Analytical & Bioanalytical Electrochemistry
Volume:4 Issue: 5, Oct 2012

The electro-reduction of oxygen on silver-modified glassy carbon electrode (Ag/GC) in acidic solution at different potentials was studied by ac-impedance spectroscopy. The influence of the electrode potential on impedance of oxygen reduction reaction is studied and a mathematical model was put forward to quantitative account for the impedance behavior of oxygen reduction. At potentials higher than -0.4 V/Ag-AgCl, a pseudo inductive behavior is observed. The conditions required for this behavior are delineated with the use of the impedance model.

Liquid state lipase enzyme sensor was used for the detection of Carbophenothion and Dibrom organophosphorus pesticides and the electrochemical behavior of both the pesticides was studied. The developed enzymatic method is based on in situ generation of p-Nitrophenol by lipase enzymatic hydrolysis of p-Nitrophenyl Acetate substrate. The electrochemically active p-Nitrophenol gives an anodic oxidation peak potential at 0.05 V vs. SCE. Based on enzymatic inhibition property of Carbophenothion and Dibrom pesticides are selected for study of lipase enzyme inhibition. The current response is based on the production of p-Nitrophenol under the influence of enzyme concentration, substrate concentration, pH and time variation effects were studied. A linear calibration for Carbophenothion and Dibrom was obtained in the various concentration ranges of 10-100 ppb and 100-1000 ppb respectively with a correlation coefficient of 0.947 and 0.936 under the optimized conditions by following the incubation time of 25 min. The electrochemical experiments were performed in 0.1 M phosphate buffer solution (pH 7.0) at room temperature. The limit of detection and limit of quantification values were found to be 37.40 ppb, 124.6 ppb and 371.7 ppb, 1239 ppb for Carbophenothion and Dibrom respectively under optimized conditions. The pesticide carbophenothion is more toxic than the dibrom as evidenced by the electrochemical studies. The developed liquid state lipase enzyme sensor takes less time for the analysis and no preconcentration extraction was needed for the study.

The advantageous features of polymer modification and dispersion of metallic particles into the organic polymer was studied by construction of poly ortho-anisidine (POA) film and Ni(ΙΙ) were used in combination with POA films by immersion of the glassy carbon modified electrode in Nickel ions solution. This modified electrode exhibits good electrocatalytic activity toward the electrooxidation of hydrazine and has been studied by cyclic voltammetry (CV) and chronoamperometry techniques. The oxidation of hydrazine is occur at a potential about 140 mV less positive than that at unmodified electrode. The electron transfer coefficient (α) was determined and the electrocatalytic oxidation peak current of hydrazine showed a linear dependent on the hydrazine concentration and a linear calibration plot were obtained in the range of 5×10-5 M-1.4×10-2 M with cyclic voltammetry method. The detection limit (2σ) were determined as 3.9×10-5 M.

The applicability of Water Hyacinth (Eichhornia crassipes) as an important aquatic weed plant in sub-tropical regions of the world makes it a useful bio-accumulator and biosorbent for some organic pollutants including phenolic pollutants and some nitrogenous organic pollutants form wastewater. The experimental conditions upon using the investigated biomass were optimized to achieve a reduction of the chemical oxygen demand (COD) and the total organic carbon (TOC) by about 90%. Also the sorption of the reported pollutants was examined as a function of its initial concentration in wastewater, pH, weight of roots and contact time. The concentration of phenolic pollutants and nitrogenous organic compounds in influent and effluent of wastewater and in the collected water samples were monitored using several coated wire ion selective electrodes (ISEs). Each ion selective electrode is designed specifically to monitor one type of pollutants. The results obtained using the dried roots of water hyacinth is compared to that obtained when a granular activated carbon (GAC) is used. Preliminary results show that the outlet of the purification biomass meets most of the regulator’s limits for discharge of treated wastewater in Egypt. Therefore, the treated effluents can be used safely in different applications such as irrigation of golf course, green way or park. If it is sufficiently clean it can also be used for ground water recharge, in recharging of batteries or in some industrial use. Moreover, such water hyacinth roots can be used as an effective tool for the treatment and reuse of wastewater as they have been shown to adsorb and accumulate toxic elements.

The electrochemical oxidation of some catechols has been studied in the presence of N-phenylacetoacetamide in aqueous sodium phosphate buffer (pH=7), using cyclic voltammetry and controlled-potential coulometry. All the catechol derivatives were converted into benzofuran derivatives through a Michael-type addition reaction of N-phenylacetoacetamide to anodically generated o-quinones. The electrochemical syntheses benzofuran derivatives of were successfully performed in one pot in an undivided cell using an environmentally friendly method.

Ion selective electrode technique was developed for determination of pregabalin. The key to construct such an electrode is to produce a sensitive and selective membrane that responds to a particular ionic species. Such membrane is usually prepared by in corporating an appropriate ion exchanger and solvent mediator into a poly (vinyl chloride) or (PVC) membrane matrix. The present work originates from the fact that pregabalin behaves as a cation in 0.1 N HCl solution and forms a precipitate with anionic potassium tetrakis p-chlorophenyl borate which used in fabrication of the membrane sensor. The potentiometric response was linear with constant slope over a drug concentration range of 10-6–10-3 M with slope of 53±1 mV/decade. The developed method was applied successfully for the determination of pregabalin in the pure powder form, pharmaceutical formulation and in spiked human plasma without any interference.

A novel chemically modified electrode containing Cd(II) (ttpy) Complex was achieved on the surface of gold electrode by sol-gel technique. The electrochemical behavior of modified electrode was characterized by cyclic voltammetry in detail. The film electrode obtained was very stable and exhibited electrocatalytic response for oxidation of hydrazine. Results showed at bare Au electrode, a small oxidation peak current was observed at about 0.26 V, And a well- formed sharp catalytic oxidation peak at about 0.154 V was observed at Cd(II) complex modified electrode. The transfer coefficient (α) for electrocatalytic oxidation of hydrazine and the diffusion coefficient of this substance under the experimental conditions were also investigated.

A highly Co2+ ion-selective polyvinyl chloride (PVC) membrane sensor based on a derivative of calix[4]arene (L) as an excellent sensing material is successfully developed. The electrodes display a Nernstian behavior (29.7±0.4 mV decade−1) over wide Co2+ ion concentration ranges from 1.9×10-7 to 1.0×10-1 M with very low limits of detection (8. ×10-8 M). The electrodes have a relatively fast response time (<50 s), a satisfactory reproducibility and relatively long life time. The proposed sensor shows a fairly good selectivity toward C 2+ ion in comparison whit other common cations. The potentiometric responses are independent of the pH of the test solutions in the range of 2.5–8.4. The practical utility of the proposed electrodes have been demonstrated by their use in potentiometric titration of cobalt with EDTA. It was also successfully applied in determination of cobalt ions in some aqueous samples.