Si-29-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 us ed as the precursors to fabricate an organic-inorganic hybrid composite by sol-gel processing, The hydrolysis and initial condensation reactions of TE OS 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 var ious silicon species during the reaction indicate that TEOS hydrolyzes and condenses faster than C-18-TEOS, The rate of hydrolysis for C-18-TEOS, howe ver, increases when reacting in the C-18-TEOS/TEOS hybrid mixture, indicati ng that tile condensation reactions involving TEOS species drive the reacti on of C-18-TEOS. The formation of cross-condensed products leads to the com posite with octadecyl groups incorporated into the final glass material, Th e 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 c olumns were tested for open tubular capillary electrochromatography (OT-CEC ). Coating of the columns was performed after the maximum degree of condens ation was achieved, which has been shown to correlate with maximum chromato graphic retention.