On-line coupling of in vivo microdialysis with capillary electrophoresis/electrochemistry

A separation-based biosensor that couples microdialysis directly to capilla ry electrophoresis with electrochemical detection (CEEC) is described. The system employs a 60 nl injection valve and a gap junction interface. For su ccessful electrochemical detection, it is necessary to apply the separation voltage at the gap interface. This is in contrast to previously reported o ptically based systems in which it was possible to place the high voltage a t the detection end. To protect the experimental animal from the high volta ge employed for the separation, a cellulose acetate-based decoupler was pla ced between the injection valve and the injection interface. The effects of interface gap distance, transfer buffer flow rate and capillary i.d. on se paration efficiency and peak height were investigated. In particular, it wa s found that electrokinetic injection of positively charged analytes into t he CE was affected by the magnitude of the second field set up in the trans fer capillary. The use of a 25 mu m diameter capillary for the transfer lin e and a 75 mu m capillary for the CE separation gave the best detector resp onse and highest separation efficiency. The potential of this system for bi oanalytical studies was demonstrated by monitoring transdermal delivery of nicotine following administration of a nicotine patch. Cutaneous concentrat ions of nicotine were monitored over a 24 h period with a resolution of 10 min. (C) 1999 Elsevier Science B.V. All rights reserved.