Determination of ascorbic acid at solid electrodes modified with L-cysteine

Gold and glassy carbon electrode surfaces were modified with L-cysteine, and the electrochemical behavior of ascorbic acid (AA) was investigated on these new surfaces. To improve the efficiency of electrodes, the electrode surfaces were modified and optimum conditions for AA determination were established. Electrochemical experiments were performed at different potential ranges, the concentration of AA, scan rates, number of polymerization cycles and pH values. Using cyclic voltammetry (CV) technique, optimum conditions were determined as the potential scanning range of 0.2 to 1.5 V vs. Ag/AgCl in 0.1 M phosphate buffer solution (pH 7.02) for the L-cysteine/Au electrode, and -1.95 to 1.9 V vs. Ag/AgCl in 0.1 M phosphate buffer solution (pH 2.7) for the L-cysteine/GC electrode. For the characterization of both modified electrode surfaces, a series of physicochemical techniques was also applied. The usability and selectivity of these two proposed modified electrodes for the determination of AA were investigated using square wave voltammetry (SWV) in the presence of possible interferents, i.e., glycine, L-glutamic acid and uric acid

Effect of different copper salts on the electrochemical determination of Cu(II) by the application of the graphene oxide-modified glassy carbon electrode

In this study, graphene oxide and reduced graphene oxide nanoparticles were synthesized by Hummers method and characterized Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy, scanning electron microscopy and thermogravimetric analysis. Then, glassy carbon electrode surfaces were modified with synthesized and characterized graphene oxide (GO) and reduced graphene oxide (red-GO) using physical immobilization. Bare and modified surfaces were characterized by cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. Application of graphene oxide (GO/GC) and reduced graphene oxide-modified glassy carbon (red-GO/GC) surfaces for the electrochemical determination of copper(II) using different copper salts such as CuSO4·5H2O, Cu(NO3)2·3H2O and CuCI2 were performed by differential pulse voltammetry. The GO/GC surface was found to be suitable for selective determination of Cu(II) in the solutions containing the mixture of heavy metal ions (Zn(II), Pb(II), Cd(II), Fe(III) and Mn(II)) and showed high stability and reproducibility. The GO/GC surface was treated with CuSO4·5H2O, Cu(NO3)2·3H2O and CuCI2 salts solution in optimum conditions and afterward SEM images were measured 10 µm in size and radius of these ions in Cu(II)/GO/GC surfaces. Thus the determination of copper ions on the GO/GC surface was made for the first time by comparing the effect of the types of copper salts. When it was evaluated in terms of inorganic theory, the results were found to be in harmony

Electrochemical determination of Cu(II) ions using glassy carbon electrode modified by some nanomaterials and 3-nitro aniline

The aim of this research was to investigate the effect of the several nanomaterials in electrochemical determination of Cu(II) ions. For this aim, firstly the deposition of graphene oxide (GO), graphene, magnetite (Fe3O4), gold-chitosan (AuChts) or multilayer carbon nanotubes (MWCNTs) on the glassy carbon (GC) electrode surface was performed. Then the electrochemical modification of electrode by poly-3-nitroaniline (poly-3NA) was performed by 100 potential cycles in the range between +0.9 V and +1.4 V vs. Ag/AgNO3 at the sweep rate of 100 mV/s. For electrochemical reduction of nitro groups present on modified GC electrode surface, potential cycling was performed in 100 mM HCl between −0.1 V and −0.8 V vs. Ag/AgCl/(KClsat.) at the sweep rate of 100 mV/s. Nanomaterial and poly-3NA modified electrodes were applied in the determination of Cu(II) ions by differential pulse voltammetry. It was determined that GC electrodes consecutively modified with MWCNTs, poly-3NA and then by electrochemical reduction of nitro groups were the most sensitive towards Cu(II) ions with detection limit of 0.5 × 10−9 M