Fakhradin Mirkhalaf

A highly sensitive nanostructure-based electrochemical sensor for electrocatalytic determination of norepinephrine in the presence of acetaminophen and tryptophan.

A new electrochemical sensor for the determination of norepinephrine (NE), acetaminophen (AC) and tryptophan (Trp) is described. The sensor is based on carbon paste electrode (CPE) modified with 3,4-dihydroxybenzaldehyde-2,4-dinitrophenylhydrazone (DDP) and takes the advantages of carbon nanotubes (CNTs), which makes the modified electrode highly sensitive for the electrochemical detection of these compounds. Cyclic voltammetry (CV) at various scan rates was used to investigate the redox properties of the modified electrode. The apparent charge transfer rate constant, k(s), and transfer coefficient, α, for electron transfer between DDP and CNT paste electrode were calculated. The mediated oxidation of NE at the modified electrode was investigated by CV and the values of k, α and diffusion coefficient (D) were calculated. Under the optimum pH of 7.0, the oxidation of NE occurs at a potential about 215 mV less positive than that of the unmodified CPE. Differential pulse voltammetry (DPV) of NE at the modified electrode exhibited two linear dynamic ranges with a detection limit (3σ) of 77±2 nM. DPV was used for simultaneous determination of NE, AC and Trp at the modified electrode, and quantitation of NE in some real samples by the standard addition method.

Application of 2-(3,4-dihydroxyphenyl)-1,3-dithialone self-assembled monolayer on gold electrode as a nanosensor for electrocatalytic determination of dopamine and uric acid

The electrooxidation of dopamine (DA), uric acid (UA) and their mixture on a gold electrode modified by a self-assembled monolayer of 2-(3,4-dihydroxyphenyl)-1,3-dithialone has been studied by cyclic voltammetry (CV), chronoamperometry and differential pulse voltammetry (DPV). CV was used to investigate the redox properties of the modified electrode at various scan rates and the apparent charge transfer rate constant (k(s)), and transfer coefficient (α) were calculated. The mediated oxidation of DA at the modified electrode under the optimum condition (pH = 7.0) in CV occurs at a potential about 220 mV less positive than that of the unmodified gold electrode. The values of electron transfer coefficients (α), catalytic rate constant (k) and diffusion coefficient (D) were calculated for DA, using electrochemical methods. DPV exhibited a linear dynamic range over the concentration range of 0.2-250.0 μM and a detection limit (3σ) of 0.07 μM for DA. The modified electrode was used for simultaneous determination of DA and UA by DPV. The results showed that the electrode is highly efficient for the catalytic electrooxidation of DA and UA, leading to a remarkable peak resolution (~350 mV) for two compounds. The electrode was used for the determination of DA in an injection sample.

Simultaneous and selective voltammetric determination of epinephrine, acetaminophen and folic acid at a ZrO2 nanoparticles modified carbon paste electrode

A new carbon paste electrode modified with ZrO2 nanoparticles (ZONMCPE) was prepared, and used to study the electrooxidation of epinephrine (EP), acetaminophen (AC), folic acid (FA) and their mixtures by electrochemical methods. The modified electrode displayed strong resolving function for the overlapping voltammetric responses of EP, AC and FA into three well-defined peaks. The potential differences between EP − AC, AC − FA and EP − FA were 210, 290 and 500 mV respectively. Differential pulse voltammetry (DPV) peak currents of EP, AC and FA increased linearly with their concentration at the ranges of 2.0 × 10−7–2.2 × 10−3 M, 1.0 × 10−6–2.5 × 10−3 M and 2.0 × 10−5–2.5 × 10−3 M, respectively. The detection limits for EP, AC and FA were found to be 9.5 × 10−8, 9.1 × 10−7and 9.8 × 10−6 M, respectively.

Blocking properties of gold electrodes modified with 4-nitrophenyl and 4-decylphenyl groups

The electrochemical properties of Au electrodes grafted with 4-nitrophenyl and 4-decylphenyl groups have been studied. The electrografting of gold electrode surface with aryl groups was carried out by electroreduction of the corresponding diazonium salts in acetonitrile. The nitrophenyl film growth on gold was examined by atomic force microscopy, electrochemical quartz crystal microbalance and X-ray photoelectron spectroscopy. These measurements showed that a multilayer film of nitrophenyl groups was formed. Cyclic voltammetry was used to study the blocking properties of aryl-modified gold electrodes towards the Fe(CN)63−/4− redox system. The reduction of oxygen was strongly suppressed on these electrodes as evidenced by the rotating disc electrode results.