Determination of mercury in freeze-dried muscle samples of pike, cod and perch using an ASV-technique

Determination of mercury in fish muscle samples can be made by an anodic stripping voltammetric technique (ASV) using a gold disc as the working electrode. Prior to analysis deep-frozen fish were thawed and then dissected using quartz scalpels. The freeze-dried samples were homogenised by the brittle fracture technique. Two wet digestion procedures were investigated, namely the HNO3/HCIO4 and the HNO3/H2SO4 system, and both were found to be useful. In order to complete the oxidation, the sample had to be UV-irradiated. The stripping procedure can be done in either a new medium - 0.1 M HCIO4 and 2.5 mM HCl - or directly in the sample solution. Using HNO3 and H2SO4 as oxidising agents and subsequently stripping the mercury directly in the sample solution is recommended, as the analytical procedure will be simpler and more time-saving. The concentrations obtained for pike, cod and perch, caught at a near-shore Baltic Sea station off the Forsmark nuclear power plant in Sweden, were 19.6, 0.84 and 5.1 (micrograms/g dry weight), respectively. On comparison with results obtained from neutron activation analysis, good agreement was found.