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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.3, #2)
Analytical and legal aspects of the threshold limit value concept by B. Neidhart; Winfried Mummenhoff; Anja Schmolke; Peter Beaven (pp. 44-50).
The stipulation of threshold limit values (TLV) and the association of legal consequences with their contravention involves the tacit presumption that procedures for monitoring adherence to the TLV are both possible and are applied. However, monitoring is an analytical chemistry problem and hence the limitations of the TLV concept are determined by the realities of analytical chemistry.
Keywords: Key words Threshold limit ranges; Threshold limit values; Legal aspects; Analytical aspects
Homogeneity testing of reference materials by J. Pauwels; Andrée Lamberty; Heinz Schimmel (pp. 51-55).
Homogeneity testing is of the highest importance for the certification of reference materials, as it should demonstrate the validity of the certified values and their uncertainties in the analysis of individual units or portions thereof. However, the conclusions drawn from the results of these studies may often be questioned. It is proposed to improve this situation by quantifying the effect of homogeneity studies in terms of their impact on the uncertainty of certified values. Here it should be noted that the between-units variability directly affects the certified uncertainty, whereas the within-unit inhomogeneity only defines the minimum representative test portion.
Keywords: Key words Reference material; Homogeneity testing; Within-unit heterogeneity; Between-units heterogeneity
The International Measurement Evaluation Programme (IMEP) IMEP-6: "Trace elements in water" by L. Van Nevel; Philip D. P. Taylor; U. Örnemark; John R. Moody; Klaus G. Heumann; Paul De Bièvre (pp. 56-68).
The sixth round of the International Measurement Evaluation Programme (IMEP) is presented. The programme offers reference values, established by primary methods of measurement, against which participating laboratories can evaluate their performance. The degree of comparability is thus established against the most objective references available at present. In IMEP-6, reference values for total concentrations of 14 trace elements in a synthetic and a natural water were established mainly by isotope dilution mass spectrometry (IDMS). For the majority of the measurands, results traceable to the international system of units (SI) and having expanded uncertainties, U (k=2), of 2% could be established. Measurements results from 165 field laboratories in 29 countries are evaluated and presented as descriptive (regional, national and intercontinental) pictures of the participants' self-declared degree of experience, status of accreditation, performance (including target values for uncertainty set by authorities) and instrumental methods used. The participants' use of certified reference materials and calibrants has been documented, and some comments on this matter are raised. The results and characteristics for IMEP-6 are compared with those of IMEP-3 (1991–1993) and discussed in view of the forthcoming IMEP-9 (1998).
Keywords: Key words Trace elements; Water; Intercomparison; Comparability; Traceability
Uncertainty calculation and implementation of the static volumetric method for the preparation of NO and SO2 standard gas mixtures by M. Gerboles; Elias Diaz; Alberto Noriega-Guerra (pp. 69-78).
The European Reference Laboratory of Air Pollution implements the static volumetric method for the preparation of nitrogen monoxide and sulphur dioxide reference standard gas mixtures. According to the new ISO guide for the expression of uncertainty, the uncertainty of these standards is up to 0.8% for nitrogen monoxide in the range 100 to 600 ppbv, and up to 0.4% for sulphur dioxide in the range 200 to 400 ppbv. The values presented in the present paper suggest that there is a 95% probability of the true value lying within the interval specified. To attain such low uncertainty values, the standard procedure for the implementation of the static volumetric method must be rigorously followed, and instruments must be carefully maintained.
Keywords: Key words Uncertainty calculation; Calibration; Static volumetric method; Air pollution monitoring
The NATA scheme for accreditation of certifiers of reference materials by Ian Robert Juniper (pp. 79-82).
Certified reference materials are widely used for the calibration of measuring equipment and for the evaluation or validation of measurement procedures. The use of reference materials makes possible the transfer of the values of measured or assigned quantities between testing, analytical and measurement laboratories, both nationally and internationally. There is an increasing number of reference materials producers in other countries, and a demonstration of their scientific and technical competence is now more widely considered to be a basic requirement for ensuring the quality of reference materials. This article outlines recent activities by international bodies and their culmination in a scheme of accreditation of certifiers of reference materials which has been developed by the National Association of Testing Authorities, Australia (NATA).
Keywords: Key words Accreditation requirements; Reference materials; Certified values
The 14th Australian Symposium on Analytical Chemistry. Adelaide, 5–9 July 1997 by G. Price (pp. 82-83).
The Analytical Division of the Royal Australian Chemical Institute (RACI) held its 14th biennial symposium on analytical chemistry (14AC) in Adelaide, South Australia on 5–9 July 1997 [1]. The theme, "A broader view of the world" was an explicit invitation from the organisers to analysts to "take time away from their laboratories and consider how their work affects the world . . . A major challenge to chemists is to redefine their role in industry, education and the community and face, head-on, the demands brought about by free trade, economic rationalism and the environment." Part of this challenge, as reflected in invited plenary and keynote speakers as well as the cut and thrust of debate on the conference floor, is to address the important role of chemical measurement and confidence in the domestic and international systems of measurement.
Keywords: Key words Measurement system; Practical metrology; Chemical analysis; Traceability; Quality
Eurolab Workshop – Confidence in testing: customers' needs. Copenhagen, 11 September 1997
by Bent Larsen (pp. 83-84).