Christopher Mansfield, Westminster College
Physical Science
The method currently used to measure monomethylmercury (MMHg) in natural waters involves a lengthy distillation step in order to remove certain ions and dissolved organic matter that have been reported to interfere with the subsequent reaction in which MMHg is ethylated. It has recently been reported that the analysis of MMHg in seawater by direct ethylation was successfully carried out, thus removing the day-long distillation. However, the effect of many potential interfering ions and compounds on this method have not been characterized, and it has not been tested for use in natural freshwaters or the hypersaline waters of the Great Salt Lake. Thus, these became the two goals of this project. We found that optimal ethylation conditions included buffering samples to pH 4.0-4.1, reducing the amount of sodium tetraethylborate, adding EDTA to complex interfering trace metals, and adding chloride to overcome interferences by thiols and organic matter. We have since employed this improved method to analyze MMHg in natural water samples from fresh and saline lakes, achieving > 90% MMHg spike recoveries without the use of distillation.