Direct chromium speciation using thermospray: Preliminary studies with inductively coupled plasma mass spectrometry

Thermospray (TSP) sample introduction methods have been found to selectivel y deposit Cr(III) in the presence of Cr(VI) and thus provide a direct, nonc hromatographic speciation capability for these chromium oxidation states. P revious results have shown that the sensitivity for Cr(III) could be reduce d to a negligible level compared with the sensitivity for Cr(VI) by adjusti ng sample and thermospray operating parameters, with detection by inductive ly coupled plasma atomic emission spectrometry (ICP-AES). Hence a rapid, se nsitive chromium speciation method with limits of detection (LODs) at the 0 .5 ng/ml level was developed. In this paper, application of this approach t o inductively coupled plasma mass spectrometry (ICP-MS) was intended to fur ther reduce the LODs for Cr detection and further elucidate the kinetics an d optimum conditions for efficient, quantitative Cr(III) deposition. These preliminary results show that for Cr(III) concentrations below 10 ng/ml, LO Ds and accurate, selective measurements of Cr(VI) down to the 50 pg/ml are possible. However, the deposition process of Cr(III) is incomplete fur Cr(I II) concentrations above 10 ng/ml under the currently established condition s, restricting the sub-nanogram-per-milliliter accuracy of the selective de tection of Cr(VI) with these higher concentrations of Cr(III). The results also suggest that the process is not kinetically limited or at equilibrium in the present configuration. (C) 1999 Academic Press.