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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.17, #5)

What to measure? by H. Emons (pp. 483-484).

Rounding error effects in the presence of underlying measurement error by Tom Burr; Stephen Croft; Michael S. Hamada; Stephen Vardeman; Brian Weaver (pp. 485-490).
A previous related paper considered rounding error effects in the presence of underlying measurement error and presented a Bayesian approach to estimate instrument input random error standard deviation. This addendum to the previous paper emphasizes that the effects of random error depend on the true (and usually unknown) value of the measurand, in terms of both the variance and the item-specific bias. However, it is shown that if we assume that the true values are uniformly distributed, then instrument variance and item-specific bias can be combined into an “effective random error variance” and a strategy to estimate the effective random error variance is provided.

Keywords: Bayesian methods; Effective random error variance; Instrument resolution; Item-specific bias; Likelihood


Using target measurement uncertainty to determine fitness for purpose by M. L. Jane Weitzel; Wesley M. Johnson (pp. 491-495).
The methods an analytical laboratory uses must be validated to be fit for purpose. The fitness for purpose of a quantitative method used to determine the concentration of a substance when assessing compliance to requirements can be described by the maximum measurement uncertainty. This is called the target measurement uncertainty. Acceptance criteria for precision and bias in the method validation are then established in terms of the target measurement uncertainty. The target measurement uncertainty can be decided by following a process which involves determining the required concentration range of the measurand; determining the acceptable level of risks of incorrect decisions of compliance; developing a suitable decision rule, with guard bands if appropriate; using the probability of making an incorrect decision of compliance based on the decision rule; and assessing the impact of bias. A key participant in this process is the end user of the data, the laboratory customer. This paper presents the concepts concerning target measurement uncertainty introduced in recently published international guidelines to the practicing analytical chemist who is not generally familiar with these concepts. Three examples are used to illustrate the process.

Keywords: Measurement uncertainty; Decision rule; Target measurement uncertainty; Guard band; Analytical target profile; Compliance


Traceability of measurement results in chemistry: a case study of certification of three new pharmaceutical reference materials by Raquel Nogueira; Gisele E. B. Silva; Suzane M. Queiroz; Monique G. Mello; Werickson F. C. Rocha (pp. 497-510).
This paper compares the results of the studies carried out with three new candidate certified reference materials (CRM) of captopril, metronidazole, and sodium diclofenac, which are the first CRMs of these active pharmaceutical ingredients (APIs) reported in the literature. The studies were carried out according to the ISO Guides 34: 2009 and 35: 2006 and included the determination of organic, inorganic, and volatile impurities mass fractions, evaluation of homogeneity and stability under transport and storage conditions, calculation of API mass fractions by mass balance, cross-checking of obtained results, and estimation of measurement uncertainties. The certified property values and corresponding expanded uncertainties, obtained from the combined standard uncertainties multiplied by the coverage factor (k = 2), for a confidence level of 95 %, were (995.65 ± 0.93) mg/g for captopril, (998.87 ± 0.15) mg/g for metronidazole, and (999.76 ± 0.10) mg/g for sodium diclofenac. These new CRMs are intended to be used in assay and tests methods, including equipment calibration, method validation, as well as assignment of traceable property values and corresponding uncertainties to non-certified reference materials, with the objective to ensure metrological traceability of measurement results to the International System of Units, as well as results accuracy and comparability.

Keywords: Captopril; Metronidazole; Sodium diclofenac; Active pharmaceutical ingredients (API); Certified reference materials (CRM); Analytical quality control


Twenty-year review of laboratory performance on enteric parasitology external quality assessment surveys 1992–2011, Ontario Canada by Christine Ann Fleming (pp. 511-517).
Quality Management Program–Laboratory Services (QMP–LS) is a mandatory external quality assessment (EQA) and accreditation programme for laboratories in Ontario. This report summarizes performance of Ontario laboratories on QMP–LS enteric parasitology EQA surveys and compares this performance over time. The results reported by participating laboratories were assessed against the expected results as determined by reference or referee laboratories. The number of laboratories licensed for parasitology decreased dramatically over the 20 years. On average, more than 80 % of participants and often more than 90 % were able to detect and identify the species and stages for the majority of parasites. Many of the challenges contained multiple parasites and about half contained low numbers, which affected performance on individual samples. The level of performance by Ontario laboratories on parasitology EQA surveys was consistently high over the 20 years. The parasites that presented the most difficulty were Enteromonas hominis and Trichomonas hominis.

