Preparation of surface-coated macroporous silica (core-shell silica monolith) for HPLC separations

Utilizing the spontaneous wetting of oligomeric silica-phase via phase-separation onto a solid surface in a confined dimension, sub-micrometer thick mesoporous layers have been coated on the surface of nonporous skeletons of preformed macroporous silica gels. The size and volume of mesopores within the layers could be controlled by subsequent aging conditions similarly to those reported for fully porous monolithic silica. Comparison of HPLC efficiencies of these novel type monolithic gels, core-shell silica monoliths, with those of a conventional silica monolith revealed that the retention factor per unit surface area became larger for core-shell silica monoliths. The increase in dynamic accessibility of analyte molecules to the mesopores well explain the improved retention factors in core-shell silica monoliths. Core-shell monoliths with mesoporous layers coated on the surface of micrometer-sized fully-sintered continuous silica skeletons for HPLC separations.