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DIVISION S-2-SOIL CHEMISTRY

Application of Capillary Electrophoresis to Anion Speciation in Soil Water Extracts

II. Arsenic

^a CSIRO Land and Water and the Cooperative Research Centre for Soil and Land Management, Private Mail Bag No. 2, Glen Osmond, South Australia 5064
^b Soil, Plant and Ecological Sciences Division, P.O. Box 84, Lincoln Univ., Canterbury, New Zealand
^c Dep. of Land and Water, Univ. of Adelaide, Waite Campus, Urrbrae, South Australia 5064
^d Dep. of Crop and Plant Sciences, Univ. of Georgia, Athens, GA 30602 USA
^e Dionex Corporation, 1228 Titan Way, Sunnyvale, CA 94088-3606 USA

ravi.naidu{at}adl.clw.csiro.au

A method has been developed for the speciation of arsenic (AsO^-₂, AsO^3-₄, and dimethylarsinic [DMA]) in natural soil solutions from contaminated sites in Australia. The separation of these anions was achieved by capillary zone electrophoresis (CZE) using a fused silica capillary (72-cm by 50-µm i.d.) with a basic chromate buffer and on-column indirect UV detection at 254 nm. Method parameters, such as electrolyte pH, run voltage, and capillary temperature were studied in order to establish suitable analytical conditions. The ideal separation for As(III) and DMA was achieved with a buffer pH of 8.0, a run voltage of 25 kV, and a capillary temperature of 30°C. Under these conditions, As(V) and orthophosphate ions comigrated. However, the use of a chromate buffer at pH 10, a run voltage of 20 kV, and capillary temperature of 20°C led to complete separation of As(V) and phosphate peaks. Results of these investigations together with recovery test data suggest that separation of the As species from soil solutions can be achieved in less than 5 min with detection limits of 0.50, 0.10, and 0.10 mg L^-1 for As(III), As(V), and DMA, respectively.

Abbreviations: CZE, capillary zone electrophoresis • DMA, dimethylarsinic acid • HPLC, high performance liquid chromatography • IC, ion chromatography • ICP, inductively coupled plasma • MMA, monomethyl arsinic acid • MS, mass spectometry • RCF, relative centrifugal force