Analytical & Bioanalytical Electrochemistry
Volume:6 Issue: 3, Jun 2014

The field of Electro-chemical sensors development is now highly grown for the determination of traces amounts of drugs. A novel polyvinylchloride membrane sensor for the determination of lamivudine is prepared and characterized. The sensor is based on the use of the ion association complex of lamivudine anion with iron(II)-phenanthroline counter cation as an ion exchange site in the polyvinylchloride matrix. The performancecharacteristics of this sensor was evaluated according to IUPAC recommendations, whichreveal a fast, stable and linear response for lamivudine over the concentration range of 10-6 to 10-2 mol L-1 for the sensor with anionic slope of 27.3 mV per concentration decade for the sensor. The direct potentiometric determination of lamivudine using the proposed sensor gave recovery of 99.57±0.62% for the sensor. The proposed sensor displayed useful analytical characteristics for the determination of lamivudine in bulk powder, pharmaceutical formulations, and biological fluids (plasma) and in the presence of some related impurities, namely cytosine, uracil and salicylic acid. Validation of the method shows suitability of the proposed sensor for the use in quality control assessment of lamivudine. The developed method was found to be simple, accurate and precise when compared with an official high performance liquid chromatographic method. Also the method allows direct determination of lamivudine without pretreatment or separation steps in turbid or colored solutions in presence of some related impurities.

Corrosion inhibition of carbon steel in 1.0 M HCl solution by 1-(aminoNphenylmethanethio)thiosemicarbazide (APTSC) was investigated by potentiodynamic polarization, Electrochemical Impedance Spectroscopy (EIS) and Fast Fourier Transform Continuous Cyclic Voltammetry (FFTCCV). Polarization studies revealed that APTSC is a mixed-type corrosion inhibitor. The results showed that the inhibition efficiency increased with increasing the inhibitor concentration and maximum inhibition was obtained 92% at 1.0×10−3 M of APTSC. EIS results confirmed that the inhibitor is adsorbed on the carbon steel surface, leading to increase the polarization resistance (Rp) and decrease the doublelayer capacitance. FFTCCV confirmed that the addition of inhibitor into the HCl solution decreased the rate of carbon steel corrosion. Also, it was found that after about 3400 s, the inhibitor reaches to its maximum surface coverage.

The isomerization control, provided by a conducting polymer (CP) based electrochemical sensing coating, was described phenomenologically and mathematically (by using the linear stability theory and bifurcation analysis). The steady-state stability requirements and oscillatory and monotonic instabilities´ conditions were derived from the differential equation system analysis. The changes in model for different cases also were presented.

In this study, the electrochemical behaviour of AISI 410 stainless steel at open circuit potential (OCP) in acidic solutions was investigated. For this purpose, the passivation parameters and semiconductor properties of passive films were derived from potentiodynamic polarization, Mott–Schottky analysis and electrochemical impedance spectroscopy (EIS). The potentiodynamic polarization curves suggested that AISI 410 stainless steel showed excellent passive behaviour in HNO3 solutions. Also, the polarization curves showed that the corrosion potential and corrosion current density of AISI 410 stainless steel increased with the increase in the concentration of solutions. For all HNO3 solutions, Mott–Schottky analysis showed two positive slopes in the main passive region (n-type behaviour). Also, this analysis indicated that the donor densities (ND1 and ND2) for the passive films formed on AISI 410 stainless steel are in the range 1021 cm-3 and increased with HNO3 solutions. EIS results showed that the reciprocal capacitance of the passive film is directly proportional to its thickness which increases with decreasing HNO3 concentration. It is thus clear that dilute HNO3 solutions offer better conditions for forming passive films with higher protection behaviour, due to the growth of a much thicker and less defective films.

Two novel polymeric membrane sensors were developed for determination of Metoclopramide (MCP), based on the use of metoclopramide-barbiturate (MCP-B) and metoclopramide-flavinate (MCP-F) ion pairs as electroactive materials in PVC matrix, in presence of o-nitrophenyloctylether (o-NPOE) as a solvent mediator, in plasticized PVC membranes. The suggested two-sensors show a near-Nernstian response for MCP over a wide concentration range of 1×10-5-1×10-2 M. The proposed sensors have a fast response time and can be used for more than 4 weeks without any considerable divergence in potentials. They exhibit comparatively good selectivity with respect to related substances, dosage forms additives, acidic-degradates, alkaline earth and some transition and heavy metal ions.

