Laterally attached liquid crystalline polymers as stationary phases in reversed-phase high-performance liquid chromatography V. Study of retention mechanism using linear solvation energy relationships

A linear solvation energy relationship model was used to characterize the r etention behavior of a stationary phase based upon a nematic side-on liquid crystalline polymer (SOLCP) in reversed-phase liquid chromatography. The s et of solutes was constituted of a high variety of compounds whose molecula r sizes were considerably smaller than the mesogenic unit size. The results showed good statistical fits for these retention data in 65:35, 75:25 and 85:15 (v/v) methanol-water mobile phases. Both the cavity term and excess m olar refraction are the most important favorable retention-governing parame ters, whereas the solute hydrogen bond acceptor basicity is the most unfavo rable retention parameter. Hydrophobicity and pi-pi interactions decrease s trongly when the percentage of methanol increases, leading to an important retention decrease despite the fact that the hydrogen bond interaction weak ens as the organic solvent is added. The shape recognition ability of this side-on Liquid crystalline stationary phase on polycyclic aromatic hydrocar bon solutes is partly explained by the solutes' high polarizability due to the presence of pi -electrons. However, the solute polarizability is not su fficient and a stationary phase's "structure effect" must to be taken into account for the shape discrimination observed. The strong interaction betwe en liquid crystal molecules caused likely a adsorption retention mechanism rather than a partition mechanism. (C) 2001 Elsevier Science B.V. All right s reserved.