High Temporal Resolution Monitoring of Glutamate and Aspartate in Vivo Using Microdialysis On-Line with Capillary Electrophoresis with Laser-Induced Fluorescence Detection

An automated method for high temporal resolution monitoring of the neurotransmitters glutamate and aspartate in vivo using capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection was developed. Microdialysis probes placed in the striatum of anesthetized rats were coupled on-line with the CE system by an automated flow-gated interface. Analytes were derivatized on-line with o-phthaldialdehyde/β-mercaptoethanol and detected by LIF using the 354 nm line (7 mW) of a He−Cd laser for excitation. With dialysis flow rates of 1.2 μL/min, the detection limit at the dialysis probe was 200 nM for glutamate and aspartate. Glutamate and aspartate could be resolved in less than 5 s with over 200 000 theoretical plates. The sampling time was limited by the separation time while the temporal resolution was limited to ∼12 s because of band broadening that occurs within the probe and its associated tubing. The high temporal resolution allowed the first simultaneous monitoring of glutamate and aspartate overflow during acute electrical stimulation in the rat brain.