Nonelectroactive recognition: Monitoring of perphenazine by its subsecond adsorption on an Au microelectrode by the fast fourier transform continuous cyclic voltammetric technique (FFTCCV)

A novel method for determining perphenazine in flow-injection systems has been developed in this work. The method was successfully applied for fast determination of perphenazine in its pharmaceutical formulations. Being very simple, precise, accurate, time-saving, and economical, this method has many advantages compared to all of the previously reported methods. Some investigations were also performed to find the effects of various parameters on the sensitivity of the proposed method. The conditions responsible for the performance were a pH value of 2, a scan rate value of 30 V/s, an accumulation potential of 500 mV, and an accumulation time of 0.8 s. Some of the advantages of the proposed method are as follows: the removal of oxygen from the test solution is not required anymore, the detection limit of the method is subnanomolar, and finally, the method is fast enough to determine such compounds in a wide variety of chromatographic methods. We also introduce a special computer-based numerical method to calculate the analyte signal and noise reduction. After subtraction of the background current from noise, the electrode response was calculated based on partial and total charge exchanges at the electrode surface. The integration range of currents was set for all the potential scan ranges, including oxidation and reduction of the Au surface electrode, to obtain a sensitive determination. The waveform potential was continuously applied on an Au disk microelectrode (a radius of 12.5 μm). The detention limit of the method for perphenazine was 15 pg/ml. For eight runs, the relative standard deviation of the method at 1.1 × 10⁻⁸ M was 2.1%. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 9, pp. 1093–1102. The text was submitted by the authors in English.     

Cu(II) Hexacyanoferrate(III) Modified Carbon Paste Electrode; Application for Electrocatalytic Detection of Nitrite

Copper hexacyanoferrate (CuHCF) film‐modified carbon paste electrode (CPE) has been prepared from various electrolytic aqueous solutions using consecutive cyclic voltammetry. The cyclic voltammograms showed the direct deposition of CuHCF films from the mixing of Cu²⁺ and Fe(CN)₆^3? ions and each time with one of the six cations: H⁺, Na⁺, K⁺, NH₄⁺, Mg²⁺, and Al³⁺. The CuHCF film showed a single redox couple that exhibited a cation effect (Na⁺, K⁺, Mg²⁺, and NH₄⁺) and anion effect (Cl^?, NO₃^?, SO₄^2?, ClO₄^?, and BrO₃^?) in the cyclic voltammograms. Voltammetric studies have indicated that in presence of nitrite, the cathodic peak current of CuHCF increases, followed by a decrease in the corresponding anodic current. This indicated that nitrite was reduced by the redox mediator immobilized on the electrode surface via an electrocatalytic mechanism. The process of reduction and its kinetics were investigated by using cyclic voltammetry, differential pulse voltammetry, chronoamperometry and chronocoulometry techniques. The electrocatalytic ability about 800 mV can be seen. The rate constant of the catalytic reduction of nitrite was found to be 7.9×10⁵ cm³ mol^?1 s^?1. Linearity range obtained was 5×10^?5?8.4×10^?3 by cyclic voltammetry and 8×10^?6?1.3×10^?3 and 4×10^?3?2×10^?2 by differential pulse voltammetry.     

Acetylferrocene Modified Carbon Paste Electrode; A Sensor for Electrocatalytic Determination of Hydrazine

The electrocatalytic oxidation of hydrazine at a carbon paste electrode spiked with acetylferrocene as a mediator was studied by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. In contrast to other ferrocenic compounds, acetylferrocene exhibits a chemical irreversible behavior, but it can act as an effective mediator for electrocatalytic oxidation of hydrazine, too. The heterogeneous electron transfer rate constant between acetylferrocene and the electrode substrate (carbon paste) and the diffusion coefficient of spiked acetylferrocene in silicon oil were estimated to be about 3.45×10^?4 cm s^?1 and 4.45×10^?9 cm² s^?1, respectively. It has been found that under the optimum conditions (pH 7.5) the oxidation of hydrazine occurs at a potential of about 228 mV less positive than that of an unmodified carbon paste electrode. The catalytic oxidation peak current of hydrazine was linearly dependent on its concentration and the obtained linear range was 3.09×10^?5 M–1.03×10^?3 M. The detection limit (2σ) has been determined as 2.7×10^?5 M by cyclic voltammetry. Also, the peak current was increased linearly with the concentration of hydrazine in the range of 1×10^?5 M–1×10^?3 M by differential pulse voltammetry with a detection limit of 1×10^?5 M. This catalytic oxidation of hydrazine has been applied as a selective, simple, and precise new method for the determination of hydrazine in water samples.     

Stripping Voltammetry of Cerium(IIl) with a Chemically Modified Carbon Paste Electrode Containing Functionalized Nanoporous Silica Gel

This research introduces the design of an adsorptive stripping voltammetric method for the cerium(III) determination at a carbon paste electrode, chemically modified with dipyridyl‐functionalized nanoporous silica gel (DPNSG‐CPE). The electroanalytical procedure comprised two steps: the Ce(III) chemical accumulation at ?200 mV followed by the electrochemical detection of the Ce(III)/dipyridyl complex, using anodic stripping voltammetry. The factors, influencing the adsorptive stripping performance, were optimized including the modifier quantity in the paste, the electrolyte concentrations, the solution pH and the accumulation potential or time. The resulting electrode demonstrated a linear response over a wide range of Ce(III) concentration (1.0–28 ng mL^?1). The precision for seven determinations of 4 and 10 ng mL^?1 Ce(III) was 3.2% and 2.5% (relative standard deviation), respectively. The prepared electrode was used for the cerium determination in real samples and very good recovery results were obtained.     

