Evaluation of a Graphite-Polyurethane Composite Electrode Modified with Copper Nanoparticles as an Amperometric Flow Detector in a Wall-Jet System for the Determination of Cysteine

A graphite-polyurethane composite electrode (GPUE) was modified by electrodeposition of copper nanoparticles (CuNP) followed by electrochemical treatment in NaOH (GPUE-CuNP), in order to prepare an amperometric sensor for the determination of cysteine (Cys). Cyclic votammograms of Cys solutions at GPUE-CuNP allowed the description of a sequence of electrochemical reactions involving Cys oxidation and Cu-0/Cu+ equilibrium, generating a stable Cys-Cu+ complex. The presence of these nanoparticles was confirmed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) data. Hence, the developed device was then used as a Cys amperometric flow detector in a wall-jet system, after evaluation of flow injection parameters in an undescribed approach. In this system, a limit of detection (LOD) of 4.24 mu mol L-1 was obtained with an analytical frequency of 36 determinations h(-1). Intra-day and inter-day reproducibility and repeatability of the modified surface was evaluated. Then the GPUE-CuNP performance was investigated in the determination of Cys content in food supplements. Interference tests were carried out with pyridoxine, ascorbic acid, tryptophan and SO42- ions. The main interference was attributed to the interaction of some of these substances with copper oxides.