Determination of total mercury in fish and sea products by direct thermal decomposition atomic absorption spectrometry

A Zeeman Mercury analyzer Model RA-915+ (Lumex, St. Petersburg, Russia), based on the direct thermal evaporation of Hg from solid samples was used for developing a method for the determination of Hg in fish and other seafood. The method does not require any chemical pretreatment of samples. This greatly simplifies the analytical procedure and minimises potential sources of contamination. The limit of detection (3 s criteria) and limit of quantification (10 s criteria) for the determination of Hg in wet fish samples with a mass of 250 mg was found to be 0.6 ng g−1 and 2.0 ng g−1, respectively. Time taken for the analysis of one sample is about 3 min. The accuracy of the method was confirmed by the analysis of certified reference materials of different types and by comparative analysis of fish samples using the accepted method of cold vapour generation. Excellent correspondence to the certified values was obtained. It was found that the mercury concentration in most fish species purchased from the Tshwane fish market were below the 0.5 mg kg−1 (500 ng g−1), wet weight, recommended by the FAO/WHO. It was also found that the direct thermal decomposition method for the determination of mercury is a more environmentally friendly alternative since it does not generate chemical waste.