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Abstract
Comprehensive studies have been carried out on the effect of the silica support in preparing optimized bond-phase packing for high-performance liquid chromatography. Different covalently bonded reversed-phase silica-based chromatographic materials have been investigated with respect to lingand density, residual silanol group type, and concentration. Results from diffuse-reflectance Fourier-transform infrared spectroscopy, elemental and thermogravimetric analysis, and 1H solid-state- and 29Si cross-polarization magic-angle spinning nuclear magnetic resonance techniques were combined with liquid chromatographic data to provide quantative insights regarding the properties of silica-based bonded-phase packings. We have determined that unfavorable adsorption of basic compouds and low hysdrlytic stability of alkyl bonded-phase ligands can attrilbuted to the existence of siolated, non-hydrogen-bridged, high acidic SiOH groups. Contrary to comon belief, a stable silica support with the lowest adsorptivity for basic compounds must contain the highest possible (and not the lowest) concentration of homogeneously distributed, associated or bonded SiOH groups to ensure a minium concentration of deleterious highly acidic, isolated silanols. Under these conditions, silica-based bonded-phase packings exhibit higher hydrolytic staility and a substantially lower order of adsorptivity towards basic organic compounds.
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