Speciation analysis of mercury in water samples using dispersive liquid-liquid microextraction combined with high-performance liquid chromatography

A novel approach for preconcentration and speciation analysis of trace amount of mercury from water samples was proposed by dispersive liquid-liquid microextraction (DLLME) coupled to high performance liquid chromatography with diode array detection (HPLC-DAD). Mercury species (Hg2+, methylmercury (MeHg+) and phenylmercury (PhHg+)) were complexed with dithizone (DZ) to form hydrophobic chelates and then extracted into the fine drops of extraction solvent dispersed in the aqueous sample by dispersive solvent. After extraction, the sedimented phase was analyzed by HPLC-DAD. Some important parameters affecting the DLLME such as extraction solvent and dispersive solvent type and volume, concentration of dithizone solution, sample pH, extraction time and salt effect were investigated. Ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM][PF6]) was found to be a suitable extractant for the chelates. Under the optimized conditions (extraction solvent: 70 mu L of ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM][PF6]); dispersive solvent: 0.75 mL of methanol containing dithizone (0.02%, m/v); pH: 4; extraction time: 5 min: and without salt addition), the limits of detection for Hg2+, MeHg+ and PhHg+ were 0.32, 0.96 and 1.91 mu g L-1 (SN-1 = 3) respectively, and the relative standard deviation (RSD) was between 4.1 and 7.3% (n = 5). Three real water samples (tap water, river water and lake water) spiked with mercury species were detected by the developed method, and the relative recoveries obtained for Hg2+. MeHg+ and PhHg+ were 89.6-101.3%, 85.6-102.0% and 81.3-97.6%, respectively. (C) 2011 Elsevier B.V. All rights reserved.