Endcapping of Octadecylsilyl-Silica Gels Using Supercritical Fluid as Reaction Medium

A method for endcapping of octadecylsilyl (ODS)-silica gels was developed using supercritical carbon dioxide as a silylation medium. The effects of temperature and pressure of carbon dioxide on the deactivation of the gels were investigated under the silylation conditions at 100 - 220°C and 11.8 - 24.5 MPa. High-performance liquid chromatographic evaluation using caffeine and phenol as test compounds indicated that the most inert gels were obtained from the endcapping under 180°C and 24.5 MPa. Endcapped ODS-silica gels, which were commercially available, could be further deactivated under these conditions. The inertness of the gels was also evaluated by supercritical fluid chromatography (SFC) using pyridine and phenol as test compounds. The effectiveness of the proposed method was clearly observed in the SFC evaluation.

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