Modeling ion-exchange adsorption of proteins in a spherical particle

This paper presents a simple model of single- and multicomponent protein adsorption in a spherical particle. The model includes radial diffusion of salt and protein in the liquid phase coupled to adsorption by an ion-exchange mechanism described by the steric mass action isotherm. The molecular diffusivities of the protein and salt are reduced in the model by a factor which accounts for the tortuous nature of the pores and pore constrictions. The model parameters are selected from published values in the chromatographic literature. Of particular interest are the observations of induced salt gradients during protein adsorption and of multicomponent displacement when more that one protein is adsorbed simultaneously. These results cannot be predicted on the basis of the traditional Langmuir isotherm or other currently available descriptions of adsorption. The use of such a model during stationary phase design is discussed.