Determination of total arsenic and toxicologically relevant arsenic species in fish by using electrothermal and hydride generation atomic absorption spectrometry

Abstract

A scheme for the determination of total As by electrothermal atomic absorption spectrometry (ETAAS) and the sum of toxicologically relevant arsenic species (As(III), As(V), monomethylarsonate (MMA) and dimethylarsinate (DMA) using hydride generation AAS (HGAAS) in fish samples was developed. Simple and fast microwave assisted extraction in tetramethylammonium hydroxide (TMAH, 0.075% m / v) or in water–methanol mixture (80 + 20 v / v) for 20 min is proposed for quantitative leaching of arsenic species from fish tissue. Total As was measured by ETAAS directly in the TMAH extract under optimal instrumental parameters (pyrolysis temperature 1400 °C and atomization temperature 2000 °C) with Pd as modifier ensuring thermal stabilization and isoformation of all extracted arsenic species. The analytical features of the method are as follows: limit of detection (LOD) 0.45 μg g − 1 (dry wt.), within-run and between-run precision in the range 4–8% and 5–12%, respectively, for arsenic contents 0.5–30 μg g − 1 and recoveries 98–102%. The sum of toxicologically relevant arsenic species (As(III) + As(V) + MMA + DMA) was determined by flow injection HGAAS directly from the TMAH extract or water–methanol mixture and trapping of arsines onto Zr–Ir coated graphite tube followed by ETAAS measurement. l-cysteine is used as reagent for leveling off responses of different arsenic species in the presence of TMAH or water–methanol mixture. The LODs achieved are 0.0038 and 0.0031 μg g − 1 (dry wt.), respectively, for fish extracts in TMAH and in water–methanol mixture. Within-batch and between-batch RSDs are in the range 3–5% and 4–7% for arsenic contents of 0.009–0.25 μg g − 1 (dry wt.) for TMAH extracts and 2–4% and 3–6% for methanol water extracts, respectively. Selective reaction media for generation of respective hydrides from arsenic species were recommended for further speciation purposes in methanol–water extracts, viz. citrate buffer (pH 5.2) for the determination of As(III), 0.2 mol L − 1 acetic acid for the determination of As(III) + DMA and 7 mol L − 1 hydrochloric acid for the determination of inorganic As(III) + As(V). LODs are 0.0035, 0.0051 and 0.0046 μg g − 1 (dry wt.) for As(III), DMA and As(V). The relative standard deviation is 4–8% for three arsenic species at As levels of 0.009–0.5 μg g − 1 (dry wt.). The accuracy of the proposed speciation scheme is confirmed by the analysis of certified reference materials.