Study on analytical method for methymecury in sediment by gas chromatography-atomic fluorescence spectrometry using Grignard reagents for alkylation

Abstract

The analytical method for methylmercury in sediment samples was performed using an hyphenated system of gas chromatograph coupled atomic fluorescence detector (GC-AFS). Methylmercury in sediment samples was leached and extracted into dichloromethane with the assistance of HNO₃, KCl and CuSO₄. Dichloromethane was evaporated resulting in the relocation of MeHg to the  aqueous phase. MeHg was then extracted in the form of diethyldithiocarmate complex into hexane followed by the alkylation processes with Grignard reagents, butyl magnesium chloride and ethyl magnesium chloride. The alkylation reactions were optimized with respect to the mounts of Grignard reagents, the reaction temperature and time for the best alkylation yields and least extent of trans-alkylation and degradation of the alkylated products. The alkylated MeHg compounds were analyzed by GC-AFS. The analytical method for methylmercury was validated using certified reference material ERM-CC580. The instrumental limit of detection was 1.4 pg as Hg. The method limits of detection for EtMgCl and BuMgCl were 0.18  were 0.18 ng/g and 0.19 ng/g, respectively. This method can be used to analyze MeHg in sediment samples.