METHYLMERCURY DETERMINATION AS VOLATILE METHYLMERCURY HYDRIDE BY PURGE AND TRAP GAS-CHROMATOGRAPHY IN LINE WITH FOURIER-TRANSFORM INFRARED-SPECTROSCOPY

We report a novel aqueous derivatization of methylmercury chloride by NaBH4 to methylmercury hydride (CH3HgH), a volatile and unexpectedly stable species which we determined has a half-life of approximately 2 h. The analytical apparatus consisted of a purge and trap (PT) unit linked to a gas chromatograph (GC), in line with a Fourier transform infrared spectrometer (FTIR). The sample was purged with nitrogen, and volatile compounds were concentrated in a cold trap. The trap was heated, and the methylmercury hydride was separated from other gaseous compounds by a wide-bore GC column linked to the FTIR spectrometer. The detection limit of the method was 0.15-mu-g and was linear up to 40-mu-g of MeHgH. The concentration of methylmercury in a reference tuna fish as determined by PT/GC/FTIR was the same as that determined by conventional analyses in an 11-laboratory intercalibration. Analytical methods employed previously have not permitted identification of the methylmercury hydride species. Our results also suggest the need to investigate further the occurrence in nature of this highly volatile and unexpectedly stable species, especially in view of previous reports of biohydridization of other metal and metalloid species.