In this paper a new graphical method, derived from the Steric Mass Action model of non-linear ion-exchange chromatography, is presented for the determination of solute affinity in ion exchange displacement systems. The affinity of solutes in these systems is described by a dynamic affinity parameter which is a function of the linear steric mass action parameters of the solutes and the characteristic velocity of the displacer front. This method can be employed to determine the elution order of the feed solutes in the isotachic displacement train as well as the ability of a given molecule to act as a displacer for a given protein mixture. The ideal model of ion-exchange displacement chromatography and a transient model are employed to study selectivity reversals and resolving power in ion-exchange displacement systems. The work presented here provides a theoretical framework for studying dynamic affinity, resolving power, and displacer design for ion-exchange displacement chromatography.