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Chromatographic retention and thermodynamics of the adsorption of α-phenylcarboxylic acid enantiomers on a chiral stationary phase with a grafted antibiotic eremomycin: Effect of eluent pH

ABSTRACT The effect of the pH of aqueous–ethanol mobile phases on the retention and adsorption thermodynamics of the optical isomers of several α-phenylcarboxylic acids on a chiral stationary phase “Nautilus-E” with a grafted antibiotic, eremomycin, was studied. It was determined that ionic interactions dominated in the retention of α-phenylcarboxylic acid enantiomers. It was revealed that the Nautilus-E adsorbent was most selective to acids, the adsorption of which is an enthalpy-controlled process. It was found that the nature of adsorption was changed by varying the eluent pH. The dissociation constants of α-phenylcarboxylic acids have been determined by chromatographic method in aqueous–ethanol solution. A statistical analysis of the phenomenon of enthalpy-entropy compensation was performed, and a manifestation of the false compensation effect was established. It was shown that the spatial configuration of the molecule and the presence of polar groups on a chiral carbon atom in its structure have a greater influence on the chiral recognition mechanism of acid enantiomers using the Nautilus-E CSP. GRAPHICAL ABSTRACT