Non-exclusion phenomena in size exclusion chromatography with inorganic porous packing: a thermodynamic treatment

Abstract

Diverse theoretical expressions have been used to describe the deviations in solute retention in size exclusion chromatography (s.e.c.) with mixed eluents. Most of them are based on the Flory-Huggins (FH) thermodynamic model of polymer solutions. Recently, and using a modified FH theory, we have calculated distribution coefficients K p, in s.e.c. with organic packings. A thermodynamic extension of FH formalism to a rigid gel (i.e. silica-based) in a binary solvent has allowed us to describe the elution mechanisms of a polymer molecule in these systems. The approach used is based on the determination of the polymer concentration ratio between the mobile and quasi-stationary phases, taking into account exclusively FH binary interaction parameters between polymer solute and two components of the eluent. The contribution of preferential solvation of the polymer at a given solvent (eluent) composition has also been analysed. This assumption has been verified using chromatographic data of different polystyrene standards in benzene-methanol, butanone-heptane and carbon tetrachloride-methanol on Spherosil as column packing. Assuming a cylindrical profile for the pores and considering the influence of the preferential solvation of the polymer in each phase, a good correlation between experimental and predicted values of K p has been obtained.