Abstract

A new method has been developed for the simultaneous determination of As^V, monomethylarsenic (MMA), dimethylarsenic (DMA), As^III, and arsenobetaine (AsB) in aqueous samples. The method utilizes a multi-mode ion exchange column coupled with a hexapole collision cell inductively coupled plasma mass spectrometer (ICP-MS). A mixture of 10 mM NH₄NO₃ and 0.05% HNO₃ was used as the mobile phase, pumped by a high-performance liquid chromatography (HPLC) pump running in an isocratic mode at a flow rate of 0.4 mL min⁻¹. Under these conditions, the five As species were separated within 14 min. The column outlet was connected directly to the ICP-MS via a low flow Meinhard concentric nebulizer. A river water certified reference material (SLRS-4), spiked with five As species at 20 µg L⁻¹ (As cation) each, was used to validate the chromatographic separation and quantification in a real sample matrix. Based on replicate analyses of SLRS-4, the precision varied from 2% for As^V to 10% for MMA. The detection limits (3s) ranged from 0.02 µg L⁻¹ for AsB to 0.4 µg L⁻¹ for MMA. The new method was applied to water samples collected during As toxicity test experiments. The results indicated that transformation of inorganic As species (As^V and As^III) occurred during the toxicity test experiments, but no methylation of inorganic As species was detected.