An integrated decoupler for capillary electrophoresis with electrochemicaldetection: Application to analysis of brain microdialysate

An approach to capillary electrophoresis with electrochemical detection (CE -EC) suitable for determination of dopamine in 1-min brain microdialysate s amples is described. The CE-EC system includes an electrochemical detection cell that permits easy, precise, and permanent alignment of a carbon fiber microelectrode with a separation capillary (30-mu m i.d., 75-cm length). A mperometric detection was performed at a constant applied potential of 600 mV with respect to a Ag/AgCl reference electrode. Decoupling of the electro phoretic current from the amperometric detector was accomplished with an in tegrated end-column decoupler prepared by etching the capillary outlet with HF. The decoupler produces baseline noise of 50 fA, or less, in the presen ce of 10-20-mu A current in the separation capillary. The low baseline nois e affords low mass (attomoles) and low concentration (nanomolar) detection limits for dopamine and 4-methylcatechol. A peak attributable to dopamine w as identified in electropherograms of brain microdialysate samples obtained from anesthetized rats. Identification of the dopamine peak was confirmed by pharmacological methods. Dopamine was readily detected in 1-min brain mi crodialysate samples. The dopamine concentration in 1-min brain microdialys is samples was significantly altered by drug treatments and by brief electr ical stimulation of dopaminergic axons.