Ion-exchange Chromatography:
In this case, column packings have charge bearing functional groups attached to a polymer matrix. The functional groups are eternally bonded ionic groups associated with counterions of the opposite charge. Some ion-exchange packings bear negatively charged groups and are used for exchanging cationic species whereas others are designed for exchanging anionic species. Similarly, some functional groups such as -COOH or -PO32- have weak acidic or basic properties whereas some others have considerable affinity for heavy metal cations. Several structural types of packings, as shown in Fig. 8.9, have been used in ion-exchange HPLC.
Of these, the pellicular type consists of a resin coating, about 1-2 µm thick, on a glass bead of 30-40 µm diameter. The Superficially porous resins are acquired by coating glass beads with a thin layer of silica microspheres on which ion exchanger is bonded. This raises the interface among the resin and mobile phase. Either type of these packings has low exchange capacity, 0.01 - 0.1 meq/g. The exchanger may also be bonded to silica microparticles by means of silylation reactions or polymerized into pores of a superficially porous silica gel.