Analytical approach for routine methylmercury determination in seafood using gas chromatography-atomic fluorescence spectrometry

Two methodologies have been developed for the analysis of mercury species in seafood by capillary gas chromatography coupled to an AFS detector via pyrolysis. The first one is based on the ethylation of both, inorganic and methylmercury species (Method 1), in which clean-up is not necessary because a small amount of sample is required. In the second one, monoalkylated mercury species are extracted into organic phases after forming the corresponding chlorides (Method 2). In this case the elimination of the interfering compounds from the matrix requires a clean-up step, which enables the treatment of higher quantities of sample. Both procedures can be considered complementary because the concentration range applicable for each one of them is different: 0.75–10 (mu)gHg g^-1, in dry basis for methylmercury (Method 1) and 6–1000 ngHg g^-1 (Method 2). The range of application for natural samples can be easily selected by a preliminary analysis of total mercury, because most mercury in seafood is present as MeHg. Optimum parameters for both procedures have been evaluated, and the methods were validated with two standard reference materials (BCR-463 and NIST2977). Finally, the methods have been applied to the analysis of seafood samples. Detection limits of MeHg range from 1.7 to 220 ngHg g^-1 (dry basis) depending of the methodology selected and the weight of sample. The method can be successfully applied to commercially available seafood samples, and considered for routine analysis.