29Si-NMR studies of the sol-gel hybrid solution containing octadecyltriethoxysilane and tetraethoxysilane used to fabricate a stationary phase for open tubular capillary electrochromatography

n-Octadecyltriethoxysilane (C-18-TEOS) and tetraethoxysilane (TEOS! were used as the precursors to fabricate an organic-inorganic hybrid composite by sol-gel processing, The hydrolysis and initial condensation reactions of TEOS and C-18-TEOS/TEOS mixtures were studied be Si-29-NMR spectroscopy. The rate of disappearance of the silane precursors and the evolution of the various silicon species during the reaction indicate that TEOS hydrolyzes and condenses faster than C-18-TEOS, The rate of hydrolysis for C-18-TEOS, however, increases when reacting in the C-18-TEOS/TEOS hybrid mixture, indicating that the condensation reactions involving TEOS species drive the reaction of C-18-TEOS. The formation of cross-condensed products leads to the composite with octadecyl groups incorporated into the final glass material, The maximum degree of condensation in the C-18-TEOS/TEOS mixture was observed after 2 h of reaction. Fused-silica capillary columns were coated with the C-18-TEOS/TEOS mixture while in its liquid-like stage. After drying, the columns were tested for open tubular capillary electrochromatography (OT-CEC). Coating of the columns was performed after the maximum degree of condensation was achieved, which has been shown to correlate with maximum chromatographic retention.