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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.13, #6)
Promoting analytical quality control of trace-element data to be presented in international journals and reports by Lars Jorhem (pp. 289-292).
The analytical quality of published data on trace elements in food has previously been shown to be of a generally poor quality and, therefore, not always reliable. The responsibility for this problem is shared among authors, editors, reviewers, and publishers, and it is based on the lack of clear instructions, to all parties, on how quality should be safeguarded. This has been noted by CEN/TC 275/WG 10, which has started preliminary work on such a guideline. This paper describes the background and what such a guideline could be based on.
Keywords: Analytical quality; Quality control; Guideline; CEN/TC 275/WG 10
Application of consistency checking to evaluation of uncertainty in multiple replicate measurements by Rüdiger Kessel; Michael Berglund; Roger Wellum (pp. 293-298).
Use of repeated measurements in quantitative chemical analysis is common but leads to the problem of how to combine the measurement values and produce a result with an uncertainty following the GUM. There is often confusion between repeated indications or observations of an input quantity, for whose uncertainty the GUM prescribes a type A evaluation, and complete measurements repeated on multiple sub-samples, as considered here. A solution for combining repeated measurement results and their individual uncertainties based on simple interval logic is proposed here. The individual measurement values and their uncertainties are compared with the calculated average value to see if this implies that another, possibly unknown, source of uncertainty is present. The model of the individual results is modified for this possible between-replicate effect so that the repeated measurements are consistent. Lack of consistency is a strong indication that the measurement is not fully under control and needs further development or investigation. This is not always possible, however and the method given here is proposed to ensure that the values of the repeated measurements agree with each other. A simple numerical example is given showing how the method can be implemented in practice.
Keywords: Uncertainty of measurement; Multiple replicates; Consistency test; Repeated measurements
Production of “in house” reference materials for ELISA screening of bovine urine and liver samples for clenbuterol by Isabel Pinheiro; Bruno Jesuíno; Jorge Barbosa; Fernando Ramos; José Matos; Maria Irene Noronha da Silveira (pp. 299-304).
Clenbuterol screening of bovines is done by analysis of urine, for monitoring living animals, and liver, for monitoring animals after slaughter. ELISA has generally been used as the main method for these purposes. Nevertheless, in Europe, methods must be validated according to Commission Decision (EC) 657/2007 criteria, i.e. by use of reference materials. Production of “in house” reference materials is a possibility, but the homogeneity, storage temperature, and period of stability of these materials must be investigated in the laboratory itself. This paper reports GC–MS evaluation of an “in-house”-produced batch of aliquots of bovine urine and liver, fortified with 10.0 ng/ml and 10.0 ng/g clenbuterol, respectively, and stored at −20 °C and at −60 °C. For urine stored for 20 weeks at −20 °C and at 60 °C the stability of clenbuterol was proved at the 95% confidence level. For liver, however, it was demonstrated at the same confidence level that clenbuterol was highly unstable during storage for 20 weeks at either of the temperatures studied.
Keywords: Clenbuterol; Reference materials; Stability; ELISA; GC–MS; Urine; Liver; “In house”
Uncertainty of the concentration of a copper calibration solution by Oto Mestek; Kateřina Mališová; Richard Koplík; Jan Polák; Miloslav Suchánek (pp. 305-310).
The postulated uncertainty of many commercially available standard solutions is estimated on the basis of uncertainties of individual preparation steps. The declared concentration of Cu standard solution (1000 ± 2) mg/L was verified by gravimetric analysis (found (1000.7 ± 0.4) mg/L), isotope dilution with commercial and laboratory-prepared isotope-enriched solutions (found (1000.6 ± 16.8) mg/L and (1002.4 ± 3.6) mg/L, respectively), and by atomic absorption spectrometry (found (1001.4 ± 5.3) mg/L). Uncertainty budgets of all used methods are given and the procedures of uncertainty estimation are fully documented.
Keywords: Copper; Calibration; Uncertainty; Standard solution; Gravimetry; Isotope dilution; Atomic absorption spectrometry
Revisiting type-A uncertainties relating to the measurement of mass fraction of lead using isotope-dilution inductively coupled plasma mass spectrometry: a way of improving measurement precision and expanded uncertainty by James Chung Wah Lam; Yiu Chung Yip; Wai Fong Tong (pp. 311-319).
A quadrupole inductively coupled plasma mass spectrometer (Q-ICP-MS) has been used for determination of lead in plant materials using isotope-dilution inductively coupled plasma mass spectrometry. The accuracy of the method was demonstrated by analysis of a matrix certified reference material, NIST SRM 1547 Peach Leaves. Specific instrumental parameters of Q-ICP-MS, including isotope analysis mode, integration time per point, number of points per mass, and number of measurements, were optimized to obtain the best measurement precision. The precision (expressed as relative standard deviation) associated with replicate measurement of the 208Pb/206Pb isotope ratio and its mass-bias correction factor was <0.2%. Following “Example A7” of the Eurachem/CITAC Guide, the relative expanded uncertainty, U rel, (coverage factor k = 2) was found to be ±1.1%, which fulfilled the target value of ±2% maximum and was lower than the uncertainty of ±3.4% reported by NIST based on isotope-dilution thermal ionization mass spectrometry. Sample recovery of 99% was obtained.
Keywords: Q-ICP-MS; ID-ICP-MS; Precision; Lead isotope ratios; Uncertainty
On the specific experience of national metrology institutes (NMIs) with national accreditation bodies (NABs) by Janko Drnovsek (pp. 321-325).
The following paper addresses the experience of certain national metrology institutes (NMIs) with national accreditation bodies (NABs), in particular in small countries with emerging economies in new EU or candidate member states. Specific cases have been analysed primarily in some Central and South-East European countries. NABs under consideration are, in principle, members of European Co-operation for Accreditation (EA). EA cross-frontier policy in these cases will be discussed and resulting dilemmas outlined. Focus will be given to the problems of NMIs also performing calibrations, commercial calibration laboratories, and their relations with NABs. Due to numerous problems of smaller NABs, cross-frontier policy should stimulate cooperation between foreign and local accreditation bodies not only at the request of the calibration laboratory or some other conformity assessment body, but at the request of the local accreditation body in order to provide the best service for their local economy. As a solution to the accreditation problems, this paper proposes a process of gradual formation of a common European pool of experts, real-life common practices and, finally, maybe even some form of joint European accreditation service.
Keywords: Metrology; National metrology institutes; Accreditation; Calibration laboratories; Calibration measurement capabilities; Cross-frontier policy; Common pool of experts; Joint European accreditation service
Comment on a Letter to the Editor by M. Rösslein, M. Wolf, B. Wampfler, and W. Wegscheider
by Günther Meinrath (pp. 331-333).
Comment on the Editorial “Does accreditation ensure competence in Measurement?” by Peter Unger (pp. 339-339).
There must be a common understanding of the concepts related to laboratory accreditation by both assessors and laboratories to be accredited.