Improved end-column amperometric detection for capillary electrophoresis

An amperometric detector for end-column detection in capillary electrophoresis is described. The influence of the high voltage on the detection performance is studied. As a consequence of these studies it is shown that the end-column detection strategy operates up to capillary dimensions of 50 mu m I.D. without using any electrical-field decoupler design. The shift of the working electrode potential resulting from the presence of the high voltage electrical field is compensated by selecting a more positive potential setting via the potentiostat. The detector performance is characterized in terms of attainable separation efficiencies (300 000 theoretical plates for homovanillic acid), limits of detection (5 . 10-(8) mol/l for serotonin) and coulometric efficiencies (8.9% for homovanillic acid). Practical aspects associated with the use of microdisk electrodes instead of carbon fiber electrodes are addressed.