The partitioning behavior of the [Fe(CN)(5)(NO)](2-) and [Fe(CN)(6)](3-) anions were studied in aqueous two-phase systems (ATPS) formed by potassium phosphate and macromolecules-poly(ethylene oxide) (1500 g mol(-1)) and triblock copolymers, PEO-PPO-PEO, where PEO and PPO are poly(ethylene oxide) and poly(propylene oxide), respectively. Two copolymers with different hydrophobicity were used, L35 (50% EO and 1900 g mol(-1)) and F68 (80% EO and 8400 g mol(-1)). The partition coefficient for the [Fe(CN)(5)(NO)](2-) and [Fe(CN)(6)](3-) anions in each ATPS were investigated as a function of the temperature, tie-line length and phases hydrophobicity. The relative order of the partition coefficient is L35 < F68 < PEO for the anions. Upon increasing the temperature, the partition coefficient of the both anions decreased, indicating an exothermic process in the partitioning. The thermodynamic parameters obtained for Van't Hoff equation and calorimetric measurements shows that the transfer of anions to the top phase is enthalpic driven. (c) 2007 Elsevier B.V. All rights reserved.