Analysis of polyethoxylated surfactants in microemulsion-oil-water systems

A normal-phase method for the separation of ethylene oxide number (EON) oligomers by high performance liquid chromatography (HPLC) is described. Isocratic HPLC with mixed solvent on silica column allows to separate oligomers up to EON = 18. Gradient programming moves the limit up to EON = 20. For higher EON values (up to 50) a NH2 column has to be used, either with isocratic or gradient mode. Detection was performed using UV detector. The partition of surfactant in the oil-water system over the entire concentration range below the CMC was determined. Surfactant-oil-water systems were studied according to the unidimensional scan. The surfactant content in the oil, microemulsion and water phases was determined by HPLC. The addition of a lipophilic alcohol in a Winsor III system produced a decrease in the partition coefficient of the surfactant between the water and oil phases. (C) 2000 Elsevier Science B.V. All rights reserved.