Overview

The most commonly utilized modes of chromatography employed preparatively at high pressure will be summarized in this chapter. The mode of chromatography is defined by the mechanism of interaction between the analyte and the stationary phase. Over one hundred years ago Mikhail Tswett ^[3.1] discovered that differing solvents selectively desorbed pigments from the leaves of plants. Contrary to the common belief that different pigments were soluble in different solvents, he correctly deduced that the selective desorption was due to variation in the interaction of the carotenoids with the cellulose based substrate of the leaves. To demonstrate his theory, Tswett logically chose filter paper as his stationary phase and this hydrophilic interaction between analyte and stationary phase is what we now refer to as Normal Phase Chromatography .

Before proceeding with a discussion on the individual modes of separation it is worth reviewing a brief glossary of terms in association with the stationary phase properties. A simple strategy for selection of the stationary phase will naturally follow, in order to help the reader to choose a supplier wisely.

There are two main classes of polymeric support utilized in the preparation of stationary phases for all modes of chromatography, namely silica and polystyrene-divinylbenzene copolymer. For simplicity, from this point on, the former will be referred to as silica and the latter class as polymeric.