Partition model applied to the retention process of basic analytes in reversed-phase and ion-pairing liquid chromatography

The partition model is applied to the liquid chromatographic separation process in order to explain the retention of dissociable basic solutes in both variants: reversed-phase mechanism and ion-pairing reversed-phase mechanism. This model takes into consideration two major parameters: the pH of the aqueous component in the mobile phase and the hydrophobicity of the analytes. According to this model a single mathematical framework can be developed in order to explain the dependence of both retention mechanisms on the experimental parameters. This framework started from the dissociation equilibria of the analytes and the distributions of the undissociated species and ion-pairs between the mobile phase and the stationary phase, seen as a continuum and homogeneous bulk due to the hydrocarbonaceous ligands. The partition model becomes useful when the retention data are extrapolated in view of estimating the octanol/water distribution coefficient, and in the case of the attempts to correct the octanol/water distribution coefficient obtained from the retention data for a better agreement with the value resulting from shake-flask experiments.