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In this paper, the use of a carbon paste electrode (CPE) modified by (E)‐3‐((2‐(2,4‐dinitrophenyl)hydrazono)methyl)benzene‐1,2‐diol (DHB) and carbon nanotubes (CNTs) for the determination of glutathione (GSH), uric acid (UA) and penicillamine (PA) is described. Initially, cyclic voltammetry was used to investigate the redox properties of the modified electrode in phosphate buffer. Next, the electrocatalytic oxidation of GSH via EC′ mechanism at the modified electrode was described. At the optimum pH of 7.0, the oxidation of GSH occurs at a potential that is 530 mV less positive than that of an unmodified carbon paste electrode. The values of the diffusion coefficient (D=2.5×10−6 cm2 s−1) and the catalytic rate constant (k=1.7×103 M−1 s−1) were calculated for GSH, using chronoamperometry. Based on differential pulse voltammetry, the oxidation of GSH exhibited a dynamic range between 0.4 and 700.0 µM and a detection limit (3σ) of 70.0 nM. Also, simultaneous determination of GSH, UA and PA was described at the modified electrode. Finally, this method was used for the determination of these substances in synthetic solutions and blood serum samples.

In this paper electropolymerization of a thin film of para-phenylenediamine (PPD) is studied at glassy carbon electrode (GCE) in sulfuric acid media by cyclic voltammetry. The results showed that this polymer was conducting and had a reproducible redox couple in the potential region from 0.0 to 0.4 V in phosphate buffer solution. This modified GCE (p-PPD-GCE) was applied for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) using differential pulse voltammetry (DPV). The p-PPD-GCE in 0.1 M phosphate buffer solution (pH 5.0) separated the DPV signals of AA, DA and UA with sufficient potential differences between AA-DA and DA-UA and also enhanced their oxidation peak currents. The oxidation currents were increased from 2.0 to 2000.0 mM for AA, 10.0 to 1250.0 mM for DA and 50.0 to 1600.0 mM for UA. The detection limits were evaluated as 0.4, 1.0 and 2.5 mM for AA, DA and UA, respectively (S/N = 3).