4.6 Article

Effect of 2-propanol content on solute retention mechanisms determined using amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phase under normal- and reversed-phase conditions

Journal

JOURNAL OF CHROMATOGRAPHY A
Volume 1650, Issue -, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.chroma.2021.462226

Keywords

Retention mechanism; Polysaccharide-based sorbent; Normal phase; Reversed phase; Modeling

Funding

  1. Ministry of Science and Technology of Taiwan [MOST 109-2221-E-027-037 -MY3]

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The study explores the balance between electrostatic interactions and solvophobic interactions in immobilized amylose sorbents, and investigates the retention behaviors of pantolactone enantiomers in both normal and reversed-phase modes. Different types of sorbent interactions and changes in enantiomeric elution order are observed at different IPA concentrations, emphasizing the importance of both electrostatic and solvophobic interactions in chiral recognition.
The electrostatic interactions between chiral solutes and polysaccharide (PS)-based chiral selectors are the key to achieving chiral recognition; however, PS-based sorbents, derivatized of phenyl moieties, can exhibit considerably non-polar characteristics, and they are also useful for the separation of enantiomers in the reversed-phase mode. In this study, an immobilized amylose 3,5-dimethylphenylcarbamate-based sorbent was used to investigate the balance between electrostatic interactions and solvophobic interactions, with complementary effects on solute retention behavior when the isopropanol (IPA) concentration was altered. It was proposed that in both normal-and reversed-phase modes, information on the retention mechanisms could be obtained by observing the curvature of the logarithm of the retention factor versus the logarithm of the IPA concentration, and the slope values of the curves were related to the number of displaced IPA molecules upon solute adsorption. Using the proposed model and the two-site adsorption model, the retention behaviors of pantolactone (PL) enantiomers in both normal and reversed-phase modes were investigated. The PL & minus;sorbent interactions were classified into four types: electrostatic/enantioselective, electrostatic/nonselective, solvophobic/enantioselective, and solvophobic/nonselective. At IPA concentrations below 50 vol.% in n-hexane, the retention behaviors of PL were dominated by electrostatic/enantioselective sites, whereas at IPA concentrations beyond 50 vol.%, the solvophobic interactions of PL & minus;sorbent were strengthened and mostly nonselective. By contrast, in the reversed-phase mode, a reverse in the enantiomeric elution order of PL was observed at 10 vol.% IPA, and considerably different enantioselectivity behaviors were found below and above 20 vol.%, indicating an abrupt change in the sorbent molecular environment. At IPA concentrations beyond 40 vol.%, the presence of PL-sorbent electrostatic interactions enhanced chiral recognition. (c) 2021 Elsevier B.V. All rights reserved.

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