Analytical & Bioanalytical Electrochemistry
Volume:9 Issue: 1, Feb 2017

In the present work two selective and sensitive polyvinyl chloride matrix membrane electrodes were developed for the determination of analgin and camylofin dihydrochloride. Sensor I was developed using tetraheptylammonium bromide as an anion exchanger with 2-nitrophenyl octyl ether as a plasticizer for the determination of the anionic drug analgin. Sensor II was developed using potassium tetrakis 4-chlorophenyl borate as a cationic exchanger and dioctyl phthalate as a plasticizer for the determination of the cationic drug camylofin. Selective molecular recognition component 4-tert-butylcalix [8]arene was used as ionophore to improve the selectivity of sensor II. The linearity range of the proposed sensors was (1.56×10-4-1.00×10-2) and (1.00×10-6-1.00×10-2) mol L-1 with Nernstian slopes of (-53.45±2.93) and (30.20±1.66) for the sensors I and II, respectively. The Nernstian slopes were also estimated over the pH ranges of 4.5-10.5 and 4.5-7.5 for both sensors. The proposed sensors showed useful analytical features for the determination of both drugs in bulk powder, in laboratory prepared mixtures and in their combined solid dosage form. The method was validated according to ICH guidelines.

The electrochemical oxidation of 2,4-dichlorophenol (2,4-DCP) at a glassy carbon (GC) electrode modified with Nickel phthalocyanine (NiPc), a complex of nickel without any substitutents, was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. The modification of the electrode was performed by repetitive cyclic voltammetric scans in NiPc solution. The number of optimum cycles was obtained 70. Nickel phthalocyanine with different thickness was characterised by electrochemical impedance spectroscopy and it was corresponding to cyclic voltammograms. Also the catalytic activity of the modified electrode (GC/NiPc) was investigated. It was found that, GC/NiPc electrode had significant response for 2,4-DCP oxidation. Therefore, it can be a good candidate for electrooxidation of 2,4-DCP. By using this technique the small amounts of DCP compound in waste waters can be detected.

Zircaloy-4, one of zirconium alloys, has outstanding corrosion resistance to nitric acid. Utilizing potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott–Schottky analyses, the electrochemical behavior of zircaloy-4 in nitric acid solutions were evaluated under open circuit potential (OCP) condition. At first, where the concentration of nitric acid increased from 0.01 to 0.05 M, the corrosion current density decreased. However, it amplified rapidly while the concentration increased from 0.05 to 0.50 M. Moreover, the EIS studies demonstrated an inverse trend for polarization resistance values. Mott–Schottky analysis indicated that the passive films displayed p-type semiconductive characteristics. Also, this analysis showed that the acceptor densities decreases by increasing nitric acid concentration from 0.01 to 0.05 M, whereas it increases when the nitric acid concentration reaches from 0.05 to 0.50 M. This trend was consistent resulting in potentiodynamic polarization and EIS measurements.

A new polyvinylchloride membrane sensor for Cd2 ions has been prepared using 2–acetylthiophene Semicarbazone (ATS) ligand as an electroactive ionophore and dibutylphthalate (DBP) as a plasticizing agent. The best performance was recorded with a membrane composition of PVC: DBP: Ionophore: NaTPB as 31: 64: 3.2: 1.8 (w/w %). The sensor exhibits a Nernstian response for Cd2 ions over a wide concentration range (1.0×10–5 to 1.0×10–1 M) with a slope of 29.4±0.2 mV decade–1. It has a fast response time of ˂10 s and can be used for at least 5 weeks without any divergence in potential. The electrode can be used in the pH range from 3.4 to 7.6. The proposed sensor revealed relatively good selectivity and high sensitivity for Cd2 ions in presence of a number of mono, di and trivalent interfering cations within the working range of the electrode. The electrode was successfully applied for the direct determination of Cd2 in solution and, as an indicator electrode, in potentiometric titration of cadmium ions using ethylenediamine tetraacetic acid (EDTA) as titrant.

The poly(methionine) modified carbon paste electrode (MCPE) was fabricated for the electroanalysis of catechol (CC) and hydroquinone (HQ) in phosphate buffer solution (PBS) of pH 7.4 by cyclic voltammetric (CV) and differential pulse voltammetric (DPV) techniques. The modified electrode shows selective and sensitive response for the simultaneous determination of CC and HQ in a binary mixture. The peak to peak separation of CC and HQ was 0.115 V and 0.112 V by CV and DPV techniques respectively. The effect of concentration and scan rate reveals the electrode process was controlled by the adsorption of the analytes. This study provides a new method for the modification of working electrode for the voltammetric determination of the CC and HQ.

