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

Abstract

Tetraethoxysilane (TEOS) and octyltriethoxysilane (C8-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, C8-TEOS, and the C8-TEOS/TEOS hybrid mixture were studied by 29Si and 1H NMR spectroscopy. The reaction of methyltriethoxysilane (C1-TEOS) and ethyltriethoxysilane (C2-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 C8-TEOS when each precursor reacts individually. However, the rate of hydrolysis for C8-TEOS increases when reacting in a C8-TEOS/TEOS (1:1 mole ratio) mixture, driven by the condensation of hydrolyzed TEOS...