Measurement of water-soluble arsenic species in freeze-dried marine animal tissues by microwave-assisted extraction and HPLC-ICP-MS

Abstract

A microwave-assisted procedure is outlined for the extraction of water-soluble arsenic in freeze-dried marine animal tissues. The optimum microwave-assisted conditions were three extractions with 50% (v/v) methanol–water at 70 to 75 °C for 5 min. Quantitative extraction of arsenic in the water-soluble fraction of dogfish muscle (Dorm-2: 103 ± 2%) is consistent with that reported in the literature for this tissue. Lower extraction efficiencies for arsenic were found for liver (e.g. Dolt-1: 75 ± 5%; Pomatomus saltatrix: 80%), digestive (e.g. Tort-2: 92 ± 5%; Mugil cephalus stomach: 58%) and whole (e.g. Mussel CRM 278R: 66.1 ± 0.5%; Bembicium auratum: 76.4%) tissues. Arsenic extraction efficiencies in the water-soluble fraction were slightly higher for Dogfish Liver (Dolt-1) and Oyster (SRM 1566a) compared to that reported in the literature for these tissues. These results indicate that when samples are prepared in a similar manner, the efficiency to extract arsenic in the methanol–water soluble fraction will depend on the marine animal species and tissue analysed. The robustness of the microwave-assisted extraction procedure to identify and quantify arsenic species in freeze-dried marine animal tissues was determined using high performance liquid chromatography-inductively coupled plasma-mass spectrometry and the certified reference materials Dogfish Muscle (Dorm-2) and Lobster Hepatopancreas (Tort-2). Arsenic species determined in Dorm-2 tissue were AsB (16.80 ± 0.14 µg g⁻¹), TMAP (0.17 ± 0.01 µg g⁻¹), AsC (0.023 ± 0.002 µg g⁻¹), TETRA (0.24 ± 0.02 µg g⁻¹) and DMA (0.280 ± 0.004 µg g⁻¹). Arsenic species determined in Tort-2 tissue were AsB (13.10 ± 0.08 µg g⁻¹), TMAP (1.20 ± 0.03 µg g⁻¹), AsC (trace), TETRA (0.055 ± 0.005 µg g⁻¹), DMA (1.03 ± 0.10 µg g⁻¹), MA (0.20 ± 0.01 µg g⁻¹), As⁺⁵ (0.41 ± 0.03 µg g⁻¹) and phosphate arsenoribose (0.13 ± 0.03 µg g⁻¹). Two unknown anionic and one cationic arsenic species were also identified in Tort-2 tissue.