Topics - Spherical silica
There are two types of silica gel employed in chromatography either as a stationary phase per se
or for the production of bonded phases. The two forms are irregular silica
and spherical silica
. Irregular silica packing is obtained by grinding and grading amorphous silica to the required particle size. Spherical silica can be prepared by two basic methods. It can be prepared by spraying a neutralized silicate solution (a colloidal silica sol) into fine droplets before gelling has taken place and subsequently drying the droplets in a stream of hot air. The second method is to disperse a silica sol in the form of an emulsion (containing spherical droplets of silica sol) in an appropriate organic solvent and allowing the silica sol to gel (sometimes catalytically promoted by hydrochloric acid or some other catalyst). Spherical silica particles are claimed to give better columns than irregular silica particles but this will depnd very much on the packing procedure employed.