Abstract
Several procedures, involving various solvents and ultrasound, were evaluated for the extraction of four arsenic species, arsenite (As(III)), arsenate (As(V)), monomethylarsonate (MMA) and dimethylarsinate (DMA), from a silt loam soil to which species had been added at a concentration of 20 mg kg−1. The best extraction was by a two-stage procedure: shaking for 24 h in the presence of 0.1 mol l−1 phosphoric acid followed by shaking for 24 h in 1.0 mol l−1 sodium hydroxide solution. The arsenic species in the extracts were separated by high performance ion-exchange liquid chromatography, derivatized to hydrides by reaction with tetrahydroborate(III) in a multi-mode sample introduction system (MSIS) and quantified by ICP-OES. Detection limits in solution ranged from 0.4 (As(III) and DMA) to 1 (MMA and As(V)) µg l−1, corresponding to 10 and 25 µg kg−1 in a 0.2 g soil sample and 5 ml of extractant. The most significant change over time was that As(III) was converted to As(V). When each species was added individually, arsenic was 100% recovered over a period of several months. When all four species were added together, the recovery was 89%. As the precipitation of humic acids was slow, the sodium hydroxide extract could be acidified and analyzed without loss of analyte species.
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