Analytical & Bioanalytical Electrochemistry
Volume:13 Issue: 1, Aug 2021

The work is devoted to the selection of optimal conditions for electrophoretic determination of heterocyclic thioamides which showed chemical activity to molecular iodine. It gives a reason to believe that the thioamides can be considered in the future as the basis for the development of antithyroid drugs. Due to the high sensitivity, the method of СE is versatile and successfully applied in toxicology and for monitoring pharmaceuticals in body fluids and tissues. The developed CE-technique of determination of 2-thioxo-5-(3,4,5-trimethoxybenzylidene) thiazolidin-4-one (I), 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione potassium salt (II) and 4-amino-5-(furan-2-yl)-4H-1,2,4-triazole-3-thione (III) by aqueous capillary electrophoresis allows to estimate the content of compounds in the range of 3.10-25 µg/mL for (I), 2.64-159 µg/mL for (II) and 1.45-12.80 µg/mL for (III). The technique was tested in analysis of urine. Selected conditions of the liquid-phase extraction are suitable for determination of compounds (II) and (III) in the urine. The optimal conditions of liquid-phase extraction which allow to extract approximately 74-97% of studied compounds were determined.

In this work, we are interested in the study of the anti-corrosion effect of new organic compounds of the typebenzimidazolium derivativesnominated 1,3-Dinonyl-2-(nonylthio)-1H-benzimidazolium bromide (ImdC7B), 1,3-Didecyl-2-(decylthio)-1H-benzimidazolium bromide (ImdC8B) and 1,3-Didodecyl-2-(dodecylthio)-1H-benzimidazolium bromide (ImdC9B)on the corrosion of mild steel (MS) in 1 M hydrochloric acid and 1 M HCl media exploiting electrochemical techniques [polarization curves (PC) and impedance spectroscopy (IS)]. In addition to that a correlation between molecular structures and inhibitory activity was carried out exploiting the DFT (Density Functional Theory) method and molecular dynamics (MD) simulation. The results obtained show an increase in efficiency with concentration. A maximum of 94.7%, 95.7% and 96.9% is reached for a concentration of 10-3 M of ImdC7B, ImdC8B and ImdC9B respectively. Polarization curves studies have demonstrated that these compounds are some mixed inhibitors. The ImdC7B, ImdC8B and ImdC9Bare adsorbed on the surface of MS according to Langmuir model. Reactivity parameters predicted from density functional theory calculations suggested the involvement of protonated forms of the molecules in the inhibitive process, which is also supported by the adsorption characteristics derived from MD simulations.

Donepezil hydrochloride (DPH), an indan and piperidine derivative, is a selective medicament of Alzheimer’s disease. Two highly selective and eco-friendly membrane based sensors have been designed to determine DPH. Sodium tetraphenyl boron (STPB) and sodium phosphotungestate (SPT) have been used as ion-exchangers, for construction of Sensors 1 and 2, respectively, with β-cyclodextrin (β-CD) as ionophore and nitrophenyl octyl ether (NPOE) as a plasticizer. The sensors are highly capable to determine DPH of linear concentration range 1.0 × 10-6 to 8.0 × 10-3 M at the pH ranged between 5 and 8. The Nernstian slopes of 58.51±0.80 and 57.16±0.67, for Sensor 1 and 2, respectively, reflected the appropriate functioning of electrode sensors in relative to concentration of DPH. The limits of detections (LOD) for both the sensors have also been reported. The results from validation of both the sensors reflected high selectivity for measuring potential of DPH solutions. Sensors have been subjected to validity check through accuracy, precision, robustness and ruggedness. Specific functioning of Sensor 1 and 2 permitted to achieve 99.26% as mean recovery of DPH from tablets analyses. The outcome of statistical tests between the results from sensors 1 and 2 with reference method pronounced the extraordinary applicability of the methods to determine DPH in pharmaceuticals. These methods are greener approaches due to the non-usage of any organic toxic solvent and pre-treatment and extraction steps’ absence.

