Abstract: An analytical method, carbon nanotubes assisted solid-phase extraction combined with dispersive liquid-liquid microextration based on solidification of floating organic droplet(SPE/CNT-DLLME/SFO), was developed to determine estriol(E3), bisphenol A(BPA), 17α-ethinyl estradiol(EE2) and 17β-estradiol(E2) in aqueous samples. Both solid-phase extraction and dispersive liquid-liquid microextraction were investigated and optimized using central composite design, and the optimized conditions were obtained as follow: carbon nanotubes 30 mg, water sample 210 mL, flow rate of water sample 2.0 mL/min, extractant volume(dodecanol) 50 μL, dispersant(methanol) volume 0.2 mL, and without the addition of salts. Under the selected extraction conditions, linearity range of this established method were in the range of 0.05-100 μg/L for E3 and BPA, 0.05-50 μg/L for EE2 and E2, and the correlation coefficients (R²) were 0.9993-0.9999. The limits of detection were ranged from 3.3 to 48.4 ng/L. The recoveries of estrogens under different spiked levels (0.40 and 4.00 μg/L) for E3, BPA, EE2 and E2 were 107.5%-120.8%, 92.5%-108.3%, 103.5%-121.0% and 102.5%-132.5%, and the relative deviations were 2.47%-13.28%, 1.73%-11.94%, 1.72%-8.36% and 3.54%-11.95%, respectively. The average of enrichment factor for E3, BPA, EE2 and E2 were 461, 1075, 2074 and 949, respectively. Additionally, the established method could be applied to the analysis of estrogenic hormones in water samples collected from tap water, barrel-drain and commercial mineral water. Though it needs long time for solid phase extraction and large volume sample, compared with some other methods, the present method has many advantages such as low limit of detection which is on the same level as GC/MS(gas chromatography/mass spectrometry), high enrichment factor, simplicity of operation, low cost, and therefore it is an alternative method that could be widely used for the analysis of trace level of environmental estrogens.

Key words: Carbon nanotube, Solid-phase extraction-dispersive liquid-liquid microextraction, Environmental estrogen, High performance liquid chromatography, Trace analysis