ADSORPTION, THERMOGRAVIMETRIC, AND CHROMATOGRAPHIC STUDIES OF BARE SILICAS AND SILICA-BASED OCTYL BONDED PHASES

Structural and surface properties of seven chromatographic silica gels were characterized by means of nitrogen adsorption and high-resolutio n thermogravimetry. The retention of alkyl benzenes was measured using the corresponding commercial octyl-bonded phases. The partition-displ acement model was used to evaluate the equilibrium sorption constant a nd the surface excess of acetonitrile for each octyl phase. Most of th e stationary phases studied showed similar sorption properties and, co nsequently, comparable values of the acetonitrile surface excess. Only for one of the phases studied the surface excess was much higher, and that was attributed to the difference in the silanol coverage of the stationary phase.