Analytical & Bioanalytical Electrochemistry
Volume:7 Issue: 6, Dec 2015

We have investigated the electrochemical interaction between mechlorethamine and organic solvents i.e. acetone and acetonitrile, in the presence and absence of 4-chloro butyronitrile (CBN) using cyclic voltammetric technique. We found the reactivity (chemical reactivity) of mechlorethamine through the value of the forward reaction rate constants (Kf) in acetone and acetonitrile, in the presence and absence of CBN were 0.1601 s-1, 0.4828 s-1, 0.1365 s-1, 0.2724 s-1, respectively. These values of Kf were determined from the curves of Kft versus t with correlation coefficient values are higher than 0.9500. The values of Kf affected by the donor number (DN) of solvents and also the structure of the nucleophilic compound were added. This is due to acetone has a larger DN than acetonitrile therefore Kf in acetone is higher than that in acetonitrile. CBN reduces the value of the chemical reactivities of mechlorethamine in both solvents. This can occur because CBN is a simple structure that is why it can interact directly with mechlorethamine.

A novel analytical approach has been developed and evaluated for the quantitative analysis of paraquat herbicides which can be found at trace levels in the presence of ascorbic acid and uric acid. The experimental results suggest that a carbon ionic liquid electrode modified with multi-walled carbon nanotubes and nickel hydroxide nanoparticles accelerates the electron transfer reactions of paraquat. The best responses were obtained with differential potential and chronoamperometry methods in Phosphate buffer (pH, 7.5). The influence of various parameters on the electrode was investigated. Under the optimized working conditions, calibration graphs were linear in the concentration ranges of 0.0025–25 mg L-1 with a detection limit (S/N=3.0) of 0.8 ppb. The proposed electrode was used for determination of paraquat in fruits and River water samples with satisfactory results.

A new carbon paste electrode modified with NiSO4 (NSCPE) was fabricated and employed in electrocatalytic oxidation of 2-thiouracil (2-TU) for the first time using cyclic voltammetry (CV), square wave voltammetry (SWV) and differential pulse voltammetry (DPV) as diagnostic techniques. Characterization of the NSCPE was carried out by CV and scanning electron microscope (SEM) techniques. All experimental parameters have been optimized. The plausible mechanism of oxidation of 2-TU was proposed. The DPV of 2-TU gave a good linear response in the range of 10-100×10-8M with a limit of detection 2.1×10-9 M and limit of quantification 6.9×10-9M. The proposed method was successfully applied for quantitative determination of 2-TU in pharmaceutical formulations and urine as real sample.

Inhibition of corrosion of mild steel by ethanol extract of Prosopis Juliflora was studied by both potentiodynamic method and weight loss method. A 24 full factorial design was performed to determine the optimal condition of corrosion inhibition and to determine the variable which affects the inhibition of corrosion of mild steel by the ethanol extract of Prosopis Juliflora. The variable that was studied were concentration of the medium (HCl, 0.1 M and 1 M), concentration of the inhibitor (100 ppm and 700 ppm), temperature (303 K and 333 K) and time (1h and 5 h). A linear mathematical model was applied to the experimental results, to determine the effect of each variables and their relationship were determined. Statistical analysis such as ANNOVA (Analysis of Variance), F-test and student t-test, surface analysis were carried out in experimental data and the results indicated that the effect of the temperature is greatest followed by the concentration of the inhibitor and least effect was shown by the concentration of the time. Concentration of medium on the corrosion inhibition of mild steel by ethanol extract of Prosopis Juliflora was found to show a negative effect. The statistical model was found to have most excellent fit with high coefficient of determination (R2=0.997) for the inhibition of corrosion. The effect of the factor on the Corrosion inhibition was also investigated by the response surface methodology (RSM) based on Box-Behnken design (BBD).

Pluronic P123, a type of Poloxamers materials, was examined as an inhibitor for decreasing zinc corrosion in alkaline media (4.0 M NaOH). This material was used in the form of the particles dispersed in electrolyte (suspension form). Its effect was examined by electrochemical methods potentiodynamic polarization (Tafel) and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) was used to analysis the electrode surface in presence and abcense of the inhibitor. The obtained results indicate that P-123 inhibits zinc corrosion in 4.0 M NaOH electrolyte and zinc corrosion decreases with increasing the value of P-123 particles. Moreover, the results of potentiodynamic polarization reveal that the inhibitor affects both the anodic and cathodic branch, so it is mix type. The obtained inhibition efficiency from potentiodynamic polarization and EIS showed a reasonable agreement. In addition, for battery application, it was found that P-123 increases Zn/CuO battery performance.

