A simplified design model for a chromatographic ion exclusion column is developed in which the flxed bed of resin is dividl~d into a number of perfectly mixed equilibrium stages and the liquid Aow rate is constant. The model is represented by the following dimensionless differential equation which results from the combination of a material balance about the rth stage and a second-degree phase equilibrium relationship: ( 1 /h}(f, - 1/;,-1l + K (clf,/dT) + M>/;, (df,/dT) = 0, where K and Mare dimensionless groups while 1 /his the number of equilibrium stages. 1/; and T are dimensionless concentration and time, respectively. The numerical solutions of this E~quation for single, square wave inputs are presented for different values of the dimension· less groups, feed volumes, and number of stages. The resulting calculated elution curves and experimentally determined curves are compared. Design applications are discussed.