A STUDY OF THE ADSORPTION ACTIVITIES OF SILANOL SURFACE-STRUCTURES ONA FUSED-SILICA MODEL SUBSTRATE BY SI-29 CP MAS NMR AND INVERSE COMBINING GAS-CHROMATOGRAPHIC DATA

The possibilities of inverse gas-solid chromatography (IGC) in obtaini ng chromatographic data on fumed silica were examined. Aerosil A-200, a fused silica model substrate in Si-29 nuclear magnetic resonance ana lysis, was trimethylsilylated to different degrees. IGC was used to ve ry reproducibly determine the free specific energies of adsorption of several functionalized probe solutes. Hydrogen bonding solutes have a free specific energy of adsorption that is at least about 50% higher t han that of non-hydrogen bonding probe solutes. NMR was used in combin ation with elemental analysis to calculate surface concentrations of t he different chemical surface structures. IGC data and surface concent rations were combined in order to determine the contribution of each t ype of surface structure to the total free specific adsorption energy. It could be concluded that residual silanols from the reaction of dih ydroxydisiloxysiloxane (Q(2) groups) with trimethylchlorosilane posses s a higher adsorption activity than the silanols initially present.