A quantitative relationship between the affinity of component to adsorbent in liquid–solid system, βa, and composition of bulk solution

Based on the stoichiometric displacement theory for adsorption (SDT-A) of solute, an equation expressing the linear relationship between the affinity of component to adsorbent, βa, and the logarithm of the molar concentration of solvent in the bulk solution, log aD, was derived. The derived equation was tested by the derivatives of benzene under different methanol concentrations by frontal analysis (FA) of reversed-phase liquid chromatography (RPLC). A satisfactory result was obtained. Moreover, the n and q terms’ values (moles of the solvent separately released from the adsorbent and solute, respectively, as 1 mol of solute is adsorbed) which are summed in the stoichiometric parameter Z (Z=n+q), are very useful but hard to obtain only by RPLC alone. However, both were obtained from this relationship and tested with the presented method. It was also examined by the combination of the SDT-A with stoichiometric displacement theory for retention (SDT-R). Both n and q were further validated to follow the homologue rule. More solvent was released by adsorbent than by solute (n>q) and the fraction of solvent released by the adsorbent increased when the group attached to benzene was nonpolar.