Dielectric barrier discharge induced atomization of gaseous methylethylmercury after NaBEt₄ derivatization with purge and trap preconcentration for methylmercury determination in seawater by GC-AFS

A novel method suitable for methylmercury (CH₃Hg) analysis in seawater by gas chromatography (GC)-atomic fluorescence spectrometry (AFS) based on dielectric barrier discharge (DBD) induced atomization of gaseous methylethylmercury (CH₃HgC₂H₅) after sodium tetraethylborate (NaBEt₄) derivatization with purge and trap preconcentration was developed in this work. In the proposed method, with NaBEt₄ used as derivatization reagent, the nonvolatile CH₃Hg could be converted to the gaseous CH₃HgC₂H₅ and trapped in a quartz tube with Tenax sorbent for preconcentration. A DBD atomizer was employed for the atomization of CH₃HgC₂H₅ to Hg⁰ between the GC separation and AFS detection instead of the conventional thermal decomposition atomizer, which had not been reported before. The DBD atomizer not only produces a comparable atomization efficiency for CH₃HgC₂H₅ to the thermal decomposition atomizer, but also can be operated at room temperature with low power consumption (5 W). The effects of DBD input discharge voltage, DBD discharge distance, N₂ gas purge time, and thermal desorption time on CH₃Hg determination were evaluated. The method provided good reproducibility (RSD, 2.0%) and low detection limits of CH₃Hg (LOD, 0.0008 ng L⁻¹). The proposed method was validated by the analysis of a certified reference material (GBW08675) and successfully applied to the determination of CH₃Hg in sub ng L⁻¹ level in different seawater samples.