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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.11, #7)
“Quantity” and “amount”: a major terminological headache (in the usage of the English language)
by Paul De Bièvre (pp. 317-318).
Uncertainty calculation for calibrators of the IFCC HbA1c standardization network by Andrea Konnert; Sabine Arends; Stefan Schubert; Christoph Berding; Cas Weykamp; Carla Siebelder (pp. 319-328).
Within the last decade, the IFCC HbA1c standardization network has established the metrologically highest reference measurement procedure for HbA1c testing. Based on this procedure, reference calibrators are produced which in turn provide the starting point for the standardization of the manufactures routine HbA1c assays. According to the IVD directive, the uncertainty of the reference calibrators must be calculated and reported together with their assigned values. Within this article, we elaborate the uncertainty calculation according to GUM (guide to the expression of uncertainty in measurement) in detail. Finally, the results are validated by a simulation study.
Keywords: HbA1c reference method; Uncertainty; Standardization
Preparation and certification of high-grade gold geochemical reference material by V. Balaram; M. L. Patil; A. K. Agrawal; D. V. Subba Rao; S. N. Charan; M. Satyanarayanan; Ramavati Mathur; K. Kapilavastu; D. S. Sarma; M. Sankara Gowda; S. L. Ramesh; P. Sangurmath; K. V. Anjaiah; B. Dasaram; R. K. Saxena; Zahida Begum (pp. 329-335).
One high-grade gold geochemical reference material-BND 3401.01 has been prepared by the National Geophysical Research Institute (NGRI), Hyderabad in collaboration with the Hutti Gold Mines Company Limited (HGML), Hutti and National Physical Laboratory (NPL), New Delhi, in India. The sample is a sheared gold-sulphide-bearing quartz vein emplaced in a sheared acid volcanic rock that was collected at the 2400-foot level from the middle reef of Hutti deposit located in the north-western periphery of the late-Archaean Hutti-Maski greenstone belt, Karnataka, India. Fifteen institutions in India, Canada, China and Tanzania having experience in geochemical analysis had participated in this collaborative analysis programme. The sample was extensively characterized for its major, minor, trace and ultra-trace element composition by using a variety of analytical techniques. Usable values were provided for major, minor and several trace elements including all rare earth elements (REE). The certified value for the gold concentration in BND 3401.01 gold ore is 12.1±0.7 mg/kg.
Keywords: Gold reference material; BND 3401.01; REE; Trace elements; International collaborative analysis; Certified value
Laboratory accreditation in Italy for reference solution production of sucrose in water by Paola Fisicaro; Francesca Durbiano; Francesca Giuffredi (pp. 336-342).
The accreditation of Chemifarm srl laboratory for the calibration of two characteristics on the same aqueous solution has been achieved. The process has been executed by the Italian accreditation body for calibration laboratories (SIT). This is the first example of a producer of certified reference solutions in Italy. The solutions are mixtures of sucrose in water at several concentrations and are characterised for refractive index in the range of 1.33299 to 1.38115 and for mass fraction of sucrose in the range of 0 to 30 (commercially expressed in Brix degrees). Both traceability paths, obtained through refractometric and gravimetric methods, are reported. Furthermore, the paper describes the approach adopted to match the criteria based on ISO Guide 34 and ILAC-G 12, the documents with requirements for certified reference material producers, in compliance with those of ISO/IEC 17025, the norm for the laboratory accreditation.
Keywords: Laboratory accreditation; CRM producer; Refractive index; Sucrose in water mass fraction; Brix degree
Statistical analysis of findings in external and internal audits and assessments in a testing laboratory by Denis Glavič-Cindro; Matic Korun (pp. 343-348).
A statistical analysis of findings in assessments by an accreditation body, external audits and internal audits in an accredited testing laboratory for gamma-ray spectrometry is presented. The frequencies of observations reported in different areas were examined and analysed. The differences are interpreted in terms of the varying importance associated with the different areas as perceived by auditors and assessors.
Keywords: Quality assurance; Internal audit; External audit; Assessment by an accreditation body; ISO/IEC 17025; u-test
Proficiency testing as a tool for implementing internal quality control: the case of ochratoxin A in cocoa powder by C. Brera; S. Grossi; F. Debegnach; B. De Santis; V. Minardi; M. Miraglia (pp. 349-355).
