APPLICATION OF MICROWAVE DIGESTION TO THE PREPARATION OF SEDIMENT SAMPLES FOR ARSENIC SPECIATION

Several extraction procedures are described allowing arsenic speciatio n in sediments. The extraction of organometallic compounds such as dim ethylarsinic acid or monomethylarsonic acid is quite simple since thes e compounds are stable in the different extraction media (HCl/HNO3, H3 PO4, ammonium oxalate) and are easily released independent of the extr action mode (magnetic stirring or microwave solubilization). Extractio n yields are higher than 96% for these two arsenic forms. An HCl/HNO3 microwave solubilization procedure allows the quantitative solubilizat ion of mineral arsenic, but the differentiation between the two oxidat ion states is not possible owing to the oxidation of As(III) to As(V). Extractions with orthophosphoric acid or ammonium oxalate allow the s olubilization of mineral arsenic with extraction yields ranging from 9 0 to 95% and the differentiation between As(III) and As(V). Neverthele ss, the amount of As(III) is underestimated owing to its partial oxida tion. The usefulness and advantages of microwave solubilization compar ed with conventional extraction procedures are discussed.