in an apparatus for liquid chromatography the improvement which comprises a chromatographic column packed with a solid packing material comprising porous silica gel particles , having a specific surface area of 5 to 1500 m 2 / g , an average pore diameter of 20 to 2000 a and a crosslinked polymer selected from the group consisting of polystyrene , sulfonated polystyrene , polymethyl methacrylate and polyacrylonitrile coating the surface of the fine holes of the porous silica gel particles in an amount of 5 to 50 wt .% of the polymer to silica gel particles , wherein said crosslinked polymer does not contain any extractable polymer .