Determination of Estrogens in Human Urine by Vortex-Assisted Dispersive Liquid–Liquid Microextraction Based on Floating Organic Acid Droplet Combined with High-Performance Liquid Chromatography-Fluorescence Detection

A novel vortex-assisted dispersive liquid–liquid microextraction method based on floating organic acid (VA-DLLME-FOA) droplet combined with high-performance liquid chromatography-fluorescence detection was successfully developed for extraction and preconcentration of three estrogens (estriol (E3), 17β-estradiol (βE2), and estrone (E1)) in human urine. In this method, estrogens were extracted into fine droplets of nonanoic acid, which floated on the top of the sample solution. Vortex-mix instead of organic dispersive solvent was applied to assist the dispersion of the extraction solvent into aqueous samples; due to the elimination of dispersive solvent, high extraction efficiency and enrichment factor could be achieved. Factors affecting VA-DLLME-FOA (type and volume of the extraction solvent, sample pH, vortex-mix time, and centrifugation) were optimized. The relative standard deviations (RSD%, n = 5) were 1.56–2.98% and the limits of detection were 0.01 ng mL−1 for E3, 0.01 ng mL−1 for βE2, and 0.06 ng mL−1 for E1. Recoveries of the estrogens in spiked human urine samples were in the range of 96.8–102.3%. The results showed that VA-DLLME-FOA was a simple, sensitive, low-cost, minimum organic solvent consumption and efficient analytical method for the separation and determination of estrogens in human urine samples.