A new method for the determination of loratadine at an Au microelectrode in flowing systems with the use of fast continuous cyclic voltammetry

This research presents a new method for the fast monitoring of loratadine in pharmaceutical formulation. The method employs the fast Fourier transformation continuous cyclic voltammetry (FFTCV) at a gold microelectrode in a flowing-solution system. Three considerable advantages of the technique are demonstrated. First, there is not any requirement for the oxygen removal from the test solution; second, a subnanomolar detection limit is gained; and, finally, the speed of the method for the determination of a compound is in a broad range of chromatographic methods. A special computer-based numerical method is also introduced for the calculation of the analyte signal and noise reduction. The electrode response was calculated in accordance with the partial and total charge exchanges on the electrode surface after the background current subtraction from that of the noise. The integration range of the currents was set for all potential scan ranges, including the oxidation and reduction of the Au surface electrode in order to obtain a sensitive determination. The objective of the performed experiments was to study the effects of different parameters on the method sensitivity. It was concluded that the method had a linear concentration range of 40–765000 pg/mL (r = 0.999) with a limit of detection and quantitation of 12 and 40 pg/mL, respectively. For the achievement of these optimum results, the parameter values were set to 80 V/s for the scan rate, 0.7 s for the accumulation time, 300 mV for the accumulation potential, and 2 for the pH. The text was submitted by the authors in English.     

Current analytical methods for plant auxin quantification – A review

Plant hormones, and especially auxins, are low molecular weight compounds highly involved in the control of plant growth and development. Auxins are also broadly used in horticulture, as part of vegetative plant propagation protocols, allowing the cloning of genotypes of interest. Over the years, large efforts have been put in the development of more sensitive and precise methods of analysis and quantification of plant hormone levels in plant tissues. Although analytical techniques have evolved, and new methods have been implemented, sample preparation is still the limiting step of auxin analysis. In this review, the current methods of auxin analysis are discussed. Sample preparation procedures, including extraction, purification and derivatization, are reviewed and compared. The different analytical techniques, ranging from chromatographic and mass spectrometry methods to immunoassays and electrokinetic methods, as well as other types of detection are also discussed. Considering that auxin analysis mirrors the evolution in analytical chemistry, the number of publications describing new and/or improved methods is always increasing and we considered appropriate to update the available information. For that reason, this article aims to review the current advances in auxin analysis, and thus only reports from the past 15 years will be covered.     

Effect of thickness on the capacitive behavior and stability of ultrathin polyaniline for high speed super capacitors

In this work four polyaniline (PANI) film electrode with different thickness were synthesized by electrochemical method on the surface of glassy carbon (GC) electrode. Four polymer films with various thicknesses from 0.5 to 11 μm were synthesized. Electropolymerization occurs in low monomer concentration. Morphology study of electrode shows that surface structure of polymers depends on film thickness. Capacitance of electrode was studied by CV and charge-discharge (CD) methods. Specific capacitance (SC) of electrodes using cyclic voltammetry were calculated 620, 247 F g^–1 for thinnest and thickest polymer film, respectively. Stability of electrodes was studied during 1000 voltammogram cycles. Results show that with the increase of thickness the stability of electrodes enhanced and reach to a maximum and then decreased.     

A CONVENIENT METHOD FOR THE SYNTHESIS OF PHOSPHOROTHIOATES AND THEIR ANTICHOLINESTERASE ACTIVITIES

A simple, efficient, and general method has been developed for the synthesis of phosphorothioates through a one-pot reaction of alkyl halides with the mixture of diethyl phosphite in the presence of NH ₄ OAc/S/CaO under solvent–free conditions. The anticholinesterase activities of eight different phosphorothioates were investigated on acetylcholinesterase from electric eel.     

Performance of glucose electrooxidation on Ni–Co composition dispersed on the poly(isonicotinic acid) (SDS) film

Poly(isonicotinic acid) (PINA) film was electrosynthesized on carbon paste electrode (CPE) by using the repeated potential cycling technique in aqueous solution containing isonicotinic acid (INA), sulfuric acid and sodium dodecyl sulfate (SDS). Then, nickel and cobalt ions were incorporated by immersion of CPE/PINA prepared in the presence of SDS (CPE/PINA(SDS)) in a solution with different proportions of nickel chloride and cobalt chloride. The electrochemical characterization of mixed hydroxides containing cobalt and nickel at the surface of the modified electrode is presented. The modified electrodes were successfully used in the electrocatalytic oxidation of glucose. Finally, the electrocatalytic oxidation peak currents of glucose exhibited a good linear dependence on concentration, and its quantification can be done easily. The good analytical performance, low cost and straightforward preparation method make this novel electrode material promising for the development of an effective glucose sensor.