Determination of I/I isotope ratios in liquid solutions and environmental soil samples by ICP-MS with hexapole collision cell

The determination of I in environmental samples at ultratrace levels is very difficult by ICP-MS due to a high noise caused by Xe impurities in argon plasma gas (interference of Xe), possible IH2 1 interference and an insufficient abundance ratio sensitivity of the ICP mass spectrometer for I/I isotope ratio measurement. A sensitive, powerful and fast analytical technique for iodine isotope ratio measurements in aqueous solutions and contaminated soil samples directly without sample preparation using ICP-MS with a hexapole collision cell (ICP-CC-QMS) was developed. Oxygen is used as reaction and carrier gas for iodine thermal desorption via the gas phase from solid environmental material in the sample introduction device coupled on-line to ICP-CC-QMS. A mixture of oxygen and helium as reaction gases in the hexapole collision cell was applied for reducing disturbing background intensity of Xe. After optimization of measurement procedures the detection limit for I in aqueous solution was 8 6 10 g ml, which is better by about two orders of magnitude in comparison to the detection limit for I in sector field ICP-MS. The detection limit for direct I determination in contaminated environmental (soil) samples via gas-phase desorption without any additional sample preparation was 3 6 10 g g (30 ppt). Furthermore, the results of the determination of I/I isotope ratios at the 10–10 level in synthetic laboratory standards and environmental soil samples from contaminated areas are given.