Study of the Solution in the Synthesis of a Sol−Gel Composite Used as a Chromatographic Phase

Tetraethoxysilane (TEOS) and octyltriethoxysilane (C 8 -TEOS) were used in the synthesis of an organic−inorganic hybrid glass composite by the sol−gel process. This composite was used as the stationary phase for chromatographic and electrophoretic separations when cast onto the inner walls of capillary columns. To investigate the reactions leading to the final chromatographic material, the hydrolysis and initial condensation reactions of TEOS, C 8 -TEOS, and the C 8 -TEOS/TEOS hybrid mixture were studied by 29 Si and 1 H NMR spectroscopy. The reaction of methyltriethoxysilane (C 1 -TEOS) and ethyltriethoxysilane (C 2 -TEOS) were also followed for comparison purposes. The formation of the various silicon species and the degree of substitution on the Si atom in the reactions revealed that TEOS hydrolyzes faster than C 8 -TEOS when each precursor reacts individually. However, the rate of hydrolysis for C 8 -TEOS increases when reacting in a C 8 -TEOS/TEOS (1:1 mole ratio) mixture, driven by the condensation of hydrolyzed TEOS species with those of C 8 -TEOS. The rate of hydrolysis for alkyl-monosubstituted alkoxysilanes and TEOS followed the trend C 1 -TEOS > C 2 -TEOS > TEOS > C 8 -TEOS. The maximum degree of condensation in the C 8 -TEOS/TEOS reaction mixture was observed after 7 h of reaction. The maximum chromatographic retention on the columns fabricated with the C 8 -TEOS/TEOS sol−gel composite correlates with the maximum degree of condensation and with a C 8 -TEOS/TEOS mole ratio of 1:1.