Amperometric detection of dopamine in the presence of ascorbic acid using a nafion coated glassy carbon electrode modified with catechin hydrate as a natural antioxidant

Catechin hydrate (trans-3,3',4',5,7-penta-hydroxyflavone) is a derivative of catechol, and it is one of the natural antioxidant and anticarcinogenic compounds found in many fruits and agricultural foods. A new electrode was prepared by electrodeposition of a catechin-hydrate film on the surface of an activated glassy carbon electrode, followed by coating with nafion layer. Cyclic voltammetry was used for the deposition process, and the resulting modified electrode was found to retain the activity of the quinone/hydroquinone group anticipated for a surface-immobilized redox couple. The cyclic voltammograms of the modified electrode indicated that the surface-confined catechin-hydrate was strongly dependent on the solution pH. The electrochemical behaviour and stability of the modified electrode were studied by cyclic voltammetry. The apparent charge transfer rate constant (k(s)) and electron transfer coefficient (alpha) between the electrode surface and adsorbed catechin hydrate were calculated as 0.41 and 0.31 s(z-1) 0.31, respectively. The modified electrode exhibits an electrocatalytic effect on dopamine oxidation in the pH range of 2 to 7. The modified electrode was used for the electrocatalytic oxidation of dopamine in the presence of ascorbic acid and the elimination of the interference by ascorbic acid (AA) when present in a 200-fold concentration excess. A very large decrease (400 mV) in the overpotential for the oxidation of dopamine and current increase were observed on the surface of the modified electrode. Dopamine was determined amperometrically at the modified electrode in the concentration range of 100 nM to 0.1 mM. The detection limit (signal to noise is 3) and sensitivity are 11 nM and 16 nA/muM, respectively. The modified electrode was employed to determine DA in biological mediums.