Polydopamine-supported immobilization of covalent-organic framework-5 in capillary as stationary phase for electrochromatographic separation

• COF-5 was developed as a novel stationary phase for OT-CEC.
• The immobilization of COF-5 was carried out by the mussel-inspired polydopamine-supported method.
• Layer-by-layer method was used for the preparation of multilayer COF-5-coated capillary.
• The electrochromatographic performance of COF-5-coated OT column was investigated.
• The (COF-5-PDA)3@capillary exhibited excellent separation ability, high efficiency, good stability and repeatability.

Covalent-organic frameworks (COFs) are attractive materials for their fascinating properties, such as rigid structures, exceptional thermal stabilities, low densities, and permanent porosity with specific surface areas, which indicate potential for application in chromatography similar to related metal-organic frameworks (MOFs). However, the utilization of COFs in analytical chemistry is far behind as compared to that of the MOFs due to the challenging work of their immobilization. Here, we have successfully demonstrated the growth of the boron COF-5 on the inner wall of the fused silica capillary by a developed polydopamine-supported method. Combined with the layer-by-layer strategy, multilayer COF-5-coated capillary was obtained. The formation of COF-5 on polydopamine-coated substrate has been confirmed by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction. A novel stationary phase of COF-5 was developed on the basis of successful growth of COF-5 on polydopamine for open-tubular capillary electrochromatography (OT-CEC). Baseline separation of neutral, acidic and basic analytes was achieved on multilayer COF-5-coated capillary column. The fabricated capillary columns showed high column efficiency (154,060 plates/m for methylbenzene), excellent stability and repeatability. The precision (relative standard deviation (RSD), n = 3) of retention time, peak height, and peak area for tested neutral compounds were in the range of 1.2–1.3%, 1.8–4.2%, and 0.9–2.4%, respectively. To the best of our knowledge, it was the first demonstration that COF-5 was developed as a novel stationary phase.