In this study, the inhibition efficiency of two bio-inhibitors to decrease the corrosion rate of carbon steel in acidic solutions is investigated. These green inhibitors contained the protein prepared from the Hyalomma tick and leech extract. Both potentiodynamic polarization and electrochemical impedance spectroscopy measurements were utilized for this research. When the inhibitor concentration increased, the inhibition efficiency increased for both inhibitors; however, adsorption isotherm mechanisms for these inhibitors were different. In addition, the inhibition efficiency for the leech extract was higher than the Hyalomma tick extract in corrosive solutions. This inhibition efficiency range in the H2SO4 solution was about 93-97% based on polarization test results. Changes in corrosion potential showed that molecules adsorption of both bio-inhibitors on steel substrates acted as mixed inhibitors. Calculated ΔGads values for corrosion reactions in the presence of both bio-inhibitors demonstrated that a physical adsorption event has happened on steel substrates. Based on the EIS test results, when the concentration of Hyalomma tick extract increased to 0.06 g/L, the suggested electrical circuits changed due to the formation of a layer of inhibitor molecules on the steel substrate in the HCl solution.

In this study, TiN coatings were deposited on Ti-6Al-4V alloy surface using cathodic arc evaporation (CAE) deposition process at three different bias voltages (-150, -200 and -250 V) applied to the substrate. In this regard, the effect of bias voltage on the microstructure and corrosion behavior of coatings was studied. The microstructure of the coated specimens was analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). The corrosion behavior of the coatings was studied by potentiodynamic polarization (PDP) experiments and electrochemical impedance spectroscopy (EIS) in the simulated media. Studies on SEM images showed that formed coatings at bias of -200 V exhibited the least amount of needle like cavities (0.4%) and macroparticles. Studying the effect of bias voltage on the corrosion behavior of the coatings deposited at three bias voltages showed that the maximum corrosion resistance was obtained at -200 V and this voltage had the least current density in polarization measurements (5.59×10-7 A/cm2). So, it was considered as the optimal bias voltage.

The essential oil of Lavandula intermedia Walberton's Silver Edge (LAV) has been studied as a carbon steel corrosion inhibitor in 1 M hydrochloric acid using electrochemical obstacle spectroscopy (EIS), Tafel's polarization methods. the effect of extract concentration of (LAV) and immersion time on inhibition efficacy were studied. The effect of immersion time on the effectiveness of steel corrosion inhibition in 1M HCl was also studied in the 0.5 – 12 hour time interval. The results revealed that the essential oil of (LAV) tested reduces the kinetic process of the corrosion process of steel in medium 1 M HCl. Its efficiency increases with concentration and reaches a maximum value of 84% to 1% of LAVs. This corrosion inhibition effect attributed to was associated with the formation of a protective film provided to the metal surface by the complex chemical constituents of the oil extracted from (LAV), which is confirmed by surface analysis by scanning electron microscopy spectroscopy (SEM).

Herein, an eco-friendly and rapid voltammetric method is suggested for simultaneous assay of Aceclofenac (ACL) and Ezogabine (EZO) in biological fluids. Aceclofenac (ACL) and Ezogabine (EZO) are co-administrative drugs which are prescribed for the treatment of epilepsy associated with chronic inflammatory. The voltammetric method is based on the electrochemical oxidation of ACL and EZO at an edge plane pyrolytic graphite electrode using differential pulse voltammetry (DPV). Moreover, the electrochemical oxidation at carbon paste electrode and carbon paste electrodes modified with nanoparticles have been remarked. A number of crucial parameters which affect the electrochemical process at the electrode surface have been optimized. The method is linear over the concentration ranges from 0.2 to 100.0 µM and from 2.0 to 70.0 µM for ACL and EZO, respectively. The average recovery was found to be 100±2% with satisfactory %RSD (<1.5%) for both compounds. The method was applied successfully for simultaneous determination of ACL and EZO in biological samples with satisfactory accuracy and precision.

