Selection of reference methods for the determination of selenium in biological materials |
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Authors: | K Heydorn and B Griepink |
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Institution: | (1) Risø National Laboratory, DK-4000 Roskilde, Denmark;(2) Community Bureau of Reference, B-1049 Brussels, Belgium |
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Abstract: | Summary Over the period 1985–1989 the European Community Bureau of Reference (BCR) has certified 7 biological reference materials for selenium with concentrations ranging from 0.03 to 10 mg/kg. Certification analyses were carried out by the most experienced laboratories in the Member States, using Fluorimetry, Hydride formation, combined with ICP or AAS, Electrothermal AAS with or without Zeeman-background correction, Instrumental or radiochemical NAA. Results from these exercises are available in a form suitable for estimating the experimental precision of the various methods as a function of concentration. With the same number of replicates for all analyses the logarithm of the observed standard deviations have constant variance, independent of concentration; for each method the absolute and relative standard deviations can therefore be estimated by means of non-linear regression. Analytical bias was monitored plotting results and their estimated standard deviations from individual laboratories versus certified confidence intervals. For concentrations of Se <0.3 mg/kg fluorimetry was selected as a reference method; above this level INAA is recommended; both are capable of producing unbiased results. |
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