This work presents a general rate model for ion-exchange in column chromatography with the steric massaction isotherm that is suitable for ion-exchange systems involving macromolecules such as large proteins. This comprehensive model considers axial dispersion, interfacial film mass transfer between the bulk-fluid phase and the particle phase, and intraparticle diffusion. The model system has been solved numerically using the finite element method and the orthogonal collocation method with a graphical user interface for Windows based personal computers. The effect of pH is modeled by including buffers, acids, and bases as species in the model system, allowing the induced pH gradients resulted from H + or OH -sorption by the ion exchanger to be described in the model. Feed profiles of all the species can be specified individually allowing complicated gradient patterns. The software, known as Chromulator-IEX, may be a useful tool for the investigation of ion-exchange chromatography behavior and its scale-up.