On-line speciation of mercury in fish by cold vapour atomic fluorescence through ultrasound-assisted extraction

Abstract

A fully mechanized procedure has been developed for the speciation of mercury in fish samples by using cold vapour atomic fluorescence spectrometry (CV-AFS). Sample slurries in an acid mixture in the presence of a surfactant and with traces of K₂Cr₂O₇, were injected into a flow system, sonicated and merged with 1 ml of an oxidant mixture of KBr/KBrO₃ heated at 50 °C in a water bath and total Hg determined by CV-AFS. Sonicated sample slurries were also measured, in the absence of KBr/KBrO₃, in order to obtain a second series of data which could be employed to establish the concentrations of free Hg(II). Different compositions of the acidic extractant solutions were evaluated by mixing HCl, HNO₃, H₂SO₄ and H₂O₂. The best results were obtained for a diluted mixture of HCl 3 mol l⁻¹, H₂SO₄ 1.4 mol l⁻¹, HNO₃ 0.11 mol l⁻¹and H₂O₂ 0.22 mol l⁻¹. The method provides a detection limit of 7 µg kg⁻¹ in dried sample and a mean relative standard deviation in actual samples of 6.8%. Quantitative recoveries were obtained for the determination of Hg and methylmercury (MeHg) in a SRM DORM-2 (dogfish muscle) and a SRM TORT-2 (lobster hepatopancreas) certified reference materials.