Determination of methylmercury and phenylmercury in water samples by liquid–liquid–liquid microextraction coupled with capillary electrophoresis

A novel method for determination of methylmercury (MeHg) and phenylmercury (PhHg) by liquid–liquid–liquid microextraction (LLLME) coupled with capillary electrophoresis (CE) with ultraviolet (UV) technique was developed. The method based on MeHg and PhHg was complexed with 1-(2-pyridylazo)-2-naphthol (PAN) to form hydrophobic complexes. When the sample solution was stirred, analytes were extracted into the organic layer (200 μL toluene) and back-extracted simultaneously into the 4.0 μL 0.1% (w/v) l-cysteine microdrop. The factors affecting on the LLLME of two mercury species, including sample pH, complex reagent concentration, extraction time, volume of organic solvent, stirring rate and phase volume ratio, were investigated. Under the optimized conditions, the detection limits (S/N = 3) of MeHg and PhHg were 0.94 and 0.43 ng mL−1 (as Hg), respectively. The precisions (RSDs, c = 10 ng mL−1, n = 7) were in the range of 3.3–3.4% for migration time, 6.1–7.2% for peak area response, and 6.7–7.5% for peak height response for the two mercury species. The enrichment factors of 324 for MeHg and 210 for PhHg were obtained with 40 min LLLME. The developed method was successfully applied to the determination of trace amounts of MeHg and PhHg in water samples.