The most commonly used packing in liquid chromatography. It has an amorphous structure, is porous, and consists of siloxane and silanol groups. It is used as a bare packing for adsorption, as the suppon in liquid-liquid chromatography or for chemically bonded phases, and. with various pore sizes as packing in size-exclusion chromatography. Microparticulate silicas of 5- and 10-mym average particle diameter are used in HPLC.