Determination of methylmercury in human blood using capillary gas chromatography and selected-ion monitoring.

A capillary gas chromatographic method, using selected-ion monitoring in the electron-impact mode, was developed for the analysis of methylmercury (MeHg) in human blood. The samples, spiked with the internal standard propylmercury bromide (PropHgBr), were, after addition of sodium bromide and cupric sulfate, extracted with toluene. The organic phase was extracted with an ethanol-water solution of sodium thiosulfate. After addition of sodium bromide solution, the ethanol-water phase was extracted with toluene. Methylated derivatives (MeHgCH2Br and PropHgCH2Br) were formed by the addition of a diethyl ether solution of diazomethane. The chromatographic properties of the derivatives were much better than those of the non-methylated compounds. The m/z 215 fragment of MeHgCH2Br and the molecular ion m/z 338 of PropHgCH2Br were monitored. The calibration graphs, with a linear correlation coefficient of 0.992 (n = 12) in the 1-5 micrograms/l concentration range, passed through the origin. The detection limit for MeHg in human blood was ca. 0.5 microgram/l. Analysis of spiked blood samples at concentrations of about 2 and 10 micrograms/l gave a relative standard deviation of 4.2 and 5.5%, respectively (n = 10).