Thermodynamic Insights into the Separation of Carotenoids in Reversed-Phase Liquid Chromatography

The retention mechanism of four major carotenoids, two xanthophylls (i.e., lutein and zeaxanthin) and two carotenes (i.e., lycopene and -carotene),was investigated in reversed-phase liquid chromatography with the aimof thermodynamic analysis. The experimental variables considered in this study were the composition ofmobile phase (MP) and the temperature.Chromatographic elutions were undertaken under linear, isocratic conditions by using a C18 stationary phase, four different MP compositions (by varying the ratio methanol/acetonitrile from 66.5/28.5 to 47.5/47.5 v/v), and column temperatures in the range 283–313 K. TraditionalVan’tHoff analysis has been used to estimate changes of standard enthalpy (Δ∘) andGibbs free energy (Δ∘) associated with the solute transfer from the mobile to the stationary phase at eachmobile phase composition.The thermodynamic quantities have been correlated to the structure of investigated carotenoids and their interaction with the octadecyl silica stationary phase.