The derivatization of azlactone-functional beads with small amine-functional ligands was studied with the objective of controlling coupled ligand density. When weakly acidic or weakly basic ligands were coupled in the presence of quenchers, ligand density was readily and reproducibly controlled by the molar ratio of ligand to quencher in the coupling solution. In addition, protein ion exchange capacities were linearly related to coupled ligand densities as well as to molar ratios, even at densities where multiple ionic interactions with the protein were to be expected. These results attest to the versatility of this coupling chemistry and may have broad application for the preparation of derivatized supports useful for large-scale protein separations.