Inclusion complex-based solid-phase extraction of steroidal compounds with entrapped β-cyclodextrin polymer

Although the hydrophobic interaction-based solid-phase extraction (SPE) has been widely used, the extraction yields of steroids including androgens, estrogens, and corticoids were slightly different along with the physical and chemical properties of each molecule. A new SPE technique based on the formation of an inclusion complex with β-cyclodextrin (βCD) has been achieved for comprehensive sample purification in mass spectrometric analysis of 45 endogenous or synthetic androgens, 11 endogenous estrogens, and 21 corticoids. A copolymer of βCD with epichlorohydrin was prepared by a cross-linking reaction followed by entrapment with 0.3 M CaCl₂ to yield an improved SPE sorbent and the hydrolyzed urine samples were applied for purification. Steroidal compounds tested on the entrapped βCD polymer were extracted with tetrahydrofuran and the overall recoveries ranged from 82% to 112% for 77 steroids in urine. Especially, the hydroxylated estrogens showed an excellent binding capacity (96-116% recovery) to βCD through hydrogen bonding between their phenolic hydroxyl and exterior hydroxyl groups. A comparison between SPE methods with βCD and Oasis HLB as a conventional cartridge showed that the extraction efficiency of polar steroids was significantly increased in the βCD experiment, which has no connection with different polarity of steroid molecules. Due to its multi-functional mechanism derived from molecular inclusion and chemical interactions, this new SPE sorbent resulted in better selectivity and extraction efficiency than that obtained using the conventionally used hydrophobicity-based SPE method.