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 accidenta lly generate MMHg from inorganic Hg2+ during sample preparation. Most of th e tested techniques, among them alkaline and acidic leaching as well as atm ospheric pressure distillation, were prone to spurious formation of (CH3Hg)-Hg-200 from Hg-200(2+) added to certified reference materials. 0.006 - 0. 05 % of the added stable inorganic Hg isotope was converted to MMHg. Only l eaching using a H2SO4/KBr/CuSO4 mixture did not, cause any artifacts. In ce rtain sediment samples where the MMHg fraction is less than 1%, the degree of artifactual formation observed can be significant. To calculate the orig inal MMHg content in such samples the application of a species specific iso tope addition method (SSIA) is proposed and was evaluated. (C) 1999 Elsevie r Science Ltd. All rights reserved.