Endcapping of octadecylsilyl-silica gels using supercritical fluid as reaction medium

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