What is the best method to remove 2,3-diphosphoglycerate from hemoglobin?

We have compared the efficiency of four methods to remove 2,3-diphosphoglycerate (DPG) from hemoglobin (Hb), comprising dialysis, repeated ultrafiltration, gel filtration, and ion-exchange chromatography. All the methods eventually yielded hemoglobin solutions with a ratio of <0.002 mol of DPG/mol of Hb₄ and identical oxygen-binding properties but differed with respect to duration and versatility. Considering these factors, we found the combination of an ion-retardation resin and a mixed-bed resin to be most satisfactory.