Analytical & Bioanalytical Electrochemistry
Volume:9 Issue: 6, Sep 2017

In this work, the role of anodic passive potential on the passive and electrochemical response of pure Ta in 0.1 M H2SO4 solution was studied. Electrochemical impedance spectroscopy (EIS) plots showed that corrosion resistance of the passive film on the pure Ta increased with the increasing of anodic passive potential. In addition, the semiconductive behavior of the passive films formed on pure Ta in 0.1 M H2SO4 solution is evaluated by employing Mott–Schottky (M–S) analysis. Although, semiconducting response of pure Ta in 0.1 M H2SO4 solution remains the same as n-type, anodic passive potential significantly affect the levels of donor concentrations. Indeed, M–S analysis revealed that less donor densities in passive film due to higher anodic passive potential deteriorated corrosion resistance of the pure Ta. Also, M–S analysis revealed that flat band potential is quite sensitive to anodic passive potential.

Usually, nitrates are found naturally in low concentrations in water, but they can also have an artificial origin due to their use as crop fertilizer (mineral and organic fertilizers, animal manure). Excess not absorbed by plants are leached by rain and remains in the soil. In this paper we are going to study the effect of nitrates (NO3-) existence in soil on metal degradation of two series of brass (α and αβ) used as a support fittings which are suitable for connecting domestic service lines. This work aims at specifying the best alloys which are recommended to be used in Moroccan Azrou soil medium. This research paper was applied by using electrochemical impedance spectroscopy (EIS) methods and polarization curves. It was found that EC6 is the most resistant alloy between all brasses in this soil which containing 2 g/L of NO3-. Moreover, we have studied the role and effects of various additional elements which exist in different brasses and they are responsible for increasing the corrosion resistance.

In this paper, a sensitive and convenient electrochemical sensor based on stacked cysteic acid film and gold nanoparticles (AuNPs) composite modified glassy carbon electrode (GCE) was developed for the determination of Methadone (MET). Electrochemical investigation of the modified electrode is achieved using cyclic voltammetry (CV), differential pulse voltammograms (DPV) and field emission scanning electron microscopy. The effective surface areas of AuNPs/cysteic acid/GCE increased for about 4-fold larger than that of the unmodified GCE. The kinetic parameters of the electron transfer coefficient (α) and number of electrons involved in the rate determining step (nα) for the oxidation of MET were determined utilizing CV. The designed modified electrode was revealed linear responses in the ranges of 0.024 to 4.45 μM and 4.45 to 12.67 μM with a limit of detection (LOD) of 0.014 μM (S/N=3). Excellent recovery results were obtained for determination of MET in spiked human blood plasma and urine samples at the modified electrode.

A simple and sensitive voltammetric method was developed for simultaneous determination of pyridine-2-aldoxime (PAM-2) and the neurotransmitter dopamine (DA) at poly(3,4-ethylenedioxythiophene) (PEDOT) modified glassy carbon electrode. The electrochemical behavior of DA and PAM-2 were investigated using cyclic voltammetry. PAM-2 was irreversibly oxidized at 650 mV while DA was reversibly oxidized and reduced at about 185 mV and 147 mV, respectively. The observed significant oxidation peak potential difference between PAM-2 and DA allowed the simultaneous determination of both species using square wave adsorptive stripping voltammetry. Under optimized conditions, the voltammetric responses gave linear ranges of 3.0×10−6–1.5×10-4 M and 1.0×10−7–1.0×10−4 M with detection limits of 1.9×10−7 M and 3.1×10−8 M for PAM-2 and DA, respectively. The determination of PAM-2 and DA in human blood serum samples was successfully carried out with a very good recovery result 95.17% and 101.6%, respectively.

This work reports the voltammetric determination of epinephrine (EP) using ZnO-graphene oxide nanocomposite (ZnO-GO). The electrochemical behaviors of epinephrine at ZnO-GO nanocomposite modified graphite screen printed electrodes (SPE) were studied by cyclic voltammetry and differential pulse voltammetry. The outcomes confirmed that the proposed electrode demonstrate excellent electrocatalytic activity towards the oxidation of epinephrine in phosphate buffer solution (PBS, pH 7.0). The fabricated electrode possess lowest detection limit of 0.07 μM for epinephrine with the very wide dynamic linear range of 0.5 µM to 500.0 µM. Finally, the modified sensor was successfully implemented to detect epinephrine in epinephrine injection and urine samples.

