Voltammetric determination of ascorbic acid in the presence of acetaminophen and tryptophan using an improved carbon nanotube paste electrode

A carbon paste electrode (CPE) modified with carbon nanotubes and 5-amino-3',4'-dimethyl- bi-phenyl-2-ol (5ADB) is prepared. Under the optimum pH of 7.0, the oxidation of ascorbic acid (AA) on the modified CPE occurs at a potential about 280 mV less positive than that on the unmodified CPE. Some kinetic and thermodynamic parameters for electrocatalytic oxidation of AA, including electron transfer coefficient (alpha = 0.58) and diffusion coefficient (D = 2.2 x 10(-6) cm(2)/s), are also determined. AA, acetaminophen (AC), and tryptophan (TRP) were detected simultaneously using the modified CPE. The peak potentials recorded using the modified CPE in phosphate-buffered solution at pH 7.0 were 265, 465, and 780 mV for AA, AC, and TRP, respectively. The modified CPE was successfully used to determine the concentrations of AA, AC, and TRP in real samples. (c) 2013, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.