The overall topic of the investigation was the sepn. of basic proteins by cation exchange displacement chromatog. For this purpose two principal column morphologies were compared for the sepn. of RNase A and a-chymotrypsinogen, two proteins found in the bovine pancreas. These were a column packed with porous particles (Macro-Prep S, 10 mm, 1000 .ANG.) and a monolithic column (UNOTM S1). Both columns are strong cation exchangers, carrying -SO3--groups linked to a hydrophilic polymer support. Poly(diallyl-dimethylammonium chloride) (PDADMAC), a linear cationic polyelectrolyte composed of 100-200 quaternary pyrrolidinium rings, was used as displacer. The steric mass action (SMA) model and, in particular, the operating regime and dynamic affinity plots were used to aid method development. To date the SMA model has been applied primarily to simulate non-linear displacement chromatog. of proteins using low molar mass displacers. Here, the model is applied to polyelectrolytes with a molar mass below 20 000 g mol-1, which corresponds to a d.p. below 125 and an av. contour length of less than 60 nm. The columns were characterized in terms of the adsorption isotherms (affinity, capacity) of the investigated proteins and the displacer. [on SciFinder (R)]