Abstract

The feasibility of determining trace iodine, bromine, selenium and arsenic simultaneously in geological samples by inductively coupled plasma mass spectrometry (ICP-MS) was investigated. The samples were mixed with flux (sodium carbonate and zinc oxide), sintered at 650 °C for 40 min in a muffle furnace and then dissolved in hot water. The cations were separated from the sample solution by using a cation-exchange resin. The analyte anions were determined by ICP-MS directly. The signal responses for the different anion species in different solution media were assessed. The sintering temperature, holding time, and amounts of flux and cation-exchange resin were optimised. The ion signal intensity of I⁻ in nitric acid was much higher than that of IO₃⁻ and IO₄⁻. In addition, the observed I⁻ signal in nitric acid was not stable. Weak acid solution or dilute ammonia solution was found to be a suitable medium for determination of these elements. Ammonia solution is also effective in eliminating the memory effect of iodine and bromine. The method was applied to the determination of trace Br, I, Se and As in a series of Chinese geological reference materials (GRM, soils and stream sediments). Most of the results were found to be in reasonable agreement with the certified values. The limits of quantitation for Br, I, Se and As were 0.15, 0.03, 0.004 and 0.04 µg g⁻¹, respectively. Precision was between 0.8 and 2.8% RSD. It was shown that the method has great potential for the routine determination of total iodine, bromine, selenium and arsenic in geological samples.