In this study, passive behavior and semiconducting properties of Alloy 22 in hydrochloric acid solutions were evaluated. Corrosion and passive current density was measured from potentiodynamic polarization plots. Also, passive film resistance and passive film capacitance were estimated by electrochemical impedance spectroscopy (EIS), and finally defect (donor and acceptor) density was drawn from Mott–Schottky analysis. Mott–Schottky plots revealed that Alloy 22 in hydrochloric acid solutions behave as n-type and p-type semiconductors. Also, this analysis indicated that both donor and acceptor densities are in the range 1021 cm-3 and increased with solution concentration. In conclusion, EIS and Mott–Schottky analysis revealed that dilute hydrochloric acid solutions offer better conditions of the passive film formation on Alloy 22 with higher protection behavior than concentrated hydrochloric acid solutions, due to the growth of a much thicker and less defective films.

A new simple, sensitive and selective electrochemical method for the determination of Nitrobenzene (NB) and 4-Nitrophenol (4-NP) at L-Cystine modified glassy carbon electrode was developed with the help of cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. Based on the effect of pH, a detailed electrochemical redox mechanism was proposed and the number of electrons involved in the R-NO2→ R-NO2¯● step was determined. The kinetic parameters such as heterogeneous rate constants (ks) and charge transfer coefficient (α) values were calculated and was found to be as 0.711×10-6 s-1, 1.486×10-6 s-1 and 0.521, 0.501 for both NB and 4-NP respectively. The NB and 4-NP systems were controlled by diffusion process and the diffusion coefficients values were determined as 3.24×10-7 cm2/s and 7.04×10-7 cm2/s for NB and 4-NP respectively. The limit of detection (LOD) and limit of quantification (LOQ) values were evaluated as 7.46×10-6 M, 24.9×10-6 M with linear dynamic range from 30 μM to 105 μM for NB and 0.1049×10-6 M, 0.349×10-6 M with linear dynamic range from 0.5 μM to 6 μM for 4-NP respectively. The developed method was effectively applied for the simultaneous determination of NB and 4-NP. Moreover the surface nature of the electrode was investigated by the electrochemical impedance spectroscopy. Finally the developed method was successfully applied for the real sample analysis with satisfactory recovery values having low RSD values.

A novel electrode was developed for potentiometric determination of dexamethasone sodium phosphate (DSP) using tetraheptyl ammonium bromide (THB) as an anionic exchanger in polyvinyl chloride (PVC) matrix and 2-nitrophenyl octyl ether (2- NPOE) as a plasticizer. Linear responses of 1×10−5 to 1×10−2 M with slope of 26.50±0.39 mV/decade within working pH range 8-12 were achieved. The percentage recovery of determination of DSP by the proposed DSP selective electrode was 99.96±0.95. Determination of DSP in its pharmaceutical formulations by the proposed electrode revealed its applicability for determination. Moreover, the electrode exhibits good selectivity for DSP with respect to a large number of interfering substances and co-formulated drugs. The fabricated sensor was validated according to ICH guidelines and successfully applied for determination of the studied drug in pure form and pharmaceutical formulations without any interference from additives either labeled or non-labeled. The obtained results have been statistically compared to that of an official spectrophotometric method to give a conclusion that there is no significant difference between the proposed methods and the official one with respect to accuracy and precision.

Diltiazem (DZ) is a common benzodiazepine family, which is a calcium channel blocker usually supplied and used as a hydrochloride salt. The widespread use of the pharmaceutical has naturally created an increasing need for its analysis. It is therefore the main objective of the present work to develop an all-solid-state (ASS) polymeric-membrane-electrode (PME) for the analysis of DZ hydrochloride in pharmaceutical formulations. The developed ASS-PME is based on the application of an ion-pair agent in its sensing element. Experiments showed that the optimal results could be achieved with a PME containing 10% wt. of the ion-pair agent (i.e. DZ-tetrakis (p-chlorophenyl) borate (TPClPB)), 56% wt. of dibutyl phthalate (DBP) as the membrane solvent, 30% wt. of polyvinyl chloride (PVC), and 4% wt. of a room temperature ionic liquid (RTIL). Next the polymeric membrane was coated on an ASS element made of a composite of an epoxy resin, graphite and multiwalled carbon nanotubes (MWCNTs) which was deposited on a copper wire, as the internal contact. The DZ-ASS-PME revealed a potential response of 56.8±0.3 mV/decade over a wide concentration range of 2.0×10-7 to 1.0×10-3 M and was found to be suitable for applied to the analysis of DZ, as proved by the application of the ASS-PME in the measurement of DZ concentration in DZ tablets.

2-Chlorobenzoyl ferrocene (2CBF) was synthesized and used to construct a modified carbon nanotube paste electrode. The electro-oxidation of isoproterenol at the surface of the modified electrode was studied using cyclic voltammetry (CV), chronoamperometry (CHA) and square wave voltammetry (SWV). Under the optimized conditions, the square wave voltammetric peak currents of isoproterenol increased linearly with isoproterenol concentration in the range of 2.5×10-7 to 8.0×10−5 M and detection limit of 9.0×10-8 M was obtained for isoproterenol. Finally this modified electrode was used for determination of isoproterenol in real samples.