Synthesis and characterization of new generation open tubular silica capillaries for liquid chromatography

The chromatographic performance gain of open tubular (OT) silica capillaries over packed beds has been demonstrated theoretically. However, experimental progress in the preparative realization of these columns is still lacking behind as thick films are required for a sufficient mass loadability. Here, silica sol-gel chemistry in confined spaces was applied to the preparation of thick-film OT capillaries comprising a mesoporous layer with a thickness of approximately 500 nm covalently attached to the capillary wall. Samples were synthesized varying both in length and inner diameter (ID) and the resulting layer morphology was investigated using scanning electron microscopy. The chromatographic performance of these first generation columns was evaluated by normal phase chromatography utilizing standard capillary-LC equipment. Separations of small molecules in a 15 μm ID column provided high theoretical plate numbers (up to 170,000) and a good retention capacity within reasonable retention times (<1 h), bearing the unavoidable trade-off between column efficiency and analysis time.