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Published figures for trace element concentrations in body fluids and tissues of apparently healthy subjects are widely divergent. For a considerable time, the apparent disparities were readily ascribed to biological sources of variation such as age, sex, dietary habits, physiological conditions, environmental exposure, geographical circumstances, or similar influences. Growing evidence, however, suggests that this interpretation may be seriously questioned in numerous instances. First, values obtained in reference materials leave no doubt that some previous studies must have been subject to gross analytical inaccuracies. Second, it has now been thoroughly documented that inadequate sample collection and manipulation may drastically distort the intrinsic trace element content of biological matrices. This review scrutinizes data reported by a number of investigators. In an effort to settle the currently flourishing confusion, critically selected reference values are set forth for trace element levels in human blood plasma or serum, packed blood cells, urine, lung, liver, kidney, and skeletal muscle tissue.

A method for the determination of the total iodine content in milk powder and human serum by inductively coupled plasma mass spectrometry is described. It is shown that the oxidation state of the analyte has a strong impact on the analytical performance. If iodine is present as iodide and nitric acid is used for acidification, the observed ion signal is not stable and samples spiked with iodide yield erroneous recoveries up to 750%. Hence, as the iodine in milk powder is present almost exclusively as iodide, destruction of the sample with nitric acid is not suitable. It was found that such an excessive spike recovery does not occur if ammonia solution instead of nitric acid is used as the diluent. The proposed sample preparation was tested by analysing three reference milk powders, namely Certified Reference Materials 150 and 151 Spiked Skim Milk Powder (from the Community Bureau of Reference) and Standard Reference Material 1549 Non-Fat Milk Powder (from the National Institute of Standards and Technology). Good agreement with the certified values was obtained, indicating that no significant errors are introduced. For human serum, samples treated with nitric acid or with ammonia solution gave results that were not significantly different from each other. Results are given for both a 'second-generation' biological reference material, Freeze-Dried Human Serum (University of Ghent), and for sera from healthy individuals.

A method was developed for the determination of seven trace elements (Fe, Co, Cu, Zn, Rb, Mo, and Cs) in human serum by inductively coupled plasma mass spectrometry (ICP-MS). Sample preparation was kept as limited as possible. As the only sample pretreatment serum samples were diluted with nitric acid and indium was added as an internal standard. The results for iron, cobalt, copper, and zinc were corrected for interferences from polyatomic ions by using a blank solution containing the same concentration of sodium, sulfur, chlorine, and calcium as human serum. For copper and zinc the corrections are small, whereas for iron and cobalt they are important. No interferences occur for the considered isotopes of rubidium, molybdenum, and cesium. In order to test the accuracy and precision of the analytical technique, a "second-generation biological reference material (human serum)" was analyzed. The results obtained by ICP-MS for the seven elements considered showed good agreement with the certified values.

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