Chemically Bonded Phase Chromatography
It is a liquid chromatography using a chemically bonded phase as a stationary phase, which is formed by chemically reacting an organic molecule to a surface of a carrier (silica gel) by a covalent bond to form a uniform, firm monolayer thin layer.
The separation mechanism is both adsorption and distribution. For most bonded phases, the distribution mechanism is dominant. Typically, the carrier of the chemically bonded phase is silica gel, and the surface of the silica gel has a silanol group, ≡Si-OH, which reacts with a suitable organic compound to obtain a chemically bonded phase of various properties.
On the surface of the silica gel, due to the steric structural disorder of the bonding groups, all 6 silanol groups per square nanometer for chemical bonding are not able to participate in the bonding reaction. The ratio of the number of silanol groups participating in the reaction to the total number of silica groups is referred to as the surface coverage of the stationary phase.
When the surface coverage of the ODS bond is 98%, that is, 2% of silanol groups remain, and the partitioning action is dominant. When the surface coverage of ODS is 50%, there is both distribution and adsorption.