Use of peak sharpening effects to improve the separation of chiral compounds with molecularly imprinted porous polymer layer open‐tubular capillaries

This investigation demonstrates the application of a new peak sharpening technique to improve the separation of difficult‐to‐resolve racemic mixtures in capillary electro‐chromatography. Molecularly imprinted porous layer open tubular (MIP‐PLOT) capillaries, prepared by a layer‐on‐layer polymerization approach with Z‐ l ‐Asp‐OH as the template, were selected to validate the approach. SEM revealed that the polymer film thickness can be varied by changes in both the polymer composition and the layer‐on‐layer regime. Capillaries made with methacrylic acid as the functional monomer could not separate the Z‐Asp‐OH racemate, due to weak interactions between the MIP‐PLOT material and the target analytes. In contrast, MIP‐PLOT capillaries prepared with 4‐vinylpyridine as the functional monomer resulted in increased ionic interactions with the target analytes. Separation of the enantiomers could be enhanced when a peak zone sharpening effect was exploited through the use of specific BGE compositions and by taking advantage of eigenpeak phenomena. In this manner, the position of a sharpening zone and the peak shape of the sample analytes could be fine‐tuned, so that when the sharpening zone and the target analyte co‐migrated the separation of the Z‐ l ‐Asp‐OH enantiomer from its d ‐enantiomer in a racemic mixture could be achieved under overloading conditions.