Determination of Estrogens in Water Samples by Ionic Liquid-Based Dispersive Liquid-Liquid Microextraction Combined with High Performance Liquid Chromatography

Abstract

Using 1-hexyl-3-methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]) ionic liquid as extraction solvent, five estrogens including estrone (E₁), 17β-estradiol (E₂), estriol (E₃), 17α -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 µg L⁻¹ for E₂, E₃, and EE₂ detected with FLD, and 1–100 µg L⁻¹ for E₁ 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 µg L⁻¹. The relative standard deviations (RSD) for six replication experiments at the concentration of 5.0 µg 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 µg L⁻¹, respectively.

Keywords:

• Dispersive liquid-liquid microextraction
• Estrogens
• Fluorescence detector
• Ionic liquid
• Photodiode array detector

Acknowledgments

This work was supported by the National Natural Science Foundation of China (No. 41072257, No. 401170399, No. 21001032) and Guangdong Provincial Natural Science Foundation of China (No. 8451009101001037).

Notes

^a Stir bar sorptive extraction HPLC-UV.

^b Cloud point extraction HPLC-UV.

^c Dispersive liquid–liquid microextraction method based on the solidification of a floating organic drop HPLC-UV.