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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.14, #5)
From GUM to alternative methods for measurement uncertainty evaluation by Marc Priel (pp. 235-241).
Since the advent of the Guide to the expression of Uncertainty in Measurement (GUM) in 1995 laying the principles of uncertainty evaluation numerous projects have been carried out to develop alternative practical methods that are easier to implement namely when it is impossible to model the measurement process for technical or economical aspects. In this paper, the author presents the recent evolution of measurement uncertainty evaluation methods. The evaluation of measurement uncertainty can be presented according to two axes based on intralaboratory and interlaboratory approaches. The intralaboratory approach includes “the modelling approach” (application of the procedure described in section 8 of the GUM, known as GUM uncertainty framework) and “the single laboratory validation approach”. The interlaboratory approaches are based on collaborative studies and they are respectively named “interlaboratory validation approach” and “proficiency testing approach”.
Keywords: Measurement uncertainty; Proficiency testing; Internal quality control; External Quality Assessment Scheme (EQAS); Uncertainty in biological analysis
Monitoring performance of nucleic acid-based diagnostic measurement system users by EQA by H. J. Staines; L. Garcia-Fernandez; R. Pogothata; P. S. Wallace; W. G. MacKay; A. M. Van Loon (pp. 243-252).
External quality assurance (EQA) programmes allow a laboratory to monitor independently its performance and provide feedback to identify and investigate potential areas of concern. However, both the definition of appropriate ‘performance indicators’ and their statistical analysis vary across EQA providers. Typically, performance scores have an unknown statistical distribution and hence arbitrary thresholds are used to measure performance. In this paper, we introduce a scoring system based on well-known statistical principles. The system is simple, flexible and easy to interpret. It can be used to measure performance for single samples or across a panel so providing useful and meaningful information to participants in EQA programmes. The score is illustrated using the 2005 QCMD Hepatitis B Virus Proficiency programme.
Keywords: Quality assessment; Scoring system; Nucleic acid-based diagnostics; Proficiency test data; Statistical methods; Bayesian model
A new approach for proficiency test exercise data evaluation by A. V. Harms (pp. 253-261).
In this paper, a new data evaluation method for proficiency test exercises consisting of a combination of a z-test, a zeta test and an uncertainty outlier test is presented. This new method is compared with eight other evaluation methods (both measurement uncertainty using and measurement uncertainty ignoring) in common use and/or recommended by ISO 13528. The data set used to test the evaluation methods is real data and consists of the 95Nb results of the National Physical Laboratory Environmental Radioactivity Proficiency Test Exercise 2007. The evaluation of 14 out of 32 results were affected by the choice of method.
Keywords: Proficiency test exercise; Data evaluation; Uncertainty; z-test; Zeta test
Development of a reference measurement procedure for the determination of methylmercury in fish products by Sébastien Sannac; Paola Fisicaro; Guillaume Labarraque; Florence Pannier; Martine Potin-Gautier (pp. 263-267).
The development of an analytical procedure for speciation analysis of methylmercury in fish products is presented. The method is based on high-performance liquid chromatography hyphenated to inductively coupled plasma-mass spectrometry. The metrological approach is stressed out in this paper, in order to provide reliable and comparable results. A complete uncertainty budget has been evaluated and the method has been validated by the use of a certified reference material. Moreover, the detection could rely on the isotope dilution mass spectrometry, a powerful strategy capable of highly accurate results traceable to the “Système International d’Unités” and recognised by the “Comité Consultatif pour la Quantité de Matière” as a primary method of measurement.
Keywords: Speciation analysis; Methylmercury; Species-specific isotope dilution
Proficiency tests to evaluate commercially available IVD kits for glucose and cholesterol measurements by Melina Pérez Urquiza; Yoshito Mitani; Hector O. Nava Jaimes (pp. 269-271).
