This study has implemented and calibrated a model that describes the separation of the monomer of monoclonal antibodies from the dimer and larger oligomers on preparative-scale using cation-exchange chromatography. A general rate model with temperature dependent diffusion was coupled to a pH- and temperature-dependent steric mass action model. The model was shown to predict the retention of the monomer, dimer, and oligomer at low loadings for different pH levels and temperatures. Additionally, the model was shown to adequately predict the elution behavior of the monomer and soluble aggregates at high loadings within the same ranges with some limitations. The model was not able to accurately describe the shape of the product break-through curves or the slight levels of co-elution of the dimer and oligomer with the monomer at higher pH. The model was used to predict how 12 process variations impact the separation. The model is used to establish an elution end collection criterion such that the step can robustly provide the target purity of monomers.