MODELING NONLINEAR ELUTION OF PROTEINS IN ION-EXCHANGE CHROMATOGRAPHY

The problem of non-linear elution of a band of protein in isocratic io n-exchange chromatography leads to a pair of coupled non-linear partia l differential equations. The equilibrium may be modeled using the Ste ric Mass Action (SMA) model of ion exchange, which treats both the sal t dependence of protein adsorption and the steric shielding present un der non-linear conditions. Neglecting axial dispersion, a model of ide al chromatography is formulated that may be solved by the method of ch aracteristics. The predictions of this relatively simple model are sho wn to agree with experimental results concerning the non-linear elutio n of cytochrome c in a strong cation-exchange column. Of particular in terest is the existence of two plateaus in the solution of this proble m for large injection volumes. While this result cannot be understood or predicted on the basis of the traditional Langmuir isotherm or othe r currently available descriptions of adsorption, the chromatographic model presented in this work makes this otherwise anomalous result cle ar. Further, the use of such a model during parameter estimation is di scussed.