DETERMINATION OF NATURAL AND ISOTOPICALLY ENRICHED CHROMIUM IN URINE BY ISOTOPE-DILUTION GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

A method is described for the determination of chromium and its enrich ed stable isotopes in human urine by isotope dilution mass spectrometr y. A volatile chelate is formed with trifluoroacetylacetone (TFA) and the fragment ions corresponding to Cr(TFA)(2)(+) in the 356-360 m/z re gion are monitored. The chelate is thermally stable and exhibits no me mory effects when isotope ratios change. The detection limit for the m ethod is 0.03 ng of Cr/g, and the accuracy is verified by certified re ference materials and by an independent method. The method is highly s pecific for chromium, due to the combined properties of the chelating agent, chromatographic column, and mass-specific detector. In addition to total chromium determinations, the method can also be used to quan titate enriched stable isotopes of chromium used as metabolic tags in tracer experiments in human nutrition studies.