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The extraction equilibrium in the systems aqueous solution of a hydroxycarboxylic acid−solution of trialkylamine in an organic diluent can be largely modified by the nature of the diluent. Binary diluents composed of a neutral paraffinic solvent and an active modifier can be used to adjust the desired equilibrium behavior of a particular system. In the present work the equilibria in the systems aqueous solutions of citric acid−solutions of trialkylamine in binary diluents have been measured. Chloroform or methyl isobutyl ketone has been used as modifiers and n-heptane as neutral diluent. Besides these two data systems earlier data for the system with 1-octanol as modifier are also considered. Different mathematical models for correlating these data are proposed comprising specific effects of formation of various acid−amine complexes and nonspecific effects of interactions among the components of the organic phase. The optimum parameter values of the individual models are presented, and the goodness of fit of models applied to a particular system is compared. When comparing the three modifiers investigated, are found a striking difference between octanol and chloroform on one side and MIBK on the other side. Whereas the systems with the former modifiers do not show a tendency to overloading of amine, the latter system exhibits strong overloading at higher aqueous acid concentrations.

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