The Redox Kinetics of Adsorbed ATX-I at Carbon Electrodes by Anodic Stripping Square-Wave Voltammetry

Abstract

The selective adsorptive accumulation of altertoxin I (ATX‐I) from a mixture of Alternaria alternata mycotoxins (fungal metabolites) at carbon electrodes is studied by cyclic (CV) and square‐wave voltammetry (SWV). The selection of the best experimental reaction medium which minimizes the accumulation time is analyzed and discussed. The Freundlich adsorption isotherm resulted in being the best one to describe the specific interaction of ATX‐I with carbon electrodes by using a fitting procedure of experimental fractional surface coverage vs. the ATX‐I bulk concentration (cATX–*. SWV was also used to generate Ip vs. cATX‐I* calibration plots from pure commercial reagent solutions. A detection limit of 3×10–9 M could be determined from calibration plots performed at f=100 Hz for a signal to noise ratio of 2:1, being this value two orders of magnitude smaller than that obtained previously by us from the diffusion controlled ATX‐I oxidation peak. Ip/f vs. f plots from SW voltammograms performed at different cATX‐I as well as different accumulation times showed the so‐called “quasireversible maxima”. A splitting of the voltammetric peak was also observed by increasing the SW amplitude at a given frequency. A value of (0.342±0.003) V was determined for the formal potential of the adsorbed redox couple from the split voltammetric peak. A full characterization of the surface redox process was obtained by applying the methods of “split SW peak” and the “quasireversible maximum”. In the 20 % acetonitrile (ACN)+80 % 1 M HClO4 aqueous solution reaction medium, the formal rate constant and the anodic transfer coefficient were (685±27) s–1 and (0.48±0.03), respectively. Besides, the number of electrons exchanged during the redox reaction was calculated as n≈1.

Characterization of the surface redox process of adsorbed morin at glassy carbon electrodes

“…We have already studied the application of this methodology to carry out a full characterization of altertoxin I adsorbed at carbon paste electrodes [35] and both the redox coupled of cercosporin [36] and the ochratoxin A electro-oxidation product [37] adsorbed at GC electrodes.…”