One of the key challenges in analytical chemistry is the separation of chiral compounds. Although various chiral stationary phases are available for high-performance liquid chromatography, the development of stationary phase materials for other analytical separation modes is lagging behind. The development of new chiral stationary phases for the analysis of chiral products, e.g. pharmaceuticals, generics or counterfeit products, relies on the availability of suitable chiral selectors. Currently, this is based on very slow, resource-intensive processes. The use of molecular imprinting polymers (MIPs) as chiral stationary phase materials can overcome some of these constraints.

In this investigation, a fabrication method has been developed for the preparation of chiral MIP porous layer open tubular (PLOT) capillary columns for the use in capillary electrochromatography (CEC). The work demonstrates MIP PLOT capillary column synthesis based on ‘in-capillary’ ultraviolet (UV) initiated polymerization using light emitting diodes (LEDs) in conjunction with continuous capillary delivery. The non-steroidal anti-inflammatory drug S-ketoprofen was used as the template for imprinting. The relationships between direct exposure times, UV-light intensity and polymer layer thickness were determined, as well as the effects of capillary delivery rate and multiple exposures on the layer thickness for various compositions of the pre-polymerisation mixtures. Polymer surface morphology and layer thickness were investigated by scanning electron microscopy (SEM). The separation performance of the prepared S-ketoprofen-imprinted MIP-PLOT capillaries for the ketoprofen racemate was investigated using CEC and capillary liquid chromatography. 

In contrast to currently available methods which require expensive and complex chiral selectors, such MIP-based stationary phases using non-chiral polymer precursors in PLOT capillaries create enantio-selective nanocavities through molecular self-assembly processes and thus are inherently much ‘greener' (as assessed by E-factor metrics) as they use much less energy and materials. The described fabrication methods provide tailor-made chiral MIP-PLOT capillary columns for the separation of chiral compounds of chemical and biological origin in complex analyte mixtures.