Determination of methylmercury in fish by gas chromatography direct current plasma atomic emission spectrometry

Abstract

Gas chromatography (GC) has been interfaced very simply and inexpensively with a direct current plasma (DCP) atomic emission spectrometer in order to perform highly specific and selective determinations of methylmercury (MeHg) in fish samples. A simple, isothermal, low-cost GC was constructed which could be dedicated to the DCP, allowing routine qualitative and quantitative determinations of organomercury species in complex food matrices. Optimisation of the GC-DCP interface was accomplished, followed by a determination of the detection limits, the linearity of the calibration graph and comparison of the results with those obtained by GC-electron-capture detection (ECD) and total mercury by cold-vapour atomic absorption spectrometry. In most instances, qualitative and quantitative results for incurred and spiked levels did not agree for the GC-DCP and GC-ECD approaches. An additional extraction procedure has also been developed for MeHg from fish samples involving extraction with an organic solvent, concentration and injection on to the GC column. Depending on the particular organic solvent employed, artifact formation of MeHg can occur as a result of the extraction-GC conditions. Methods to avoid an artifact situation are suggested, and the possible implications of this for the currently accepted AOAC method involving GC-ECD.