The synthesis and characterization of endcapped silica hydride stationary phase

Abstract

THE SYNTHESIS AND CHARACTERIZATION OF ENDCAPPED SILICA HYDRIDE STATIONARY PHASE by Prema Gangadhara The silanization/hydrosilation process was developed to overcome some of the drawbacks associated with the use of organosilane reagents for the synthesis of high pressure liquid chromatography (HPLC) stationary phases. The first step is called silanization, in which silica or other oxides react with triethoxysilane (TES), resulting in the formation of a silica hydride surface. Endcapping the stationary phase using trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDS) eliminates the unreacted and accessible silanols on the silica hydride intermediate. This research employed the modification of bare silica to silica hydride via silanization. Endcapping after silanization eliminated accessible and unreacted silanols. Endcapping was confirmed by using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The stationary phase was characterized for its hydrophobicity and silanophilicity properties. The effectiveness of the stationary phase was determined for its aqueous normal phase and reversed-phase chromatographic behavior. The performance was compared with the performance of C8 silica hydride column under similar conditions. This research confirmed that endcapped columns could be used in the aqueous normal phase and reversed-phase modes. Endcapping increased the hydrophobicity of the surface, which in turn increased the efficiency of separation for nonpolar solutes.