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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.12, #12)
The identification of the measurand can have an effect on the magnitude of the measurement uncertainty
by Paul De Bièvre (pp. 613-614).
A convenient and economic approach to achieve SI-traceable reference values to be used in drinking-water interlaboratory comparisons by Olaf Rienitz; Detlef Schiel; Bernd Güttler; Michael Koch; Ulrich Borchers (pp. 615-622).
Metrologically traceable reference values add an essential benefit to interlaboratory comparisons: unlike consensus values, they can be used to establish national and international comparability. Furthermore, the participating laboratories obtain a reliable and unbiased benchmark to check their results for accuracy. Usually, metrologically traceable reference values are obtained by so-called primary methods which demand excessive efforts at great expense. Within the framework of two national drinking-water interlaboratory comparisons (proficiency testing rounds), a new approach to provide metrologically traceable reference values was applied. It is solely based on existing data which were collected during the comparison itself. Lead (Pb) measurements serve as an example to show how metrologically traceable reference values were derived from the lead amount added during sample preparation and the amount of lead already present in the drinking-water matrix used to prepare these samples. Within this approach, the matrix content is calculated in a way similar to a standard addition experiment. An uncertainty budget for the reference value was set up which describes the link to the corresponding SI units. Isotope dilution mass spectrometry (IDMS) as a primary method was used to validate this approach in the case of cadmium, chromium, copper, lead, and nickel.
Keywords: Metrological traceability; Drinking water; Proficiency testing; Reference values; Heavy metals
Visualisation of interlaboratory comparison results in PomPlots by Yana Spasova; Stefaan Pommé; Uwe Wätjen (pp. 623-627).
In this work a novel graphical method is applied to the presentation of intercomparison results. This is demonstrated with the results of a recent intercomparison in measuring the 137Cs, 40K, and 90Sr activity concentration in milk powder. The “PomPlot”, an intuitive graphical method, is used for producing a summary overview of the participants’ results of a common measurand. The “PomPlot” displays (relative) deviations of individual results from the reference value on the horizontal axis and (relative) uncertainties on the vertical axis.
Keywords: Interlaboratory comparison; PomPlot; Uncertainty
Development of an obidoxime chloride reference material: a metrological approach to the determination of chromatographic purity by Ilana Schumacher; Paul Gorenbein; Arthur Raskin; Ilya Kuselman (pp. 629-636).
A metrological approach to determination of the chromatographic purity of obidoxime chloride and the corresponding obidoxime chloride reference material (RM) with a certified chromatographic purity value have been developed. This value was defined as the ratio of the sum of peak areas of obidoxime chloride isomers to the total peak area of detected substances including impurities (%) under specified HPLC–UV conditions. The RM homogeneity and stability were studied using HPLC with UV detection and evaluated as satisfactory. The certified value calculated from the results of an interlaboratory trial was equal to 99.9% with the expanded uncertainty of 0.6% at the level of confidence 0.95 and the coverage factor 2. The RM certified value, like other results of chromatographic purity determination traceable to the reference measurement procedure, is not traceable directly to the SI mole. However, the results are comparable in metrologically traceable environments, i.e. when relevant measuring laboratory instruments are calibrated with traceability chains to the corresponding SI units. Therefore, the RM can be used as a measurement standard (calibrator) for analytical instruments and as a control sample for quality control of HPLC obidoxime chloride assay results.
Keywords: Obidoxime chloride; Reference material; Chromatographic purity; Metrological approach; HPLC
Do proficiency tests always verify laboratories’ performance? The case of FAPAS PT 0270 by Małgorzata Olejnik; Teresa Szprengier-Juszkiewicz; Piotr Jedziniak; Jan Żmudzki (pp. 637-641).
In this paper, the case of FAPAS PT 0270 “Doramectin and Oxfendazole in Sheep Liver” is discussed. During evaluation of the data received from participants (determination of total, oxidised oxfendazole residue and calculation of the sum of oxfendazole and oxfendazole sulfone residues), significant differences were observed between the results obtained by use of two analytical approaches. This phenomenon can be explained by the route of oxfendazole metabolism, which results in the presence of fenbendazole in the sample. This was not predicted by the provider; consequently, not all the necessary tests on the material were conducted. Due to the high uncertainty of the z-scores in this test, the results of the PT cannot be used for purposes of evaluation, and the benefits of participation in PT 0270 are questionable.
Keywords: Proficiency testing; Residues in food; Oxfendazole; Fenbendazole
Between-examiner reproducibility in manual differential leukocyte counting by Xavier Fuentes-Arderiu; Mariona García-Panyella; Dolors Dot-Bach (pp. 643-645).
In manual–visual differential leukocyte counts, the counting itself may be different depending on the examiner. We estimated the between-examiner (B-E) reproducibility in differential leukocyte counting. During 2 months, daily, after performing manual–visual differential leukocyte counts, two slides with blood films were retained. Next day these two blood films were re-examined by different examiners. For each type of leukocyte the B-E reproducibility was estimated from the 58 pairs of data obtained by four technicians. The B-E coefficient of variation for each type of leukocyte was: basophilocytes, 263.2%; eosinophilocytes, 68.8%; lymphocytes, 32.5%; metamyelocytes, 69.6%; monocytes, 55.0%; myelocytes, 132.5%; and neutrophilocytes, 6.6%. For each type of leukocyte the coefficient of variation is the sought estimate of the average reproducibility due to the “human factor” as a whole, without regard to any examiner in particular. Knowledge of this component of day-to-day imprecision, and its follow-up, may be used to decide corrective actions (training of the examiner, etc.) and to set critical differences to interpret the significance of changes in serial results.
Keywords: Imprecision; Reproducibility; Laboratory practice; Leukocytes; Quality control; Statistics
The determination of adsorbable organically bound halogens (AOX) in soil: interlaboratory comparisons and reference materials by R. Becker; H.-G. Buge; I. Nehls (pp. 647-651).
The interlaboratory variability in the quantification of adsorbable organically bound halogens (AOX) in industrially contaminated soil is presented. Three consecutive rounds of a proficiency testing scheme, in which between 88 and 119 routine laboratories participated, yielded relative reproducibility standard deviations between 7 and 20% at AOX contents between 10.9 and 268 mg kg−1. Nineteen laboratories with established proficiency were invited to participate in the certification of the AOX content in three soil reference materials meant for the internal quality control in analytical laboratories. The certified values are (1349 ± 59) mg kg−1, (80 ± 7) mg kg−1 and (102 ± 8) mg kg−1, respectively.
Keywords: Certified reference materials; European Reference Material; Proficiency testing; Organohalogen compounds; Summation parameter
Quality control techniques for chemical analysis: some current shortcomings and possible future developments by M. J. Gardner (pp. 653-657).
Current approaches to quality control in chemical analysis are examined. Issues that frequently cause problems are proposed. Future developments relating to ways in which the incidence of mistakes might be reduced are discussed as possible supplements to more well-established quality control measures.
Keywords: Quality control; Laboratory performance; Mistake-proofing
Workshop on “Trends in Uncertainty Evaluation and Interlaboratory Comparison Analysis”: a participant’s view
by Heinrich Kipphardt (pp. 659-660).
The meaning of ‘concentration’ by René Dybkaer (pp. 661-663).
Terminology within a small laboratory community can be informal without danger of misunderstanding, but communication with a wider audience and not least in publications, needs unequivocal terms for defined concepts. As an example, the many meanings of “concentration” are explored to present a systematic nomenclature, including a concept diagram.
Keywords: Concentration; Concept system; Kind-of-quantity; Systematic terminology