Adsorption of mandelic acid enantiomers on chiral stationary phase with grafted antibiotic eremomycin: The effect of the eluent pH

Abstract

The adsorption of mandelic acid enantiomers on the Nautilus-E chiral stationary phase with eremomycin as a grafted antibiotic, as affected by ${}_W{}^{S}pH$ value of the water-ethanol eluent under conditions of an overloaded column, was studied. Adsorption equilibrium under experimental conditions, when mandelic acid dissociates both completely and then very weakly, was studied. The adsorption isotherms of S- and R-mandelic acid were plotted by the Glueckauf method and inverse method using bi-Langmuir model, as well as the tri-Langmuir model assuming independent adsorption on three types of adsorption centers, with two of them being high-energy enantioselective (ion-exchange and molecular adsorption) and the third – the low-energy nonselective types of sites. This model takes into account the ionization of mandelic acid in the eluent and a change in the ${}_W{}^{S}pH$ value in the mass transfer zone caused by its ionization. The saturated capacity and binding energy of all the types of adsorption sites depend on ${}_W{}^{S}pH$ of the eluent. Nonselective interactions contribute to the adsorption of mandelic acid mainly. To determine the adsorption isotherms of mandelic acid enantiomers on Nautilus-E CSP in the absence of its dissociation and distortion of the elution profiles, the Glueckauf method and the bi-Langmuir model were identified as an acceptable choice.

Graphical Abstract

Keywords:

• Adsorption
• chiral stationary phase
• enantiomers
• eremomycin
• liquid chromatography
• mandelic acid

Acknowledgments

This work was financially supported by the Russian Foundation for Basic Research under the Grant Nr. 18-03-00053-A. The authors acknowledge Dr. L.D. Asnin (Perm National Research Polytechnic University, Perm, Russia) and E.P. Naymushin (Institute of Technical Chemistry of the Ural Branch of the Russian Academy of Science, Perm, Russia) for their valuable comments. The work was carried out using the equipment of The Core Facilities Center “Research of materials and matter” at the PFRC UB RAS.

Additional information

Funding

This work was supported by the Russian Foundation for Basic Research, Российский Фонд Фундаментальных Исследований (РФФИ) [grant number 18-03-00053-A].