Investigation of molecular dimensions of polystyrene as a function of the solvent composition: application to liquid chromatography at the exclusion-adsorption transition point

Liquid chromatography of polystyrene standards at the exclusion-adsorption transition point was undertaken with silica adsorbents of different porosity in various eluents. To better understand the elementary phenomena involved in these peculiar conditions, we have investigated by viscometry and light scattering the behavior of model polystyrene chains in solvent mixtures corresponding to the critical conditions. This study shows that the “critical conditions” can be obtained if the polymer chains enter the pores of the absorbent and also that this technique is limited to a certain molar mass range. The polarity index, P′, of the eluent, reflecting its ability to interact with the polymer chains and also with the stationary phase, is the parameter to be considered to define the characteristics of this elution mode.