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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.7, #6)


The use of uncertainty estimates of test results in comparisons with acceptance limits by H. Andersson (pp. 228-233).
When a test is performed in order to qualify a material or a product for a certain use, the result is generally compared with an acceptance limit. The test result has an uncertainty which should be estimated and stated (e.g. in accordance with GUM). Very often this is not the case. Further, discussions often arise on the issue of how the uncertainty shall be considered in relationship to the acceptance limit. The intention of this note is to describe, in simple terms, the statistical background and to give some recommendations. In short, there are two clean-cut, extreme situations. The first case is when the uncertainty of the testing procedure is the dominating factor. Here it is found that the estimates of single laboratories cannot, generally, be used for comparisons with acceptance limits. One should have standardised, well-verified estimates based on comprehensive investigations of the method. It can also be concluded that comparisons between test results and acceptance limits have to be made with regard to the actual circumstances, as, e.g. how the acceptance limit is related to the risk. In the second case, the variation in the property of the material or product dominates and the uncertainty of the testing procedure is negligible. When the results are non-quantitative (go – no go), statistical methods can be used to estimate the risk taken with a certain sampling and acceptance strategy that a certain proportion of the batch to be delivered does not qualify. This should be considered more often in standardisation of product test methods. When the results are quantitative, a statistical analysis should be performed and the uncertainty should be compared with the acceptance limit as before, from the actual circumstances. When effects of testing uncertainty and product variation are comparable a sound treatment requires extensive experimental work. No short cuts can be made without loss of confidence!

Keywords: Keywords Uncertainty; Conformity assessment; Acceptance limit


Experience of implementing of ISO/IEC 17025: conclusions and recommendations of a workshop by J. Forstén (pp. 234-236).
The first experiences of implementing of ISO/IEC 17025 have been obtained by the accreditation bodies and laboratories following the standard, and a workshop to discuss the experiences was arranged. This presentation gives the conclusions and recommendations from the workshop based on the lectures and discussions. In general, the adoption of ISO/IEC 17025 has been a smooth process.

Keywords: Keywords ISO/IEC 17025; Implementation experience


ISO compliant laboratory quality systems and incident monitoring improve the implementation of laboratory information systems by L. Burnett; D. Chesher; D. Groot-Obbink; G. Hegedus; M. Mackay; A. Proos; C. Rochester; W. Shaw; A. Webber (pp. 237-241).
Quality systems can provide a means of measuring the rate of occurrence of defined incidents and non-conformities. We have studied the application of laboratory quality systems to monitoring the implementation of laboratory information systems (LIS) in two similar size tertiary hospital pathology laboratories in Australia. At one site, one department implemented a quality system accredited to ISO 9001–1987 and ISO 9001–1994 while the rest of the organisation did not have a formal quality system; this site implemented the Cerner PathNet LIS. At the other site, the organisation was in the process of implementing ISO/IEC Guide 25–1990 and ISO/IEC 17025–1999; this site implemented the PJACC AUSLAB LIS. The rate of quality system incidents and non-conformities was used to track the progress of implementation of the LIS. We found that different quality systems appeared equally useful in monitoring the rate of occurrence of incidents. However, the presence of a formal quality system greatly improved the proportion of incidents that could be investigated and resolved at root cause level. Incident monitoring, as part of a formal quality system, proved to be a useful tool in monitoring and managing the implementation of these LIS.

Keywords: Key words Quality system; Laboratory information system; Incident monitoring; Pathology; Medical laboratory


Estimation of uncertainty in routine pH measurement by I. Leito; Liisi Strauss; E. Koort; Viljar Pihl (pp. 242-249).
A procedure for estimation of measurement uncertainty of routine pH measurement (pH meter with two-point calibration, with or without automatic temperature compensation, combination glass electrode) based on the ISO method is presented. It is based on a mathematical model of pH measurement that involves nine input parameters. Altogether 14 components of uncertainty are identified and quantified. No single uncertainty estimate can be ascribed to a pH measurement procedure: the uncertainty of pH strongly depends on changes in experimental details and on the pH value itself. The uncertainty is the lowest near the isopotential point and in the center of the calibration line and can increase by a factor of 2 (depending on the details of the measurement procedure) when moving from around pH 7 to around pH 2 or 11. Therefore it is necessary to estimate the uncertainty separately for each measurement. For routine pH measurement the uncertainty cannot be significantly reduced by using more accurate standard solutions than ±0.02 pH units – the uncertainty improvement is small. A major problem in estimating the uncertainty of pH is the residual junction potential, which is almost impossible to take rigorously into account in the framework of a routine pH measurement.1

Keywords: Keywords Measurement uncertainty; Sources of uncertainty; ISO; EURACHEM; pH


Interlaboratory comparisons and improvements of methods for acid number determination in used motor oils by Elena Kardash-Strochkova; Yakov I. Tur’yan; I. Kuselman; Naphtali Brodsky (pp. 250-254).
The results of two interlaboratory comparisons of acid number determinations in used motor oils are discussed. It is shown that the comparability of the measurement results is not as good as that required by known standards for petroleum products. The problem is motor oil contaminants which accumulated during use, and which are the source of a matrix effect in the acid number determination. The standard methods’ drawbacks are analyzed and some improvements are proposed. Repeatability and accuracy of the improved methods are evaluated.

Keywords: Keywords Motor oils; Acid numbers; Matrix effect; Measurement methods; Interlaboratory comparisons


EA, today and tomorrow by Daniel Pierre (pp. 255-256).
This article presents the European co-operation for Accreditation (EA) as it is to day and tries to focus on the main goals on which we will be challenged in the very near future.

Keywords: Keywords Accreditation; Conformity assessment; Laboratory; Inspection; Certification; EU; EFTA; MLA; MRA; IAF; ILAC; TBT; Globalisation; Trade; One-stop-testing; Testing-and-certification
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