Hydrophobic-dispersive partition coefficient in alkyl-bonded reversed-phase systems with water—methanol mobile phases

Abstract

Based on a recently proposed model of monomeric alkyl-bonded silica, the hydrophobic-dispersive partition coefficient is considered as a complex function of the polarity of the solute and of its molecular geometry, of the eluent composition and of the amount of the alkyl ligates bonded. An equation for the coefficient is derived by following the thermodynamic approach and using the solubility parameter concept; it involves energy terms reflecting the solute interactions with the reversed-phase system. A variety of experimental data is used for evaluation of the enthalpy effects governing the retention of different solutes in RP-18—water—methanol systems. The results are correlated with changes in mobile phase composition and the amount of alkyl ligates in the packings. Conclusions are drawn concerning the rŏle of hydrophobic bonding and its significance to the retention.