Speciation of As(III), As(V), MMA and DMA in contaminated soil extracts byHPLC-ICP/MS

A method to separate and quantify two inorganic arsenic species As(III) and As(V) and two organic arsenic species, monomethylarsonic acid (MMA) and di methylarsinic acid (DMA), by HPLC-ICP/MS has been developed. The separation of arsenic species was achieved on the anionic exchange column IonPac(R)AS 11 (Dionex) with NaOH as mobile phase. The technique was successfully appli ed to analyze extracts of two contaminated soils, sampled at a former tanne ry site (soil I) and a former paint production site (soil 2). The soils wer e extracted at pH values similar to the natural environment. Extractions we re performed at different pH values with 0.3 M ammonium oxalate (pH = 3), m illi-Q water (pH = 5.8), 0.3 M sodium carbonate (pH = 8) and 0.3 M sodium b icarbonate (pH = 11). No organically bound arsenic was found in the extract s. As(V) was the major component. Only up to 0.04% of the total arsenic con tained in soil 1 were mobilized. The highest amount of extracted arsenic wa s found at the highest pH. In the milli-Q water extract of soil 1 As(III) a nd As(V) were found. High amounts of As(V) were found in the extracts of so il 2. Up to 20% of the total arsenic bound to soil 2 constituents were rele ased. The results show that the mobilization of arsenic depended on the pH value of the extraction solution and the kind of extracted soil. Dramatic c onsequences have to be expected for pH changes in the environment especiall y in cases where soils contain high amounts of mobile arsenic.