The preparation of biological reference materials for use in inter-laboratory studies on the analysis of chlorobiphenyls, organochlorine pesticides and trace metals

Eleven biological reference materials were prepared and packed in tins, glass jars and plastic foil to be used in inter-laboratory studies on chlorobiphenyls, organochlorine pesticides and trace metals. The samples were sterilized and packed as wet tissue, which is unique for the purpose of inter-laboratory studies, and offers the advantage of studying the extraction and destruction steps of the analytical methods. Homogeneity tests were carried out by determination of Na, K, and the lipid content. Stability tests were carried out by determinations of Na, K, lipid and moisture content. The maximum variance due to inhomogeneity was estimated at 1%, except in cod liver, in which a higher variance due to inhomogeneity was observed. The stability of the samples was good over a period of six months at temperatures up to 37°C, although due to a sweating-effect of the plastic foil, samples packed in that material suffered from a small concentration effect in the order of 1%.