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Microdialysis sampling was coupled on-line to micellar electrokinetic chromatography (MEKC) to monitor extracellular dopamine concentration in the brains of rats. Microdialysis probes were perfused at 0.3 μL/min and the dialysate mixed on-line with 6 mM naphthalene-2,3-dicarboxaldehye and 10 mM potassium cyanide pumped at 0.12 μL/min each into a reaction capillary. The reaction mixture was delivered into a flow-gated interface and separated at 90-s intervals. The MEKC separation buffer consisted of 30 mM phosphate, 6.5 mM SDS, and 2 mM HP-β-CD at pH 7.4, and the electric field was 850 V/cm applied across a 14-cm separation distance. Analytes were detected by laser-induced fluorescence excited using the 413-nm line of a 14-mW diode-pumped laser. The detection limit for dopamine was 2 nM when sampling by dialysis. The basal dopamine concentration in dialysates collected from the striatum of …