TABLE OF CONTENTS The majority of applications utilizing ion exchange as a mode of chromatography are generally carried out at low to medium pressure. This approach is commonplace in the biotechnology arena where it is predominantly used for the purification of biological macromolecules such as proteins. However, it is worth summarising the high pressure application of the technique since it is particularly useful for the purification of synthetic oligonucleotides. The DNA therapeutics market is extremely buoyant at present and most pharmaceutical companies have their foot in the door or are at least collaborating with a group or company investigating oligonucleotide based drugs. The predicted market potential ranges from hundreds of kilograms to multi-tonne requirements. Therefore the subsequent growth in synthesis will be mirrored by a concurrent growth in purification developments.
Ion exchange chromatography, as the name suggests, separates molecules by taking advantage of a charge differential. There are understandably two approaches to ion exchange separations, so both cation and anion exchange stationary phases are commercially available. The stationary phases are predominantly polymer based and functionalized with acidic groups to produce cation exchange materials, or basic groups to produce anion exchangers. Cation exchange media are generally of carboxylic acid or sulfonic acid functionality to provide weak and strong cation exchangers, respectively. Conversely, the weak and strong anion exchange media are typically functionalized as tertiary or quaternary amines. Ion exchange chromatography is generally carried out in aqueous environment where the charged components of a mixture are desorbed from the stationary phase...
