Effect of skeleton size on the performance of octadecylsilylated continuous porous silica columns in reversed-phase liquid chromatography

We prepared continuous porous silica rods that had silica skeletons with sizes of 1.0-1.7 mu m and through-pores of 1.5-1.8 mu m, and evaluated their performance as a column in reversed-phase liquid chromatography. The mesoporous silica monoliths (mesopore size: 14 or 24 nm) were derivatized to C-18 phase by on-column reaction with octadecyldimethyl-N,N-diethylaminosilane. The C-18 silica rods gave minimum plate heights of 10-15 mu m for aromatic hydrocarbons in 80% methanol and of 20-30 mu m for insulin in acetonitrile-water mixtures in the presence of trifluoroacetic acid. The performance of the silica rods at a high flow-rate was much better than that of conventional columns packed with 5 mu m C-18 silica particles with pores of 12 or 30 nm, especially for high-molecular-mass species. Silica rods with the smaller sized silica skeletons resulted in Van Deemter plots showing a minimum plate height at the higher linear velocity of the mobile phase and a smaller dependence of plate height on the linear velocity. Separation impedance of less than 1000 was achieved with the continuous silica columns. The higher performance and lower pressure drop of silica rods at high flow-rates compared with particle-packed columns is provided by the small silica skeletons and large through-pores.