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 electrode in the presence of large excess of ascorbic acid and 3,4-dihydroxyphenyl acetic acid (dopac) is described. The electrochemical detection was performed at a glassy carbon electrode modified with a melanin-type polymer obtained by polymerization of 3.0×10-3M L-dopa in 0.050M phosphate buffer solution pH 7.40 by applying 1.00V for 60min. The polymeric film exhibits attractive permselectivity excluding anionic species such as potassium ferricyanide, ascorbic acid, dopac and uric acid. Cationic species such as epinephrine, norepinephrine and dopamine and neutral ones such as catechol and hydrogen peroxide can be oxidized at the polymer-modified electrode. The use of ascorbic acid in the measurement solution allows the amplification of dopamine oxidation signal due to the reduction of the electrochemically generated dopaminequinone. By using 1.0×10-3M ascorbic acid, the detection limit for dopamine is 5.0nM. The interference for the maximum physiological concentrations of ascorbic acid and dopac in nervous centers, i.e. 500µM ascorbic acid and 50µM dopac is 8.1 and 1.4%, respectively.