Speciation of trace elements in biological materials: trends and problems.

In the determination of trace elements in biological materials, speciation is of particular importance as the essential effects or toxicity of an element and its metabolic behaviour depend to a large extent on the chemical forms in which it is present in the organism. Speciation is relatively easy if a property of a particular compound can be measured directly in the sample without interference from the other components of the material, e.g., the enzymic activities of the metallo-enzymes. Another possibility for speciation is immunoassay, which likewise allows direct determination of a particular trace element. At present, however, with most trace elements both fractionation methods and analytical procedures have to be combined and speciation has to be carried out by determining the elemental content in the separated fractions. The methods and apparatus used in taking, storing and preparing the samples can, therefore, not be selected solely according to the requirements of trace element determination, but it is also essential to ensure that the biological structures of the components to be separated remain intact. In this work the need for speciation in the investigation of the toxic and essential effects of trace elements is shown with the help of some examples, and the problems that can occur in the various steps of sampling, storage and sample preparation are discussed.