DETERMINATION OF ESTROGENS IN WATER SAMPLES BY IONIC LIQUID-BASED DISPERSIVE LIQUID-LIQUID MICROEXTRACTION COMBINED WITH HIGH PERFORMANCE LIQUID CHROMATOGRAPHY

Using 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6MIM][PF6]) ionic liquid as extraction solvent, five estrogens including estrone (E-1), 17 beta-estradiol (E-2), estriol (E-3), 17 alpha-ethynylestradiol (EE2), and diethylstilbestrol (DES) in water samples were determined by dispersive liquid-liquid microextraction (DLLME) followed by high performance liquid chromatography with a photodiode array detector and a fluorescence detector (HPLC-DAD-FLD). The extraction procedure was induced by the formation of cloudy solution, which was composed of fine drops of [C6MIM][PF6] dispersed entirely into the sample solution with the help of a disperser solvent (acetone). Parameters including both extraction and disperser solvents and their volumes, extraction and centrifugal time, sample pH, and salt effect were investigated and optimized. Under the optimized conditions, 110-349 fold enrichment factors of analytes were obtained. The calibration curves were linear in the concentration range of 0.2-100 mu g L-1 for E-2, E-3, and EE2 detected with FLD, and 1-100 mu g L-1 for E-1 and DES detected with DAD. The correlation coefficient of the calibration curve was between 0.9990 and 0.9997. The limits of detection (LOD, S/N = 3) for the five estrogens were in the range of 0.08-0.5 mu g L-1. The relative standard deviations (RSD) for six replication experiments at the concentration of 5.0 mu g L-1 were <= 5.7%. The proposed method was applied to the analysis of three water samples from different sources (river water, waste water, and sea water). The relative recoveries of spiked water samples are satisfied with 89.3-102.4% and 88.7-105.2% at two different concentration levels of 5.0 and 50.0 mu g L-1, respectively.