Analytical & Bioanalytical Electrochemistry
Volume:3 Issue: 3, Jun 2011

Cysteine self assembled monolayer-modified gold (Cys/Au) electrode is used to immobilize superoxide dismutase (SOD) and establish a direct electron transfer between enzyme and electrode surface. However, due to the redox activity of copper ion on Cys monolayer, there would be an ambiguity in electrochemical studies of immobilized SOD on Cys/Au electrode. We designed a series of experiments to clarify the role of Cys in this process. Comparison between voltammograms of different electrodes revealed that the current intensity was increasing by the order of Cu+2/Cys/Au>SOD/Cys/Au>Cys/Au, while their electrochemical working windows were overlapping. Furthermore, for these electrodes the electron transfer rate constant were 0.77, 0.73, and 0.29 s-1 and the surface concentration of electroactive species were 1.05×10-10, 1.51×10-11, 1.50×10-11 mol cm-2, respectively. When phosphate buffer solution (PBS) was prepared by ultrapure phosphate salts (copper ion free) no redox response was observed while, by deliberately addition of Cu2+ the Cys/Au electrode showed a redox response. EDTA as chelating agent could pick up Cu2+ from PBS and consequently no electrochemical response was observed for Cys/Au electrode. Comparing these results indicated that the source of the inherent electrochemical activity of Cys/Au electrode is Cu+2. Finally, the Cys/Au electrode was also examined as a sensing system for determination of O2 •−.

4-aminophenol is the main impurity present in preparations of paracetamol. Using the cyclic voltammetry, the electrode behaviour of 4-aminophenol has been studied in 0.1 M phosphate buffer solutions at carbon paste electrode and surfactant modified carbon paste electrode. The optimal potential window of wide range from -0.4 V to 0.7 V was selected. The electron transfer kinetics of the CTAB/CPE in the detection of analyte was determined by the scan rate effect and concentration variation studies. The scan rate effect showed the electrode process is adsorption controlled. The oxidation peak currents represented a linear dependence on 4-aminophenol concentration from 1 mM to 4 mM with correlation coefficient r2=0.9942. The effect of cationic surfactant shows good high sensitivity and stability for the redox process of the 4-amino phenol. The detection limit was found to be 1×10-7 M.

The development of new porous materials has opened unprecedented opportunities for a wide range of applications. In the present work, a three-dimensionally interconnected porous polypyrrole structure was proposed for biosensing. Silica nanoparticles with good monodispersion and uniformity of the spheres synthesized by improved Stöber methods was used as template for porous polypyrrole electrodeposition. Voltammetric and electrochemical impedance measurements showed that the polypyrrole 3D-network arrays provided excellent matrices for the immobilization of horseradish peroxidase. The immobilized horseradish peroxidase on these polypyrrole 3D-network arrays retained its bioactivity effectively and displayed a pair of redox peaks with a formal potential of -0.275 V and an excellent electrocatalytic response toward the reduction of hydrogen peroxide (H2O2). This allowed the detection of H2O2 concentration with a linear range from 1 M to 7.94 M. The detection limit was found to be 0.22 M at a signal-to-noise ratio of 3. This method provided an alternative way for the biosensor construction.

Corrosion inhibition of mild steel in 2N HCl medium in presence of newly synthesized organic compounds, 2-chloroquinoline-3-carbaldehyde (FQ), [(1Z)-(2-chloro quinoline-3-yl) methylene)] hydrazone (FQMH), 2-6- Bis- {(2-chloro quinoline- ylmethylene}- amino}-hexanoic acid (FQHA) and (3Z)-4-(2-chloro quinoline-3-yl)-2-(mercapto methyl)but-3-enoic acid (FQBA) were investigated by weight loss and galvanostatic polarisation techniques. Effect of concentration, time of immersion and temperature effect on corrosion inhibition efficiency was evaluated. The inhibiting performances of all the compounds were found to increase with the increase in concentrations.

