Electrochemical investigation of a graphite-polyurethane composite electrode modified with electrodeposited gold nanoparticles in the voltammetric determination of tryptophan

Gold nanoparticles (AuNP) were electrodeposited onto the surface of a graphite-polyurethane composite electrode (EGPU), followed by electrochemical treatment in NaOH medium using cyclic voltammetry. After characterization and optimization of the experimental conditions, the resulting device (EGPU-tAuNP) was used for voltammetric determination of tryptophan (TRP). Analyses using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) revealed a homogeneous covering of the electrode surface, with no alteration of the morphology due to the electrochemical treatment in NaOH. Electrochemical Impedance Spectroscopy (EIS) measurements showed that modification with AuNP and electrochemical treatment in basic media reduces the electron-transfer resistance and improves the electron-transfer rate. Chronocoulometric data and cyclic voltammograms obtained in the presence of 100.0 mu mol L-1 TRP revealed an increase in the peak current and a displacement of the peak potential to more negative values after the pretreatment in basic medium. A mechanism involving the Au-0/Au3+ reaction on the electrode surface and TRP oxidation was proposed. Under optimized conditions, using differential pulse voltammetry (DPV), the EGPU-tAuNP presented a detection limit of 5.3 x 10(-8) mol L-1 for the analysis of TRP. The device was used for the determination of TRP in synthetic urine and commercial poly-amino acids supplement. Tests of interference were carried out with biologically relevant compounds. The standard additions procedure could be used to overcome interferences in the analysis of synthetic urine containing creatinine.