Porous silica microsphere column packings for high-speed liquid—liquid chromatography

Abstract

A new column packing for high-performance liquid chromatography, porous microspheres of silica produced by the agglutination of colloidal silica particles, has recently been introduced for use in adsorption chromatography. The narrow-size range, relatively homogeneous pore structure and short diffusion path lengths of these <10-μ particles result in very high column efficiencies, and the relatively large, highly available surface area provides for high sample capacity. The microsphere packing displays retention and efficiency characteristics which are less dependent on water content than wide-pore silica gel. Columns of the microspheres may be prepared which are reproducible in chromatographic performance, using a simple high-pressure slurry-packing procedure. More than 10,000 theoretical plates have been obtained on a single 25-cm-long column of 5-μ microspheres at carrier velocities of about 0.7 cm/sec. Plate heights of about five particle diameters and more than thirty-six effective plates/sec have been demonstrated for solutes with capacity factors ( k′) in the 2–5 range. These columns may be connected in series using low-volume fittings with little loss in efficiency. Columns of the 5-μ particles appear to be limited by mobile phase mass transfer effects, contrasted to the stagnant mobile phase mass transfer limitations exhibited by similar 8- to 9-μ particles.