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

Abstract

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.

Capillary Electrophoresis: Trends and Recent Advances

“…In an attempt to enhance the separation of chiral compounds, Kulsing et al used peak sharpening effects in CEC by employing molecularly imprinted porous layer OT. 34 Enantioseparation required overloading and introduction of an acetonitrile-enriched sharpening zone.…”

Recent developments in open tubular capillary electrochromatography from 2016 to 2017

“…Scanning electron microscopy (SEM) has become an indispensable characterisation method for a visual confirmation of the surface morphology of coated surfaces. SEM images of successfully coated surfaces were described to show rough surfaces , hilly or bumpy surfaces , with distinct shapes of the embedded material , good layer density and homogeneity or uniformity , and more importantly significant layer thickness as opposed to the smooth surfaces seen in bare silica surfaces. Some SEM scans were performed on flat silica surfaces for detailed characterisation because of the inherent difficulty in successfully imaging wall coatings for a capillary format.…”

“…An MIP in porous layer open tubular (MIP‐PLOT) format was fabricated by Kulsing and co‐workers for the chiral separation and peak sharpening of a Z‐Asp‐OH racemates . Using a traditional dilution polymerisation method with Z‐L‐Asp‐OH as the template, 4‐vinylpyridine (4VP) was the choice functional monomer which increased ionic interactions with the negatively charged analytes.…”

Chiral Separations by Capillary Electrophoresis and related Techniques with Different Chiral Selectors: A Review

“…However, it can also act as a host for enantiomeric separations as chiral reagents [123]. To examine the enantiomeric separation of BINOL with R-and S-enantiomers, a coating with molecularly imprinted polymer was performed on silica gel [ [126]. In their study in 2014, the MIP-coated capillaries were applied for the separations of the ketoprofen racemic mixture.…”