Studies of Siloxane Phases Bonded to Silica Gel for Use in High Performance Liquid Chromatography

Abstract

Stable siloxane phases were chemically bonded to totally porous and porous layer bead silica gels of different particle diameters and surface areas using one step and multistep silylation reactions. Direct one-step reaction between organosilane and silica without intentional polymerization was found to be the optimum and most reproducible bonding technique. Use of 10-µm silica as the base material gave the best chromatographic efficiency. Both non-polar silanes and ones containing polar functional groups were bonded successfully. For high surface area silica, bonded phase coverages depended on the organosilane reactant and varied from 7 to 17 weight percent. Infrared spectra of micropellets prepared from bonded and unbonded silica were consistent with the above coverages and revealed that residual silanols remained, even after multistep silylation. Isocratic and gradient elution experiments with polar phases showed interesting correlations between bonded phase functionality and chromatographic retention with useful differences in selectivity. Bonded phases containing basic functional groups, such as amino, diamino and pyridyl showed the most selective interactions with polar solutes. In reverse phase chromatography, phases containing longer side chains of n-dodecyl or n-octadecyl silanes gave greater retention and selectivity than did n-hexylsilane.