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

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.