CONTINUOUS IN-VIVO MONITORING OF AMINO-ACID NEUROTRANSMITTERS BY MICRODIALYSIS SAMPLING WITH ONLINE DERIVATIZATION AND CAPILLARY ELECTROPHORESIS SEPARATION

A separation-based biosensor has been developed that is capable of nea r-real-time analysis of aspartate and glutamate with a temporal resolu tion of less than 2 min in anesthetized or awake, freely moving animal s. The instrument consists of a microdialysis sampling system, an on-l ine reactor, an injection interface, and a CE-LIF system. Primary amin e analytes are derivatized with NDA/CN following microdialysis samplin g using an online reactor to produce fluorescent CBI derivatives. The reaction takes approximately 1 min. The derivatized sample then travel s to a microinjection valve which alternately sends CE running buffer and reacted microdialysis sample to the CE column via an injection int erface. The interface allows a controllable volume of 10-20 nL to be i njected onto the CE separation capillary. Separation of aspartate and glutamate from the other amino acids present in the microdialysis samp le was achieved within 70 s. Detection limits for glutamate and aspart ate using laser-induced fluorescence detection were 0.1 mu M. The line ar dynamic range was acceptable for the determination of aspartate and glutamate in dialysate samples where the levels are between 1 and 10 mu M. Full automation of the system was achieved by computer control o f the valve, the interface, and the data collection system. The perfor mance of this system was demonstrated in an anesthetized rat by monito ring ECF levels of aspartate and glutamate released in brain after sti mulation with high concentrations of K+.