A new carbon paste electrode was modified by Fe3O4 magnetic nanoparticles coated by [3-(trimetoxysilil)-1-propanthiol] (TMSPT) with the help of permanent magnet and used for voltammetric investigation of ketotifen. The cyclic voltammetry indicated that Fe3O4@TMSPT modified electrode significantly enhanced the oxidation peak current of ketotifen than the bare electrode in a Britton Robinson buffer solution (pH 7). Cyclic voltammetric study at various scan rates and different pHs indicate that the mechanism ofoxidation of ketotifen at the Fe3O4@TMSPT modified electrode is an irreversible with twoelectrons reaction in a diffusion process. Factors influencing the detection processes wereoptimized and heterogeneous rate constant (k0) was calculated. Under optimal conditionsusing differential pulse voltammetry, the modified electrode showed a linear response to the concentration of ketotifen in the range of 2.5×10-7–3.0×10-5 M with a detection limit of 4.5×10-8 M. The method was utilized for the determination of ketotifen in ketotifen fumarate tablets with satisfactory results.

In the present investigation we have synthesized four chalcones namely 3-(4- chlorophenyl)-1-(2, 4-dihydroxyphenyl) prop-2-en-1-one (CHAL-1), 1-(2, 4-dihydroxyphenyl)-3-p-tolylprop-2-en-1-one (CHAL-2) 1-(2, 4-dihydroxyphenyl)-3-(2- hydroxyphenyl) prop-2-en-1-one (CHAL-3) and 1-(2, 4-dihydroxyphenyl)-3-(4-hydroxy-3- methoxyphenyl) prop-2-en-1-one (CHAL-4) and premeditated their corrosion inhibition property on mild steel (MS) in 1M HCl using chemical and electrochemical methods. The scanning electron microscopic (SEM) study reveals the formation of protective film of chalcones on MS surface. Presence of elements on MS surface was also studied using high energy dispersive (EDX) technique. Potentiodynamic polarization study reveals that chalcones are of mixed type inhibitors. Weight –loss experiment also performed at different temperature in order to derive thermodynamic parameters and to explain mechanism of adsorption.

The corrosion inhibition effect of Ephedra Sarcocarpa (ES) extract on copper (Cu) in 2.0 M HCl medium has been investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods. The polarization studies showed that ES extract acts as cathodic type protection and maximum inhibition efficiency 95% in 2.0 M HCl is obtained at 0.5 g/L ES extract at 298 K. EIS was used to investigate the mechanism of corrosion inhibition. The Nyquist plots show an increase of the charge transfer resistance with increasing of the inhibitor concentration and decreases double layer capacitance. The inhibitory action of the extract was discussed in view of the Langmuir adsorption isotherm.

Observation of the patients used levothyroxine tablets but still have problem with their thyroid, leads to analysis of pharmaceutical formulation in the first step. Common instrumental methods for the active ingredient analysis of different pharmaceutics are timeconsuming and pricy and require a skilled operator. In this study, for the first time, an electrochemical sensor which is capable of evaluating the active ingredient of Levothyroxine in formulations is introduced. The proposed sensor, which is a PVC membrane electrode, offers advantages of rapidity, inexpensively, and portability. The sensor responds based on ion-exchange mechanism. Levothyroxine-Hexadecyltrimethylammonium ion-pair (LEVHTA) was employed as a sensing element in construction of the membrane electrode. PVC membrane electrode was made after series of experiments. The best PVC membrane electrode performance was achieved by a membrane composition of 30% PVC, 60% DBP, and 7% LEV-HTA ion-pair. The proposed method was successfully applied in determination of levothyroxine in some pharmaceutical formulations. Five samples from the vary batches, coded differently, were sent for high performance liquid chromatography (HPLC) analysis. The results of two methods were compared using parametric tests. Pearson correlation test was used to assess the correlation between these findings. A strong correlation was found between the active ingredient content measured using electrochemical sensor and official method (HPLC) (ρ=0.98 P<0.05).

The triiodide-selective sensor with a PVC membrane containing ion pair of methyl violet triiodide as electro-active substance was developed. The operating рН range of the triiodide sensor is 2–12. The linearity ranges of triiodide sensor function are 9×10-6–1×10-1 M, the sensor super Nernstian slope are 76 mV/decade. The efficiency of the use of sensor for povidone-iodine determination was shown by potentiometric titration methods.