Chromspurenbestimmungen in anorganischen, organischen und w��rigen Proben mit der massenspektrometrischen Isotopenverd�nnungsanalyse

Abstract

It is shown that chromium traces in different inorganic, organic and aqueous samples can be determined over a wide concentration range with isotope dilution mass spectrometry. Electrolytic or chromatographic isolation steps are added to a system of sample preparation units for oligo-element determinations to analyse chromium besides other heavy metals. The isotope ratio52Cr/53Cr is measured in a thermal quadrupole mass spectrometer using a single-filament ion source with additions of silica gel and boric acid. In water samples, which contain humic substances, chromium concentrations of a few ng/g and less can be determined with relative standard deviations of about 1% and better. A differentiation is possible into the total chromium content and into chromium species which carry out isotope exchange reactions and those which are inert for an isotope exchange reaction. The chromium concentrations of four standard reference materials (two plants BCR 60 and 61, one tissue BCR 278, one sewage sludge BCR 144), which are not certified for chromium, are determined to be 29.4 Μg/g, 534 Μg/g, 0.78 Μg/g, and 466.1 Μg/g, respectively. In three different sediments total chromium concentrations between 100 Μg/g and 180 Μg/g are analysed with relative standard deviations of 0.6%–1.2%. Using aqua regia instead of nitric acid and hydrofluoric acid for the decomposition of sediments, only 60%–90% of the total chromium content is determined. However, the analysed chromium proportion dissolved in aqua regia is slightly higher when using isotope dilution mass spectrometry compared with other analytical methods. The detection limit is 0.3 pg chromium per g for water samples, 1.8 ng/g for organic substances, and 6 ng/g for materials with high inorganic proportions as for sediments, sewage sludges and soils.