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 t he synthesis of an organic-inorganic hybrid glass composite by the sol-gel process. This composite was used as the stationary phase for chromatographi c and electrophoretic separations when cast onto the inner walls of capilla ry columns, To investigate the reactions leading to the final chromatograph ic material, the hydrolysis and initial condensation reactions of TEOS, C-8 -TEOS, and the C-8-TEOS/TEOS hybrid mixture were studied by Si-29 and H-1 N MR spectroscopy. The reaction of methyltriethoxysilane (C-1-TEOS) and ethyl triethoxysilane (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 hydrolys is 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 max imum degree of condensation in the C-8-TEOS/TEOS reaction mixture was obser ved after 7 h of reaction. The maximum chromatographic retention on the col umns fabricated with the C-8-TEOS/TEOS sol-gel composite correlates with th e maximum degree of condensation and with a C-8-TEOS/TEOS mole ratio of 1:1 .