Ion selectivity in the high-performance cation-exchange chromatography of proteins

The effects of varying the ionic composition of some aqueous mobile phases were observed during the analysis of five proteins by gradient elution on a weak cation-exchange column, SynChropak CM 300. Changes in both selectivity and band broadening occurred when either cations or anions were varied, contrary to similar studies for small molecules. Cations generally follow the same order for retentive properties for proteins as they do for small molecules. However, anions affect the retention of proteins in an inverse order from the way they affect small molecules on anion-exchange.