[Assessment of factors causing pre-analytic variabililty].

Preanalytical variability can affect the results of trace element determinations. Even using sensitive and reliable analytical methods, the analysis of a contaminated specimen can only lead to erroneous results. Analyte contents in a sample can be altered during collection, storage and pretreatment, including simple dilution. Anticoagulants, plastic and glassware used for collection and storage, reagents, including water, and the laboratory environment itself, under particular conditions, can significantly contribute to this variability. The most common sources of contamination of biological matrices and some preventive measures are discussed. Operative procedures for the collection and storage of biological samples, specifically designed in dependence of analyte and matrix type, are reported.