A chemically modified microelectrode has been prepared successfully by means of electrodepositing nickel hexacyanoferrate(II-III)on a microdisk platinum electrode. This modified electrode could catalyze the oxidation of dopamine and, moreover, eliminate theelectrode poisoning caused by the electrochemical polymerization of dopamine at the bare platinum electrode. However, the oxidation ofascorbic acid could also be catalyzed at this modified electrode, thus interfering with the electrochemical response of dopamine. When themodified electrode was further covered with Nation