Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.10, #12)
Evaluation of measurement data for Cd, Cr and Pb in certain uncontaminated foodstuffs published in surveys: analytical quality vs. uncertainty of measurements by Lars Jorhem; Joakim Engman; Birgitta Sundström; Anders Nilsson (pp. 647-658).
Results for Cd, Cr and Pb at trace levels, in the same type of uncontaminated foodstuffs, often vary with several orders of magnitude, which normally is not the case for metals occurring at macro levels. In this paper we have been able to show that surveys that display results spanning a great range are linked to poor analytical quality control (AQC). A model for grading the quality of analytical publications was tested on 105 surveys, published during the 10 last years, on Cd, Cr and Pb in milk and in muscle tissue from domestic animals and fish. The result showed that as the description of the quality procedures increased, the span of results in a given study decreased. This correlation was statistically significant for cadmium in meat and fish muscle and for lead in milk at p<0.05. The papers were then ranked according to their quality, in order to indicate the level of confidence a reader can have in the results. Papers published in journals specialising in food and analysis/chemistry generally got higher ranking than papers published in other fields of expertise, e.g. toxicology or environment. The results also showed that there is no visible trend towards improvement in how quality procedures are described over the last decade.
Keywords: Analytical quality control; Survey ranking; Trace elements; Published data; Foodstuffs
Nonparametric assessment of comparability of analytical results obtained in proficiency testing based on a metrological approach by Ilya Kuselman (pp. 659-663).
A nonparametric sign test is implemented for assessment of comparability of proficiency testing (PT) results when their distribution differs from the normal or other known distribution. It allows testing the null hypothesis about insignificance of the bias of median of results obtained in PT from the traceable certified value of the reference material used in PT as test items, i.e., the hypothesis stating that comparability of the PT results is successful. Probability of type I error of rejecting the null hypothesis when it is true, and probability of type II error of it not rejecting when it is false (the alternative hypothesis about unsuccessful comparability is true) are considered. The test can be helpful for PT providers and laboratory accreditation bodies in analysis of PT results when the comparability criterion developed for a normal results distribution (Accred. Qual. Assur. 10:466–470) is not applicable.
Keywords: Proficiency testing; Distribution of analytical results; Comparability; Test of hypotheses; Reliability
A new terminology for the approaches to the quantification of the measurement uncertainty by Ricardo J. N. B. da Silva; Júlia R. Santos; M. F. G. F. C. Camões (pp. 664-671).
A new terminology for the approaches to the quantification of the measurement uncertainty is presented, with a view to a better understanding of the available methodologies for the estimation of the measurement quality and differences among them. The knowledge of the merits, disadvantages and differences in the estimation process, of the available approaches, is essential for the production of metrologically correct and fit-to-purpose uncertainty estimations. The presented terminology is based on the level of the analytical information used to estimate the measurement uncertainty (e.g., supralaboratory or intralaboratory information), instead of the direction of information flow (“bottom-up” or “top-down”) towards the level of information where the test is performed, avoiding the use of the same designation for significantly different approaches. The proposed terminology is applied to the approaches considered on 19 examples of the quantification of the measurement uncertainty presented at the Eurachem/CITAC CG4 Guide, Eurolab Technical Report 1/2002 and Nordtest Technical Report 537. Additionally, differences of magnitude in the measurement uncertainty estimated by various approaches are discussed.
Keywords: Uncertainty; Terminology; Metrology; Quality
Laboratory authorization versus accreditation in transitional economies: case study of Serbia by Mića Jovanović; Jovan Jovanovic (pp. 672-680).
Many CEE governments are still using various systems of laboratory authorization together with ISO/IEC 17025 laboratory accreditation. It is difficult to understand from the EU prospective, the existence of two parallel laboratory competence verification systems. The basic relations between laboratory accreditation and authorization: independence and succession have been defined. The case study of testing laboratory accreditation versus authorization in Serbia, has been presented and discussed. Relevant requests and procedures for water quality, food and air quality testing laboratory authorization were analysed in detail. Comparative analyses of accreditation and authorization have established: (i) independent relations, (ii) relevant regulation is in collision and barely legal, (iii) authorization is (technically) on the far lower level than accreditation is, and (iv) authorization requests cause high space and personnel costs. It has been concluded that it is not adequate to perform two policies at the same time: one EU oriented—laboratory accreditation, and one non-EU oriented—laboratory authorization. The policy proposal is that all CEE countries should abandon existing laboratory authorization procedures and replace them by accreditation. Proposed goal could be reached in rather a short transition process of 2–3 years.
Keywords: Laboratory accreditation; Laboratory authorization; Mutual laboratory recognition in Central and Eastern European (CEE) countries
A silicon metal quality-control standard preparation by means of collaborative trials of Brazilian laboratories by Queenie Siu Hang Chui; João Marcos de Almeida Bispo; Celia Omine Iamashita (pp. 681-685).
A powdered silicon metal material was prepared as a quality-control standard to provide the Brazilian quality-control laboratories with a means to verify the quality of their results, when determining Ca, Al, Fe, Mn and Ti present as impurities. The material was prepared and its homogeneity tested using one-way ANOVA with an ICP-OES analytical technique. The participating laboratories in the first collaborative trial were requested to use their routine procedures that included XRF, ICP-OES and FAAS techniques to analyse the distributed samples. The statistical analysis results showed that the interlaboratory variabilities were very high. By implementing a suggested protocol to put the solid sample into a solution, the participating laboratories showed better performances in the second run. By attributing values to the prepared material the analytes’ results were obtained in a new collaborative trial. Statistically the data were evaluated with two-way ANOVA. The values and their associated uncertainties included inhomogeneity and characterisation uncertainties.
Keywords: Powdered silicon metal; Collaborative trial; Uncertainty; Quality-control standard; Homogeneity
Conventional true values compared by Sarela García-Santamarina; Mariona García-Panyella; Xavier Fuentes-Arderiu (pp. 686-689).
According to ISO/CD 18113-1:2005, the conventional true value of a control material can be an assigned value (obtained with a primary or reference measurement procedure), a consensus value or a procedure-defined value. The present study demonstrates that, for some biological quantities, the overall consensus value (“trimmed” mean value”) obtained in a proficiency testing program, which includes all results independently of the method of measurement, is not acceptable as a surrogate for a primary or reference method value. Therefore, for the biological quantities taken into account in this study, overall consensus value is not as good as primary or reference method value to estimate systematic error.
Keywords: Conventional true value; Consensus value; Systematic error; Proficiency testing; Metrology
The ‘RM family’—Identification of all of its members by Hendrik Emons (pp. 690-691).
Subgroups of reference materials are briefly outlined based on accompanying information and crucial material characteristics for their application. It is proposed to include, besides the certified reference materials, calibrants and so-called quality control materials under the family name ‘reference materials’.
Keywords: Reference materials; Classification; Terminology
International Laboratory Accreditation Cooperation (ILAC) update news from the Secretariat
by Alan Squirrell; Annette Dever; Florence Fung; Mohan Sabaratnam; Alison Hay (pp. 692-698).