“…The electrochemical techniques have been effectively applied to study the redox properties of several biologically important compounds [20,21]. As reported previously, the redox behavior of indole derivatives was investigated using various electrodes: pyrolytic carbon [22], glassy carbon [17,23], platinum [24], lead dioxide [25] boron-doped diamond [26,27], and other electrodes [28][29][30]. Among the studied indole compounds with a substituent at C3, the results of electrochemical oxidation of indole-3-acetic acid, indole-3-propionic acid, indole-3-butyric acid, indol-3-acetamide, tryptamine, gramine and tryptophan were reported for the measurements done with the usage of a glassy carbon electrode as the working electrode [23,31].…”