| Abstract: | The adsorptive accumulation of cercosporin (CER) at glassy carbon electrodes is studied by square‐wave voltammetry (SWV). The Freundlich adsorption isotherm resulted in being the best one to describe the specific interaction of CER with glassy carbon electrodes by using a fitting procedure of experimental fractional surface coverage vs. the CER bulk concentration (c*CER). SWV was also used to generate Q vs. c*CER and Ip, n. vs. c*CER calibration plots from pure commercial reagent solutions. Theoretical detection limits of 1.8×10?7 and 9.7×10?8 M were calculated from Q. vs. c*CER and Ip, n vs. c*CER plots, respectively. The lowest concentration value measured experimentally from calibration plots performed at a f =40 Hz for a signal to noise ratio of 2 : 1 was 3.7×10?8 M, being this value two orders of magnitude smaller than that obtained previously by us from the diffusion controlled CER reduction peak. Ip, n./f vs. f plots from SW voltammograms performed at different c*CER as well as different accumulation times showed the so‐called “quasi‐reversible maxima”. A splitting of the voltammetric peak was also observed by increasing the SW amplitude at a given frequency. A value of (?0.260±0.011) 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 the “quasi‐reversible maximum” and the “split SW peak”. In 1 M HClO4 aqueous solution, the formal rate constant and the anodic transfer coefficient were (3.5±0.5)×102 s?1 and (0.50±0.03), respectively. Besides, the number of electrons exchanged during the redox reaction was calculated as n≈1. |
