Study of the Chromatographic Properties of Proteins on a Silica-Based Polymeric Cation-Exchange Stationary Phase

A cation exchange stationary phase, a sulfonated copolymer from N, N' dimethylacrylamide and glycidylacrylate deposited on silica, is used for the separation of basic proteins. Their retention properties were studied from the plot of ln k' vs. ln 1/[NaCl] where k' is the retention capacity factor, and [NaCl] the displacing salt concentration in the aqueous phase. The influence of pH on protein retention was examined. According to the "net charge concept" the basic proteins are retained on the sulfonated copolymer at mobile phase pH below their isoelectric point. However a systematic deviation from this concept was observed at pH > 7 since the retention of these proteins increases with the pH of the eluent. This behavior, the influence of the amount of copolymer deposited on silica and the comparison with a non sulfonated copolymer stationary phase reveals that the residual hydroxy sites of the silica support play a role in the retention mechanism of basic proteins.