Analytical & Bioanalytical Electrochemistry
Volume:6 Issue: 6, Dec 2014

The electrochemical behavior of alloy C in NaOH solutions under open circuit potential (OCP) condition was investigated in this research by using potentiodynamic polarization, Mott–Schottky analysis and electrochemical impedance spectroscopy (EIS). Potentiodynamic polarization curves suggested that alloy C showed excellent passive behavior in NaOH solutions. Mott–Schottky analysis revealed that the passive films displayed p-type semiconductive characteristics, where the Ni(II) vacancies (over the oxygen vacancies and interstitials) preponderated. Also, the Mott–Schottky analysis indicated that the acceptor density decreases with decreasing NaOH concentration. EIS measurements showed that dilute NaOH solutions offer better conditions for forming passive films with higher protection behavior, due to the growth of a much thicker and less defective films.

The inhibition behavior of 1-(1-Naphthalenylmethyl) quinolinium chloride (NMQ) on the corrosion of mild steel in 1.00 M hydrochloric acid has been investigated. Weight loss measurements, potentiodynamic polarization and electrochemical impedance (EIS) techniques were used to study the corrosion inhibition process. The results revealed thatmaximum corrosion protection was 99% at 50 ppm of NMQ. Polarization measurements indicate that inhibitor has mainly cathodic inhibition effects and therefore control of hydrogen evolution is done. From EIS measurements it is found that charge transfer resistance values increased and double layer capacitance values decreased by increasing the inhibitor concentration. The adsorption of NMQ on the mild steel follows the Langmuirisotherm model, calculated value of adsorption free energy was (–43.6) kJ mol-1 and adsorption constant was 107.5.

A new acetate selective poly (vinyl chloride) membrane sensor based on newly synthesized nickel complex of Schiff base, N,N'-benzene-1,2-diylbis[1-(1H-pyrrol-2- yl)ethanimine] as an ionophore was prepared. The electrode show Nernstian slope of 31.4±1 mV/decade with improved linear range of 1.6×10-7 to 1.0×10-2 M, with a lower detection limit of 1.0×10-7 M between pH range of 3.0-9.5, giving a relatively fast response within (5s) and can be used for at least 2 months without any divergence in potential. The selectivity coefficient was calculated using matched potential method. The proposed electrode was successfully applied as an indicator electrode for the titration of arsenate ion with sodium thiocynide. It was also be used for the determination of arsenate ion in different water samples.

Due to the importance of selective determination of the rare earth elements, construction of a novel holmium PVC membrane sensor based on 3-[(pyridine-2- ylmethylene)-amino]-2-thioxo-4-one (PMAT) as a neutral carrier, (DBP) as a plasticizer and (KTpClPB) as anionic additive is reported. The sensor has a Nernstian slope of 21.0±0.4 mV per decade and a linear dynamic range between 1.0×10-6 and 1.0×10-2 mol L-1. The mentioned sensor can be used in pH range of 4-7.5 and has a detection limit of 7.0×10-7 mol L-1. It has at least 4 weeks applicability life time, possesses the advantages of fast response time, and very good selectivity over a large number of cations, especially for lanthanide ions. The sensor was used as an indicator electrode in the potentiometric titration of fluoride ions of mouthwash with 1.0×10-3 mol L-1 solution of Ho3+ ion.

The construction and electrochemical response characteristics of three selective electrodes were investigated using precipitation based technique with phosphotungstate and phosphomolybdate; respectively upon using polyvinyl chloride (PVC) matrix and dioctylphthalate (DOP) as a plasticizer. The resultant membrane sensors were tinidazolephosphotungestate (TND-PTA) electrode (sensors 1), tinidazole phosphomolybdate (TNDPMA) electrode (sensors 2) and clarithromycin phosphotungestate (CLR-PTA) electrode (sensors 3). Linear responses of TND and CLR within the concentration ranges of 10−6 to 10−2 mol/L for sensors 1, 2 and 3 were observed. Nernstian slopes of 58.3, 57.1 and 58.8 mV/decade were observed over the pH range of 3-7 for sensors 1and 2 and over range of 3-8 for sensor 3, respectively. The selectivity coefficients of the developed sensors indicated excellent selectivity for TND and CLR. The proposed sensors displayed useful analytical characteristics for the determination of TND and CLR in bulk powder and pharmaceutical formulation (Helicure® tablets).

