Gas Chromatographic Characterization of Silica Bonded with a Phenylpolysiloxane Film

Abstract

A method of synthesizing modified silica with a dense grafted phenylpolysiloxane layer is described. Gas chromatography at zero surface coverage has been used for investigating the adsorption properties of both modified and initial silicas. It was shown that the thermodynamic parameters for retention (retention volume, V_a; heat, q; and entropy, ΔS⁰, of adsorption) and the Kovats retention indices I for different classes of organic compounds are essentially changed with surface modification. The increase in V_a and q for n-alkanes on phenyl-bonded silica was interpreted as due to penetration of the solutes into the grafted phenylpolysiloxane layer. The significant reduction in retention parameters for all compounds capable of specific interaction, including the formation of hydrogen bonds, on the phenyl-bonded silica relative to the initial silica has allowed conclusions to be drawn regarding the weak role of residual silanol groups in the retention process. These conclusions have been confirmed by a comparison of the chromatographic properties of phenyl-bonded silica and the polymethylphenylsiloxanes OV-17 and OV-25.