In an affinity-type purification, ligands dissociated from the stationary phase that would otherwise leach into the species being purified are captured by a second ligand that is also incorporated into the stationary phase, the second ligand exhibiting an affinity-type interaction with the dissociated first ligand with sufficient specificity to avoid the undesired retention by the second ligand of species from the liquid sample or source liquid other than the species sought to be purified in the affinity column.