Microwave-assisted Capillary Electrophoresis with Electrochemical Detection Sascha Förster, Frank-Michael Matysik, Mohamed Ghanem, Frank Marken a) Institute of Analytical Chemistry, University of Leipzig, Germany b) Department of Chemistry, University of Bath, UK Capillary electrophoresis (CE) is one of the most efficient separation methods in analytical chemistry. It is associated with several advantages like automation, high efficiency and miniaturization. The CE technique has a broad potential of analytical applications ranging from small ions up to whole cells. CE measurements require only small quantities of chemicals and small sample volumes. Particularly, the combination of CE with electrochemical detection (ED) makes it possible to analyze species which do not show UV absorption. Microwave radiation (MW) offers an activation of electrochemical processes by self-focusing at the electrode surface. It produces a stable local increase in temperature and serves for the localised acceleration of chemical reactions and the increase of signals in conjunction with analytical voltammetry. Additionally, the convective effects of the buffer solution close to the electrode surface can lead to a focusing of the liquid flow outside of the capillary to the working electrode and consequently to a further increase of analytical signals. The aim of this work was to demonstrate for the first time the combination of CE with microwave-assisted electrochemical detection. A new detection cell was constructed to allow an accurate positioning of the working electrode and the separation capillary in the microwave field. A cooling of the capillary and an optimal irradiation and focusing of the microwave radiation must be realized. Investigations concerning the influence of the microwaves on the detection performance and the stability of the electrode surface have been carried out. A calibration of temperature, mass transport, and kinetic effects of the microwave radiation on the model system K₄[Fe(CN)₆] / K₃[Fe(CN)₆] were measured. The influence of the MWs during the electrophoretic separation on the signal height, the peak symmetry and migration time were determined for a cationic ferrocene derivative, methanol, and for ascorbic acid. A clear increase in temperature was observed and consequently a change of the equilibrium potentials and an increase of the steady-state current of the cyclic voltammetric characterization of the electrochemical systems were found. Thermal effects and associated convective movements were not measurable because of the small distance of only 50 µm between the working electrode and the separation capillary. However, the kinetic effects on signal magnitude were clearly proven by using ascorbic acid as a model compound. A significant enhancement of sensitivity could be exploited for CE-ED measurements of ascorbic acid in presence of MW radiation.

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