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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.2, #1)
Trace metals (Cu, Pb, Zn, Cd, Al, Li, Fe, Mn, Ni, Co) in marine suspended particulate matter: an international ICES intercomparison exercise by C. Pohl (pp. 2-10).
The aim of this intercomparison exercise was to assess the comparability of trace metal analyses of blank filters and of marine suspended particulate matter (SPM) on filters performed by laboratories in ICES member countries. Fifteen experts from the United Kingdom, Canada, France, Germany, the Netherlands, Norway, Poland, Russia, and the United States were invited to participate in this exercise for trace metal analyses of Cu, Pb, Zn, Cd, Al, Li, Fe, Mn, Ni and Co (tentative) in SPM. Each filter analysed in this project was an individual sample, the absolute loadings on the filters varying from 0.8 to 2 mg of SPM. The inter-laboratory means and the relative standard deviations (RSD) from the grand mean for the metals determined were: Al 67.5 mg/g, 8.3%, Fe 51.7 mg/g, 10.9%, Cd 1.5 μg/g, 22.7%, Cu 39 μg/g, 13.3%, Pb 38 μg/g, 34.7%, Mn 1060 μg/g, 13%, Ni 49.2 μg/g, 29%, Zn 182 μg/g, 32.5%, Li 52.8 μg/g, 26.1%, Co 15.4 μg/g, 23.6%. In general, the exercise demonstrated that it is possible for the various participants to collect very small amounts of SPM and analyse it by the different determination techniques. Compared to earlier exercises, comparability between laboratories was still difficult to achieve and limited.
Keywords: Key words Trace metals; Intercomparison; Suspended particulate material; ICES; Quality assurance
The traceability of analytical measurements by M. Buzoianu; H. Y. Aboul-Enein (pp. 11-17).
Traceability to the System International (SI) is an important prerequisite for international comparability and uniformity of chemical measurements to ensure mutual recognition of the results. In theory, all measurements can be traced back to the seven base units of the SI. Although the traceability system works well for most physical measurements, in many analytical and in some spectrophotometric measurements this system is not satisfactory. This paper describes the particular and practical problems and the contribution of the Romanian National Institute of Metrology in this field. The paper discusses the following concepts: clearly defined targets in the form of requirement specification, knowledge of trueness and/or measurement uncertainty, and traceability through an unbroken chain of calibration to primary standards. Traceability and uncertainty being two concepts inherently coupled, two examples of assessment of the uncertainty of measurement results are given for two spectrophotometric methods currently used in chemical laboratories.
Keywords: Key words Traceability; Quality; Measurement uncertainty; Spectrophotometric system
Accuracy and reliability of radiometric measurements – results of a laboratory proficiency test with labelled sediment by H. Mundschenk (pp. 18-29).
In 1995, a laboratory proficiency test was carried out in Germany with labelled sediment which was analyzed by 40 participants (operators of nuclear power plants, officially authorized institutions of the German Federal States, and laboratories of research centers). Preparation and certification of the labelled material were described in detail. The deviations of the laboratory means from the corresponding certified reference values of ten radionuclides were determined. Outliers of type 2 were recognized by means of the Grubbs test and eliminated. The consistency of laboratory means and reference values was tested by a modified t test. To describe the reliability of the measurements performed, a radioanalytical quality index which has been defined elsewhere was used. By use of this index, the radioanalytical quality of laboratory means and the means of laboratory means could be evaluated and a very realistic picture of the "state-of-the-practice" of the participating laboratories obtained. In some cases, it was possible to identify systematic errors and to explain their causes by physical phenomena.
Keywords: Key words Proficiency test; Quality index; Radionuclides in sediment; Gamma-ray spectrometry; Reference material
The application of the measurement uncertainty concept to in-process control in pharmaceutical development by S. Küppers (pp. 30-35).
Any analytical data is used to provide information about a sample. The "possible error" of the measurement can be of extreme importance in order to have complete information. The measurement uncertainty concept is a way to achieve quantitative information about this "possible error" using an estimation procedure. On the basis of the analytical result, the chemist makes a decision on the next step of the development process. If the uncertainty is unknown, the information is not complete; therefore this decision might be impossible. The major problem for the in-process control (IPC) procedure is that not only the repeatability but also the intermediate precision (which expresses the variations within laboratories related to different days, different analysts, different equipment, etc.) has to be good enough to make a decision. Unfortunately, the statistical information achieved from one single analytical run only gives information about the repeatability. This paper shows that the estimation of the measurement uncertainty for IPC is a way to solve the problem and gives the necessary information about the quality of the procedure. An example demonstrates that an estimate of uncertainty based on the standard deviations of an analytical method gives a value similar to one based on the standard deviations obtained from a control chart. Therefore, the estimation is both a very useful and also a very cost-effective tool. Though measurement uncertainty cannot replace validation in general, it is a viable alternative to validation for all methods that will never be used routinely.
Keywords: Key words Measurement uncertainty; Quality control tool; Customer support
Accreditation and quality assurance in Swiss chemical laboratories
by H. P. Ischi; P. R. Radvila (pp. 36-39).
Glossary of analytical terms (VII)
by J. Fleming; H. Albus; B. Neidhart; W. Wegscheider (pp. 51-52).