Partitioning of the natural dye norbixin has been studied in aqueous two-phase system (ATPS) that are formed by mixing aqueous solutions of a polymer (or copolymer) and an organic salt (sodium tartrate or succinate). In this work, the norbixin partition coefficient (K-N) was optimized, taking into account the variables of polymer concentration, salt concentration and pH. It was found that K-N is highly dependent on the electrolyte nature, system hydrophobicity and TLL values. Testing produced K-N values between 8 and 130, indicating the great potential of ATPS as a method for norbixin pre-concentration/purification. Thermodynamic transfer parameters (Delta(tr)G, Delta H-tr, Delta S-tr) indicate that the preferential concentration of norbixin in the top phase is favored by enthalpic and entropic contributions. (c) 2012 Elsevier B.V. All rights reserved.