Analytical & Bioanalytical Electrochemistry
Volume:6 Issue: 2, Apr 2014

Detailed mechanism of cupferron electroreduction can be judged only on the parameters of kinetics of the reduction process, and on final products established. No stable intermediates were obtained or detected till now. The mechanism suggested earlier by Kolthoff and Liberti (1948) is logically acceptable, but it includes some intermediates with doubtful stability. Analysis of published data on reduction kinetics of some substances closely related to cupferron allowed to make a supposition that diazonium cation can be a reasonable intermediate in this process.

The potentiometric response characteristics and analytical applications of a poly(vinyl chloride) (PVC)-free all-solid-state ion-selective electrode for chlorhexidine (CHX) are examined and compared to those of PVC-based solid-state electrode. The PVC-free electrode is prepared by direct incorporation of chlorhexidine-tetraphenyl borate (CHX-TPB) as a sensing element into a commercial nail varnish (NV) containing cellulose acetate propionate. The composite was applied onto a 3 mm diameter graphite disk-electrode. The electrode exhibited a Nernestian slope of 29 mV/decade in the concentration range from 10-5 to ≤10-3 mol/L with a detection limit of 4×10-6 mol/L. The electrode is independent of pH in the range from 3.6 to 7.9. Cationic inorganic ions showed negligible interference, whereas, a strong electrode response was observed for cetrimide and benzalkonium chloride with selectivity coefficients of 8.62 and 7.59 respectively. Comparable pH working range and selectivity pattern were observed with the PVC-based electrode. The electrode was used for determination of CHX in mouthwash and gargle, without extraction, with high precision (%RSD≤2) and accuracy (±2%). The new electrode is simple, economical and rapid when compared to the PVC-based electrode.

Poly (3-methyl) thiophene /graphene based electrochemical sensor is developed to study the electrochemical behavior of cyfluthrin with cyclic voltammetry and differential pulse voltammetry. In comparison to bare glassy carbon electrode (GCE), enhanced peak currents and reduced peak potentials are observed for the nanocomposite electrode. Differential pulse voltammetry (DPV) signals are used to optimize experimental parameters such as pH, accumulation time and potential, pulse amplitude, step potential and rest time. A differential pulse adsorptive stripping voltammetric method is developed for the determination of cyfluthrin with linear range, 1.0×10-8–1.1×10-6 M and detection limit of 2.7×10-9 M. The voltammetric procedure is effectively applied for well water samples with recoveries in the range of 92.40 to 98.30%.

Electroanalysis of mefenamic acid using platinum powder composite microelectrode (PPCM) by cyclic voltammetry (CV) method in buffer phosphate has been carried out. PPCM was prepare by Pt powder and PVC in 4 mL tetrahydrofuran (THF) solvent and swirled flatly to homogeneous followed by drying in an oven at 100°C for 3 hours. The mixture was placed in 0.5 cm diameter stainless steel mould and pressed at 10 ton/cm2. Cyclic voltammetry method was performed in a three electrodes system using PPCM as a working electrode, an Ag/AgCl (saturated KCl) as reference electrode and platinum wire as the counter electrode. Electroanalysis of mefenamic acid was performed in a buffer phosphate solution (pH 4). The results of the study showed that the correlation of determination using PPCM electrode for electroanalysis of mefenamic acid was R2=0.995. Precision, LOQ, LOD and recovery of the PPCM towards mefenamic acid were found to be 1.01%, 27.94 ppm, 93.13 ppm and 100.88%, respectively. As a conclusion, PPCM electrode is very good for electroanalysis of mefenamic acid in pharmaceutical product.

The effect of surface modification of glassy carbon electrode (GCE) by multi-walled carbon nanotubes (MWNTs) and Nafion (Nafion/MWCNT/MGCE) has been studied to voltammetric determination pethidine (PTD) as a potent opiate analgesic for humans for the first time. Cyclic Voltammetry (CV) and scanning electron microscopy (SEM) were used to characterize the properties of the modified electrode. The Nafion/MWCNT/MGCE exhibited a well-defined anodic peak at pH 7.0 at a potential of ~ 0.85 V for the oxidation of PTD as compared to 1.2 V at GCE. Using differential pulse voltammetry (DPV) technique a linear calibration curve was obtained over PTD concentration range 1.0-80.0 μM in phosphate buffer solution of pH 7.0 with detection limit of 0.83 μM. The method has been found selective and successfully implemented for the determination of PTD in human urine and injection samples using standard addition method. The electrode exhibited an efficient catalytic response with good reproducibility and stability.

