In situ immobilization of layered double hydroxides as stationary phase for capillary electrochromatography

Layered double hydroxides (LDHs) have gained much attention in absorption and extraction fields due to their special structure and properties like high porosity, large surface area and excellent anion exchange capacity. However, LDHs are rarely used in capillary electrochromatography (CEC) by date due to the lack of appropriate immobilization method. In this work, by utilizing the unique coordination bonding between metal ions on LDHs and catechol groups on polydopamine layer, a polydopamine modification method was developed for in situ immobilization of LDHs on the inner surface of fused silica capillary. The formation of CoAl-LDHs on polydopamine-immobilized capillary has been characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. The CoAl-LDHs-modified open-tubular capillary exhibited good separation performance towards neutral compounds by cation-π interaction and hydrophobic interaction. More interestingly, by virtue of the coordination interaction between metal ions on LDHs layer and phenolic hydroxyl groups, the LDHs-modified capillary has shown good separation efficiency towards various phenolic compounds. Repeatability of the column was studied, with the relative standard deviations for intra-day, inter-day and column-to-column lower than 4.3%.