Mercury speciation by liquid chromatography coupled with on-line chemical vapour generation and atomic fluorescence spectrometric detection (LC–CVGAFS)

Abstract

Reverse phase chromatography (RPC) coupled on-line with UV–vis diode array detector (DAD) and cold vapour generation atomic fluorescence spectrometry (CVGAFS) is proposed for the speciation and determination of inorganic and organic mercury (methylmercury, ethylmercury and phenylmercury) in the form of cysteine, penicillamine and glutathione complexes. The mercury–thiol complexes are separated on a C 18 Reverse Phase column and oxidized on-line with bromine, generated in situ by KBr/KBrO 3 in HCl medium, in order to fast convert organic mercury species to inorganic mercury in less than 2.5 s, at room temperature, in a 30 cm knitted coil. Hg(II) is selectively detected by AFS in a Ar/H 2 miniaturized flame after sodium borohydride reduction to Hg 0. Under optimized conditions, on-line bromine treatment gives recoveries of thiol-complexed methylmercury, ethylmercury and phenylmercury with respect to inorganic mercury ranging between 79 and 85%, 80 and 85%, 63 and 76%, respectively, depending on the complexing thiol employed. Optimized elution conditions were provided in the three complexing agents. The detection limits (LODc) for inorganic mercury, methylmercury, ethylmercury and phenylmercury, in the optimized conditions complexed with thiols were about 16, 18, 18 and 20 pg (as mercury), respectively, a relative standard deviation (R.S.D) ranging between 1.5 and 2.0%, and a linear dynamic range between 0.1 and 100 ng injected. LC–DAD–CVGAFS method has been validated by analysing two certificate reference material, DORM-2 and NIES CRM 13, obtaining 98 ± 6 and 97 ± 5% of methylmercury recovered, respectively.