Analytical & Bioanalytical Electrochemistry
Volume:7 Issue: 3, Jun 2015

This study determined the semiconductor character of the anodically passive films formed on zirconium in 0.5 M NaOH (pH=13.3), estimated the dopant levels in these films, and estimated the passive film thickness as a function of the film formation potential. Mott–Schottky analysis revealed that the anodically passive films displayed n-type semiconductive characteristics, where oxygen vacancies and cation interstitials preponderated. Based on the Mott–Schottky analysis, it was shown that the calculated donor density increased with increases in formation potential. Moreover, the results indicated that the thickness of the anodically passive films increased linearly with the film formation potential.

The voltammetric study of Cu (II) in presence of aspartic acid (Aa) and L-phenyl alanine (Pa) respectively has been carried out in buffer solution of different pH, scan rate and variation of Aa or Pa concentration. Cu(II) in presence of Aa and Pa has been found to undergo two anodic peaks follows two step two electron transfer anodic reaction. The peak positions of the voltammogram of Cu(II) in presence of Aa or Pa shifted with respect to that of uncoordinated Cu(II). The peak current of Cu(II) with ligands (Aa, Pa) decrease significantly compared with that of uncoordinated Cu(II) in the same experimental conditions. These behaviors may ascribe the formation of complex of Cu(II) with Aa and Cu(II) with Pa. The linear behavior of peak current with the square root of scan rate of Cu complexes indicates that the electrochemical processes are diffusion controlled. The effects of pH of Cu-Aa and Cu-Pa complexes were studied by varying pH from 3.5 to 5.5. The oxidation peak current increases with the decrease in pH. At higher pH (pH>7) the complexes were almost electroinactive. This attributed that the electrochemical oxidation of the complexes are facilitated in lower pH media. The slope of the plots of Ep against pH of Cu- Aa and Cu-Pa complexes are 35-39 mV, indicates that the oxidation of Cu-Aa and Cu-Pa complexes proceeded via 2e−/2H+ processes. The complexes were formed by the addition of Aa or Pa into Cu(II) and the maximum interaction has been found for 1:3 molar ratio at pH 3.5. The mode of interaction of Aa and Pa with Cu(II) has been found to be similar.

An efficient multi-walled carbon nanotube/gold colloidal nanoparticle paste electrode (MWCNTs/ Au Nps PE) was prepared for detection of hydrazine in the presence of pyrogallol red as a mediator in the homogenous solution. The prepared MWCNTs/ Au Nps PE and multi-walled carbon nanotube paste electrode (MWCNTs PE) were characterized by Raman spectroscopy, scanning electron microscopy and cyclic voltammetry. The MWCNTs/ Au Nps PE exhibited a very large decrease in the over potential (0.3V to 0.0V) and significant enhanced peak current response for detection of hydrazine in the presence of pyrogallol red as a mediator in the Na2CO3 - KCl solution. The mass transfer of hydrazine on the surface of MWCNTs/Au Nps PE was controlled by adsorption process. The proposed method exhibits outstanding sensitivity (2.5 μA/μM) and low detection limit (0.4 μM) at 0.0V. All the results indicated a good potential application of this sensor in the detection of hydrazine. The use of MWCNTs/ Au Nps PE was demonstrated for detection of hydrazine in the drinking water samples.

The electroanalytical system with the hydrazine detection by Michael addition reaction with naphthlaminosulphonic acids was mathematically described. The corresponding mathematical model has been developed and analyzed by linear stability theory and bifurcation analysis. The steady-state stability conditions, corresponding to the better response, were developed. The presence of oscillatory and monotonic instabilities was also confirmed.

The electro-oxidation of epinephrine (EPI), acetaminophen (ACT) and Mefenamic acid (MEF) has been investigated by application of nickel hydroxide nanoparticles / multi-walled carbon nanotubes modified glassy carbon electrode (MWCNT-NHNPs/GCE) using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CA) methods. The modified electrode showed suitable electrochemical responses for EPI, ACT and MEF determination. Under the optimum conditions the electrode provides a linear response versus EPI, ACT and MEF concentrations in the range of 0.5-180 μM, 0.1-180 μM, and 0.1-85 respectively using the DPV method. Application of CA method showed linear responses for EPI and ACT concentrations in the range of 1-600 μM and 1-500 μM respectively. The CA results for MEF showed two linear range of 1-50 μM and 60-600 μM. The modified electrode was used for determination of EPI, ACT and MEF in human serum and urine with satisfactory results.

