Theoretical evaluation of K-p in size-exclusion chromatography from a thermodynamic viewpoint

The Flory-Huggins formalism developed for a ternary solvent(1)-polymer(2)-p olymer(3) system has been used to evaluate the binary and ternary interacti on functions. The raw data are the two-phase equilibrium compositions of th e three components determined by liquid chromatography. These interaction f unctions have been used to evaluate theoretically the distribution coeffici ent of solute-gel interactions in size exclusion chromatography (SEC), K-p. For a system solvent(1)-polymer(2)-gel matrix(3), a new expression for Kp has been obtained from a thermodynamic point of view. The proposed equation is a function of the fraction of gel matrix in the ternary phase, of the m olar volumes of solvent and polymer and of the binary and ternary interacti on functions. For the systems studied, values of K-p higher and lower than unity have been obtained at different hydrodynamic volumes which evidences the existence of secondary mechanisms. These calculations lead to a better understanding of the separation mechanism in chromatographic experiments.