Chromatofocusing is a protein-separation technique that allows resolution of single proteins and other ampholytes from a complex mixture according to differences in their isoelectric point.
[1] Chromatofocusing uses ion exchange resins and is typically performed on fast protein liquid chromatography (FPLC) or similar equipment capable of producing continuous buffer gradients, though this is not a requirement.
This changes the net surface charge of bound molecules, altering their avidity for the resin.
Chromatofocusing is a powerful purification technique with respect to proteins as it can resolve very similar species differing by less than 0.05 pH units[2] that may not separate well, or at all, using traditional ion exchange strategies.
A major drawback to this technique is that some proteins will aggregate when they are present at relatively high concentrations and carry no net surface charge.