PH-gradient ion-exchange chromatography: An analytical tool for design and optimization of protein separations

Abstract

This work demonstrates that a highly linear, controllable and wide-ranged pH-gradient can be generated through an ion-exchange chromatography (IEC) column. Such a pH-gradient anion-exchange chromatography was evaluated with 17 model proteins and found that acidic (p I < 6) and basic (p I > 8) proteins elute roughly at their p I, whereas neutral proteins (p I 6–8) elute at pH 8–9 regardless their p I values. Because of the flat nature of protein titration curves from pH ∼6 to ∼9, neutral proteins indeed exhibit nearly zero net charge at pH ∼9. The elution-pH in pH-gradient IEC or the titration curve, but not the p I, was identified as the key parameter for pH optimization of preparative IEC in a fast and rational way. The pH-gradient IEC was also applied and found to be an excellent analytical tool for the fractionation of crude protein mixtures.