Electrochemical investigations were performed using an Autolab potentiostat (Metrohm Autolab B.V., Netherlands) controlled by the NOVA software (version 2.1.5) in a three-electrode cell with Ag|AgCl|0.3 M NaCl reference electrode, Pt foil counter electrode, and a glassy carbon disk electrode (GCE from Mineral, Poland) as the working electrode of 0.0706 cm 2 surface area. Before each electrochemical experiment, the surface of the glassy carbon electrode was polished using 1 and 0.3 μm alumina powder on a Buehler polishing cloth. After polishing, to remove traces of alumina from the electrode surface, the working electrode was rinsed with appropriate amounts of ultrapure water (resistivity 18.2 MΩ•cm). The reference electrode was separated from the working solution by an electrolytic bridge filled with a 0.1 M phosphate buffer solution. The potential of the reference electrode was calibrated on the basis of ruthenium electrode process. The formal potential of hexaammineruthenium(III) chloride reduction in 0.5 M KNO3 is 0.172 ±0.002 V Cycling voltammetry (CV) measurements were performed in different scan rates and at least 3 scans were recorded. The experimental conditions for differential pulse voltammetry (DPV) were step 5 mV, modulation amplitude 50 mV, modulation time 0.1 s, interval time 1 s and scan rate 5 mV/s. For square wave voltammetry (SWV), the experimental conditions were frequency 25 Hz step 2 mV, modulation amplitude 50 mV corresponding to an effective scan rate of 50 mV/s. The acquisition of voltammetric curves was repeated at least 3 times for each solution of 0.5 mM 8AQ. All electrochemical measurements were performed using mixture of 0.1 M NaH2PO4 and 0.1 M Na2HPO4 (which at pH range 5 to 8 is phosphate buffer) as the supporting electrolyte at room temperature, under argon atmosphere. The pH was adjusted by adding small volumes of concentrated NaOH or H3PO4 solutions and carefully controlled before, during and end the end of experiments.