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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.3, #6)
Are we on the right track towards improving the quality of test results?
by Jarl Forstén (pp. 222-223).
The rational use of proficiency tests and intercomparisons by H. O. F. Andersson (pp. 224-226).
Interlaboratory comparisons (in the following abbreviated as intercomparisons) regarding tests, analyses or measurements are among the most worthwhile measures a laboratory can take in order to confirm that its services to clients include the provision of correct results within a stated uncertainty. They give a picture of the whole performance of the laboratory, and they should be used much more than at present. Unfortunately such intercomparisons are, and are made, expensive and prestigious by the formalisms employed in many cases. The connection between intercomparisons and proficiency tests and their use for different purposes is briefly discussed. Some suggestions are made on how to improve the present state of the art, i.e. how to increase the use of intercomparisons, how to perform them efficiently and how to make optimal use of the results.
Keywords: Key words Proficiency test; Intercomparison; Accreditation; Method validation
Customers' needs in relation to uncertainty and uncertainty budgets by M. Golze (pp. 227-230).
The general requirement of Quality Management standards to include in test reports a statement of the uncertainty of the results reflects the fact that a test result is rather useless without a knowledge of its accuracy. After an outline of the basic concepts of uncertainty, the need for uncertainty statements is illustrated for different ranges of applications.
Keywords: Key words Uncertainty; Uncertainty statement
Measurement uncertainty – a reliable concept in food analysis and for the use of recovery data? by Paul Willetts; R. Wood (pp. 231-236).
Steps which are taken to implement the concept of measurement uncertainty in analytical chemical laboratories should take full account of existing internationally agreed protocols for analytical quality assurance and reflect the needs of particular analytical sectors. For the food sector this may mean that for official purposes the use of the term measurement uncertainty is replaced by the term measurement reliability and that a quantitative estimation of this is made based on existing collaborative trial data. In many analytical sectors, the differing strategies currently followed for the determination and use of recovery information are an important cause of the non-comparability of analytical results. Guidelines which are being prepared for the estimation and use of recovery information in analytical measurement may provide a more unified approach which includes measurement uncertainty as a key concept in the use of recovery data.
Evaluating uncertainty in analytical measurements: the pursuit of correctness by R. Kadis (pp. 237-241).
Simple in principle, the evaluation of uncertainty, especially in chemical analysis, is not a routine task and needs great care to be correct. This can be seen, particularly, from an examination of the EURACHEM Guide, Quantifying Uncertainty in Analytical Measurement (1995), which is the most important document on the subject. The examination reveals, in the author's opinion, a shortage of correctness in some principal details of the uncertainty estimation process as presented in worked examples in the Guide, and the author has therefore formulated some "in pursuit of correctness" rules for estimating uncertainty. The rules and respective comments are concerned with the following items: (1) choosing an appropriate distribution function in type B evaluation of uncertainty, (2) the necessity for consideration of separate contributions to the combined uncertainty, and (3) taking account of actual influence factors in the uncertainty estimation process. Furthermore, the problem of estimation of conditional versus overall uncertainty is touched upon in connection with comparative trials where only internal consistency of results is required.
Keywords: Key words Chemical analysis; Measurement uncertainty; Estimation process
Limits of detection, identification and determination: a statistical approach for practitioners by J. Vogelgesang; J. Hädrich (pp. 242-255).
For the estimation of the limits of detection, identification and determination, considerations from analytical practice were applied to the statistics of the calibration line and its prediction interval. The detection limit was the concentration calculated from the maximum height of the prediction interval at zero spiking concentration. The identification limit was twice the detection limit and was the lowest concentration that could safely be detected. The determination limit was the lowest concentration fulfilling three criteria: 1. None of the signals resulting from determination limit concentration should interfere with any signal from detection limit concentration, thus providing an unambiguous separation between the two limits. 2. Recovery should be between 70% and 120%. 3. Lowest and highest predictable signal at determination limit concentration should not deviate more than ± 30% from the average. Practical analytical guidance and the necessary mathematical formulae are presented.
Keywords: Key words Detection limit; Determination limit; Calibration line; Prediction interval; Validation
Can the new ISO Guide 25/EN 45001 create better confidence in laboratory operations? by Jarl Forstén (pp. 256-257).
Confidence in laboratory operations is discussed based on the ongoing revision of the ISO/IEC Guide 25. Confidence is a subjective attribute, which also depends on whose interest is considered. New and better-defined quality systems and technical elements will be included, and these are beneficial to the transparency of laboratory operations, as well as to the accreditation process. The ultimate aim is, of course, to satisfy customers. The testing laboratories' industrial customers are, however, generally unfamiliar with the ISO/IEC Guide 25 and accreditation. The main reason for improved confidence in testing and calibration laboratories is foreseen to come from closer interaction between laboratories and their customers.
Keywords: Key words ISO/IEC Guide 25; Testing laboratories; Accreditation; Competence