Sample validity in biological trace element and organic nutrient research studies

The state of the art of the biological trace element investigations is overviewed. Questions of biological validity, such as the influence of the 'status of sampling' of human subjects on the concentrations of selected elements are studied. Analytical validity problems, e.g. stability of Cd, Hg and Pb concentration in selected specimens, stability of selected organic nutrients in NBS SRMs, etc. are also discussed. Finally, it is concluded that the development of new biological reference materials should take into account the multidisciplinary demands of biological trace element investigations. (author) 20 refs.; 6 tables