The effect of adding surfactants to electrolyte containing rabeprazole sodium (RAB sodium) on its voltammetric response at pencil graphite electrode (PGE) was explored. The current signal due to the oxidation process as a function of the amount of the cited drug, pH of the medium, type of surfactant and accumulation time at the electrode surface was evaluated. The use of sodium dodecyl sulphate in the presence of Britton-Robinson buffer (pH=6.0) for the electrochemical determination of RAB sodium using cyclic voltammetry (CV) and Square wave adsorptive stripping voltammetry (SWAdSV) at PGE was studied. The oxidation peak current has varied linearly with the drug concentration over the range of 0.006-2.5×10-7 M and 0.5-250 µM using SWAdSV and CV, respectively. The limit of detection was found to be 0.2 nM and 0.18 µM using SWAdSV and CV, respectively. The validity of the proposed method for the determination of the studied drug in pure, pharmaceutical formulation in addition to urine was conducted.

A novel modified glassy carbon electrode based on poly aspartic acid-Fe3O4 nanoparticle / multi-walled carbon nanotubes composite (PAA-FeNPs-MWCNTs/GCE) was developed and used as an efficient sensor for simultaneous determination of piroxicam (PRX) and clopidogrel (CLO) in the presence of uric acid (UA). Response surface methodology (RSM) was utilized in optimization of the effects of various operating variables on the voltammetric response of PRX and CLO suggesting that the amount of PAA-FeNPs in the modifier matrix (% PAA-FeNPs), the solution pH and the accumulation time (t) were the three most important operating factors. The central composite design (CCD) as a response surface approach was applied for obtaining the optimum conditions as well as the maximum heights for oxidation peak currents of PRX and CLO. The differential pulse voltammetry (DPV) results showed that under the optimal experimental conditions the obtained anodic peak currents were linearly proportional to concentration in the range of 0.2-80 µM with a detection limit (S/N = 3.0) of 45 nM for PRX and in the range of 0.4-48 µM and with a detection limit of 76 nM for CLO. The applicability of the proposed method was successfully demonstrated for simultaneous determination of these compounds in human urine and blood serum samples.

The present work describes the application of expired drug Lumerax as corrosion inhibitor for mild steel (MS) in 1 M HCl after its expiry date using gravimetric measurements, electrochemical studies and surface analysis. The adsorption of Lumerax on MS surface obeys the Langmuir isotherm. And protection film confirmed by SEM and AFM. Impedance analysis showed that the presence of inhibitor considerably affects the charge transfer resistance and the double layer capacitance of MS surface. Potentiodynamic polarization shows that Lumerax behaves as a mixed type corrosion inhibitor.DFT calculations were used to evaluate the structural, electronic and reactivity parameters of the drug components (Artemether and Lumefantrine) and the theoretical investigation verifies the validity of the use of expired Lumerax drug as a novel and efficient corrosion inhibitor for mild steel.

An electrochemical amplified sensor based on carbon paste electrode modified with reduced graphene oxide/NiO nanocomposite (CPE/rGO/NiO-NC) was suggested for kojic acid determination in food samples. rGO/NiO-NC were characterized by SEM and EDAX methods. The CPE/rGO/NiO-NC showed highly catalytic activity to kojic acid electro-oxidation in aqueous solution. The oxidation currents of kojic acid increased linearly with kojic acid concentration by differential pulse voltammetric (DPV) method in the ranges of 0.3–700 μM with limit of detection ~0.09 μM. The ability of CPE/rGO/NiO-NC was check for the analysis of kojic acid in foodstuff.

In this work, for the first time, a new electrochemical detection system for Isoniazid was developed using combination of modified carbon paste electrode with Coulometric fast Fourier transformation admittance voltammetry (CFFTAV). The sensor was fabricated by using graphite powder, SiC nanoparticles and ionic liquid (CILSiCE), and casting reduced graphene oxide, ionic liquid, SWCNT, and gold nanoparticles. This electrode was characterized by SEM and electrochemical impedance spectroscopy methods. In the optimal conditions, the electrode exhibited a linear response to Isoniazid from 0.5 to 300 nM and detection limit was 0.15 nM. Moreover, the proposed sensor exhibited good accuracy and repeatability (R.S.D value of 2.45%) and long term stability, up to 70 days with a decrease of 4.1% in the response. The proposed method was used to the determination of Isoniazid in real samples, successfully.