Development of a gas chromatography inductively coupled plasma isotope dilution mass spectrometry system for accurate determination of volatile element species. Part 1. selenium speciation

Abstract

The determination of element species in the environment is often especially difficult due to their presence at low concentrations. The coupling of GC with ICP-MS offers the advantage of transferring the total analyte into the ICP-MS instrument without any loss of analyte by nebulization. The application of IDMS results in relatively accurate results. The described GC–ICP-IDMS system consists of a gas chromatograph fitted with a capillary column, for analytical separation, and a diffusion cell that is used to exactly determine the mass discrimination factor for the isotope ratio measurement and to perform an element specific optimization of the plasma conditions. The construction of a relatively simple and low cost transfer line as well as the interface between GC and ICP-MS is described in detail. The applicability of the developed GC–ICP-IDMS system for the determination of volatile element species is demonstrated by the determination of selenite. Selenite is converted into a volatile piazselenol prior to determination. Selenate is determined after conversion into selenite. By applying 62% enriched ⁸²Se selenite spike solution for the isotope dilution step, the ⁷⁷Se: ⁸²Se and ⁷⁸Se: ⁸²Se ratios, respectively, could be used for content calculation. Selenite (10 ng ml^–1) was determined in a water sample with good agreement (within 1%) between the results obtained using the two isotope ratios. The accuracy of the results was demonstrated by the analysis of standard reference materials. The detection limit of the described method was found to be 0.02 ng ml^–1.