In situ synthesis of the imine-based covalent organic framework LZU1 on the inner walls of capillaries for electrochromatographic separation of nonsteroidal drugs and amino acids

The covalent organic framework LZU1 (Lan Zhou University-1) is one of the imine-based covalent organic frameworks (COFs) that possesses attractive properties such as structural regularity, stability and good porosity. This work reports on the in-situ synthesis of COF-LZU1 on the inner walls of capillary column for open-tubular capillary electrochromatography (OT-CEC). The fused-silica capillary was first modified with 3-aminopropyltriethoxysilane and glutaraldehyde. Epitaxial growth of COF-LZU1 on the inner walls was accomplished by Schiff base reaction. The formation of COF-LZU1 was confirmed by SEM and FT-IR. The COF-LZU1 coating increases the interactions between analytes and coating, which remarkably improves the CEC separation selectivity of neutral analytes, amino acids and nonsteroidal anti-inflammatory drugs. The COF-LZU1-modified column exhibits good stability and repeatability. The precisions (relative standard deviations) for intra-day, inter-day and column-to column are <1.6%, 5.6% and 6.8%, respectively. Hence, the imine-based COFs represent attractive stationary phase for application in CEC separations.