Capillary electrochromatography - novel stationary phases & applications

Capillary electrochromatography (CEC) represents a separation technique which combines features of chromatography and electrophoresis in a unique way. Like in chromatography analytes are resolved based on the interaction with a stationary phase; yet, the mobile phase is transported through the system not by pressure but by the electroosmotic flow, one of the principles of electrophoresis. This signature combination of two separation modes results in many theoretical advantages in terms of separation efficiency and selectivity. The principles of CEC were described more than 30 years ago, and studies regarding the underlying separation mechanisms and the preparation of suitable stationary phases conducted. Even so, up to now CEC is not really relevant in routine analysis because of two reasons; first, only a few convincing applications have been reported, and second, possibly because of that CEC-capillaries are hardly commercially available. This research proposal intends to bridge this apparent discrepancy between many desired features of CEC and the (assumed) limited practical relevance of this technique. The last few years brought advancement particularly regarding the fabrication of novel stationary phases (e.g. innovative materials like polymermonoliths, surface modifications by nanoparticles), materials which either havent left developmental stage or whose practical relevance never has been evaluated. Accordingly, in this project these innovative stationary phases will be developed and optimized for the analysis of complex matrices by CEC. The latter comprises the determination of natural products (e.g. flavonoids, alkaloids or phenolic acids) in plant extracts, truly challenging samples for any separation technique. By such a targeted approach the dormant potential of CEC, an extremely powerful and versatile analytical technique will hopefully be recognized at last.

Capillary electrochromatography (CEC) is a more than 30 years old separation technique that combines features of chromatography and electrophoresis in a unique way. CEC is very versatile in respect to the utilized stationary phases, i.e. separation media, and its separation efficiency is (at least theoretically) much better than that of established techniques. However, it is still considered as an exotic alternative with little practical relevance because of two facts; first, few capillaries are commercially available and, second, the lack of convincing practical applications. The now concluded research project evaluated the potential of CEC for natural products analysis. In order to do so the entire workflow was considered, beginning with the development and fabrication of stationary phases suitable for CEC use to end with their practical application. Two entirely new materials were successfully developed. They resemble polymer monoliths based on innovative building blocks (the zwitterionic monomer (3-allyl-1-imidazol) propane sulfonate and the dicationic crosslinker 3,3-(hexane-1,6- diyl)bis(1-vinylimidazolium) bromide). Besides them the polymerization mixtures required for synthesis of the respective phases contained several other constituents, whose nature and composition had to be optimized in order to obtain materials with the desired properties (surface, pore structure, etc.); the phases were fabricated by UV-induced photopolymerization and characterized using diverse analytical techniques including scanning electron microscopy and infrared spectroscopy. Both finally developed materials enabled the fast and reproducible separation of natural products (phenolic acids and methylxanthines, respectively), which can be seen as an indicator for the potential of CEC in routine analysis too. The applied approach was time consuming and challenging, because in-depth knowledge in diverse scientific areas, such as material sciences, or organic and analytical chemistry, was required. However, it was the only way to control and optimize all relevant steps proposed in this project. That our efforts to further advance and establish CEC in analytical sciences were successful, are substantiated by publications in reputed, scientific journals.