Monolithic silica columns for high-efficiency separations by high-performance liquid chromatography

Generation of a large number of theoretical plates was attempted by capillary HPLC. Monolithic silica columns having small skeletons (ca. 2 mum) and large through-pores (ca. 8 mum) were prepared by a sol-gel method in a fused-silica capillary (50 mum I.D.), and derivatized to C-18 phase by on-column reaction. High external porosity (>80%) and large through-pores resulted in high permeability (K = 1.2 X 10(-12) m(2)). The monolithic silica column in the capillary produced a plate height of about 12 mum in 80% acetonitrile at a linear velocity of 1 mm/s. Separation impedance, E value, was found to be as low as 200, that was about an order of magnitude lower than reported values for conventional columns packed with 5 mum particles. Reproducibility of preparation within 15% was obtained for column efficiency and for pressure drop. It was possible to generate 100,000 plates by using a 130-cm column at very low pressure (<7 kg /cm(2)). A considerable decrease in column efficiency was observed at high linear velocity, and for solutes with large retention factors due to the slow mobile-phase mass transfer in the large through-pores. The monolithic silica columns, however, showed performance beyond the limit of conventional particle-packed columns in HPLC under favorable conditions. (C) 2002 Elsevier Science B.V. All rights reserved.