Comparison of different extraction techniques used for methylmercury analysis with respect to accidental formation of methylmercury during sample preparation

Different techniques commonly used to extract monomethylmercury (MMHg) from various matrices have been screened regarding their potential to accidentally generate MMHg from inorganic Hg2+ during sample preparation. Most of the tested techniques, among them alkaline and acidic leaching as well as atmospheric pressure distillation, were prone to spurious formation of CH3200Hg+ from 200Hg2+ added to certified reference materials. 0.006–0.05 % of the added stable inorganic Hg isotope was converted to MMHg. Only leaching using a H2SO4/KBr/CuSO4 mixture did not cause any artifacts. In certain sediment samples where the MMHg fraction is less than 190, the degree of artifactual formation observed can be significant. To calculate the original MMHg content in such samples the application of a species specific isotope addition method (SSIA) is proposed and was evaluated.