ACN CLUSTERS IN A WATER ACN MIXTURE, WITH IMPLICATIONS FOR THE RPLC WEAK POLAR SOLUTE RETENTION/

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 re versed-phase liquid chromatography. For the first time, using this mod el, enthalpy, entropy and the Gibbs free energy were determined for tw o physicochemical processes: (i) the transfer of the alkyl benzoate es ter from a pure aqueous mobile phase to the stationary phase and (ii) the alkyl benzoate ester solvation by the ACN clusters. These thermody namic data indicate that the main parameter determining retention is d istribution of the alkyl benzoate esters to clusters of ACN, while the interactions with the stationary phase play a minor role.