Analytical & Bioanalytical Electrochemistry
Volume:7 Issue: 4, Aug 2015

Abstract- Highly economic and selective method for the analysis of dopamine-receptor antagonist and antiemetic drug Metoclopramide is developed. In this method Metoclopramide is analyzed electrochemically by using pre-treated pencil graphite electrode (PTPGE) by differential pulse and cyclic voltammetry. The PTPGE showed very good result with significant enhancement of the peak current. The dependence of the current on pH, concentration and scan rate was investigated to optimize the experimental conditions for determination of Metoclopramide. The oxidative peak current increased linearly with the concentration of Metoclopramide in the range of 1.0×10-8 to 1.3×10-6 M. The limit of detection was found to be 1.29×10-11 M. The pre-treated electrode showed good selectivity, reproducibility and stability for the detection of trace Metoclopramide. The proposed method was successfully applied to Metoclopramide determination in pharmaceutical formulations and real samples.

This paper presents a comparative study between five ion selective electrode sensors which were constructed and validated to determine Cetrimide (CET) by direct potentiometry in pure drug and its mouthwash without sample pre-treatment. Precipitation based technique was used for sensors fabrication. The CET complexes with different types of polyvinylchloride matrix and different cationic exchangers, CET- carboxylated polyvinylchloride (sensor 1), CET- tetrakis (sensor 2), CET- phosphotungestate (sensor 3), CET-tetraphenylborate (sensor 4) and CET- carboxylated polyvinylchloride / tetrakis (sensor 5) were obtained in situ by soaking the PVC membranes in 1×10-4 M CET solution. Nitrophenyl octyl ether (NOPE) was used as plasticizer. Proposed sensors showed fast, stable Nernstian responses across a relatively wide CET concentration range of 7.81×10-6 M to 1×10-3 M (for sensor 1, 2 & 5) and 3.13×10-5 M to 1×10-3 M (for sensor 3 & 4) in the pH range of 1-10 (for sensors 1, 2 & 5) and 5-7 (for sensors 3 & 4). Suggested sensors were found to be stable for several weeks without any measurable change in sensitivity. Validation of the method according to IUPAC recommendations showed suitability and selectivity of the proposed electrodes for the use in quality control assessment of CET in presence of different interferents. Proposed sensors were successfully applied for CET determination in pure form and in its mouthwash where good responses were obtained regarding accuracy and precision.

The electrochemical behavior of the passive films formed on copper in the alkaline solutions was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott–Schottky analysis. In the Mott–Schottky analysis, no evidence for n-type behavior was obtained, indicating that the oxygen vacancies and the copper interstitials do not have any significant population density in the passive films. Also, this analysis revealed that with the decrease of solution concentration, the acceptor density of the passive films increased. The EIS plots indicated that the presence of two time constants, a high frequency incomplete semicircle and a low frequency rising arc. The EIS studies showed that the impedance value increased with decreases in solution concentration, which is consistent with the results of the polarization experiment.

The oxidation of theophylline (TP) was studied at a graphite pencil electrode (GPE) in the presence of cetyltrimethyl ammonium bromide (CTAB) by cyclic and differential pulse voltammetry. The results indicated that the electrochemical responses of theophylline are apparently improved by cetyltrimethyl ammonium bromide, due to the enhanced accumulation of theophylline at pencil graphite electrode surface. Key experimental parameters such as pH of supporting electrolyte, scan rate, concentration and interferents were investigated. Under optimal conditions, the peak current was proportional to theophylline concentration in the range of 1.0×10−7 to 1.3×10−6 M with a detection limit of 2.63×10−9 M by differential pulse voltammetry. The proposed method was successfully applied to the determination of theophylline in tablet and urine samples.

For the first time, a carbon paste electrode modified with copper sulfide nanostructures for determination of gabapentin (GP) was described. In CV studies, no oxidation response of gabapentin can be seen at the unmodified electrode, but at the copper sulfide nanostructures modified carbon paste electrode (CSN-MCPE), a large anodic peak appears, indicating that the anodic oxidation of gabapentin could be catalyzed at CSN-MCPE. This proves that the copper sulfide nanostructures bear the main role in electrocatalytic oxidation of gabapentin. It has been shown that using the CSN-MCPE, gabapentin can be determined by DPV and amperometry with limit of detections 0.5 and 0.73 μmol L–1, respectively. The electrode response towards gabapentin was quite reproducible and a long-term stability of the electrode (more than 45 day) was observed. Furthermore, the proposed modified electrode was successfully applied to the determination of gabapentin in real samples. High sensitivity, excellent selectivity and ease of preparation are acknowledges of this electrode.

