DETERMINATION OF METHYLMERCURY IN 2 MUSSEL TISSUE STANDARD REFERENCE MATERIALS BY PREIRRADATION SEPARATION AND NEUTRON-ACTIVATION ANALYSIS

A method was developed for the measurement of organically bound mercur y in two mussel tissue Standard Reference Materials (SRM): SRM 2974 Or ganics in Mussel Tissue and SRM 2976 Mussel Tissue. Organomercury comp ounds 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 t o neutron activation analysis (NAA) for mercury determination. Other a nalytical methods were used to confirm that most (greater than or equa l to 99 %) of the organically bound mercury is present in the form of methylmercury for these two mussel reference materials. With this esta blished, the results from the determination of organomercury compounds for this work are reported as the amount of mercury in the form of me thylmercury. The average and standard deviation of the results of anal yses 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 d eviation from analyses of seven aliquots of SRM 2976 Mussel Tissue wer e 27.9 +/- 3.9 ng g(-1) (95% CI, +/- 5.2 ng g(-1)); results from analy ses 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 an alytical methods, and were used in the certification df methylmercury concentrations in these two SRMs.