29-Silicon NMR evidence for the improved chromatographic siloxane bond stability of bulky alkylsilane ligands on a silica surface

A stable bond stationary phase for reversed-phase high-performance liquid chromatography, with a diisobutyl- n-octadecylsilane derivatized surface, was studied using 29Si cross-polarization magic angle spinning (CP MAS) NMR. Fumed silica surfaces (Aerosil), trimethylsilylated to different extents, w...

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Bibliographic Details
Published in:Journal of Chromatography A 1994-12, Vol.688 (1), p.25-29
Main Authors: Scholten, Alex B., de Haan, Jan W., Claessens, Henk A., van de Ven, Leo J.M., Cramers, Carel A.
Format: Article
Language:English
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Summary:A stable bond stationary phase for reversed-phase high-performance liquid chromatography, with a diisobutyl- n-octadecylsilane derivatized surface, was studied using 29Si cross-polarization magic angle spinning (CP MAS) NMR. Fumed silica surfaces (Aerosil), trimethylsilylated to different extents, were used to illustrate the effect of ligand surface loading on the hydrogen bonding contribution to the ligand silane CP MAS NMR signal. Spectral comparison of the diisobutyl- n-octadecylsilane derivatized silica with the conventional dimethyl- n-octadecylsilane derivatized silica revealed significantly decreased hydrogen bonding of residual silanols to the ligand siloxane bond in the diisobutyl- n-octadecyl phase. This illustrates the increased steric protection of the ligand siloxane bond by the bulky alkyl substituents, which is assumed to be the reason for the improved hydrolytic stability at low pH of this phase.
ISSN:0021-9673
DOI:10.1016/0021-9673(94)00928-7