ABSTRACT
Perhaps the most promising alternative to Reversed-phase chromatography (RPC) for peptide work is ion-exchange chromatography (IEC). The most commonly-encountered Strong cation-exchange (SCX) packings for high-performance liquid chromatography contain sulfopropyl-groups. Anion-exchange chromatography has been used for acidic peptides and cation-exchange chromatography for basic ones, generally involving salt gradients at a pH near neutrality. For cation-exchange chromatography at pH 3, weak cation-exchange columns are not suitable since the functional carboxyl- groups are predominantly uncharged at pH 3. In contrast, adsorption in SCX chromatography is effected by the relatively small number of basic residues. The hydrophilic interactions dominate the chromatography at levels of acetonitrile above 70%; electrostatic effects become secondary under these conditions. At high levels of organic solvent, it functions in a Hydrophilic Interaction Chromatography mode, sensitive to the composition of all the amino acids in a peptide but in the opposite sense from RPC. This new mode of chromatography can effect separations not possible with RPC or SCX.
