Nonionic surfactants display different behaviors in aqueous solution, depending on their concentration and the presence of small amounts of salts and/or ionic surfactants. Here, cloud point values of the aqueous two-phase micellar system formed by the nonionic surfactant Triton X-114 were determined in water and in McIlvaine buffer (pH 6.5), either in the presence or absence of various salts at different concentrations. The presence of salts lowered the cloud point values according to the sequence: 0.25 M MgSO4 center dot 7H(2)O > 0.5 M NaCl > 0.05 M MgSO4 center dot 7H2O approximate to 0.5 M CaCl2 center dot 2H(2)O approximate to 0.1 M NaCl > 0.1 M CaCl2 center dot 2H(2)O. These results demonstrate that the presence of electrolytes influences the cloud point of Triton X-114 system and that knowledge of this parameter is paramount before starting partitioning studies. (C) 2013 Elsevier B.V. All rights reserved.