A novel aqueous two-phase system (ATPS) can be formed by mixing a polymer and a cationic-anionic surfactant. In this work we investigated the protein partitioning in ATPS formed by mixing dodecyltriethylammonium bromide/sodium dodecylsulfate and ethylene oxide (EO)-propylene oxide (PO) random copolymers (EO~2~0PO~8~0). Affinity ligands were attached to polymers and affinity partitioning of proteins was investigated. A multi-step partitioning procedure was developed by diluting the surfactant-enriched phase or by raising the temperature of polymer-enriched phase. After partitioning was completed, the surfactants could be removed when the phases were further diluted, and EO-PO copolymers could be separated by raising the temperature above the cloud point of copolymer. The recycling of cationic-anionic surfactants and EO-PO copolymers is discussed.

Key words: PROTEIN, SURFACTANTS, BLOCK COPOLYMER, POLYETHYLENE GLYCOL