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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.

In order to evaluate the potential of inductively coupled plasma mass spectrometry for the analysis of biological materials, a systematic study on the occurrence of spectral interferences was carried out. All polyatomic ions originating from the matrix elements Ca, Cl, P, K, C, Na and S that give rise to spectral overlap with the analyte elements were examined systematically. For these matrix elements, which are representative of most biological materials, a list of all the polyatomic ions, which can be seen to interfere up to a matrix element concentration of 1 g l-1, is given. In addition, for each spectral interference, the corresponding apparent analyte concentration was calculated for different matrix concentrations. In this way, an interference factor (IF) could be calculated for each spectral overlap so that the extent and importance of each potential spectral interference can be estimated. This factor is defined as follows: IF = 10(6) x apparent concentration (analyte element)/concentration (matrix element). A study on the formation and short- and long-term stability of polyatomic ions was also carried out to evaluate the use of some simple correction procedures to overcome spectral overlaps. Finally, a review of the correction procedures applied to biological materials is given together with some examples

A description is given of the experimental arrangement for thermospray nebulization of discrete liquid samples (100 microl) into an inductively coupled plasma-mass spectrometer (ICP-MS). The determination of ultratrace levels of platinum in environmental and biological materials is described. This method comprises an off-line sample enrichment by adsorptive chromatography, elution with ethanol and subsequent analysis of the evaporated eluate. The quantification of the concentration was performed with isotope dilution. The recovery, precision, accuracy and detection limit of the method are discussed.