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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.11, #10)


Stability testing in an integrated scheme by Wolfram Bremser; Roland Becker; Heinrich Kipphardt; Petra Lehnik-Habrink; Ulrich Panne; Antje Töpfer (pp. 489-495).
ISO Guide 35 deals with RM stability issues and scrutinizes the evaluation of stability testing results under the assumption that either there is no trend at all (a rather rare situation), or any observed deterministic change is insignificant and thus can be neglected. However, market demands for reliable reference materials are obviously not limited to stable or at least seemingly stable materials. In many analytical applications, analytes and measurands under consideration are known, or at least suspected, to be unstable on time scales that may vary widely from measurand to measurand. The Federal Institute for Materials Research and Testing (BAM) has developed (and successfully uses) an integrated approach in its certification practice. The approach is based on an initial stability study and subsequent post-certification monitoring. Data evaluation is model-based and takes advantage of all information collected in the stability testing scheme(s). It thus allows one to deal with any kind of instability observed, to assess limiting time intervals at any stress condition in the range tested, to estimate a final expiry date for materials with detected instabilities or the maximum admissible re-testing interval for seemingly stable materials, and to assess maximum admissible stress loads during delivery of the material to the customer. The article describes (and exemplifies) typical study layout, the model selection, and the integrated data assessment.

Keywords: Certified reference materials; Stability; Shelf life; Arrhenius model; ERM


Exhaust gas analysers and optimised sampling, uncertainties and costs by L. R. Pendrill; H. Källgren (pp. 496-505).
Decision-making in the conformity assessment of exhaust gas analysers with due account of measurement uncertainty and limited sampling is considered. Risks of incorrect decisions where test results lie in the vicinity of a specification limit are assessed in terms of percentage probability and the costs of measurement and environmental consequences, with examples based on the metrological requirements on these analysers stipulated in the new EU Measurement Instrument Directive. An optimised uncertainty methodology is proposed for the first time in legal metrology based on quantitative testing of new instruments for type approval and initial verification, and gives valuable insight into traditional rules limiting uncertainty in conformity assessment in general. Further, an analysis of subsequent verification of exhaust gas analysers in use in society, leads to a new optimised uncertainty methodology based on attribute sampling.

Keywords: Gas analysis; Measurement; Uncertainty; Sampling; Risks; Costs


Method validation for the analysis of pesticide residues in grain by thin-layer chromatography by Osman Tiryaki (pp. 506-513).
Method validation is an important requirement in the practice of pesticide residue analysis and is the process of verifying that a method is fit for its purpose. To make a correct decision on the validity of the method, the following method performance parameters have to be taken into consideration: scope, specificity, limit of detection, limit of quantification, linear range, accuracy, precision, repeatability, reproducibility, recovery, ruggedness and robustness. The goal of this study was to validate previously adapted thin-layer chromatographic methods for the pesticide residue analysis in grain. Confirmation of validation parameters for some compounds was also performed by gas chromatographic analysis.

Keywords: Method validation; TLC detection method; Precision; Calibration


Automated statistical control of activities measured by gamma-ray spectrometry by Grega Milčinski; Matjaz Korun; Tim Vidmar; Branko Vodenik (pp. 515-520).
Statistical tests were performed for reviewing the results of routinely performed measurements. Within the operating procedure for routine spectral analysis the current results were compared with the average values obtained from measurements of samples of the same type collected at the same location. The agreement of the current result with the population of the results was assessed by the u-statistic, where the expected spread of the population of the results is given by their standard deviation and their uncertainties. After checking for reliability, the current result was used for updating the average and the spread of the population. Some examples are presented to illustrate how the average and the spread follow changes in the population of the measurement results.

Keywords: Checking of results; Database; Statistical techniques


Influence of silica gel humidity on the determination of hydrocarbon types in gasoline by the ASTM D 1319 standard test method in relation to proficiency test reproducibility by H. Verplaetse; M. Lacourt (pp. 521-522).
The results obtained for the olefin content of gasoline with the ASTM D1319 Standard Test Method show a strong increase with the humidity of the silica gel used, while such an increase is absent for the aromatic hydrocarbon content. These results seem to suggest that the increased experimental reproducibility, compared to the value of the ASTM D1319 Standard Test Method, which is often observed for the olefin content in proficiency tests, may be due to the use of insufficiently dry silica gel.

Keywords: Gasoline; Olefins; Aromatic hydrocarbons; Reproducibility; Proficiency test

Clinical laboratory advisory service and ISO 15189 by Xavier Fuentes-Arderiu; Virtudes Álvarez-Funes; Joan Ramon Duran-Suárez; María Luisa Granada-Ybern; Lluïsa Juan-Pereira; Rosa Maria López-Martínez; Jaume Miró-Balagué; Núria Miserachs-Busqué; Francesc Prats-Buforn (pp. 523-524).

Conformity assessment and metrology: update on the state of affairs by Pavel Klenovsky (pp. 525-533).
A couple of years ago, ISO CASCO launched a major project of transforming all the existing ISO Guides on conformity assessment to a comprehensive series of ISO standards 17000 being now in various stages of development. As the concept of traceability underpinning all measurements has been a basic mission of metrology, a number of these standards have a direct bearing on metrology. The series is logically based on a definition standard, ISO 17000, giving, among others, a guidance which activities fall under conformity assessment. The fact that calibration does not, might have important consequences which must yet be assessed. A controversial discussion on some issues has been in progress concerning ISO 17011 on accreditation bodies which touches both on national metrology institutes (NMIs) with an accreditation function and on calibration labs at large. ISO 17040 on peer review could be used with an advantage to support mutual recognition arrangements among a limited number of bodies of a specialized expertise (e.g., CIPM MRA among NMIs under the Metre Convention). ISO 17025 has been the most important standard for the metrology community and has undergone a major overhaul taking on board the uncovered requirements from ISO 9001:2000. In general, the paper will give an update on the developments outlined above and discuss the consequences and further steps from the viewpoint of metrology.

Keywords: Metrology; Calibration; Testing; Accreditation; Certification; Standard; ISO CASCO; Conformity assessment

On the calculation of decision limits in doping control by Nicolaas (Klaas) M. Faber; Ricard Boqué (pp. 536-538).
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