Speciation of Inorganic- and Methyl-Mercury in Biological Matrixes by Electrochemical Vapor Generation from an L-Cysteine Modified Graphite Electrode with Atomic Fluorescence Spectrometry Detection

A novel nonchromatographic speciation technique for ultratrace inorganic mercury (Hg2+) and methylmercury (CH3Hg+) in biological materials is developed and validated by electrolytic vapor generation (EVG) coupled with atomic fluorescence spectrometry (AFS). The studies show that CH3Hg+ and Hg2+ can be converted to Hg vapor efficiently on an L-cysteine modified graphite cathode, which has never been reported before. We observe that only Hg2+ can be converted efficiently to Hg vapor at low current mode (0.2 A). While at high current mode (2.2 A), both CH3Hg+ and Hg2+ can be reduced efficiently. As a result, we successfully establish an exact and sensitive method based on the current control to detect mercury speciation for the first time The factors of electrolytic conditions have been optimized, and the potential mechanism is discussed. Under the optimal conditions, the detection limits (3s) of Hg2+ and CH3Hg+ in aqueous solutions are 0.098 and 0.073 mu g L-1, respectively. The relative standard deviations for 6 replicate determinations of 2 mu g.L-1 Hg are determined as 3.2% and 4.7% for Hg2+ and CH3Hg+. The accuracy of the method is verified through the analysis of certified reference materials (CRM, NRC-DORM-2), and the proposed method has been applied satisfactorily to the determination of mercury speciation in several seafood samples by calibration curve mode.