coupled columns - a form of column switching. Uses a primary column connected to two secondary columns via a selector valve. Fractions from the first column can be selectively transferred to the other two columns for additional separation. Term also used to describe two or more columns connected in series to provide increased plate number.

coverage - refers to the amount of bonded phase on silica in bonded-phase chromatography. Coverage is usually described in µmole/m² or in terms of %C.

See bonding density

cross-linking - during the process of copolymerization of resins to form a three-dimensional matrix, a bifunctional monomer is added to form cross-linkages between adjacent polymer chains. The degree of cross-linking is determined by the amount of this monomer added to the reaction. For example, divinylbenzene is a typical cross-linking agent for polystyrene ion- exchange resins. The swelling and diffusion characteristics of a resin are governed by its degree of cross-linking.

See polyme-based adsorbents.

cyano phase - a stationary phase that usually consists of cyanopropylsilyl groups; used in both normal and reversed-phase chromatography.

See cyano-phase.