Adsorption of ochratoxin A (OTA) anodic oxidation product on glassy carbon electrodes in highly acidic reaction media: Its thermodynamic and kinetics characterization |
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Authors: | Eduardo Alejandro Ramírez Paola Andrea Jara Ulloa Luis Nuñez Vergara |
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Affiliation: | a Departamento de Química, Facultad de Ciencias Exactas, Físico-Químicas y Naturales. Universidad Nacional de Río Cuarto, Agencia Postal No. 3, 5800 Río Cuarto, Argentina b Laboratorio de Bioelectroquímica, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Olivos 1007, Santiago, Chile |
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Abstract: | We study the thermodynamics and kinetics of the adsorption of a redox couple having quinone nature on glassy carbon electrodes. This couple is produced by the anodic oxidation of mycotoxin ochratoxin A in 10% acetonitrile + 90% 1 M HClO4 aqueous solution. The quasi-reversible redox couple was studied by both cyclic (CV) and square wave (SWV) voltammetric techniques. The Frumkin adsorption isotherm best described the specific interaction of the redox couple with carbon electrodes. By fitting the experimental data, we obtained values of −28.4 kJ mol−1 and 0.70 ± 0.02 for the Gibbs free energy of adsorption and the interaction parameter, respectively. SWV fully characterized the thermodynamics and kinetics of the adsorbed redox couple, using a combination of the “quasi-reversible maximum” and the “splitting of SW peaks” methods. Average values of 0.609 ± 0.003 V and 0.45 ± 0.06 were obtained for the formal potential and the anodic transfer coefficient, respectively. Moreover, a formal rate constant of 10.7 s−1 was obtained. SWV was also employed to generate calibration curves. The lowest concentration of mycotoxin was 1.24 × 10−8 M (5 ppb), measured indirectly with a signal to noise ratio of 3:1. |
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Keywords: | Ochratoxin A Adsorptive accumulation Cyclic voltammetry Square wave voltammetry Thermodynamic and kinetics parameters |
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