Determination of Methylmercury, Ethylmercury, and Inorganic Mercury in Mouse Tissues, Following Administration of Thimerosal, by Species-Specific Isotope Dilution GC-Inductively Coupled Plasma-MS

Isotopically enriched HgO standards were used to synthesize CH3200Hg+ and C2H5199Hg+ using Grignard reagents. These species were employed for isotope dilution GC-ICPMS to study uptake and biotransformation of ethylmercury in mice treated with thimerosal, (sodium ethylmercurithiosalicylate) 10 mg L^-1 in drinking water ad libitum for 1, 2.5, 6, or 14 days. Prior to analysis, samples were spiked with aqueous solutions of CH3200Hg+, C2H5199Hg+, and 201Hg^2+ and then digested in 20% tetramethylammonium hydroxide and extracted at pH 9 with DDTC/toluene. Extracted mercury species were reacted with butylmagnesium chloride to form butylated derivatives. Absolute detection limits for CH3Hg+, C2H5Hg+, and Hg^2+ were 0.4, 0.2, and 0.6 pg on the basis of 3(sigma) of five separate blanks. Up to 9% of the C2H5Hg+ was decomposed to Hg^2+ during sample preparation, and it is therefore crucial to use a species-specific internal standard when determining ethylmercury. No demethylation, methylation, or ethylation during sample preparation was detected. The ethylmercury component of thimerosal was rapidly taken up in the organs of the mice (kidney, liver, and mesenterial lymph nodes), and concentrations of C2H5Hg+ as well as Hg^2+ increased over the 14 days of thimerosal treatment. This shows that C2H5Hg+ in mice to a large degree is degraded to Hg^2+. Increased concentrations of CH3Hg+ were also observed, which was found to be due to impurities in the thimerosal.