Analytical & Bioanalytical Electrochemistry
Volume:5 Issue: 1, Feb 2013

Quercetin belongs to the flavonol family. It is most abundant among the flavonoid molecules. A method was developed for quantification of quercetin in apple and onion using differential pulse voltammetry at graphene nanosheets modified glassy carbon electrode (GNs/GCE) and UV spectrophotometry as reference method. Interest graphene centers on its excellent mechanical, electrical, thermal and optical properties, it’s very high specific surface area, and our ability to influence these properties through chemical functionalization. The electrochemical behavior of quercetin at the GNs/GCE was investigated, and the results indicated that the electrode reaction was controlled by adsorption. The anodic peak current almost stops increasing after 260 s accumulation. This indicates that the accumulation of quercetin at the electrode surface nearly reaches a saturation state after 260 s. The accumulation potential was analyzed between -0.6 and 0.3 V, a maximum peak was achieved at 0.2 V. Under the optimal conditions, the peak currents of DPV increased linearly with the quercetin concentration in the range from 0.006 to 10 μM and 10 to 100 μM with limit of detection 3.9 nM. The proposed method was successfully applied in the detection of quercetin in foods.

The acetanilide modified carbon paste electrode (ANMCPE) was used for the voltammetric response of dopamine (DA) in an aqueous phosphate buffer solution (PBS). Modified carbon paste electrode was prepared by grinding the 5 mg of acetanilide (AN) with the mixture of graphite powder and silicon oil. Cyclic Voltammetric study improved the reversibility of the DA on the modified electrode. The effect of various experimental parameters such as acetanilide concentration, scan rate, and pH on the voltammetric response of DA was investigated. Under the chosen conditions, the differential pulse voltammetry peak current was found to be linear with DA concentration. The detection limit for modified electrode was found to be 6×10-7 M for DA determination.

The oxidative behaviour of zolmitriptan was studied at a glassy carbon electrode in Britton-Robinson (BR) buffer solutions using cyclic, differential pulse and square wave voltammetric techniques. The oxidation process was shown to be irreversible over the pH range (2.0-6.0) and was diffusion controlled with some adsorption character. The analytical method was developed for the determination of zolmitriptan in BR buffer solution at pH 2.0 as supporting electrolyte. The anodic peak current varied linearly with zolmitriptan concentration in the following ranges: 4.0×10-8 to 3.2×10-7 M and 4.0×10-10 to 3.2 10-9 M of zolmitriptan with limits of detection of 2.0×10-8 M and 2.0×10-10 M by differential pulse and square wave methods, respectively. Validation parameters, such as sensitivity, accuracy, precision and recovery were evaluated. The proposed method was applied to the determination of zolmitriptan in the tablet dosage form. The results were compared with those obtained by the reported methods showing higher sensitivity of our proposed method.

Silver nanoparticles dispersed in polypyrrole (PPy) matrixes coated on glassy carbon electrode (GCE), as a novel electrode, was easily synthesized by electropolymerization of pyrrole on GCE and then electrodeposited silver nanoparticles on PPy electrode. The electrochemical behavior and electro-catalytic activity of silver nanoparticles/PPy/GCE were characterized by cyclic voltammetry. The morphology of electrodes was characterized by scanning electron microscopy. The electrochemical sensor exhibited strong electro-catalytic activity with toward reduction of nitrate. The detection limit of nitrate was found to be 2.0 μM. Moreover, the sensor showed excellent sensitivity, selectivity, and stability.

Nanostructure multilayer alloy coatings (NMAC) of Co-Ni were developed on copper in layered manner using different current pulses. NMAC of Co-Ni was deposited galvaostatically from acid sulphate bath under different combination of cyclic cathode current densities (CCCD’s) and number of layers. Corrosion behaviors of coatings were evaluated in 1 M hydrochloric acid, as representative corrosion medium. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) study revealed that NMAC (Co-Ni) 2.0/4.0/6.0/60/three exhibits~160 times better corrosion resistance than monolayer coating, deposited from same bath for same time. Better corrosion protection was attributed to the increased effect of interface, arising from the exceptional thinness of the layers. As composition of alloys in successive layers were varied, consequent to the deposition current density (c.d.), the change in phase structure of the deposits were observed, confirmed by X-ray diffraction (XRD) study. Layer formation and surface after corrosion tests were examined by scanning electron microscopy (SEM) and optical profilometer, and reasons responsible for better protection were analyzed.

