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Low‐molecular‐weight chiral cation exchangers: Novel chiral stationary phases and their application for enantioseparation of chiral bases by nonaqueous capillary electrochromatography
Author(s) -
Tobler Ernst,
Lämmerhofer Michael,
Wuggenig Frank,
Hammerschmidt Friedrich,
Lindner Wolfgang
Publication year - 2002
Publication title -
electrophoresis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.666
H-Index - 158
eISSN - 1522-2683
pISSN - 0173-0835
DOI - 10.1002/1522-2683(200202)23:3<462::aid-elps462>3.0.co;2-8
Subject(s) - capillary electrochromatography , chemistry , enantiomer , chiral derivatizing agent , amino acid , electrochromatography , chiral column chromatography , chiral resolution , chromatography , organic chemistry , capillary electrophoresis , biochemistry
Cation exchange type chiral stationary phases (CSPs) based on 3,5‐dichlorobenzoyl amino acid and amino phosphonic acid derivatives as chiral selectors (SOs) and silica as chromatographic support were developed and applied to enantiomer separations of chiral bases by nonaqueous capillary electrochromatography (NA‐CEC). As a rationale for efficient CSP development we adopted the combined use of the “reciprocity principle of chiral recognition” and nonaqueous ion‐pair CE as screening assay. Thus, ( S )‐atenolol was employed as chiral counter‐ion added to the BGE in CE and a series of N ‐derivatized amino acids and amino phosphonic acids were screened to derive reciprocally information on their chiral recognition abilities for atenolol enantiomers. Two SO candidates, namely N ‐(3,5‐dichlorobenzoyl)‐ O ‐allyl‐tyrosine and N ‐(4‐allyloxy‐3,5‐dichlorobenzoyl)‐1‐amino‐3‐methylbutane phosphonic acid that have been identified as potential SOs in the CE screening were, after immobilization on thiol‐modified silica, evaluated in cation‐exchange NA‐CEC. The strong chiral cation exchanger with the free phosphonic acid group exhibited enhanced enantioselectivity compared to the weak chiral cation exchanger with the carboxylic acid group. A wide variety of chiral bases could be successfully resolved on the strong chiral cation exchanger with α‐values up to 2.2 and efficiencies up to 375 000 m –1 including β‐blockers and other amino alcohols, local anesthetics like etidocaine, antimalarial agents like mefloquine, Tröger’s base, phenothiazines like promethazine, and antihistaminics. The influence of several experimental parameters (electrolyte concentration, acid‐base ratio and acetonitrile‐methanol ratio) was evaluated *.