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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.14, #2)
Measuring performance in analytical measurements by Polyvios Eleftheriou; Hara Papastefanou (pp. 67-71).
This paper presents the experience from a research which was conducted, within the framework of an EU project, on the various aspects of nutritional micronutrient measurements in foods. The project examined various methods of measuring basic micronutrients in food and water, their effectiveness, their difficulties, their costs as well as other elements. Data from a number of inter-laboratory comparison providers and prepared questionnaires were collated and analyzed, and the data gathered revealed that there are major differences in the methods employed and the instrumentation used. Methods using state of the art equipment such as ICP/MS and GC/MS were used for micronutrient measurements, and the results (successes and failures (z > 2) in the measurements) are presented. The laboratories from which data were gathered were mainly from across Europe (results for more than 700 laboratory determinations are presented), and the failures range from 0 to 67% of the measurement laboratories.
Keywords: Analytical measurements; Errors in measurements; Error statistics; Uncertainty
The relationship between accreditation status and performance in a proficiency test by Michael Thompson; Kenneth Mathieson; Linda Owen; Andrew P. Damant; Roger Wood (pp. 73-78).
In the FAPAS proficiency testing scheme, participants are asked to state whether the analytical method used was accredited or not accredited. It is thus possible to compare the stated accreditation status with performance in the scheme. For this purpose, fifty qualifying examples of analyte-test material combination were selected at random from the reports from the year 2006. The accredited/non-accredited subsets of results from each example were subjected to a statistical analysis to determine whether any significant differences between the distributions of results could be detected. Outliers were removed from the datasets before the main statistical tests and considered separately. The inlying data were subjected to non-parametric tests for differences in central tendency and dispersion. A few significant examples were found, but could be reasonably attributed to chance. Among the inliers there were no grounds to reject the overall null hypothesis, that is, that accreditation has no effect on performance. However, the proportion of outliers was about twice as high among the non-accredited group.
Keywords: Proficiency test; Accreditation status; Performance
A new traceability scheme for the development of international system-traceable persistent organic pollutant reference materials by quantitative nuclear magnetic resonance by Takeshi Saito; Toshihide Ihara; Masayoshi Koike; Shinichi Kinugasa; Yoshinori Fujimine; Kazutoshi Nose; Tetsuya Hirai (pp. 79-86).
Quantitative nuclear magnetic resonance (qNMR) was used for the purity determination of neat compounds of persistent organic pollutants (POPs). qNMR is a unique quantitative method that is not only traceable to the International System of Units (SI), but it also does not require a standard of its own. The purities of the POP compounds determined in this work were traceable to a single certified reference material (CRM), which is extremely attractive for reference material producers. The purities observed by qNMR were equivalent to those observed by gas chromatography with flame ionization detection (GC/FID) or a differential scanning calorimetry (DSC) combined with a thermogravimetric analyzer (TGA). The uncertainties obtained by the qNMR method were comparable to being slightly larger than those observed by DSC.
Keywords: Quantitative NMR; Purity determination; Uncertainty; Traceability; POPs
Evaluation of measurement uncertainties for the determination of total metal content in soils by atomic absorption spectrometry by Sheila Alves; Margarida Maria Correia dos Santos; Maria Ascensão Trancoso (pp. 87-93).
In this work estimation of measurement uncertainties associated with the total metal content in soils was done by an intralaboratory approach based on method validation and quality control data, and using two certified reference materials (CRM). CRM and soil samples were analyzed following procedures based on the methods that are applied to silicate materials. All elements were determined by atomic absorption spectrometry following a quality assurance program previously established. Quality control actions were implemented in order to provide reliable data. The precision under within-laboratory reproducibility conditions was estimated from triplicate analysis. The trueness component was determined as recovery of the analyte from CRMs: soil sample, SO-2 and river clay sediment, LGC 6139. Combined measurement uncertainty was expressed in terms of precision and recovery uncertainties and the later further split on CRM replicate analysis and uncertainty of the certified value components. The results obtained are critically discussed on the basis of the different contributions. For the selection of the reference material, the CRM dependent terms are critically compared in order to fulfill specific requirements.
Keywords: Measurement uncertainty; CRM; Metal; Soil
Implementation in MATLAB of the adaptive Monte Carlo method for the evaluation of measurement uncertainties by M. Solaguren-Beascoa Fernández; J. M. Alegre Calderón; P. M. Bravo Díez (pp. 95-106).
The ISO 98:1995 Guide to the expression of uncertainty in measurement (GUM) presents important application limitations. For its improvement, different supplements are being developed that will progressively enter into effect. The first of these supplements describes an alternative method for calculating uncertainties, the Monte Carlo method (MCM), which is not restricted to the conditions of the method described in the GUM: the linearity of the model and the application of the central limit theorem. MCM requires computer calculation systems for generating pseudo-random numbers and for evaluating the model a large number of times. There are software applications that have been specifically developed for calculating uncertainties, some of which include MCM; but they do not allow the user to control all factors in the process, particularly the result stabilization criteria. On the contrary, its implementation in a mathematical program for general purposes such as MATLAB, enables total control over the process, is simple and benefits from its calculation speed. This article details programming in MATLAB for the implementation of the adaptive MCM method.
Keywords: Uncertainty; Measurement; Monte Carlo; MATLAB; Metrology
Management review checklist for ISO/IEC 17025 and ISO 15189 quality-management systems by Dimitris G. Theodorou; Panagiotis C. Anastasakis (pp. 107-110).
Management reviews are key processes in many quality-management systems, including laboratory-management systems, in accordance with ISO/IEC 17025 and ISO 15189. These reviews are fine opportunities to understand and manage all the inputs and outputs of a quality-management system. Laboratories often meet some difficulties fully exploiting the management-review process because either they do not realize the importance of this process or they do not have the experience to run this process in a way producing the intended results. This work presents a management review checklist which helps laboratories carry out an effective management review going through all the important aspects of the quality-management system.
Keywords: Management review; Checklist; ISO/IEC 17025; ISO 15189
Regulations in the field of residue and doping analysis should ensure the risk of false positive declaration is well-defined by Nicolaas (Klaas) M. Faber (pp. 111-115).
The purpose of this contribution is twofold, namely, to discuss the fundamental weaknesses of some decision criteria in the field of residue and doping analysis and to draw attention to a statistics-based solution that was proposed and thoroughly validated a decade ago, but nevertheless continues to be overlooked by practitioners.
Keywords: Residue analysis; Doping analysis; Mass spectrometry; Diagnostic ion; Abundance ratio; False positive
F. Ruggeri, R. S. Kenett and F. W. Faltin (eds): Encyclopedia of statistics in quality and reliability
by D. Brynn Hibbert (pp. 117-118).