Clusters in a Water/ACN Mixture, with Implications for the RPLC Weak Polar Solute Retention

摘要

Recently, a model was proposed to describe the existence of pockets of ACN called clusters in an ACN/water mixture. Using this mixture as a mobile phase, a novel mathematical theory is presented to describe the variation of the retention factor, k', of alkyl benzoate esters in reversed-phase liquid chromatography. For the first time, using this model, enthalpy, entropy and the Gibbs free energy were determined for two physicochemical processes: (i) the transfer of the alkyl benzoate ester from a pureaqueous mobile phase to the stationary phase and (ii) the alkyl benzoate ester solvation by the ACN clusters. These thermodynamic data indicate that the main parameter determining retention is distribution of the alkyl benzoate esters to clusters of ACN, while the interactions with the stationary phase play a minor role.