Study of Intermolecular Interactions Involved in Capillary GLC with Liquid Crystal Compounds as Stationary Phases

ABSTRACT

Abraham's equation was employed in order to investigate nonspecific intermolecular interactions involving liquid crystals. Several aromatic azo derivatives, proved to have liquid crystal behavior, were used as stationary phases in capillary gas chromatography. The polarizability, polarity, hydrophobicity and hydrogen-bond donor or acceptor characters were estimated using the Abraham solvation model. Calculations were based on the isothermal retention times for 25 compounds, in the temperature range between 70° and 170°C, both in the heating and the cooling mode. The descriptors R, π, Σα, Σβ, and logL16 (Abraham parameters) were converted into orthogonal descriptors following Randic's procedure. The above-mentioned properties involve the r, s, a, b and l coefficients, respectively, which were determined by means of multilinear regression applied to the considered set. Following the orthogonalization procedure, the polarizability term (rR*) was found to be statistically insignificant in the case of the studied compounds. Plots of these coefficients vs temperature are discussed, in order to allow estimations regarding the retention mechanism and contributions of polar and Van der Waals interactions. The variation of properties (e.g. polarity, hydrogen-bond donor and hydrogen-bond acceptor character) with temperature was assigned to the changes in the molecular geometry of the compound used as stationary phase.

Keywords: