A new procedure of electrochem. activation for carbon fiber microelectrodes was reported. The treatment was simple, at first a constant current of 30 mA for 30 s, and then a potential of -2.0 V for 10s were applied to the electrode. After activation, the pretreated electrode showed very high sensitivity and selectivity. The detection limit of 5 ?10-8 mol.dm-3 for dopamine (DA) in phosphate buffer solution (pH 7.4) was found. The potential deviation of ascorbic acid (AA) peak from DA peak was 170 mV. Semi-differential voltammetry was used for in vivo determination in the rat brain. Three peaks at +0.01, +0.18 and +0.35V were recognized as ascorbic acid, 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA), and their concns. were 1.7 ?10-4, 2.1 ?10-5 and 3.3 ?10-6 mol.dm-3 resp. The effect of the antihypertensive drug reserpine on DOPAC and 5-HIAA was observed The mechanism of activation for carbon fiber electrodes was explored. It was possible that the surface oxidation of electrodes enhanced the sensitivity and further reduction improved the selectivity.

Key words: ACTIVATION, BRAIN, CARBON FIBERS, CARBON ELECTRODES, ELECTROCHEMISTRY, DOPAMINE, MICROELECTRODE, ASCORBIC ACID, NEUROTRANSMITTER, GALVANOSTATIC METHOD