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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.18, #1)
Human errors and reliability of test results in analytical chemistry by Ilya Kuselman; Francesca Pennecchi; Aleš Fajgelj; Yury Karpov (pp. 3-9).
The present paper is a review of the main theoretical and technical aspects of human error treatment (error modelling, reduction and quantification) as applied in aviation, engineering, medicine and other fields. The aim of the review is to attract the attention of analysts and specialists in metrology and quality in chemistry to the human error problem and its influence on the reliability of test results of chemical composition and associated measurement uncertainty. Therefore, the subject of human error is interpreted in the review in application to the conditions of a chemical analytical laboratory.
Keywords: Human error; Analytical chemistry; Metrology; Quality assurance; Out-of-specification test results; Reliability; Measurement uncertainty
A review of the relationship between quality control and donor sample results obtained from serological assays used for screening blood donations for anti-HIV and hepatitis B surface antigen by Wayne Dimech; Robert Freame; Kathy Smeh; Handan Wand (pp. 11-18).
Quality control principles, initially designed for manufacturing, have been applied to clinical chemistry and later to serological testing for infectious diseases. Methods for setting control limits have been included using the effects of assay performance on clinical outcomes. However, this approach assumes that the reactivity of patient samples change proportionally with the results of quality control samples tested in the same assay. Although this may be the case for clinical chemistry, this assumption has never been tested for serological assays. During a 9-month period, 177910 and 185684 donor test results for HBsAg and anti-HIV, respectively, were analysed and compared with 712 HBsAg and 710 anti-HIV results obtained from a single batch of a multimarker quality control sample obtained from the same assays. Results of the analysis showed that the negative donor results did not change in proportion with the changes experienced by the quality control sample results as determined by regression coefficients, particularly when results obtained from different reagent batches were compared. There were insufficient results obtained from positive samples for a similar analysis. However, investigations show that, even if the reactivity of positive donor samples changed in proportion with the change in reactivity of the quality control sample, few false-negative donor test results would have occurred.
Keywords: Quality control; Serology; Infectious disease; Commutability
The BIOREMA project—part 1: Towards international comparability for biofuel analysis by Annarita Baldan; Hugo Ent; Adriaan M. H. van der Veen; Andrea Held; Manuela Ulberth-Buchgraber; Romeu J. Daroda; Valnei S. da Cunha; Stephen A. Wise; Michele Schantz; Paul J. Brewer; Richard J. C. Brown; Gavin O’Connor (pp. 19-28).
There is an increasing demand to accurately measure the quality of biofuel products (e.g. biodiesel and bio-ethanol). This demand is driven in Europe by directives promoting the use of renewable sources of energy and worldwide by national and international legislation setting out quality requirements for these fuels. Until now, there has been no international consensus on the minimum technical specifications to ensure biofuel quality. Furthermore, it is unclear which reference materials and measurement techniques are needed to provide the quality assurance and quality control framework to underpin these legislative requirements. As part of the European Commission’s 7th Framework Programme, the BIOREMA project (REference MAterials for BIOfuel specifications) demonstrated the feasibility of preparing biodiesel and bio-ethanol reference materials with reference values traceable to the international system of units for a range of parameters at levels relevant to technical specifications. However, the project concluded also that further research is needed to improve the current measurement capabilities for some parameters. Within the BIOREMA project, two global interlaboratory comparisons were carried out, using the biodiesel and bio-ethanol test materials prepared during the feasibility stage of the project, as well as two biodiesel standard reference materials from the National Institute of Standards and Technology (NIST, USA). The exercises showed that the measurement capabilities of the field laboratories were in many cases satisfactory, whereas for other laboratories the availability and regular use of certified reference materials would likely enhance the measurement capabilities for many of the parameters studied. A general overview of the BIOREMA project is presented in this paper. The details of the production of the two types of BIOREMA reference materials, and the results of the interlaboratory comparison for the bio-ethanol and biodiesel study materials, are discussed in parts 2 and 3 of this series of papers.
Keywords: Biofuel; Biodiesel; Bio-ethanol; Interlaboratory comparison; Reference material; Comparability
The BIOREMA project—Part 2: International interlaboratory comparison for biodiesel test methods by Manuela Ulberth-Buchgraber; Monica Potalivo; Andrea Held; Annarita Baldan; Adriaan M. H. van der Veen; Hugo Ent; Valnei S. Cunha; Romeu J. Daroda; Brian Lang; Michele Schantz; Ruth Hearn; Richard J. C. Brown; Paul J. Brewer (pp. 29-39).
The results of an interlaboratory comparison, using various measurement methods to carry out biodiesel testing, are presented and the findings are discussed. The interlaboratory comparison was organised within the framework of an EU-funded project called BIOREMA. A general overview of the project and results of an interlaboratory comparison on bioethanol are published as Part 1 and 2 of this series of papers. In the study presented here, reference values, provided by national metrology institutes and expert laboratories, were used for evaluating the results. Consensus values, derived from the results of all participants, were used to assess any bias between the results from the national metrology institutes and testing laboratories. The emphasis in this interlaboratory comparison was not the performance rating of the individual laboratories, but recognising and interpreting differences caused by the measurement methods applied. For most biodiesel parameters, a good agreement of measurement results was found among different methods, and between the consensus and reference values. The study material was a rapeseed oil fatty acid methyl ester, for which it was demonstrated that it is feasible to prepare and characterise reference materials for biodiesel with well-established reference values for many parameters.