Experimental investigations concerning the preparation and characterisation of the system [Ag2HgI4:0.x AgI] (x=0.2, 0.4, 0.6 mol. wt. %),, have been undertaken with a view to evaluate the transport properties of the mixed system and to identify the fast ion conducting compositions. Powder samples of various compositions containing 0.2, 0.4 and 0.6 mol. wt. % [Ag2HgI4:0.x AgI] (x=0.2, 0.4, 0.6 mol. wt. %), were synthesized by solid state reaction. Samples were analyzed using powder X-ray diffraction (XRD), differential thermal analysis (DTA) and thermo-gravimetric analysis techniques in order to determine their crystal structure and phase transition temperatures. These studies have revealed the formation of new substances having phase transition temperatures similar to that of AgI. Detailed electrical conductivity measurements carried out in the frequency range 100 Hz- 10 kHz and over the temperature range 90°-170 °C by a Gen Rad 1659 RLC Digibridge have identified the best conducting composition namely 4 mol. wt.% [Ag2HgI4:AgI], exhibiting an electrical conductivity of 1.14×10-1 S cm-2 K at 393 K and an activation energy of 1.6 eV for Ag+ ion migration within the solid. The occurrence of fast ion transport due to silver ion migration in several compositions of the above mixed system has been explained on the basis of “hard and soft acids and bases” principle and ion exchange chemistry.

The dezincification of brass is a problem that has often been encountered in the process of corrosion of brass in aqueous solution. Thus the inhibiting substances must used to reduce the dissolution of these metallic materials. The present work aimed to study the effect of 3-phenyl-1,2,4-triazole-5-thione (PTS) on Cu/Zn brass corrosion in 3% NaCl solution. This latter is prepared with a new method in our laboratory. The efficiency of (PTS) as brass (alloy 60 Cu-Zn) corrosion inhibitor in %3 NaCl solution was investigated using electrochemical impedance spectroscopy and potentiodynamic measurements.The results showed that the PTS is an excellent inhibitor. The inhibiting efficiency increased by an increase of its concentration. At 10-3 M the important polarization resistance value of the anodic branch at high current density is believed to be due to the resistance of the inhibitor film formed. The spectroscopic techniques showed that the PTS can be also used as an inhibitor of the dezincification of the brass in the same solution. Consequently, we have concluded that the PTS has good inhibiting effect to stop brass dezincification phenomenon.

The electrochemical oxidation of Doxycycline Hyclate has been carried out in Britton - Robinson buffer at carbon paste and glassy carbon electrodes. Doxycycline Hyclate exhibits a well-defined irreversible oxidation peak in a broad pH range (2-11). Differential pulse voltammetry was used to determine Doxycycline Hyclate in pure form. The peak current varied linearly in the following ranges: 2.0×10-7- 3.0×10-6 mol L-1 and 2.0×10-7 - 2.6×10-6 mol L-1 in case of carbon paste electrode and glassy carbon electrode, respectively. In case of carbon paste electrode the limits of detection (LOD) and quantification (LOQ) were 6.56×10-8 mol L-1 and 2.19×10-7 mol L-1, respectively. For glassy carbon electrode the LOD and LOQ were 9.55×10-8 mol L-1 and 3.18×10-7 mol L-1, respectively. The percentage recoveries were found in the following ranges: 99.58-101.16% and 99.46-100.98% for carbon paste electrode and glassy carbon electrode, respectively. The relative standard deviations were found in the following ranges: 0.53-1.79% and 0.48-1.96% in case of carbon paste electrode and glassy carbon electrode, respectively. Differential pulse voltammetry was successfully applied for the determination of Doxycycline Hyclate in pharmaceutical form.

Zn-Ni, Zn-Co and Zn-Ni-Co alloy coatings were electrodeposited galvanostatically using sulphate bath, having THC as additive. The bath composition and operating parameters have been optimized by standard Hull cell method. The effects of current density (c.d.), pH on composition, thickness, hardness of the deposit were studied. Under all conditions of deposition, the bath followed anomalous type of codeposition with preferential deposition of less noble metal. Corrosion resistances of the coatings were measured by potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) method showed that under optimal conditions, the corrosion resistance of Zn-Ni-Co alloy coatings is approximately 20 times and 18 times better than Zn-Ni and Zn-Co alloys of same thickness. The Zn-Ni-Co coating under optimal c.d. (3.0 A dm-2) was found due to its inherent high dielectric barrier, evidenced impedance signals. High partial c.d. for zinc in Zn-Ni-Co alloy system supports the possibility of a synergistic catalytic effect of Co on Fe and vice versa. X-ray diffraction study clearly indicates that improved corrosion resistance of ternary alloy is due to the change in the phase structure of the coatings, compared to binary alloys. Surface morphology and composition of the coatings were examined by using Scanning Electron Microscopy (SEM), interfaced with EDX facility, respectively. The ternary Zn-Ni-Co coating may thus replace the conventional Zn-Ni and Zn-Co coatings in a variety of applications.