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Separation and On-Line Distinction of Enantiomers: A Non-Aqueous Capillary Electrophoresis Fourier Transform Infrared Spectroscopy Study

Volume 58, Number 6 (June 2004) Page 662-666

Hinsmann, Peter; Arce, Lourdes; Svasek, Peter; Lämmerhofer, Michael; Lendl, Bernhard

We report on the separation and on-line distinction of (R,S)-3,5dinitrobenzoyl leucine (DNB-Leu) enantiomers with non-aqueous capillary electrophoresis (CE) and Fourier transform infrared (FT-IR) spectroscopic detection using O-(tert-butyl carbamoyl) quinine (tBuCQN) as the chiral selector (CS). Due to stereoselective intermolecular interactions—particularly ionic interactions, hydrogen bonding, and π-π-interactions—the enantiomers undergo enantioselective complex and ion-pair formation, respectively, with the CS enabling CE separation and direct identification with FT-IR detection. Especially the (S)-enantiomer of the analyte shows significant changes in the mid-infrared region upon complexation, allowing for a clear spectral distinction between both enantiomers. In this way FT-IR spectroscopy represents a novel and attractive detection method for CE enantiomeric separations providing qualitative stereochemical information on the interactions between the chiral selector and the enantiomers, which is hardly accessible by other CE detection methods.