Analytical & Bioanalytical Electrochemistry
Volume:4 Issue: 2, Apr 2012

In the present work, electrochemical and spectroelectrochemical behaviors of 1- nitroso-2-naphthol has been studied by cyclic voltammetry and electrochemical impedance spectroscopy techniques in non-aqueous media. Cyclic voltammetric studies of 1-nitroso-2-naphthol in acetonitrile containing 100 mM tetrabutylammonium tetrafluoroborate on glassy carbon and platinum electrodes were performed between 0.0 mV and +2600 mV potential range at 100 mV s-1 scan rate with 10 cycles. Anodic peaks were observed at 475.3 mV, 958.9 mV, 1395 mV and 2103 mV for 1-nitroso-2-naphthol on the glassy carbon electrode surface vs. Ag/Ag+ reference electrode. The surface characterizations were carried out by using cyclic voltammetry and electrochemical impedance spectroscopy techniques in both aqueous and non-aqueous media. Electrochemical behaviors of 1 nitroso- 2-naphthol on glassy carbon and platinum electrode surfaces were compared.

The electrochemical behaviour of quercetin has been studied at carbon paste electrode (CPE) and β-cyclodextrin modified carbon paste electrode (β-CDMCPE) by employing cyclic voltammetry (CV) and Differential pulse voltammetry (DPV). The β-CDMCPE showed a considerable electrocatalytic effect towards the oxidation peak of quercetin, in Britton- Robinson (BR) buffer pH 2.5, (0.04 M) under, appropriate environment. The anodic peak current is linear to quercetin concentration in the range of 6×10-6 M to 2×10-5 M with detection limited of 3×10-7 M and the limit of quantification of 1.2×10-6 M respectively. The electro catalytic oxidation of quercetin at β-CDMCPE was compared with CPE. The electrochemical process was reversible and adsorption controlled. The interfacial electron transfer phenomenon of quercetin at the modified electrode was deliberated by using electrochemical impedance spectroscopy (EIS), the studies showed that β-CDMCPE was well eminent compared with bare CPE. The electrochemical sensor showed excellent sensitivity towards the determination of quercetin.

Polystyrene-based nickel arsenate membranes were prepared by sol-gel method for various electrolytes (KCl and NaCl) at different concentrations and found to be quite stable. The membrane capacitance and resistance obtained values were found to dependent on the concentration of the electrolyte and to depend on the applied oscillator frequency at isothermal temperature (25  0.1°C). The electrical double-layer at the membrane electrolyte interface was influenced and controlled by the transport of ions. An increase in concentration of electrolyte solution causes the counter ions in the form of double-layer to be pushed inside the membrane. Thus, the membrane becomes more conductive to the incoming ions, which in turn, supports the trend in the behaviour of the membrane resistance under discussion. Deviations from the ideal behaviour in the lower frequency range were attributed to the nonhomogeneous nature of the membrane used in the investigation.

In this study, we developed a hybrid biosensor based on sulfite oxidase and glucose oxidase for determination of sulfite and glucose. The principle of the measurements was based on the determination of the decrease in the differentiation of oxygen level which had been caused by the catalytic reactions of the enzymes in the bioactive layer of the biosensor. The biosensor showed a linear response for an interval of sulfite concentration between 1×10-4 and 1.75×10-3 M and for glucose concentrations between 2.5×10-5 and 1.25×10-3 M. After some optimum and characterization studies, the proposed biosensor was applied to the determination of sulfite and glucose in certain real samples, blood and pickle water.

This study is related with the determination of thiocyanate anion by using 3,12- diaza-4,5,10,11-dibenzo-16-methyl-6,9-dioxaheptadec-1(17),14,15-triene-2,13 diimenecopper(II) as ionophore. The membrane sensor with composition of 37% PVC, 60%, BES, 2% HTBP and 1% ionophore, exhibits a Nernstian response for thiocyanate ion, with a wide concentration range of 4.4×10−8−1.0×10−1 M, low detection limit (1.0×10−8 M) and slope of 60.5.±0.3 mV decade−1 of activity within pH range of 2.5–8.5 and fast response time of 5s. The sensor was also found to work satisfactorily in partially non-aqueous media up to 30% (v/v) content of methanol, ethanol or acetone and could be used for a period of 2 months without any change in response characteristics.

PVC based membrane of 1,5-diphenylthiocarbazone (dithizone) reveals a Nernstain potentiometric response with the slope of 29+2 mV per decade for Pb2+ over a concentration range (5.0×10-6-1.0×10-2 M). The used electrode was suitable in aqueous solutions in a pH range of 8 to 10. The response time of the electrode is about 15 s and was used for a period of 45 days. The proposed electrode was used in two different applications such as the determination of lead concentration in a part of lead water pipe and as an indicator electrode for potentiometric titration of Pb2+ ions.

ZnO nanoparticles were synthesized using zinc nitrate, cetyltrimethyl ammonium bromide and sodium hydroxide in co-precipitation method. The obtained particles were characterized using X-ray diffractometer (XRD), UV-Vis absorption spectroscopy (UV-Vis), Infrared absorption spectroscopy (IR) and Scanning electron microscopy (SEM). The ZnO nanoparticles are used for the preparation of modified carbon paste electrode (MCPE). The MCPE was applied for electrochemical investigation of dopamine (DA) which exhibits enhancement of current response with reduction of over potential for investigation of DA at pH.7.0. The effect of pH range from 5.5 to 8.0 was studied and the redox peak was pH dependent with a slope of 53 mV/pH. The effect of scan rate shows adsorption controlling process and the electrocatalytic currents increases linearly with increase in DA concentrations in the ranges of 0.1-20 μM. The detection limit was found to be 0.3×10-7 M.

The adsorptive and electrochemical oxidation behavior of Cilostazol has been studied at CPE and GCE in Britton - Robinson (BR) (pH 2.0 to 12.0). The anodic oxidation at 663 and 682 mV for CPE and GCE respectively. Differential pulse voltammetry was used to determine Cilostazol in the pure and in pharmaceutical formulations. The linear calibration was obtained from: 4.0×10-7–6.40×10-6 M and 5×10-7–8.7×10-6 M for carbon past and glassy carbon electrode. The percentage recoveries were found in the ranges: 99.50-100.80%, 99.20 -100.10% at carbon past and glassy carbon electrodes, respectively. The RSD for five measurements were found in the ranges: 0.403-0.742% and 0.657-0.84 %,. The method was applied to determine Cilostazol has in dilute urine sample and dosage forms and compared with official methods.