Molecularly imprinted hollow spheres for the solid phase extraction of estrogens

Solid phase extraction (SPE) is widely used in many different areas, such as environmental, biological, and food analysis, where cleaning and pre-concentration of samples are key steps in the analytical protocol. New materials have significant impact on the development of solid phase extraction. In this paper, mono-dispersed molecularly imprinted hollow spheres (MIHSs) of β-estradiol (E2) were synthesized using silica nanospheres particles as the sacrificial matrix. Compared to the corresponding non-imprinted hollow spheres (NIHSs), the MIHSs with uniform size of 290 nm have outstanding affinity in aqueous solution. Static saturation adsorption required only 15 min to achieve equilibrium, with a binding capacity (Q_max) of 44.5 μmol g^-1. The extraction of E2, ethinyl estradiol (EE), diethylstilbestrol (DES), ethisterone (ES) and estrone (E1) from water samples by MIHSs was also investigated. In the spiked samples of tap water, Qinghe river water and Zhanjiang river water, more than 90.42% of E2, but less than 79% of EE, DES, ES and E1 were recovered. The limits of detection (LOD) ranged from 0.1 to 0.26 μmol L^-1 after solid phase extraction by MIHSs and HPLC-UV analysis. The adsorption capacity of the MIHSs showed no significant deterioration after six rounds of regeneration.