Chemically modified silica gels were prepared under various conditions with γ-glycidoxypropyltrimethoxysilane in order to investigate the effect of various methods of hydrolyzing the terminal epoxide group. The silylated substrates were then examined by 13C solid-state NMR with cross-polarization and magic angle spinning. NMR results were correlated with infrared results obtained by diffuse reflectance Fourier transform infrared spectroscopy. By reaction with a primary alkyl amine the percentage of unopened epoxide may be determined by Fourier transform infrared spectroscopy. Infrared data indicate that as little as 10% epoxide remaining after attempted hydrolysis can influence chromatographic capacity factors.