This paper describes the interlaboratory study aimed at assessing the performance of 18 laboratories (14 national and 4 European) for Ochratoxin A (OTA) determination in cocoa powder samples. The study was tested at three levels of OTA covering the range in which presumably European regulatory limits could fall in the near future. For the extraction step, almost all laboratories used an aqueous solution of sodium hydrogen carbonate with the exception of one laboratory using dichloromethane consistently with the ELISA procedure adopted in the study. The clean-up step was performed by utilizing the immunoaffinity columns by the two main manufacturers (R-Biopharm Rhone and VICAM) and for the quantitative analysis, HPLC was used by all the participants except one using ELISA. From the output of the study, it can be concluded that at low level (0.19 μg/kg) 10 out of 18 (56%), at medium level (0.45 μg/kg) 11 out of 18 (61%), and at high level (1.45 μg/kg) 12 out of 18 (67%) results fell within the satisfactory ranges. This interlaboratory study provides an estimate of the performance of national and European laboratories involved in OTA determination in cocoa powder samples, which sounds extremely valuable in view of potential future legislation by the European Commission.
Keywords: Proficiency testing; Quality assurance; Food analysis; Ochratoxin A; Z-score
On the measurement of the moisture content in different matrix materials by Jochen Vogl; Markus Ostermann (pp. 356-362).
Twelve different samples were analyzed for their water content by the classical oven-drying method and a commercial moisture analyzer. Nominal values have been set by Karl Fischer titration and gravimetry. The decomposition during the drying process of samples containing organic compounds was checked by thermogravimetry coupled with Fourier transform infrared spectrometric and mass spectrometric detection. Summarizing all measurement results, the commercial moisture analyzer demonstrated an average bias for the determination of water contents, which is much smaller than the stated uncertainty and thus is negligible. Compared to the classical oven-drying method, the commercial moisture analyzer shows a smaller bias, more ease in handling and less time consumption per analysis. When validated by a reference procedure like Karl Fischer titration the commercial moisture analyzer is the method of choice for routine analysis.
Keywords: Classical oven-drying; Commercial moisture analyzer; Karl Fischer titration; Moisture; Reference materials; Thermogravimetry; Matrix samples
Considering uncertainty of measurement when assessing compliance or non-compliance with reference values given in compositional specifications and statutory limits: a proposal by E. Desimoni; B. Brunetti (pp. 363-366).
Considering the uncertainty of measurement (UOM) is mandatory when assessing compliance with reference values given in compositional specifications and statutory limits, but the matter is still open to question. Working in the signal or concentration domains and considering false negative together with false positive errors are the main points of debate. Frequently, the available approaches look too simplified for being accurate or too complex (since more rigorously formulated from a theoretical point of view) for being largely acceptable. In the Authors opinion, assessing compliance with reference values given in compositional specifications and statutory limits is a problem similar to that of estimating the limit of detection. This allows proposing a simple operational approach based on well-known and accepted assumptions and approximations. This proposal, described in the light of the most recent literature information, is aimed to stimulate a critical discussion in view of evaluating possible corrections to the generally accepted approach.
Keywords: Uncertainty of measurement; Compositional specifications; Statutory limits; False positive and false negative errors; Limit of detection; Residual standard deviation
Development of a standard for the organization of the interlaboratory comparisons in microbiology of food by Alexandre Leclercq (pp. 367-369).
The ILAC G13 Guide and the ISO IEC Guide 43-1 are the common, general and horizontal bases for accreditation of providers of proficiency testing and interlaboratory comparisons used by several accreditation bodies. Despite their widespread use, these guides omit specific technical requirements, and sometimes even elements of quality management, clearly defined for the organization of proficiency-testing schemes for microbiology of food. The Sub-Committee 9 “Microbiology of food” of ISO TC34 has created a working group (WG4) to establish a standard detailing such specific requirements for microbiology of food. This technical standard will describe those specific requirements of proficiency testing which organizers of proficiency-testing schemes and any subcontractors must satisfy in addition to the requirements of the ILAC G13 Guide and the ISO IEC Guide 43-1 to achieve accreditation or other recognition.
Keywords: Microbiology; Food; Interlaboratory comparisons; Standard