Three novel polyvinyl chloride (PVC) membrane sensors for the determination of gemifoxacin mesylate are described and characterized. The sensors are based on the use of the ion association complexes of gemifoxacin cation with ammonium reineckate counter anions as ion exchange sites in the PVC matrix. The membranes incorporate ion association complexes of gemifoxacin with dibutylsebathete (sensor 1), dioctylphthalate (sensor 2), nitrophenyl octyl ether (sensor 3). The performance characteristics of these sensors were evaluated according to IUPAC recommendations, which reveal a fast, stable and linear response for gemifoxacin over the concentration range of 10-5-10-2 M for the three sensors with cationic slopes of -14.30, -20.44 and -22.37 mV per concentration decade for the three sensors, respectively. The proposed sensors displayed useful analytical characteristics for the determination of gemifoxacin mesylate in bulk powder, pharmaceutical formulation, and biological fluids (plasma) and in the presence of its acid degradation products and thus could be used for stability-indicating studies. Validation of the method shows suitability of the proposed sensors for use in the quality control assessment of gemifoxacin mesylate. The developed method was found to be simple, accurate and precise when compared with a manufacturer HPLC method.

The general electrochemical behavior of n-propanol has been investigated on Ni/Al layered double hydroxide nanoparticles modified carbon ceramic electrode (Ni/Al LDH/NMCC) is characterized by cyclic voltammetry, steady state polarization and chronoamperometry in alkaline media a good redox behavior of Ni(III)/Ni(II) couple at the surface of these electrodes can be observed. The results showed that the electrocatalytic activity of the Ni/ALDH/NMCC electrode is much higher than those of unmodified carbon ceramic electrode under similar experimental conditions. The apparent catalytic rate constant (K) and transfer coefficient (α) were determined by cyclic voltammetry and were approximately 0.314×104 cm3 mol-1 s-1 and 0.51, respectively. The modified electrode shows a stable and linear response in the concentration range of 0.01 to 0.1 mol L−1 with a correlation coefficient of 0.9919. The modified CCEs containing Ni/Al LDH nanoparticles show good repeatability, short response time, long term stability (4 months) and excellent catalytic activity.

Two simple and sensitive conductometric procedures were investigated for the determination of torasemide (TOS) using potasium tetraphenyl borate (K TPB) and ammonium reineckate (Amm. RNC) were described. Optimized conditions including temperature, solvent and reagent concentration were studied. The suggested methods were used for conductometric determination of (TOS) in its pharmaceutical preparations. Precision, measured as relative standard deviation was less than 1% and accuracy was 99.76 %.The obtained results were comparable with data using the reported method. The proposed procedures were successfully adapted for the determination of (TOS) in plasma. For comparison, some interference was also determined by the condutometric titrations. At equimolar concentration levels, some molecules of similar structure interfere with the original drug. A reduction in interferent concentration by a factor of 10 negated the interference.

A solid state copper electrode is reported based on polypyrrole conducting polymer film doped with Ponceau 4R azo dye. The sensing film was prepared in aqueous solution via electropolymerization of pyrrole (10.0 mM) and Ponceau 4R azo dye (2.0 mM) as ionophore, potentiostatically (Eapp.=0.80 V vs. SCE) using pencil graphite as working electrode. The structural characteristics of the prepared copper electrode were studied by scanning electron microscopy, Fourier transform infrared and energy dispersive spectroscopy. The fabricated electrode showed a linear Nernstian response over the range of 1.0×10-5 to 5.0×10-2 M with slope of 29.28±0.20 mV per decade over the pH range of 4-6. The sensor shows a fast response time (<15 s), good shelf lifetime and reasonably high selectivity with respect to many cations including alkali, alkaline earth, and transition metal ions. A detection limit of 6.70 M was obtained.

The electrocatalytic oxidation of dopamine at alizarin and Triton X-100 modified carbon paste electrode has been studied by means of cyclic voltammetric technique in. M acetate buffer solution at pH 7.0. This suggests the effectively of surface modification of carbon paste electrode by Triton X-100 a non–ionic surfactant. Cyclic voltammetric investigations demonstrated the improved responses of dopamine. The modified electrode exhibited strong promoting effect and stability towards the detection of dopamine in mobilization and immobilization methods of surfactant. The presence of Triton-X 100 on the alizarin modified carbon paste electrode showed excellent electrocatalytic effect towards the detection of dopamine.