The electrochemical oxidation and reduction behavior of Acid Blue 25 (AB 25) at carbon paste electrode (CPE) was investigated by employing cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. AB 25 was an anthraquinonic and anionic dye and it gives two reversible redox systems at potential values ≈0.2 V and ≈0.56 V respectively. The effect of pH on the anionic dye was studied and it was conformed that the pH-7.0 of phosphate buffer solution (PBS) was the suitable supporting electrolyte for further studies. We have studied the effect of accumulation time, scan rate, concentration, and repeatability. We have proposed a mechanism for the redox behavior of AB 25. It was conformed that one system at 0.2 V was diffusion controlled, where as the other system at 0.56 V was controlled by adsorption process. We have determined the limit of detection (LOD) and limit of quantification (LOQ) values as 3.248×10-8 M and 10.22×10-8 M respectively. By using electrochemical impedance spectroscopic (EIS) study we have observed the surface nature of the different electrodes.

Cupferron electroreduction was studied polarographically in buffer media with pH 4.3-7.5 and 8-10. Irreversible reduction with slow transfer of the first electron was found, with α=0.45 in alkaline and α=0.33 in acidic solutions. In acidic media E1/2 of cupferron wave depends on pH linearly with a slope 0.125 V. This implies reversible protonation step preceding the electron transfer. The wave shape at the lowest pH studied clearly indicates adsorption influence on kinetics of the process, i.e. protonated cupferron reduces from adsorbed state. Mairanovskii model of surface waves was successfully applied, with α values corrected to 0.38. There is no prior protonation in alkaline solutions, but some kinetics features (such as unusually high slope of E1/2, logt1 dependence) also imply some influence of adsorption. Analysis of published data revealed that contribution of slow tautomeric equilibrium proposed in earlier works is very doubtful. Double protonation of cupferron anion at low pH should be considered instead.

A novel PVC-based membrane sensor based on 2-Amino-6-(tbutyl)-4-(pyridin-2-yl)pyrimidine)(dichlorido)palladium(II) (ATPP) for determination of trace amounts of sulfate ions is introduced. The electrode revealed Nernstian response towards sulfate over the wide concentration range from 5.0×10−1 to 4.0×10−7 M at the pH range of 2.9-9.5. The effect of solvent mediator, cationic additives and amount of ion-carrier on the behavior of the sensor was investigated. The sensor shows a short response time (<25s) in the whole concentration ranges. The detection limit of the electrode was 1.8×10−7 M and it could be used for 20 weeks without any measurable changes in the slope. The proposed electrode shows very good selectivity for sulfate ions over a wide variety of common inorganic and organic anions. It was successfully used as an indicator electrode for titration of sulfate ions with barium ions. The electrode was also applied for determination of salbutamol sulfate and paramomycine sulfate.

The characterization of atenolol photodegradation product was performed using capillary electrophoresis (CE) with ultraviolet diode array detector (UV-DAD). The optimum separation for this assay was achieved in <7 min at 298 K with a fused-silica capillary column (57 cm length and 75 μm I.D.) and a running buffer containing 60 mM acetate buffer at pH 5.3 dissolved in methanol/ethanol mixture (20:80% v/v). The samples were injected with applied voltage of 16.0 kV. It’s established that capillary electrophoresis method enables to detect atenolol photodegradation product. The suggested method has been used for the determination of the studied drug in human serum and the results were compared to the other reported methods.

A glassy carbon electrode was electropolymarized with alizarin by using cyclic voltammetric technique (CV) and electrochemical properties of Omeprazole were studied. From the scan rate effect the overall electrode process was controlled by diffusion. The peak currents and concentrations of omeprazole shows a good linear response in the range form 4×10-4 –1×10-3 M (r2=0.9975) with the detection limit of 7.15×10-7 M and sensitivity was found to be 0.0181 μA μM-1. This method has been applied successfully to the analysis of Omeprazole in tablets.