Adsorption Effects Observed in Gel Permeation Chromatography of Thiouracil

Abstract

In gel permeation chromatography (GPC), several compounds deviate from the molecular volume/elution count relationship which is prepared using satured hydrocarbons. In this paper, this problem is investigated in detail using thiouracil in aqueous solution as a model chromatographic adsorbate. The concentration dependences of elution counts and peak heights prove the adsorption of thiouracil on Sephadex G-25 when water is the solvent. Thus to investigate further the mechanisms of adsorption responsable for the chromatographic behaviour, thiouracil-Sephadex interac—tions were investigated by studying equilibrium adsorption. Isotherms of type IV of BDDT classification were found which are typically associated with a weak adsorption such as physisorption, on a porous solid. The effect of water structure perturbants, ionic strength and pH on this adsorption was consistent with the-hypothesis that with water as a solvent both aromatic adsorption and electrostatic interaction are the determinants of the affinity of this gel for a thiouracil compound. This may be particularly useful since results of equilibrium adsorption isotherms are frequently used to develop liquid chromatographic theories.