Determination of methylmercury in two mussel tissue Standard Reference Materials by pre-irradiation separation and neutron activation analysis

A method was developed for the measurement of organically bound mercury in two mussel tissue Standard Reference Materials (SRM): SRM 2974 Organics in Mussel Tissue and SRM 2976 Mussel Tissue. Organomercury compounds were distilled from a mixture of powdered sample (approximately 200 mg), sulfuric acid and copper(II) sulfate, and bound chemically to cysteine fixed on to tilter-paper. The filter papers were subjected to neutron activation analysis (NAA) for mercury determination. Other analytical methods were used to confirm that most (greater than or equal to 99 %) of the organically bound mercury is present in the form of methylmercury for these two mussel reference materials. With this established, the results from the determination of organomercury compounds for this work are reported as the amount of mercury in the form of methylmercury. The average and standard deviation of the results of analyses of four aliquots of Reference Material IAEA-350 Tuna were 3.61 +/- 0.20 mu g g(-1) [with a 95% confidence interval (95% Ct) of +/-0.69 mu g g(-1)], compared with a certified value of 3.65 mu g g(-1) and 95% Ct of 3.32-4.01 mu g g(-1). The concentration average and standard deviation from analyses of seven aliquots of SRM 2976 Mussel Tissue were 27.9 +/- 3.9 ng g(-1) (95% CI, +/- 5.2 ng g(-1)); results from analyses of five aliquots of SRM 2974 yielded 78.3 +/- 9.6 ng g(-1) (95% CI, +/- 15.0 ng g(-1)), Results obtained using this method compared well with results obtained by other investigators using three different analytical methods, and were used in the certification df methylmercury concentrations in these two SRMs.