Highly selective dopamine quantification using a glassy carbon electrode modified with a melanin-type polymer

A highly selective dopamine quantification at a new polymer-modified electr ode in the presence of large excess of ascorbic acid and 3,4-dihydroxypheny l acetic acid (dopac) is described. The electrochemical detection was perfo rmed at a glassy carbon electrode modified with a melanin-type polymer obta ined by polymerization of 3.0 x 10(-3) M L-dopa in 0.050 M phosphate buffer solution pH 7.40 by applying 1.00 V for 60 min. The polymeric film exhibit s attractive permselectivity excluding anionic species such as potassium fe rricyanide, ascorbic acid, dopac and uric acid. Cationic species such as ep inephrine, norepinephrine and dopamine and neutral ones such as catechol an d hydrogen peroxide can be oxidized at the polymer-modified electrode. The use of ascorbic acid in the measurement solution allows the amplification o f dopamine oxidation signal due to the reduction of the electrochemically g enerated dopaminequinone. By using 1.0 x 10-3 M ascorbic acid, the detectio n limit for dopamine is 5.0 nM. The interference for the maximum physiologi cal concentrations of ascorbic acid and dopac in nervous centers, i.e. 500 muM ascorbic acid and 50 muM dopac is 8.1 and 1.4%, respectively. (C) 2001 Elsevier Science B.V. All rights reserved.