The adsorption of naproxen enantiomers on the chiral stationary phase (R,R)-whelk-O1 under supercritical fluid conditions

• The adsorption isotherms of Naproxen on (R,R)-Whelk-O1 eluted with CO2 and CH3OH are measured.
• The frontal analysis and inverse methods are used and compared.
• The adsorption energy distributions of the two enantiomers were calculated.
• The heterogeneity of the adsorbent surface for each compound is discussed.
• The isotherm parameters derived from these methods are compared.

The adsorption isotherms of the Naproxen enantiomers eluted with a mixture of carbon dioxide and methanol on a (R,R)-Whelk-O1 column were measured using frontal analysis and the inverse method. Sharp breakthrough fronts provided using a modified design of the instrument allowed an accurate determination of these isotherms. The adsorption model that best accounts for the data was derived from the analysis of the adsorption isotherm data. The affinity energy distribution of the adsorption of the two enantiomers were calculated to determine the heterogeneity of the adsorbent surface for each compound. The adsorption model chosen based on the adsorbent heterogeneity was fitted to the adsorption isotherm data points and the best fitted isotherm parameters were derived from this fit. The inverse method was used as a second method to derive the parameters of the same adsorption models for the overloaded elution bands of (S)- and (R)-naproxen. The isotherm parameters derived from these independent numerical calculations are discussed and compared in the case of single component adsorption and of competitive adsorption as well.