Arsenic speciation in environmental and biological samples: Extraction and stability studies

Abstract

Our study evaluated the efficiency of consecutive extraction using several individual extractants or solvent mixtures: water, methanol:water (1:1, 9:1, 1:1–9:1 in two consecutive steps) and phosphoric acid for arsenic species extraction from rice, fish and chicken tissue, and soil samples. Arsenic species were quantified by HPLC (anionic and cationic chromatographic column) coupled to ICP-MS. The presence of As(III), As(V), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) was quantified in rice and soil whereas AsB, DMA and an unknown arsenic species were quantified in chicken tissue. AsB (major component) and one non-identified arsenic species were quantified in fish tissue. The sum of the arsenic species (as As) found in each extract for all matrices studied was equivalent to its total arsenic content. The best extraction efficiency and easiest handling were provided by the 1:1 methanol:water mixture for rice, fish and chicken tissue, and by 1 M phosphoric acid for soil. Three consecutive extractions provided quantitative recovery of As species from all matrices tested. It was demonstrated that arsenic species in rice extracts remained stable during the three-month test period, whereas in fish and chicken tissue extracts, AsB was transformed into DMA over time. MMA and DMA were stable in the 1 M phosphoric acid extracts from soils whereas As(III) gradually oxidised to As(V). As species from chicken and fish (higher protein content than rice and/or soil) became more stable as the methanol content increased in the extractant mixture used.