The first proficiency testing round 630-IL-1002, was carried out with a Reference Material DMR-180a with reference values obtained by using gas chromatography isotope dilution mass spectrometry methods, in which glucose, cholesterol and creatinine were measured. The serum pool was obtained from blood donors and all the analytes were at the normal concentration in Mexican population. The laboratories participants used different field methods to measure the analytes. The Mexican compulsory standard NOM-064-SSA1-1993 “specifications for equipments in vitro diagnostic (IVD)” requests 5% precision and 5% maximum bias of the IVD equipments in the measurements of analytes like glucose and cholesterol. The results obtained by field laboratories in the proficiency testing round are compared to the reference value and uncertainty provided by the National Metrology Institute (CENAM). The quality of measurements is dependent not only on the laboratory competence but also on the methods used by those commercially available IVD kits. It is concluded that quality assessment of measurements in clinical laboratories should be critically evaluated by using stable and certified reference materials.
Keywords: Glucose; Cholesterol; Serum; Proficiency test; Certified reference materials
Lessons from the first international proficiency test for the detection of spores from the honey bee pathogen Paenibacillus larvae by Dirk C. de Graaf; Wolfgang Ritter; Frans J. Jacobs; Marleen Brunain; Hein Imberechts; Koen Mintiens; Yves Van der Stede; Bart Verheyden; Aud Kari Fauske; Patrick Boujon; Gabriela Chioveanu; Daniel Dezmirean; Giovanni Formato; Franco Mutinelli; Hendrik-Jan Roest; Dalibor Titĕra; Stephen F. Pernal; Katia Knapen (pp. 273-276).
We report on the first proficiency test in the context of honey bee disease testing on a broad international scale. Honey samples were distributed to 12 participating laboratories for isolation and identification of spores of the etiological agent of American foulbrood, Paenibacillus larvae. Of the 11 laboratories responding to this proficiency testing event, only 6 (54%) provided data that were in full agreement with the previously determined status of the honey samples; eight (72%) laboratories fell within the threshold for qualification as defined a priori in this proficiency test (=level of agreement of at least 90%). Some lessons can now be drawn from the organizational point of view and will certainly improve new initiatives to be taken.
Keywords: Paenibacillus larvae ; American foulbrood; Diagnosis; Honey bee; Proficiency testing
Certification of the mass fractions of Pt, Pd and Rh in a used car catalyst reference material by S. Recknagel; M. Michaelis (pp. 277-280).
The high economic value of catalysts containing the platinum group elements platinum, rhodium and palladium as active components causes the need to be able to measure the precious metal loading with small uncertainty and to have suitable certified reference materials fulfilling high demands on the quality of the certified values. In European Reference Material ERM®-EB504, a used cordierite-based car catalyst material, mass fractions of platinum, palladium and rhodium were certified. The raw material was milled, homogenised and annealed before analysis. Seventeen laboratories experienced in precious metals analysis participated in the certification interlaboratory comparison, most of them analysing with inductively coupled plasma optical emission spectrometry using different sample pretreatment techniques. Homogeneity testing was carried out using X-ray fluorescence spectrometry. The certified mass fractions of Pt, Pd and Rh and their expanded uncertainties (k = 2) in ERM®-EB504 are (1777 ± 15), (279 ± 6) and (338 ± 4) mg/kg respectively.
Keywords: Precious metals; CRM; European reference material; Platinum; Rhodium; Palladium; ICP OES
Considerations with regard to the calculation of key comparison reference values and uncertainties by Ulrich Panne; Wolfram Bremser (pp. 281-287).
Much has been published over the last years on finding the best (consensus) reference value for a given set of key comparison data, and a suite of approaches proposed. In this paper, several aspects are highlighted which should be taken into account when deciding on key comparison strategies, protocols, and the best approach to reliable key comparison reference value and uncertainty. Some of these aspects are briefly discussed. The paper is intended to intensify discussions, and any comments and opinions are welcome.
Keywords: Key comparison; Reference value; Reference value uncertainty; Equivalence
The International Conference on Metrology of Environmental, Food and Nutritional Measurements (MEFNM2008)
by P. Charlet (pp. 289-289).