chromatofocusing

"a form of ion-exchange chromatography in which a resin is equilibrated at one pH and eluted at a second pH. The use of a weak ion-exchange resin causes a pH gradient to be formed at the solvent front owing to the buffering action of the resin. This pH gradient in turn leads to an ordering of proteins by isoelectric point. Molecules of charge sign opposite the resin bind; those of charge sign like the resin do not bind. For best resolution, the equilibration-buffer pH and the elution-buffer pH should bracket the pI of the product protein" (2).