Effect of the Mineralization Method on Arsenic Determination in Marine Organisms by Hydride Generation Atomic Fluorescence Spectroscopy

The efficiency of several mineralization methods for As determination in marine organisms has been evaluated. Wet mineralization in closed reactors at 150°C with acids (HNO₃/HClO₄/H₂SO₄) and K₂S₂O₈ and microwave-assisted digestion with HNO₃/H₂O₂ or with HNO₃/H₂O₂/HCl does not quantitatively destroy the organic matter of fish. This was ascertained by comparing the As content obtained by HG-AFS with that obtained by ICP-MS. Dry-ashing destroys organic As species and the resulting As recovery when HG-AFS is applied is similar to that obtained by ICP-MS. Similar arsenic contents were obtained for all the mineralization methods tested when arsenic was analysed by ICP-MS. These results indicate that when HG-AFS is applied for arsenic determination, the organic matter should be completely oxidised (e.g. by UV photo-oxidation and K₂S₂O₈) to transform organic arsenic compounds into those able to generate hydrides. The results have been validated with a fish candidate reference material (CRM) (EU SEAS plaice) with a known content of total arsenic. Arsenic speciation after 1:1 methanol-water extraction (which provides quantitative arsenic recovery after two consecutive extractions) by HPLC-ICP-MS shows that cuttlefish only contains arsenobetaine, which explains the difficulty of mineralization.