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In this work, the EC' mechanism involving ascorbate (AA−) and the oxidized form of ferrocenemethanol (FcMeOH) was explored as an analytical strategy to monitor AA− at low concentration levels. The feasibility of this approach was investigated at different mass transport regimes utilizing macro‐ (glassy carbon) and ultramicroelectrodes (5 μm radius carbon disk). Cyclic voltammograms (CV) were recorded in acetate buffer solution (pH 3.7) using a glassy carbon electrode, and an expressive increase in the anodic peak current (and decrease in the cathodic peak) was noticed in the CV in a solution containing both FcMeOH and ascorbate, confirming the presence of an electrocatalytic process (EC'). The current increase was more pronounced when the reactants and products were confined in a thin solution layer, which was created by approaching an ultramicroelectrode close to an insulator surface. At optimized experimental conditions, a correlation between ascorbate concentration and the steady‐state current measured at the ultramicroelectrode was established, allowing the development of an analytical method for ascorbate detection in the micromolar range. The proposed approach was used to quantify ascorbate in a commercial juice sample. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen peroxide (H2O2) is a versatile oxidizing agent that is synthesized commercially by the reduction of oxygen in organic medium. Electrochemical technology employing a modified gas diffusion electrode (MGDE) offers a viable alternative for the industrial-scale synthesis of the oxidant. Addition of 1% (w/w) of tert-butyl-anthraquinone (TBAQ) to carbon black deposited in the form of a microporous layer onto the disk of a rotating ring-disk electrode produced an increase in the ring current, which is directly related to H2O2 formation, and presented an efficiency of H2O2 generation of 89.6% compared with 76.6% for carbon black alone. No significant changes were detected in the number of electrons transferred in the presence of the catalyst suggesting an electrochemical/chemical mechanism for H2O2 formation. Analogous improvements in the generation of H2O2 were obtained with MGDEs comprising TBAQ on carbon black. The highest concentrations of H2O2 (301mgL−1) were produced at the fastest rate (5.9mgL−1 min−1) with the lowest energy consumption (6.0kWhkg−1) when a potential of −1.0V vs SCE was applied to a MGDE containing 1.0% of TBAQ on carbon black. It is concluded that the application of MGDEs comprising TBAQ on carbon black support offers considerable advantages in the electrogeneration of H2O2. [Copyright &y& Elsevier]