Analytical & Bioanalytical Electrochemistry
Volume:4 Issue: 4, Aug 2012

The aim of this study is to modify a glassy cabon, gold and platinum electrode with 4-methylaminobenzenediazonium salt (MABDAS) to evaluate the possible application on the detection of phenol by cyclic voltammetry (CV). Diazonium salt was reduced electrochemically and covalently electro-grafted onto GC, Au and Pt electrodes surface to form modified electrodes in non-aqueous media. The electrode surfaces were modified with MABDAS in acetonitrile (CH3CN). MAB modified GC (MAB/GC) electrode was used for the phenol determination in aqueous media. The effect of pH on the electrochemical behavior of the modified GC electrode was investigated for the phenol detection.

A novel myoglobin-based electrochemical biosensor was developed. The fabricated biosensor is based on a nanobiocomposite prepared from multiwalled carbon nanotubes and Ni(OH)2 nanoparticles that were coated with myoglobin and chitosan. Cyclic voltammogram of the electrode showed a pair of well-defined and quasi-reversible redox peaks with a formal potential (E0') of –0.330 V in 0.1 M pH=7.5 phosphate buffer solution, which was the characteristic of the Mb heme Fe(III)/Fe(II) redox couple. Immobilized Mb exhibits excellent electrocatalytic activity toward the reduction of hydrogen peroxide. The linear range for the determination of hydrogen peroxide was from 0.4 to 702 μM with a detection limit of 0.08 μM using chronoamperometry method. The kinetic parameters such as the electron transfer coefficient and the heterogeneous electron transfer rate constant for H2O2 determination were determined using electrochemical approaches. The biosensor was used for determination of H2O2 in human blood serum and the oxidant with satisfactory results.

Two novel Torasemide (TOR) sensors were investigated, using β-cyclodextrin and calix[4]arene as ionophores, where linear responses within concentration ranges of (10-7 10-2 and 10-8-10-2M) and Nernstian slopes of (58.77 and 59.214 mV/decade) over the pH range of 7-12 were obtained, respectively.The selectivity coefficients of the developed sensors indicate excellent selectivity for TOR, where the second sensor shows a higher sensitivity if compared to the first one. The proposed fabricated sensors display useful analytical characteristics for the determination of TOR (for anti-doping purpose) in bulk powder, biological fluids and in pharmaceutical formulation.

A new type of biosensor for hydroquinone (H2Q) has been synthesized based on the carbon paste electrode (CPE) immobilized with Horseradish Peroxidase (HRP), through silica sol-gel (SiSG) entrapment. The electrochemical properties of biosensor are characterized by employing the electrochemical methods like cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The proposed biosensor show high sensitivity in determination and rapid response towards H2Q under optimum conditions. The electrocatalytic response of H2Q was detected in methanol, ethanol, 2-propoanol, 1 butanol and acetone. The good results were obtained in ethanol as a solvent and acetate buffer solution (ABS) as supporting electrolyte, the experiments were carried out in combination of these two media. The anodic peak current of H2Q shows a linear relation with concentration range of 5×10-6 M to 10×10-4 M. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 1.5×10-6 M and 5.0×10-6 M respectively. The electrochemical impedance spectroscopy (EIS) result confirmed the occurrence of rapid electron transfer at HRP-SiSG/CPE. Moreover the stability, reproducibility, and repeatability of the biosensor were also studied. The proposed sensor was successfully applied for the determination of H2Q in real samples and the result were found to be commensurate.

