UNUSUAL EFFECT OF TEMPERATURE ON THE RETENTION OF ENANTIOMERS ON A CHIRAL COLUMN

The Van 't Hoff plots of data obtained by chromatographing the enantiomers of a conformationally rigid spirolactam on a commercial high-performance liquid chromatographic column packed with a stationary phase derived from (R)-N-(3,5-dinitrobenzoyl)phenylglycine are non-linear. The extent and sense of the curvature of these plots depends not only on the temperature but also on the concentration of 2-propanol in the hexane mobile phase. With low concentrations of 2-propanol, retention is seen to decrease, then increase, then decrease again as the temperature is raised. This unusual behavior is ascribed to the temperature-dependent interaction of 2-propanol with the stationary phase and/or the analyte.