Two methods for the speciation analysis of mercury in fish involving microwave-assisted digestion and gas chromatography-atomic emission spectrometry

In this paper a novel approach for the speciation analysis of mercury (methyl mercury and mercury II) in fish tissue using gas chromatography-microwave induced plasma atomic emission spectromertry is described. Focused microwave-assisted digestion which has been used previously in speciation analysis only for the determination of organotin and organoselenium compounds, was applied for sample preparation, a technique which enables mild, quick and complete dissolution of the sample. The important parameters for the digestion of fish tissues were optimised for the given analytical problem. Since no experience was available for the further treatment of the produced sample solution two different derivatisation/injection procedures were examined: 1. (1) ethylation with sodium tetraethylborate, extraction into hexane and injection with a cooled injection system and 2. (2) hydride generation with sodium tetrahydroborate together with purge-and-trap injection. The latter reaction has not been used previously for the determination of mercury species in fish samples. The optimum parameters for both procedures were evaluated and the methods were validated by analysis of a standard reference material (CRM 464). The 3σ detection limits were (1) 3.0 pg g−1 and (2) 12.5 pg g−1.