Application Note Methylmercury in Water

Since the 1950’s, mercury found in the environment has been known to have serious effects on human health.1 Most natural waters contain trace levels of methylmercury on the order of 10 to a few hundred pg/L. Monitoring methylmercury at these levels is important because of its high toxicity to humans. This method describes the automated analysis of methylmercury in water samples by aqueous phase ethylation and CVAFS (cold vapor atomic fluorescence spectrophotometer) detection. The detection limit for this method is 20-pg/L of methylmercury as Hg. This method is automated using the Tekmar Precept II autosampler, Tekmar 3000 purge and trap concentrator and Tekmar Cryofocuser.2 The three steps of this method are 1) sample clean-up, 2) derivatization and 3) analysis. The first step, sample clean-up removes dissolved organic carbon (DOC) which constitutes a serious interferant in the determination of methylmercury. This process is accomplished by distilling the sample. The second step, derivatization, transforms the methylmercury and species such as Hg+2 into methylethylmercury and diethyl mercury respectively. These derivatives are volatile and can be purged from the sample along with any trace levels of atomic mercury (Hg0). The third step in this process is analysis. The analysis is accomplished by purging the volatile derivatives from the sample and capturing the analytes onto a Tenax ® trap. The analytes are then desorbed into a Hewlett Packard 5890 gas chromatograph (GC). A pyrolysis furnace at the end of the GC colum