Polydopamine-assisted immobilization of zeolitic imidazolate framework-8 for open-tubular capillary electrochromatography.

In this work, we developed a capillary column modified with zeolitic imidazolate framework-8 as a novel stationary phase for open-tubular capillary electrochromatography. To immobilize zeolitic imidazolate framework-8 onto the inner surface of silica capillary, a bio-inspired polydopamine functionalization was used to functionalize the capillary surface with polydopamine. First, a polydopamine layer was assembled inside the capillary. Second, due to noncovalent adsorption and covalent reaction ability, polydopamine could attract and anchor zeolitic imidazolate framework-8 onto the inner surface of capillary. It has been demonstrated that zeolitic imidazolate framework-8 was successfully grafted on the inner wall of the capillary by scanning electron microscopy, and Fourier transform infrared spectroscopy. The electro-osmotic flow characteristics of capillaries were also investigated by varying the pH value and acetonitrile content of mobile phase. The zeolitic imidazolate framework-8 coating not only increased the phase ratio of open-tubular column, but also improved the interactions between tested analytes and the stationary phase. Three groups of isomers including acidic, basic, and neutral compounds were well separated on the zeolitic imidazolate framework-8 bonded column, with theoretic plate numbers up to 1.9 × 105 N for catechol. The repeatability of the prepared columns was also studied, and the relative standard deviations for intra- and interday runs were less than 5%.