A sol-gel electrode, based on ethyl 1,2,3,4-tetrahydro-6-methyl-4-phenyl-2- thioxopyrimidine-5-carboxylate (ETMPTC) as a neutral ionophore, was successfully developed for the detection of La3+ in aqueous solutions. The electrode responds to La + ion with a sensitivity of 19.7±0.1 mV/ decade over the range 1.0×10−8–1.0×10−1 M and in a pH range of 3.0–10.0. The sol-gel electrode shows detection limit of 3.5×10−9 M. The influence of membrane composition, the pH of the test solution, and the interfering ions on the electrode performance was investigated. The proposed electrode shows good discrimination of La3+ ion from several cations. The effect of temperature on the electrode response showed that the temperature higher than 65°C deteriorates the electrode performance. The electrode was found to work well under laboratory conditions. This sensor not only was used as an indicator electrode in potentiometric titration of lanthanum ion against EDTA but also was used to determination of La3+ concentration in the presence of certain interfering ions.

Ni/Al Layered double hydroxide nanoparticles modified carbon paste (Ni/Al- LDH/NMCP) electrode was prepared as a new electrode. The Ni/Al-LDH/NMCP electrode was prepared by grinding the mixture of graphite powder and silicon oil (as a binder) with sufficient amount of Ni/Al Layered double hydroxide. Then, the electrode was placed in 0.1 M NaOH and the electrode potential was cycled between 0 and 700 mV (vs. Ag/AgCl) at a scan rate of 50 mVs−1 for 20 cycles in a cyclic voltammetry regime until a stable voltammogram was obtained. Electrocatalytic activity of the modified electrode was used for the oxidation of methanol, in aqueous alkaline solution. Results showed that, the electrocatalytic activity of the Ni/Al-LDH/NMCP electrode is much higher than those of unmodified carbon paste electrode under similar experimental conditions, showing the possibility of attaining good electrocatalytic anodes for fuel cells. Kinetic parameters such as the electron transfer coefficient (α) and the number of electrons involved in theratedetermining step (nα) for the oxidation of methanol were determined utilizing cyclic voltammetry (CV). The modified electrode shows stable and linear responses in the concentration range of 0.01 to 0.1 mol L-1.

Three novel techniques for the selective determination of torasemide (TOS) in bulk powder, in formulations and in plasma were described. The three techniques were the construction and electrochemical response characteristics of novel poly (vinyl chloride) matrix membrane sensors for torasemide cation based on the use of the ion-association complexes of this cation with tetraphenyl borate, phosphotungestic acid and ammonium reineckate counter anions as ion exchange sites in a plasticized PVC matrix, either as ion selective membranes, microcoated wire or as microsized graphite selective sensors. All these sensors were prepared and fully characterized in terms of composition, life span, usable pH range, response time and temperature. The electrodes were selectively applied for the potentiometric determination of torasemide in pure form, pharmaceutical preparations and in plasma. These sensors showed near Nernstian responses with slopes of 28.3, 28.9, 27.9, 28.0, 30.0, 27.7, 28.5, 29.2 and 27.5 mv over the concentration ranges of 1.0×10-6-1.0×10- M for all sensors. The electrodes exhibit good selectivity for (TOS) with respect to a large number of inorganic cations, organic cations, sugars and amino acids. The proposed electrodes offer the advantages of simplicity, accuracy and applicability to turbid and colored samples. The behavior of the three sensors in presence of human plasma was also studied and reasonable results were obtained. All the fabricated sensors were validated according to the International Conference on Harmonization (ICH) guidelines and successfully applied for the determination of the studied drug in pure form, pharmaceutical preparations and in plasma without any interference.

A new method is presented, for the determination of copper, based on adsorptive stripping voltammetry of the complex of copper with minoxidil at a hanging mercury drop electrode (HMDE). The most suitable operating conditions and parameters, such as pH, accumulation potential, deposition time, ligand concentration and scan rate, were selected. The calibration graph for copper (II) was linear over the concentration range of 0.5 to 700 nM; the detection limit of the method was 0.09 nM. The interferences of some common ions were studied and the method was found suitable for determination of copper (II) in water anddrug samples. Moreover, by using of the proposed method, there is a considerable improvement in the detection limit, linear dynamic range and deposition time, compared to the methods other than adsorptive stripping voltammetry for the determination of copper.