Performance of a monolithic silica column in a capillary under pressure-driven and electrodriven conditions

A continuous macroporous silica gel network was prepared in a fused-silica capillary and evaluated in reserved-phase liquid chromatography. Under pressure-driven conditions, the monolithic silica column derivatized to C-18 phase (100 mu m in diameter, 25 cm in length, silica skeleton size of similar to 2.2 mu m) produced plate heights of about 23 and 81 mu m at 0.5 mm/s with a pressure drop of 0.4, kg/cm(2), and at 0.5 mm/s with 3.6 kg/cm(2), respectively, in 90% acetonitrile for hexylbenzene with a k value of 0.7. The separation impedance, E, calculated for the present monolithic silica column was much smaller at a low how rate than those for particle-packed columns, although higher E values were obtained at a higher now rate. Considerable dependence of column efficiency on the linear velocity of the mobile phase was observed despite the small size of the silica skeletons. A major source of band broadening in the HPLC mode was found in the A term of the van Deemter equation. The performance of the continuous silica capillary column in the electrodriven mode was much better than that in the pressure-driven mode. Plate heights of 7-8 mu m were obtained for alkylbenzenes at 0.7-1.3 mm/s, although the electroosmotic now was slow. In HPLC and CEC mode, the dependency of plate height k values of the solutes was observed as seen in open tube chromatography presumably due to the contribution of the large through-pores. Since monolithic silica capillary columns can provide high permeability, the pressure-driven operation at a very low pressure can afford a separation speed similar to CEC at a high electric field.