Analyte-stationary phase interactions in ion-exclusion chromatography

The currently accepted analyte-stationary phase interactions occurring in ion-exclusion chromatography are re-examined. In particular, the requirement for the existence of a Donnan membrane separating the flowing, interstitial eluent from the static, occluded, liquid acting as the stationary phase is scrutinized, together with the role of hydrophobic adsorption effects in the retention of aromatic analytes. Plots showing the interconversion of the column between the analyte and eluent forms are used to highlight some shortcomings of the currently accepted mechanism for ion-exclusion chromatography. An alternative retention mechanism for ion-exclusion chromatography is proposed, based on the presence of a potential well at the surface of the fully functionalized styrene-divinylbenzene co-polymer stationary phase. Analytes diffuse into the potential well under the effects of concentration gradients, and undergo repulsion effects from the fixed charges inside the pores. The net contributions of these two opposing processes determine the degree to which an analyte is retained on the stationary phase. Negligible hydrophobic adsorption of the analyte onto the polymeric resin supporting the stationary phase is considered to occur.