Total and inorganic mercury determination in fish tissue by flow injection cold vapour atomic fluorescence spectrometry

Abstract

A simple and reliable method for Hg determination in fish samples has been developed. Lyophilised fish tissue samples were extracted in a 25% (w/v) tetramethylammonium hydroxide (TMAH) solution; the extracts were then analysed by FI-CVAFS. This method can be used to determine total and inorganic Hg, using the same FI manifold. For total Hg determination, a 0.1% (w/v) KMnO4 solution was added to the FI manifold at the sample zone, followed by the addition of a 0.5% (w/v) SnCl2 solution, whereas inorganic Hg was determined by adding a 0.1% (w/v) L-cysteine solution followed by a 1.0% (w/v) SnCl2 solution to the FI system. The organic fraction was determined as the difference between total and inorganic Hg. Sample preparation, reagent consumption and parameters that can influence the FI-CVAFS performance were also evaluated. The limit of detection for this method is 3.7 ng g−1 for total Hg and 4.3 ng g−1 for inorganic Hg. The relative standard deviation for a 1.0 µg L−1 CH3Hg standard solution (n = 20) was 1.1%, and 1.3% for a 1.0 µg L–1 Hg2+ standard solution (n = 20). Accuracy was assessed by the analysis of Certified Reference Material (dogfish: DORM-2, NRCC). Recoveries of 99.1% for total Hg and 93.9% inorganic Hg were obtained. Mercury losses were not observed when sample solutions were re-analysed after a seven day period of storage at 4°C.