Arsenic speciation in marine certified reference materials

Abstract

This study describes the analysis of arsenicals in three marine based certified reference materials (CRMs), DORM-2, DOLT-2 and TORT-2, all produced by the National Research Council of Canada. Extraction protocols involving accelerated solvent extraction (ASE) and sonication were investigated and arsenicals were determined on-line by anion-exchange and cation-exchange high-performance liquid chromatography (HPLC). The major species in all three tissues was found to be arsenobetaine (AsB), corresponding to 90%, 67% and 73% of the water-soluble arsenic in DORM-2, DOLT-2 and TORT-2, respectively. Other species quantified were arsenocholine (AsC+), tetramethylarsonium ion (TMAs+), trimethylarsonioproprionate (TMAP), dimethylarsenic acid (DMA), monomethylarsenic acid (MMA), arsenosugar D (As-sug D), arsenate (AsV) and arsenosugar A (As-sug A). The major species detected in all three materials were AsB and DMA, which together accounted for 97.4% (DORM-2), 95.4% (DOLT-2) and 91.7% (TORT-2) of the sum of the water soluble As species. The agreement for the determination of AsB by the different methods was good for all three materials, whereas some discrepancy was evident in the results for DMA. When an ASE approach with 50% acetic acid in methanol was used for the extraction, between 22% (DOLT-2) and 58% (TORT-2) more DMA was determined compared with extraction by sonication with water. Some discrepancy was evident between the sum of the species extracted and both the total As determined in the extracts and the certified As content based on complete digestion of the materials. The sum of the species recovered by sonication corresponded to 84% (DOLT-2) to 94% (DORM-2) of the total As determined in the aqueous extract. In comparison with the certified As content of the three materials, the sums of the extracted species range from 46% (DOLT-2) to 76% (TORT-2) and 102% (DORM-2).