Methylmercury monitoring in rainwater samples using in situ ethylation in combination with GC-AFS and GC-ICP-MS techniques

Abstract

In a monitoring study an analytical technique with atomic fluorescence (AFS) detection was used for methylmercury determination in atmospheric precipitation from the Baltic Sea at ultra-trace level. The methylmercury values in atmospheric precipitation obtained by the AFS system ranged from below the detection limit to 0.32 ng l−1. The concentrations of methylmercury made up about 1–4% of the total mercury concentrations. Recently, when artifact formation of methylmercury had become an issue the analytical technique used was checked with a stable enriched mercury isotope for artifact formation of methylmercury during analysis. The analytical system, normally coupled with atomic fluorescence detection, was used with a mass spectroscopy, (ICP–MS) detector for isotope-specific mercury detection. The samples were spiked just before analysing with 200Hg2+. A possible unintentional transformation into methylmercury during the analytical procedure could be detected with the isotope-specific methylmercury determination method. The results have shown that a direct ethylation of methylmercury in an atmospheric precipitation sample by sodium tetraethylborate produced no significant amount of artifactural methylmercury due to the spiked enriched 200Hg2+. However when the water vapour distillation was applied for aqueous rain samples containing visible particles, an artifactural formation of methylmercury was observable. The particles were responsible for this formation. Copyright © 1999 John Wiley & Sons, Ltd.