Chapter 4.4. Adsorption and partition chromatography

Abstract

Publisher Summary This chapter discusses adsorption and partition chromatography. Adsorption chromatography is based on liquid–solid partition—that is, a partition of solute molecules between the liquid mobile phase and active sites on the surface of the solid stationary phase. The solid support used is most often silica or alumina, the former being far more widely used. During the chromatographic process solute molecules are adsorbed to active sites on the support surface in competition with solvent molecules. The active sites consist of hydroxyl groups (for silica silanol groups, Si-OH) and the affinity to them is greater the more polar the molecules, and the greater their ability to form hydrogen bondings. The surface structures of different brands of silica are largely identical, and thus their selectivity towards various mixtures of solutes does not exhibit great variation. Separation by liquid–liquid partition chromatography is the result of the difference in the distribution between two immiscible liquid phases of the individual components of a mixture. The liquid stationary phase is coated on a solid support, which is ideally inert. As the support relatively large pore silica (10–50 nm pore diameter) is most often used. Coating the stationary phase onto the support may be performed in various ways. The solvent evaporation technique (as in the preparation of GC column materials) may be used, provided that the stationary phase is non-volatile and that the particle size of the support exceeds 20 μm.