Improved Chiral Separations Using a Polymerized Dipeptide Anionic Chiral Surfactant in Electrokinetic Chromatography: Separations of Basic, Acidic, and Neutral Racemates

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Abstract
Two polymeric chiral anionic surfactants [poly(sodium N-undecylenyl-l-valine) (poly-l-SUV) and poly(sodium N-undecylenyl-l-valine-valine) (poly-l-SUVV)] are compared as pseudostationary phases for chiral separations of basic, acidic, and neutral enantiomers. Parameters such as pH, concentration and type of background electrolyte, concentration of polymerized chiral surfactants, and injection size were studied to investigate the migration behavior and optimize the chiral resolution of several racemic analytes. At equivalent monomer concentrations, the migration factors for cationic enantiomers were larger with poly-l-SUV than with poly-l-SUVV. In contrast, the reverse was true for anionic enantiomers. However, in both cases, chiral recognition was significantly enhanced with poly-l-SUVV as compared to that with poly-l-SUV. It is interesting to note that the separation selectivity and resolution of a neutral racemate were slightly better with the latter, but only at the expense of longer analysis time and lower efficiencies.