Keywords: External quality assessment; Proficiency testing; Enteric parasitology


A process approach to ISO/IEC 17025 in the implementation of a quality management system in testing laboratories by Inês Hexsel Grochau; Carla Schwengber ten Caten (pp. 519-527).
The introduction of quality management systems (QMS) and the accreditation of laboratories according to ISO/IEC 17025 standard are not easy tasks, mainly for those laboratories located at teaching and research institutions. During the implementation of QMS at two testing laboratories of the Federal University of Rio Grande do Sul in Brazil, new solutions to overcome some of the difficulties inherent to this type of environment have been found. The knowledge acquired through this work has led to the proposition of some general steps incorporating a process approach presented in this article, which could be of use to laboratories in their pursuit for accreditation. This proposal suggests the use of strategic planning information, links the QMS objectives to the corresponding processes and sets a few indicators to monitor both performance of and improvements to the system.

Keywords: Quality management system; Testing laboratories; Accreditation; ISO/IEC 17025; Process approach; Teaching and research institutions


Temporal stability of standard potentials of silver–silver chloride reference electrodes by Igor Maksimov; Masaki Ohata; Toshiaki Asakai; Toshihiro Suzuki; Tsutomu Miura; Akiharu Hioki; Koichi Chiba (pp. 529-533).
The four-year evolution of standard potential of a silver–silver chloride reference electrode (denoted further in the text as an Ag/AgCl electrode) is presented together with some suggestions for the improvement of pH primary measurement procedure.

Keywords: Silver–silver chloride reference electrode; Standard potential; Harned cell; pH; Temporal stability


High-precision analysis of ethanol in bioethanol by gas chromatography with flame ionization detector by Can Quan; Hong Mei Li; Ting Huang; Wei Zhang; Zhao Ting Ding; Yu Xing Shen (pp. 535-541).
This paper describes the establishment and validation of gas chromatography-flame ionization detector (GC-FID) method for the determination of ethanol amount fraction in bioethanol samples. A general view of the development and optimization of the method is presented. The main aim of this study is the calculation of validation parameters. Selectivity of the method was determined. Linearity (R 2 > 0.999) was obtained in the range from 9.0 to 3040 μg of ethanol per sample (because the mass of the test sample used was around 200 mg, this corresponds to 45–2200 μg g−1). The method showed good recoveries (average 99.0 %), and the relative standard deviation for repeatability and intermediate precision was 4.5 and 5.5 %, respectively. The limit of detection (LOD) and limit of quantification (LOQ) were calculated as 10 and 30 μg g−1, respectively. The uncertainty budget was finally done according to the “Guide to the Expression of Uncertainty in Measurement” (GUM), and the relative expanded uncertainty was 4.8 % at coverage of k = 2.

Keywords: Gas chromatography; Flame ionization detector; Bioethanol; Uncertainty


Establishing the cut-off value of a screening method by Panagiotis Steliopoulos (pp. 543-547).
Generally, the cut-off point of a screening assay is defined through a one-sided prediction limit obtained from a given sample of blanks. Depending on the assumptions one is willing to make about the underlying data distribution, different types of prediction limits can be employed. In this paper, Monte Carlo simulations are used to illustrate the coverage performance of normal, lognormal and nonparametric prediction limits under normal and non-normal conditions.

Keywords: Screening methods; Cut-off value; Prediction limits


Metrological reference values for estimating measurement bias in clinical laboratory sciences by Xavier Fuentes-Arderiu; Raül Rigo-Bonnin (pp. 549-551).
Clinical laboratory quantities are measured for monitoring or diagnostic purposes. In both cases, a modification of the measurement bias can generate a false interpretation of measurement results. On the other hand, in clinical laboratory sciences, one of the most frequently used metrological reference value for calculating measurement bias is a conventional value that corresponds to the called consensus value. But this selection probably is not the best one, and some clinical and biological considerations should be made to decide the requirement for maximum permissible measurement bias and to decide the more appropriate metrological reference value. In the clinical laboratory, the medical relevance of the measurement bias of any measurement system in use depends on the measurement bias with which the biological reference values were produced. This dependence is due to the necessity that, for interpretation purposes, the current measurement bias should be the same that is included in the biological reference limits. For this reason, it is necessary to control the changes of bias during the life span of a measuring system. Several scenarios are described for the different estimations of bias.

Keywords: Measurement bias; Biological reference values; Quality control; Clinical laboratory sciences; Clinical laboratory

International symposium on “Food and Health: from Measurement Science to Quality and Safety” by Siu-kay Wong; Della Wai-mei Sin; Robert Kaarls; Mike Sargent; Xiao-gang Chu; Thomas Yan-keung Chan; Ching-wan Lam; Katsuo Seta (pp. 557-560).
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