A procedure for the electropolymerization of alanine on the surface of bare carbon paste electrode (CPE) in presence 0.2 M acetate buffer (pH 5.0) solution as a supporting electrolyte using cyclic voltammetric technique was developed. The optimization of electropolymerized modified carbon paste electrode (MCPE) was achieved at 25 cycles. Further the poly (alanine) MCPE was used for the electrochemical detection for the folic acid (FA) at pH 5.0 and shows excellent electrocatalytic activity towards FA when compared to the bare CPE. The various parameters such as effect of scan rate, concentration of FA and the effect of pH were studied at MCPE. From the scan rate it was found that the electrode process was adsorption-controlled process. The limit of detection of FA was calculated at MCPE and the simultaneous determination FA, DA and AA shows three well defined oxidation peaks at poly (alanine) MCPE.

This paper presents a comparative study between three sensors developed to determine Citalopram Hydrobromide (CT) in the presence of its alkaline hydrolysis and oxidation induced degradation products using different ion association complexes. Sensor 1 was fabricated using phosphomolybdic acid, Sensor 2 used phosphotungestic acid and sensor 3 used the sodium tetraphenyl borate. Linear responses of CT were obtained within the concentration ranges of 1×10−6 to 1×10−2 mol L-1 for sensor 1 and 2 and 1×10−5 to 1×10−2 mol L-1 for sensor 3 over the pH range of 3.0–6.0. The selectivity coefficients of the developed sensors indicated excellent selectivity for CT. The proposed sensors displayed useful analytical characteristics for the determination of CT in bulk powder, pharmaceutical formulation, and in the presence of its degradation products and thus could be used for stability-indicating methods. The method was validated according to ICH guidelines.Statistical comparison between the results from the proposed method and the results from the reference HPLC method showed no significant difference regarding accuracy and precision.

The electrosynthesis of poly(2-anisidine) on aluminum alloy 5052 (AA5052) surface was carried out by a galvanostatic method. Various constant current densities of 5, 10, 15 and 20 mA cm-2 at deposition times of 900, 1800, 2700 and 3600 s were applied to the formation of the coatings. The results showed that the current density of 15 mA cm-2 at the deposition time of 2700 s for the polymerization stage is the best condition for the synthesis of more compact and strongly adherent coatings. The coatings were characterized by FT-IR, UV-Vis and scanning emission microscopy (SEM) techniques. The corrosion protection performance of the coatings was investigated in 3.5% NaCl solution as a corrosive environment by the potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The corrosion current decreases significantly from 5.338 μAcm-2 for uncoated electrode to 0.004 μAcm-2 for coated electrode (under optimal conditions). The results clearly ascertain that the poly(2-anisidine) has outstanding potential to protect the AA5052 alloy against corrosion in a chloride environment.

Helix-coil transition of poly aspartic acid (PASP) was investigated by dc polarography in the presence of Cd2+ and/or Zn2+ as a detecting marker which attached to the polymer. The diffusion currents (id) of Cd2+ and Zn2+ decreased sharply in the pH range of 3.5-7.0 due to the formation of the metal ions-PASP macromolecular complexes. The complex formation revealed on an increase in the magnitude at 222 nm of CD spectrum of the polymer, indicating that PASP forms helix structure by coordination of both ions in the corresponding pH region. The helix content of PASP, estimated by polarography is in good agreement with that by CD in neutral pH region. The degree of helicity induced by either of these two ions also can be determined independently by polarography. The size of the complex was calculated by Ilkovic’s equation and depends on strongly mixing ratio of PASP residue to cation marker. On the other hand in the lower acidic pH region, the coordination mode of these ions to PASP is different from that at neutral pH region. The decreases in id of the ions are independent of the further formation of helix structure. The metal ions coordinate with sparsely dissociated carboxylate groups of helical part of PASP, which bring about an aggregation of polypeptide strands. The diffusion current of the metal ion attached to the polymer, therefore, is a parameter sensitive to a conformational change of PASP from acidic through neutral pH region.

The behavior of 1,1’-{2, 6-dimethyl-4-[-2-phenylethenyl]-1,4-dihydropyridine-3,5-diyl}diethanone (DHP) have been investigated as mild steel (MS) corrosion inhibitor in 15% HCl solution by gravimetric measurements, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (Tafel), scanning electron microscopy (SEM) analysis. Quantum chemical calculation was applied to correlate electronic structure parameters with the inhibition performances. Adsorption of DHP obeys the Langmuir’s isotherm. Potentiodynamic polarization measurements showed that DHP acted as mixed type inhibitor but cathodically dominant.