Keywords: BIOREMA project; Biodiesel test methods; FAME; Interlaboratory comparison; Reference value; Proficiency test
The BIOREMA project—part 3: International interlaboratory comparison for bio-ethanol test methods by Adriaan M. H. van der Veen; Hugo Ent; Annarita Baldan; Valnei S. da Cunha; Romeu J. Daroda; Brian Lang; Michele Schantz; Manuela Ulberth-Buchgraber; Andrea Held; Ruth Hearn; Richard J. C. Brown; Paul J. Brewer (pp. 41-50).
The main objective of the reference materials for biofuel specifications (BIOREMA) project is the development of two test materials (one bio-ethanol material and one biodiesel material) with well-established reference values. Of a series of three papers, this part describes the material preparation, homogeneity study, stability study, and characterisation of the bio-ethanol material. The test material thus obtained was used in an interlaboratory comparison (ILC) to assess current practices and comparability amongst laboratories providing bio-ethanol testing services. Only 13 participants provided data, resulting in a small dataset for evaluation. Further, it appeared that for a number of laboratories, there was not sufficient material for the determination of all requested parameters. In most cases, as far as the data permit, it can be concluded that the consensus values (based on participant’s results) are in good agreement with the reference or the BIOREMA values (obtained by NMIs participating in the project). For three parameters, namely ethanol content, water content, and density, there is good agreement between the reference and consensus values. For these parameters, the reproducibility standard deviation is close to, or even smaller than, the expanded uncertainty associated with the reference value. A number of parameters show very poor reproducibility, for example, pHe, electrolytic conductivity, and acidity. The same applies to sodium and copper content, which are very low and therefore challenging parameters to measure accurately. The results of the ILC underpin the need for certified reference materials and demonstrate the requirement for more robust quality control to improve the precision and trueness of the results from testing laboratories.
Keywords: Biofuel; Bio-ethanol; Interlaboratory comparison; Reference material; Comparability
The comparison of parametric and nonparametric bootstrap methods for reference interval computation in small sample size groups by Abdurrahman Coskun; Elvan Ceyhan; Tamer C. Inal; Mustafa Serteser; Ibrahim Unsal (pp. 51-60).
According to the IFCC, to determine the population-based reference interval (RI) of a test, 120 reference individuals are required. However, for some age groups such as newborns and preterm babies, it is difficult to obtain enough reference individuals. In this study, we consider both parametric and nonparametric bootstrap methods for estimating RIs and the associated confidence intervals (CIs) in small sample size groups. We used data from four different tests [glucose, creatinine, blood urea nitrogen (BUN), and triglycerides], each in 120 individuals, to calculate the RIs and the associated CIs using nonparametric and parametric approaches. Also for each test, we selected small groups (m = 20, 30,…, 120) from among the 120 individuals and applied parametric and nonparametric bootstrap methods. The glucose and creatinine data were normally distributed, and the parametric bootstrap method provided more precise RIs (i.e., the associated CIs were narrower). In contrast, the BUN and triglyceride data were not normally distributed, and the nonparametric bootstrap method provided better results. With the bootstrap methods, the RIs and CIs of small groups were similar to those of the 120 subjects required for the nonparametric method, with a slight loss of precision. For original data with normal or close to normal distribution, the parametric bootstrap approach should be used, instead of nonparametric methods. For original data that deviate significantly from a normal distribution, the nonparametric bootstrap should be applied. Using the bootstrap methods, fewer samples are required for computing RIs, with only a slightly increased uncertainty around the end points.
Keywords: Box-Cox transformation; Confidence interval; Nonparametric bootstrap; Parametric bootstrap; Percentile; Reference interval
Uncertainty evaluation for the determination of repaglinide in human plasma by LC–MS/MS by Jian-kang Li; Yan Li; Minchun Chen; Jing Yang; Ying Song; Chao Wang; Yan-yan Jia; Ai-dong Wen (pp. 61-70).
Measurement uncertainty although introduced to medical laboratories some years ago, this concept is not familiar to all medical researchers, especially for the measurement of biological samples. Therefore, it is important to highlight the evaluation and expression of measurement uncertainty using a practical example. In accordance with published procedures for evaluating and expressing uncertainty, we analyzed the sources of uncertainty in the determination of repaglinide in human plasma using liquid chromatography–tandem mass spectrometry (LC–MS/MS). We investigated each component of uncertainty and calculated the combined and expanded uncertainties. We evaluated the uncertainty associated with repeatability, weighing, purity, solution and sample preparation, recovery, calibration fitting, and temperature. The expanded uncertainty for low, medium, and high concentrations of repaglinide was 0.090, 0.25, and 3.16 ng/mL, respectively (p = 95 %, k = 2). This example provides an important reference for the evaluation of uncertainty in biological sample determinations using LC–MS/MS and human plasma and will be helpful in explaining the reliability of test results.
Keywords: Uncertainty; Repaglinide; Human plasma; LC–MS/MS
“Analyte” is frequently used as synonym for “measurand”: is that correct?
by Paul De Bièvre (pp. 71-72).