A carbon ceramic electrode activated with MWCNTs and modified with [Rh(terpyridine)(bipyridine)Cl] (PF6)2, have been applied to the electrocatalytic oxidation of hydrazine which reduced the overpotential by about 165 mV with obviously increase the current response. Cyclic voltammetry was employed to characterize the electrochemical behavior of the chemically modified electrode. The electrocatalytic efficiency of the modified electrode towards hydrazine oxidation depends on solution pH, and optimum pH value for oxidation of hydrazine is 7.0. The overall number of electrons involved in the catalytic oxidation of hydrazine and the number of electrons involved in the rate-determining steps are 4 and 1, respectively. And diffusion coefficient of hydrazine was estimated using chronoamperometry.

The present work demonstrates that simultaneous determination of ascorbic acid (AA), uric acid (UA) and acetaminophen (ACT) can be performed on a novel single walled carbon nanotubes (SWCNTs), chitosan (CHIT) and MCM-41 composite modified glassy carbon electrode (SWCNTs-CHIT-MCM-41/GCE). The electro-oxidations of AA, UA and ACT were investigated by using differential pulse voltammetry (DPV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) methods. Under optimum conditions application of DPV method showed that the linear relationship between oxidation peak current and concentration of AA, UA and ACT were 1-160 μM, 0.1-24 μM and 0.1-21 μM with detection limits of 0.41, 0.04 and 0.03 μM, respectively

A simple square-wave adsorptive voltammetric (SWAV) method was developed for determining Captopril (CAP) in pharmaceutical formulations. The proposed method was based on the electrochemical reduction of CAP at a mercury thin film electrode (MTFE). The preparation of the TMFE/Glassy carbon electrode was very simple; also, this electrode had very good reproducibility and regeneration of its surface was very easy. This kind of electrode has the advantages of mercury electrode and a negligible amount of mercury. In this study, the MTFE in situ produced on glassy carbon electrode to the adsorptive voltammetric quantification of trace amount of CAP. MTFE was shown to be extremely useful for the voltammetric measurements of CAP at μM level. Under optimized conditions, the SW adsorptive stripping voltammetric peak current showed linear correlation with drug concentration over the range of 4.6–64.5 μM with the correlation coefficient of 0.992. The detection limit at the S/N ratio of 3 was 0.6 μM for CAP (n=6) and the relative standard deviation for 23 μM of CAP (n=6) was 6.9%. The film electrode had the advantages of acceptable sensitivity, reproducibility, and simple preparation. The MTFE applied to determination of CAP in tablet samples with satisfactory results.

A potentiometric inexpensive sensor has been designed for detection of Clobutinol Hydrochloride level, which is used for curing non-productive coughs. The sensor is capable of doing direct detection of the drug level in the chemical solution using PVC ion-exchange membranes. The ion pair used as the sensing element was made through the interaction of Clobutinol Hydrochloride and Sodium Tetra-Phenyl borate. It is shown that the highest ion-selective electrodes in sensitivity were achieved by 10% ion pair, 45.5% dioctyl phthalateand 44.5% of PVC composition. The sensor response time is found to be less than 10 seconds, with a minimum detectable range of 4.0×10-6M in 0.5×10-1M−1.0×10-5 M range.For measurements, a sensing board in direct and permanent contact with the electrodes is used. This integrated measurement system is made of an ATMEGA16L micro-controller sampling, analyzing and data storage section which makes measurements easier and faster. It also helps with reducing the side effects caused by a traditional multimeter usage such as connection cables resistance.

Carbon paste electrode was modified by surfactant modified ZSM-5 nanozeolite and the electrochemical behavior of this modified electrode was studied using cyclic voltammetry. This electrode showed enhanced electrochemical response and strong analytical activity towards the direct electrochemical oxidation of sulfide. The influence of some parameters such as different mass ratio of ZSM-5 nanozeolite and graphite, surfactant concentration, pH and scan rate of potential was investigated on the anodic peak height of the sulfide oxidation. Under optimal conditions in a buffer solution, pH 8.0, the anodic peak currents increased linearly with the concentration of sulfide and discovered two linear dynamic ranges with slopes of 0.6896 μA/μM and 5423.5 μA/M in the concentration ranges of 5×10-6 to 1×10-4 M and 3×10-4 to 0.1 M, respectively. The detection limit was achieved 1.32×10−6 mol L−1 (3σ). Also, the electron transfer coefficient (α) and diffusion coefficient (D) of sulfide at the surface of modified electrode were calculated. The proposed electrode was successfully used for the determination of sulfide in tap water and mineral water.