Speciation analysis of mercury in sediments using vortex-assisted liquid–liquid microextraction coupled to high-performance liquid chromatography-cold vapor atomic fluorescence spectrometry

A simple and fast solvent microextraction method termed vortex-assisted liquid–liquid microextraction (VALLME) coupled with high-performance liquid chromatography-vapor generation atomic fluorescence spectrometry (HPLC-CVAFS) has been developed for the trace analysis of methylmercury (MeHg+), ethylmercury (EtHg+) and inorganic mercury (Hg2+) in sediment samples. Carbon tetrachloride was used as collecting solvent for the extraction of mercury species from sediment by a vortex-assisted extraction. In VALLME, 100 μL 1% (m/v) l-Cysteine were used as extraction solvent and were injected into 4 mL carbon tetrachloride. The extraction solvent dispersed into carbon tetrachloride under vigorously shaking by a vortex agitator. The fine droplets could extract mercury species within few minutes because of the shorter diffusion distance and larger specific surface area. After centrifugation, the floating extractant phase restored its initial single microdrop shape and was used for HPLC-CVAFS analysis. The parameters affecting the extraction efficiency of the proposed VALLME such as extraction solvent, vortex time, volumes of extraction solvent and salt addition etc. were investigated. Under the optimum conditions, linearity was found in the concentration range from 0.1 to 25 ng g−1 for MeHg+, 0.2 to 65 ng g−1 for EtHg+, and 0.1 to 30 ng g−1 for Hg2+. Coefficients of determination (R2) ranged from 0.9938 to 0.9972. The limits of detection (LODs, signal-to-noise ratio (S/N)=3) were 0.028 ng g−1 for MeHg+, 0.057 ng g−1 for EtHg+, and 0.029 ng g−1 for Hg2+. Reproducibility and recoveries were assessed by testing a series of 6 sediment samples, which were spiked with different concentration levels. Finally, the proposed method was successfully applied in analyses of real nature sediment samples. In this work, VALLME was applied to the extraction of mercury species in sediment samples for the first time. Using l-Cys as extraction solvent, the extraction process is sensitive and environmentally friendly and could be achieved within 3 min.