Preparation And Evaluation Of A Polymer-Based Monolithic Mirco-Column With Silica-Microspheres Entrapped

Micro-column liquid chromatography (μ-LC) has been developed rapidly in recent years as a high efficient and fast separation technique because of its many advantages including simple preparation of the columns, low sample consumption and less environmental pollution.There are three major types of monoliths: organic monolithic columns, inorganic monolithic columns and organic-inorganic hybrid monolithic columns. Compared to its counterparts, organic monoliths have additional advantages including wide usable pH range and ease to control the pore structure by adjusting composition of polymerization mixture, and thus received more attention inμ-LC. However, organic monoliths often swell or shrink in some mobile phases, thus leading to degraded chromatographic performances and poor mechanical stability. This effect is more serious for large diameter monolithic columns and even the monoliths crack off from the inner walls of the capillaries. Therefore, the previous researches were almost concentrated on small diameter organic monolithic columns, and the researches on large diameter columns were almost seldom reported. Although small diameter capillary columns can reach good separation performances, they suffer from the drawbacks of low sample capacity and poor detection limits in the quantitative analysis.In the present study, a silica-microspheres-entrapped monolith was prepared in a 530μm i.d. fused silica capillary. The process of the preparation mainly involves: packing silica-microspheres, pre-vinylizing the microsphere surface and the capillary inner wall, entrapping the silica-microspheres in the organic polymer with functional monomer.The prepared monolithic capillary column was evaluated in terms of pore structure, durability to high pressures,permeability,ability in anti-swelling and column efficiency. The results show that the monolith is not only homogeneous in the distribution of the entrapped microspheres,narrower in the distribution of pore sizes,faster in mass-transfer and higher in column efficiency, but also more stable in mechanical strength and stronger in anti-swelling in some mobile phases. Finally, the prepared monolithic capillary column was applied for the determination of ofloxacin in commercial eye drops, and satisfactory results were obtained.