As an innovative approach, cadmium sulfide (CdS) nanorod was synthesized and applied to modify a fluorinated-tin oxide conducting glass (SnO2:F) as a matrix for urea bioelectrode. Besides, urease (Urs) was exploited as a particular enzyme for urea recognition with excellent accuracy and precision via a unique mechanism. In this case, Urs has immobilized physically over the matrix superficial (CdS/SnO2:F) electrode. Initially, the fabricated CdS nanorods qualities were deliberated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analyses while the fabricated Urs/CdS/SnO2:F bioelectrode was considered employing electrochemical impedance spectroscopy (EIS) and cyclic voltammetric (CV) techniques. The modified bioelectrode efficiency for urea analysis was presented while the parameters affecting the peak current were improved. Under the best circumstances, the novel bioelectrode illustrated a linear response over an extensive range of urea concentrations (5 to 200 mg dL-1), the detection limit was 3 mg dL-1. The projected Urs/CdS/SnO2:F bioelectrode has a fast response time of less than 3 s. The technique was exploited to the urea measurement in pharmaceutical preparation and human serum samples, and suitable outcomes were acquired.

A thin film of antimony-oxide on an antimony electrode (Sb-Sb-oxide) is a simple, robust, and low-cost electrode for pH measurement. This study reports on the effect of different electrolytic media on forming a thin-film of Sb-oxide by electrochemical methods and its stability for pH measurements. An antimony electrode was obtained by the melting and solidification of antimony powder. Sb-oxide, thus obtained by electrochemical methods, was characterized by X-ray Photoelectron Spectroscopy (XPS). The cyclic voltammetry (CV) study revealed a complex oxide formation mechanism. This mechanism could be interpreted as a stepwise formation of different Sb species, such as Sb2O3 and Sb2O5, in a low field near an open circuit potential (OCP). XPS results showed that the Sb2O3 and Sb2O5 ratio was almost similar in acidic medium, whereas Sb2O5 was dominant in phosphate solution. All the prepared Sb-Sb-oxide electrodes showed a linear electromotive force (e.m.f.) in pH 2-10, giving a slope of 0.049- 0.052 V/pH at room temperature (RT). The electrodes gave an excellent pH response, and hence they can be used in standard laboratory experiments where the accuracy of ±0.02 pH is required. However, Sb-oxide obtained in phosphate buffer solution of pH 7 showed a lower electrode sensitivity and lower stability due to dominant Sb2O5 formation.

Dexamethasone disodium phosphate (DSP) is one of the medications used for treatment of inflammatory diseases. In this work, a potentiometric sensor, based on a non-covalent imprinted polymer, was fabricated for the determination of DSP in pharmaceutical formulations. The molecularly imprinted polymer (MIP) was synthesized by precipitation polymerization using DSP as a template molecule, methacrylic acid as a functional monomer and ethylene glycol dimethacrylate as a cross-linking agent. The sensor was developed by dispersing the DSP imprinted polymer particles in o-nitrophenyl octyl ether plasticizer and embedding in poly(vinyl chloride) matrix. MIP was used as a suitable ionophore for the preparation of novel polymeric membrane (PME) and coated graphite (CGE) DSP-selective electrodes. The electrodes exhibit a Nernstian behavior for DSP ions over wide concentration ranges (1.0×10-7 - 1.0×10-1 M for PME and 1.0×10-8 - 1.0×10-1 M for CGE, Nernstian response (27.25 mV/decade for PME and 28.11 mV/decade for CGE), very low limits of detection (6.8×10-8 M for PME and 6.3×10-9 M for CGE), fast response time (~15 s for PME and ~10 s for CGE) and a satisfactory long-term stability (3 months) are characterizations of the proposed sensor. The sensor showed a high selectivity and a sensitive response to the template in aqueous system. The CGE was used in flow injection potentiometry and resulted in well-defined peaks for DSP ions with stable baseline, excellent reproducibility and very high sampling rate of 180 injections per hour. The proposed FIP system was used for the determination of trace DSP in pharmaceutical formulations.