Simultaneous determination of levodopa, carbidopa and tryptophan using nanostructured electrochemical sensor based on novel hydroquinone and carbon nanotubes: Application to the analysis of some real samples

In the present paper, the use of a novel carbon paste electrode modified by 2, 2'-[1,2-ethanediylbis (nitriloethylidyne)]-bis-hydroquinone (EBNBH) and carbon nanotubes prepared by a simple and rapid method for the determination of levodopa (LD), carbidopa (CD) and tryptophan (Trp) was described. In the first part of the work, cyclic voltammetry was used to investigate the redox properties of this modified electrode at various scan rates. The apparent charge-transfer rate constant, k(s), and transfer coefficient, alpha, for electron transfer between EBNBH and carbon nanotube paste electrode were calculated. In the second part of the work, the mediated oxidation of LD at the modified electrode was described. It has been found that under optimum condition (pH 7.0) in cyclic voltammetry, the oxidation of LD occurs at a potential about 460 mV less positive than that of an unmodified carbon paste electrode. The values of electron transfer coefficient (alpha), catalytic rate constant (k(h)') and diffusion coefficient (D) were calculated for LD, using electrochemical approaches. Differential pulse voltammetry (DPV) exhibited two linear dynamic ranges and a detection limit (3 sigma) of 0.094 mu M for LD. In the third part of the work, simultaneous determination of LD, CD and Trp at the modified electrode was described. Finally, this method was used for the determination of LD in some real samples, using standard addition method. (C) 2011 Elsevier Ltd. All rights reserved.