The role of ph of the mobile-phase in ion-interaction RP-HPLC

The dependence of retention on pH of the mobile phase is investigated in reversed-phase ion interaction chromatography, being the mobile phase an aqueous solution of 5.0 mM octylammonium and ortho-phosphoric acid at different pH values. The analytes considered were amines, diamines, amides, and species characterized by different functionalities. The behaviour of retention as a function of pH is discussed with comparison with literature data and correlation with pk_a values is shown. The optimization of separation and resolution in a mixture of acids and amines through pH variations is also presented.