Modeling of ion-exclusion and vacancy ion-exclusion chromatography on a strongly acidic cation-exchange resin in the H+ form

Ion-exclusion chromatography (IEC) can sometimes be used for se-paration of the weak acids using pure water as mobile phase. Characteristic leading (i.e. frontally tailing) peaks are obtained and retention depends on the concentration of solutes. It was recently shown that this order could be reversed. In vacant ion exclusion chromatography (vIEC) sample flows as mobile phase and pure water is injected as the sample. Symmetrical peaks are obtained; this is believed to be because of self-buffering of the solutes in the sample. The aim of the work discussed in this paper was to describe the mechanism of retention in IEC and vIEC by using the modified equi-librium–dispersive (ED) model. It was found that the retention times and peak shapes predicted by the derived equations are in good agreement with experimental data. These equations also predict new features of vIEC, and these were confirmed experimentally. It was shown that in vIEC, in con-trast with IEC, symmetrical peaks are obtained even for a single analyte.