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The electrooxidation of dopamine (DA), uric acid (UA) and their mixture on a gold electrode modified by a self-assembled monolayer of 2-(3,4-dihydroxyphenyl)-1,3-dithialone has been studied by cyclic voltammetry (CV), chronoamperometry and differential pulse voltammetry (DPV). CV was used to investigate the redox properties of the modified electrode at various scan rates and the apparent charge transfer rate constant (k(s)), and transfer coefficient (α) were calculated. The mediated oxidation of DA at the modified electrode under the optimum condition (pH = 7.0) in CV occurs at a potential about 220 mV less positive than that of the unmodified gold electrode. The values of electron transfer coefficients (α), catalytic rate constant (k) and diffusion coefficient (D) were calculated for DA, using electrochemical methods. DPV exhibited a linear dynamic range over the concentration range of 0.2-250.0 μM and a detection limit (3σ) of 0.07 μM for DA. The modified electrode was used for simultaneous determination of DA and UA by DPV. The results showed that the electrode is highly efficient for the catalytic electrooxidation of DA and UA, leading to a remarkable peak resolution (~350 mV) for two compounds. The electrode was used for the determination of DA in an injection sample.

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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.

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