Separation Strategy and Combination of Methods

A separation problem depends on the number and nature of components in a mixture. Obtaining a pure product from a synthetic reaction, for example, may require the removal of small amounts of a single by-product. In this situation, the problem could probably be resolved by an inexpensive method which is less time-consuming than chromatography — crystallisation etc. It may also be possible to separate a mixture by a single chromatographic step. In reality, however, the task is usually much more complex. For example, the isolation of a single bioactive compound from a plant extract containing several thousand components can be a daunting prospect and may involve many separation steps. The separation of cyanogenic constituents of Xeranthemum cylindraceum (Asteraceae) required LPLC, MPLC, HPLC, CTLC and DCCC for complete puri­fication (Schwind et al. 1990). In these cases, a combination of techniques is the best approach.