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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.3, #11)


New tools: Expert systems for uncertainty budgets by Siegfried Noack (pp. 436-443).
 An important part of quality assurance in any analytical laboratory is the production of comprehensive results integrating uncertainty measurements. Many testing laboratories face the problem that the expenditure required to evaluate small uncertainties (high precision and high accuracy) is often uneconomic. In most cases an uncertainty of high reliability has to be calculated from only a few data (one calibration, few replications, etc.). This problem can be solved by an expert system. To achieve this the analytical procedure has to be structured into a dialouge and divided into parts. The uncertainty has to be calculated for each part of the procedure. Addition of the individual uncertainties results in the combined and expanded uncertainty. During the dialouge the system should advise the analyst how to get an efficient and effective calculation of uncertainty. All calculations, mathematical and statistical procedures have to be surveyable but running the system should not be too time consuming for economic reasons. Within the scope of the EURECA-project initiated by the Eidgenössische Materialprüfungs- und Forschungsanstalt (EMPA), St. Gallen, Switzerland, expert system software is being developed in cooperation with other research institutes and manufacturers of analytical instruments. Using this software it will be possible to calculate the uncertainty for analytical procedures such as titration, atomic emission spectrometry (ICP-OES), atomic absorption spectrometry (AAS) and gas- and liquid chromatography (GC, HPLC).

Keywords: Key words Uncertainty; Expert system; Software; Accreditation


The International Measurement Evaluation Programme (IMEP): by L. Van Nevel; Philip D. P. Taylor; Ulf Örnemark; Paul De Bièvre (pp. 444-446).
 For the 6th measurement round of the International Measurement Evaluation Programme, "Trace Elements in Water", pictures are now available in electronic form displaying the results and answers from participating laboratories, against reference values for the amount content anchored in the SI system via Primary Methods of Measurement.

Keywords: Key words Trace elements; Water; Intercomparison; Comparability; Traceability


The IRMM International Measurement Evaluation Programme (IMEP) IMEP-4: Trace elements (Li, Cu, Zn) in serum by A. Lamberty; J. Savory; J. R. Moody; P. De Bièvre; K. J. R. Rosman; J. W. Gramlich (pp. 447-458).
 The aim of the International Measurement Evaluation Programme (IMEP) is to give an objective picture of state-of-the-practice analytical measurements by comparing them to a reference value obtained by a primary method of measurement. The referencevalue is therefore as traceable to the SI system of measurements as can presently be achieved and is independent of human or political decisions. Thus a large scale field test is made to achieve (international) comparability of measurements by comparing them with an independent metrologically established value. In the fourth measurement round, IMEP-4, three trace elements, Li, Cu and Zn, at three different levels in (bovine) serum were measured by about 12 participating laboratories using their routine methods. The (coded) results are graphically reported and compared to certified reference values established by an isotope-specific method, isotope dilution mass spectrometry, defined as a primary method of measurement by the Consultative Committee on Amount of Substance. Results indicate a spread of more than ±50%, asymmetrically distributed around the reference value with its own uncertainty range, although the self-declared accuracy of the laboratories was 5–10%. Self-assessment by participants of their analytical capabilities does not show a high correlation between self-rating ("more experienced" or "less experienced") and actual performance. In the way they have been applied, all methods seem to produce results of approximately the same quality.

Keywords: Key words International Measurement Evaluation Programme; Isotope-specific methods; Isotope dilution mass spectrometry; Trace elements in serum; Comparability and traceability of analytical measurements


Benefits arising from proficiency testing schemes: The comparison of analytical methods by N. Boley (pp. 459-461).
 The primary objective of proficiency testing (PT) is in the provision of information and support to participating laboratories, to enable them to monitor and improve the quality of their measurements. However, other benefits can be obtained from PT. These include the comparison of data for a given measurement by different methods, the validation of new methods, and the provision of information for laboratories' customers and accreditation bodies. This paper considers the subject of method comparison, and highlights some of the approaches which can be followed, as well as the practical use to which this can be put, to benefit the analytical community more widely. This is illustrated by a case study concerning the measurement of haze in beer. In this study the United Kingdom Institute of Brewing (IoB) conducted a survey of participants in the Brewing Analytes Proficiency Scheme (BAPS). From the survey data taken together with data from the BAPS scheme, the IoB is now in a position to give guidance on the use of particular instruments and procedures, as well as consider changes to the scope of the BAPS scheme to provide greater benefits for participants concerned with measuring haze.

Keywords: Key words Proficiency testing; Benefits; Analytical methods


Relationship between performance characteristics obtained from an interlaboratory study programme and combined measurement uncertainty: a case study by A. M. H. van der Veen; A. J. M. Broos; Anton Alink (pp. 462-467).
 In the interlaboratory study programme "ILS Coal Characterisation", eight interlaboratory studies were organised based on the ISO standards for coal analysis. The use of blind samples in each round allows comparability of measurement results between rounds to be assessed. Based on the results, it could be demonstrated that the vast majority of the measurement results of the laboratories were traceable to results obtained in previous rounds of this programme. The hypothesis has been formulated that the combined standard uncertainty obtained from an interlaboratory study is equal to the reproducibility standard deviation. Whether the reproducibility can be used as the basis for the certification depends on whether the interlaboratory study includes all effects to be taken into account for establishing an uncertainty statement.

Keywords: Key words Interlaboratory study; Traceability; Comparability; Reference material


How accurate must a reference material be? by Bruno Wampfler; Matthias Rösslein (pp. 468-470).
 This article deals with reference materials (RMs) used for calibration purposes. For most common spectroscopic and chromatographic methods, RMs which have a relative content uncertainty of up to 3% can be used without considerably increasing the overall measurement uncertainty of the complete procedure. It is vital that the correct amount of the RM is used to ensure the quality of the quantitative chemical analyses. This can only be guaranteed if, in addition to the correct determination of the amount, the stability of the RM in the sales packaging is considered in the quoted uncertainty. For instance when the RM is packed in a container made of polyvinylidene fluoride water losses in hot climates can result in an increase in concentration which cannot be neglected. This is also true for high density polyethylene containers (PE-HD) although to a lesser degree. When mercury solutions of 1000 mg/l to 10 000 mg/l are kept in diluted nitric acid in PE containers, a relevant reduction in amount can be measured despite the water losses. However, the solutions remain stable in glass containers.

Keywords: Key words Reference material; Stability; Calibration; Content uncertainty; Packaging

The potential of TXRF as a primary method in chemical metrology by B. Neidhart; J. Knoth; H. Schwenke (pp. 470-472).

ISO/TC 158: "Analysis of Gases" by Hugo Ent (pp. 475-476).
 This paper presents an overview of the work of ISO/TC 158: "Analysis of Gases". The standardisation of general and specific aspects of gas analysis, focusing on the preparation and use of calibration gases, to facilitate traceable and comparable measurements. ISO/TC 158 follows "market-oriented" objectives and is an advocate of the consistent use of a coherent set of ISO standards aimed at reinforcing "Good Analysis Practice" in organisations dealing with gas analysis. ISO/TC 158 acts as a centre of information in the field of gas analysis and is an active intermediary between suppliers and users of calibration gases.

Keywords: Key words Calibration gas; Gas analysis; ISO/TC 158; Standardisation
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