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This paper discusses about the improvement of electrochemical characteristics of graphite paste electrode chemically modified with chitosan through physical crosslinking of the biopolymer with sodium tripolyphosphate. Biopolymer characterizations were performed by scanning electron microscopy, Fourier transform infrared spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The electrochemical characterization of Pb with graphite paste electrode modified with chitosan crosslinked with sodium tripolyphosphate (GPE-CTS-TPP) showed that the process is quasireversible, controlled by adsorption and involves the transfer of two electrons. Additionally, the physical crosslinking process decreased the electrode resistance as well as improved the electron transfer rate. Once the GPE-CTS-TPP showed enhanced morphological and electrochemical characteristics, it was applied for Pb determination by square wave anodic stripping voltammetry. The method presented appropriate accuracy (recoveries from 95 to 108% and concordance with comparative method between 90 and 107%), high sensitivity (limit of detection and quantification of Pb were 0.73 and 2.44 μg L -1 , respectively) and could be applied to analytical determinations.

In situ recording of the voltammetric response of leaves of several Asparagales, Caryophyllales, and Saxifragales plants at platinum and graphite microelectrodes is described. These provide information on the temporal evolution of H2O2 production and electroactive defense compounds (salicylic and jasmonic acids) associated with the stress generated by electrode insertion. Comparison of voltammetric data in the absence and presence of ROS generation revealed significant differences in the kinetics of the plant response. Reported data suggest that signaling pathway changes could be associated with the phylogenetic divergence between monocots and eudicots and the subsequent separation of the Caryophyllales from other eudicots. [ABSTRACT FROM AUTHOR]

In situ recording of the voltammetric response of Aloe vera L. leaves using graphite and platinum microelectrodes inserted in the subcuticular region is described. The plant response against the mechanical stress results in changes of the voltammetric signals associated to signal transduction compounds salicylic and jasmonic acids and hydrogen peroxide, which were separately monitored. A kinetic model is proposed to describe the time variation of the respective voltammetric signatures, denoting the possibility of in vivo electrochemical monitoring of biochemical processes in plants. The obtained results suggest that two defense pathways with different participation of ROS are operative. [ABSTRACT FROM AUTHOR]

Concerning the importance of the identification and characterization of food dyes in food science, this work presents a screening method using voltammetry of immobilized microparticles for identification in solid state of sunset yellow, tartrazine yellow, brilliant blue, indigotine, and erythrosine in food matrices. Different aqueous supporting electrolyte were investigated for screening purpose and NaCl 0.1 mol L−1 showed to be suitable for evaluating dyes in solid state. By using square wave voltammetry as detection mode was possible to establish qualitative diagnostic criteria for identification of dyes in commercials powder of food dyes samples using both anodic and cathodic scan. Moreover, based on the solid-state electrochemistry profile and due to the lack of information about the electrochemical behavior of these compounds in solid state, some oxi/reduction pathways could be elucidated, and special attention was given to the case of sunset yellow dye. [ABSTRACT FROM AUTHOR]

• In situ voltammetric measurements on apple fruits are carried out. • Ascorbic acid and polyphenolic components are monitored. • A theoretical kinetic model involving three rate constants is developed. • The values of the rate constants exhibit significant differences between apple varieties. In situ recording of the voltammetric profile of different apple (Malus domestica Borkh.) varieties (Golden, Granny Smith, Reineta, Red delicious, Fuji, and Braeburn) without and with ROS generation is reported. The voltammetric response associated to the oxidation of ascorbic acid (AA) and polyphenolic (PPs) components was recorded. The obtained voltammetric profiles were satisfactorily fitted to a theoretical kinetic model consisting of the competing, dual activation pathways of AA and PPs followed by a degradative step. The rate constants for these processes were calculated from voltammetric data revealing significant differences between varieties. The activation pathways as well as the influence of electrochemical ROS generation on it were variety-sensitive while the degradative step was almost variety insensitive and lightly sensitive to ROS generation. [ABSTRACT FROM AUTHOR]

Abstract: The electrochemical behavior of ethanethiol was studied on polycrystalline gold electrodes in alkaline solution. With the help of cyclic voltammetry, differential pulse voltammetry and ex-situ X-ray photoelectron spectroscopy it is possible to propose a coherent reaction mechanism. Under the experimental condition gold thiolate and “gold hydroxide” are formed at the respective potentials. Dissolved and surface confined thiolate can be oxidized to the corresponding dithiol. The “gold hydroxide” reduction is accompanied by gold thiolate formation; the latter being stable at more negative potentials than the gold hydroxide. The experimental results indicate that thiolate ions react with the “gold hydroxide” layer by formation of a gold–thiolate layer and release of hydroxide ions to the solution. This non-electrochemical reaction is confined to the potential range where the gold–thiolate layer is stable. [Copyright &y& Elsevier]