EFFECT OF TEMPERATURE AND MOBILE PHASE ON THE RETENTION OF RETINOATES IN REVERSED-PHASE LIQUID-CHROMATOGRAPHY

The effect of temperature on the retention of seven closely related retinoates in reversed-phase liquid chromatography using three organic mobile phases was studied. Retinoates were chromatographed on an RP-18 column with aqueous organic mobile phases (90% methanol, 87% acetonitrile and 55% tetrahydrofuran). The capacity factors were measured at five temperatures (35-55-degrees-C). An increase in temperature decreased the retention. The standard enthalpy changes of the retention process (- DELTA-H0) were calculated from the slopes of Van't Hoff plots (1n k' vs. 1/T). The effect of the molecular structure on the standard enthalpy change was studied. This effect increased significantly as the organic modifier was changed in the order methanol < acetonitrile < tetrahydrofuran.