In the present study, electrocatalytic oxidation of formaldehyde was investigated on Ni/Al Layered double hydroxide nanoparticles modified carbon ceramic (Ni/Al LDH/NMCC) electrode in alkaline media (i.e. NaOH 0.1 M).The process of oxidation involved and its kinetics were established by using cyclic voltammetry, chronoamperometry as well as steady state polarization measurements. The cyclic voltammogram of the resulting modified electrode prepared under optimum conditions, shows a good redox behavior ofNi(III)/Ni(II) couple at the surface of these electrodes can be observed. A new mechanism based on the electrochemical generation of Ni(III) active sites and their subsequent consumption by the formaldehyde in question was also investigated. For Ni/Al LDH/NMCC electrode, the transfer coefficient (α), the number of electrons involved in the ratedetermining step (nα) and the catalytic rate constant (k) for modified electrode were calculated as 0.43,1 and 0.6536×104 cm3mol–1 s–1 respectively. The modified electrode shows a stable and linear response in the concentration range of 0.01 to 0.1 mol L−1 with acorrelation coefficient of 0.9906.

Mathematical and kinetic modelings of biofilm reactors were discussed. The model contains a non-linear term related to Monod and Haldane kinetics. In this paper, a simple approximate analytical expression of substrate concentration profiles is derived in terms of all dimensionless parameters. These analytical results were found to be in good agreement with numerical solution by using the Matlab program. Moreover, in we employ modified Adomian decomposition method (ADM) here to solve the second order nonlinear differential equation. This work presents the approximate analytical solution for non-linear equations in a fixed bed biofilm reactor. This analytical result could be very helpful for analyse and to optimize the parameter.

Benzo15-crown-5 (B15C5) has been examined as an ion sensing material for fabricating a PVC membrane lead ion-selective potentiometric sensor. The best performance of the electrode was observed with a membrane composition formed by 29% PVC, 60% dibutylphthalate (DBP) as plasticizing solvent mediator, 2% sodium tetraphenylborate (NaTPB) as ion excluder and 9% of B15C5 as ionophore. The electrode presents a nearlyNernstian response (a slope of 29.7±0.5 mV/decade) over a concentration range 1×10-5-1×10- 3 M of lead ions, with a limit of detection 8.4×10-6 M. Its potential response was independent on pH variation in the range 2.8-4.5. The dynamic response time of the electrode to achieve a steady potential was found to be about 25 seconds. The selectivity of the prepared electrode relative to some mono-, di-, tri- and tetra-valent metal ions was examined. This electrode can be used for 2 months without considerable divergences in the potential response. It was successfully used as an indicator electrode for the complex formation titration of lead inwater sampless by EDTA.

A novel electrochemical sensing methodology for the detection of methyl salicylate concentration, [MeS] through chronopotentiometric transients under galvanostatic mode is devised. The oxidation potential shifted cathodically, with the increase in [MeS] due to the reduction in absolute anodic current density. Either if anodic current density (ia) is lowered or [MeS] is enhanced, then the rate of oxidation is prevailed by diffusion control rather than charge-transfer limitations. The determined exchange current density was 7.9 × 10–4 A dm–2. Discrete anodic oxidation current was estimated and is about 8.49 mA in the potential range 493 to 606 mV. I order chronopotentiometric transients are having comparatively larger (0.005 Volt min.–1) and positive than the subsequent higher order transients at [MeS] = 7 mM and at ia = 0.063 Adm–2. The lower detection limit of 7 mM can be achieved with an absolute error 0.005. Off mode potential decay depends on [MeS] and ia. The anodic oxidation of salicylate di-ion occurs through three electrons transfer whereas methoxide ion takes place through one electron transfer. Diclofenac shifts the anodic potential more negatively, even at low concentrations. Nonlinear numerical simulations, to interpose anodic potential with [MeS] were carried out using MATLAB®.