Simultaneous determination of inorganic mercury and methylmercury compounds in natural waters

Abstract.

The purpose of the present work was to develop a simple, rapid, sensitive and accurate method for the simultaneous determination of inorganic mercury (Hg²⁺) and monomethylmercury compounds (MeHg) in natural water samples at the pg L^–1 level. The method is based on the simultaneous extraction of MeHg and Hg²⁺ dithizonates into an organic solvent (toluene) after acidification of about 300 mL of a water sample, followed by back extraction into an aqueous solution of Na₂S, removal of H₂S by purging with N₂, subsequent ethylation with sodium tetraethylborate, room temperature precollection on Tenax, isothermal gas chromatographic separation (GC), pyrolysis and cold vapour atomic fluorescence spectrometric detection (CV AFS) of mercury. The limit of detection calculated on the basis of three times the standard deviation of the blank was about 0.006 ng L^–1 for MeHg and 0.06 ng L^–1 for Hg²⁺ when 300 mL of water was analysed. The repeatability of the results was about 5% for MeHg and 10% for Hg²⁺. Recoveries were 90–110% for both species.