The influence of adsorption of two widely used surfactants, octylphenol decaethylene glycol ether (Triton X–100) and cetyl trimethyl ammonium bromide (CTAB) on the interfacial tension of a recommended system for liquid–liquid extraction investigations, toluene + water, at 25.0 °C is studied. The drop–weight method has been used to measure the interfacial tension. Based on generated data and in agreement with the Szyszkowski equation, a higher adsorption tendency is appropriate for Triton, compared with CTAB. The influence of CTAB in lowering interfacial tension is enhanced significantly by introducing low dosages of Triton and significant synergism is achieved for its bulk mole fractions of more than 0.30. From non–ideal binary mixtures theory, interfacial composition and attractive interaction parameters are obtained. Accordingly, the attractive interaction parameter finds its maximum absolute value at nearly equal molar bulk concentration of surfactants, for which the maximum level of synergism is also appropriate. The highest revealed degree of synergism (40.6%) is appropriate to the lowest investigated interfacial tension value. The results help to find condition to enhance mass transfer in liquid-liquid extraction process.
