Abstract

A low pressure ICP has been operated in ‘atomic' and ‘molecular' modes. Atomic mass spectra for methylmercury were obtained when the plasma was sustained in pure helium between 9 and 12 W power, and molecular spectra were obtained at 5 W power in the presence of a reagent gas. Methane, isobutane and ammonia were investigated as reagent gases, with ammonia yielding the best stability and sensitivity. A detection limit of 8 pg was obtained for Me₂Hg in ‘atomic' mode, and detection limits of 18, 48 and 20 pg were obtained for MeHgEt, MeHgCl and Me₂Hg, respectively, in ‘molecular' mode. Four extraction methods were compared for the determination of methylmercury spiked into sediment, with the best extraction efficiencies of 70–90% being obtained by microwave extraction, both with and without an ethylation step. Two extraction methods were compared for the determination of methylmercury in TORT-2 certified reference material. Microwave extraction with derivatization resulted in a found value of 0.171 ± 0.018 µg g⁻¹ compared to the certified value of 0.152 ± 0.013 µg g⁻¹.