Preparation and chromatographic performance evaluation of cucurbit[7]uril immobilized silica

Cucurbit[7]uril (CB7), one host macromolecule, possesses a hydrophobic inner cavity and two identical hydrophilic carbonyl fringe portals, thus interacting with a variety of guest molecules through hydrophobic, hydrogen bonding and ion-dipole interactions. These characteristics make CB7 a good candidate as the stationary phase (SP) modifier in high performance liquid chromatography (HPLC). In the present work, CB7 was immobilized onto silica (CB7-SiO2) by a sol-gel approach. The obtained CB7-SiO2 was characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis and elemental analysis. The chromatographic performance of CB7-SiO2 was then studied in detail, in both reversed phase (RP) and hydrophilic interaction liquid chromatographic (HILIC) modes. For probe aromatic compounds and dyes, the typical RP behavior was observed, mainly due to the predominant hydrophobic interaction between the analytes and CB7-SiO2. For probe alkaloids, the "U-shape" curves were obtained; in the methanol-rich part, HILIC performance was obvious, probably owing to hydrogen bonding and ion-dipole interactions. Compared to bare SiO2 SP, the stronger retention and different selectivity were observed on CB7-SiO2. The CB7-SiO2 SP remained stable within at least 11,000 column volumes of the MP, revealing the satisfactory stability of it. The proposed method integrated the advantages of CB7 and sol-gel method provided a feasible way for the wider application of CBs in separation science.