ), or uncertainty, with analyte concentration c (here denoting any compositional quantity), for specific analytical methods applied to a defined type of test material. In this study it is applied to examples of analytical data collected under ‘instrumental’ conditions for estimating precision. The function fitted the data well, with no systematic lack of fit. The study therefore extends the range of applications of this function.

International comparison of the determination of cadmium and lead in herb: the Comité Consultatif pour la Quantité de Matière (CCQM) pilot study CCQM-P97 by Y. C. Wong; D. W. M. Sin; Y. C. Yip; L. Valiente; A. Toervenyi; J. Wang; G. Labarraque; P. Gupta; D. Soni; Surmadi; E. Hwang; C. Yafa; O. Cankur; E. Uysal; G. Turk; R. Huertas (pp. 151-158).

A Comité Consultatif pour la Quantité de Matière (CCQM) inter-laboratory comparison program, CCQM-P97, for the analysis of cadmium and lead in Herba Demodii Styracifolii was organized by the Hong Kong Government Laboratory. The objective of the program was to establish comparability of trace metals analysis in herbal matrices amongst the participating national metrology institutes. The arithmetic mean values of the 13 participants were 0.3186 mg kg⁻¹ (RSD = 11.3%) and 1.650 mg kg⁻¹ (RSD = 11.0%) for cadmium and lead, respectively. The participants using double-isotope dilution mass spectrometry technique for their quantification were found to provide similar mean values to those of non-isotope dilution mass spectrometry users. The observation indicated that trace metal analysis in herbal matrices was not method-dependent, but the use of the highest metrological IDMS approach gave a better precision than other routine calibration methods.

Keywords: Cadmium; Lead; Herb sample; CCQM; Inter-laboratory comparison

ISO 5725 and GUM: comparison and comments by Laura Deldossi; Diego Zappa (pp. 159-166).

We compare the approach to measure uncertainties proposed in ISO 5725 and GUM from a statistician point of view. In particular we give some warnings to the application of the expanded uncertainty introduced in GUM when the input variables are few and we report some considerations on the relevant role of the interactions among the input variables in the measurement equation as well as the role of statistical design of experiments to measure uncertainties.

Keywords: Measurement equation; Confidence intervals; Design of experiments

TrainMiC^®: a programme for life-long learning in metrology in chemistry by Philip Taylor; Ewa Bulska; Steluta Duta; Nineta Majcen; Emilia Vassileva (pp. 167-173).

This article gives an overview of the programme TrainMiC^®, a European programme for Life-Long Learning in metrology in chemistry. It explains its raison d’être and puts it into perspective to other European and EU member states initiatives. The TrainMiC^® system ( http://www.trainmic.org ) is described in detail. It is explained how it has developed into a truly unique system which is operational across many parts of Europe (19 countries) via national teams. These teams use shareware pedagogic tools. The learning content has been harmonised at the European level by a joint effort of many experts across Europe working via an Editorial Board. The material has been translated in ten different languages. Possible future evolution of this Life Long Learning programme is discussed.

Keywords: Metrology in Chemistry; Quality of measurement results; Life-long learning

Congress, conferences, workshops and courses (pp. 175-176).

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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.14, #3)

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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.14, #3)