Determination of mercury(II) in water samples using dispersive liquid-liquid microextraction and back extraction along with capillary zone electrophoresis

We have developed a method for the determination of mercury in water samples that combines dispersive liquid-liquid microextraction (DLLME) with back-extraction (BE) and detection by capillary zone electrophoresis. DLLME is found to be a simple, cost-effective and rapid method for extraction and preconcentration. The BE procedure is based on the fact that the stability constant of the hydrophilic chelate of Hg(II) with L-cysteine is much larger than that of the respective complex with 1-(2-pyridylazo)-2-naphthol. Factors affecting complex formation and extraction efficiency (such as pH value, concentration of the chelating agent, time of ultrasonication and extraction, and type and quantity of disperser solvent) were optimized. Under the optimal conditions, the enrichment factor is 625, and the limit of detection is 0.62 mu g L-1. The calibration plot is linear in the range between 1 and 1,000 mu g L-1 (R (2) = 0.9991), and the relative standard deviation (RSD, for n = 6) is 4.1%. Recoveries were determined with tap water and seawater spiked at levels of 10 and 100 mu g L-1, respectively, and ranged from 86.6% to 95.1%, with corresponding RSDs of 3.95-5.90%.