Combination of sequential cloud point extraction and hydride generation atomic fluorescence spectrometry for preconcentration and determination of inorganic and methyl mercury in water samples

A sequential cloud point extraction method was established for the determination of trace mercury species in water samples by hydride generation atomic fluorescence spectrometry (HGAFS). The proposed extraction system consisted of two chief steps: isolation of inorganic mercury (Hg2+) by chelating with potassium-iodide and methyl green, and then isolation of methyl mercury (CH3Hg+) by chelating with ammonium pyrrolidine-dithiocarbamate. The nonionic surfactant Triton X-114 was chosen as the extractant, while the brominating agent was applied to convert extracted CH3Hg+ into Hg2+. Before HGAFS detection, the two surfactant-rich phases obtained in the sequential process were separately diluted to 3 mL with 5% (v/v) HCl after the addition of antifoam (0.4 mL). The effects of experimental conditions, including pH and concentration of surfactant and chelating agents, on cloud point extraction were optimized. Under the optimum conditions, the limits of detection for Hg2+ and CH3Hg+ were 0.007 and 0.018 mu g/L with the enrichment factors of 15.1 and 11.2, respectively. The proposed method was successfully used for the determination of trace Hg2+ and CH3Hg+ in water samples with satisfactory recoveries of 95-104%.