This work demonstrates a comparative study between six fabricated ion selective electrode sensors to determine Benzydamine HCL (BZ) by direct potentiometry in pure form and in its different pharmaceutical formulations. Precipitation based technique was only used for fabrication of BZ/phosphotungestate (BZ/PT) sensor, where BZ was incorporated in the membrane composition. For other sensors, the BZ association complexes with different cationic exchangers were obtained in situ by soaking the sensors membranes in 1×10-2 M BZ solution. Sensors 1-5 were named BZ/Na-tetraphenylborate, BZ/phosphomolybdate, BZ/Na-phosphotungestate, BZ/K-tetrakis and BZ/ammonium-reineckate, respectively. Dioctylphthalate (DOP) and Nitrophenyloctyl ether (NOPE) were used as plasticizers. The proposed sensors showed fast, stable Nernstian responses across a relatively wide BZ concentration range (5×10-5 to 1×10-2 M) in pH range of 4-7. The suggested sensors could be used for several weeks without any measurable change in sensitivity. Validation of the method according to IUPAC recommendations showed the suitability and selectivity of these electrodes in the quality control assessment of BZ in presence of different interferents. Sensor 4 showed the best results regarding sensitivity and accuracy. The proposed sensors were successfully applied for the determination of BZ in pure powder form and in its different pharmaceutical formulations where good recoveries were obtained.

Two triphenylimidazole substituted compounds, namely 2,4,5-triphenyl-4,5dihydro-1H-imidazole (P1) and 2-(4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)phenol (P2) were studied as inhibitors for the corrosion of carbon steel in 1.0 M hydrochloric acid (HCl) solution has been examined and characterized by weight loss, Tafel polarization and electrochemical impedance spectroscopy (EIS). It was found that the studied compounds exhibit a very good performance as inhibitors for carbon steel corrosion in 1.0 M HCl. Results show that the inhibition efficiency increases with decreasing temperature and increasing concentration of inhibitors. Good agreement between the results obtained from weight loss and electrochemical measurements. It has been determined that the adsorption for the studied inhibitors on carbon steel complies with the Langmuir adsorption isotherm at all studied temperatures. The kinetic and thermodynamic parameters for carbon steel corrosion and inhibitor adsorption, respectively, were determined and discussed. On the bases of thermodynamic adsorption parameters, comprehensive adsorption (physisorption and chemisorption) for the studied inhibitors on mild steel surface was suggested. Results show that the order of inhibition efficiency is P2>P1 due to presence of electron donating hydroxyl (−OH) groups in P2. Potentiodynamic polarization studies have shown that compounds studies acts as a mixed type of inhibitor’s. Scanning electron microscopy (SEM) was performed and discussed for surface study of uninhibited and inhibited carbon steel samples.

Hydroxyurea is an anticancer drug with high effectiveness for the treatment of different malignances. Several methods were reported for the quantification of hydroxyurea including colorimetry, high-performance liquid chromatography, and gas chromatographymass spectrometry. Herein, a sensitive, accurate and precise nanosensor using nano TiO2 and carbon paste for the quantification of low levels of hydroxyurea in serum samples was presented. After optimization of different experimental parameters, the proposed nanosensor showed a linear dynamic range of 8.0-180.0 mg L-1 with a detection limit of 0.160 mg L-1. It was found that the optimized approach could be applied to the determination of hydroxyurea in serum samples with acceptable recovery values.

A new electrochemical method was introduced for nicotinic acid measurement in pharmaceutical samples. Electrochemical behavior of nicotinic acid was studied by cyclic voltammetry and differential pulse voltammetry on carbon paste electrode. Some important parameters affecting the electrode response to nicotinic acid was investigated and optimized. The optimal electroanalysis pH was found to be 2.2. Moreover, the optimal amount of binder used for carbon paste preparation was observed to be 27.50% of total mass of the paste composite. The peak current response versus nicotinic acid concentration was linear in the range of 5.0×10−5 to 3.0×10−3 M. The detection limit was calculated to be 3.1×10−5 M. The developed method was successfully used for determination of nicotinic acid in the urine samples.