Department of Analytical Chemistry, Faculty of Chemistry, University College of Science, University of Tehran, Tehran, Iran P.O. Box 14155-6455, Tehran, Iran
A new method based on a carbon paste electrode, modified with ErO2/MnO2 nanocomposite was introduced for melatonin determination. The differential Pulse Voltammetry (DPV) method was found to be a suitable analytical technique to acquire an enhanced electro-oxidation signal and thus it was chosen as the signal recording method. The nanocomposite was characterized using Scanning electron microscopy and X-ray diffraction analysis method. The electrocatalytic activity of the carbon paste electrode modified with ErO2/MnO2-CPE toward melatonin electro-oxidation was substantiated utilizing DPV and electrochemical impedance spectroscopy ((EIS). The EIS technique gave a clear indication for the intensification the of charge transfer rate by the nanocomposite described. Different parameters, affecting the electrode efficiency were investigated and optimized. Using DPV and ErO2/MnO2-CPE, a linear dynamic range of 4.0×10-8-2.0×10-5 mol L-1 as well as a detection limit of 6.0×10-9 mol L-1 was obtained for melatonin measurement. The relative standard deviation percentage (RSD%) of four repeated measurements was found to be about 4.08%. The developed method was used for the estimation of melatonin amount in urine samples which led to satisfactory results.