Analytical & Bioanalytical Electrochemistry
Volume:9 Issue: 2, Mar 2017

To date, the development of different modified electrodes has received much attention in electrochemistry. Hence, we report an electrochemical sensor for the determination of hydroxylamine using ZnO nanorods/graphene oxide nanosheets modified graphite screen printed electrode Electrochemical determination of hydroxylamine reveals that the modified electrode showed lower detection limit of 0.5 μM with a linear ranging from 1.0 to 100.0 μM towards the hydroxylamine concentration via differential pulse voltammetry. The developed sensor also applied to the successfully determination of trace level hydroxylamine in real samples. In addition, the advantage of this type of electrode is simple, disposable and cost effective in electrochemical sensors.

The possibility of theacrine electrochemical determination has been evaluated from the theoretical point of view. The correspondent mechanism has been suggested, and the correspondent model, developed and analyzed by means of linear stability theory and bifurcation analysis. It was verified that theacrine may be electrochemically detected in neutral media over the polymers of the compounds, belonging to the quinone-hydroquinone system, serving as mediator of electrons and protons transfer. The analytical signal has to be clear and easily interpreted. The possibility of oscillatory and monotonic instabilities has also been detected.

A simple, sensitive and selective electrochemical method is developed for the determination of terazosin (TR) by using cyclic voltammetry and differential pulse voltammetry. A poly congo red carbon paste electrode (poly CR/CPE) based sensor was successfully fabricated by the electro polymerization process by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). This modified carbon paste electrode exhibited a good electro catalytic activity towards the resolution of terazosin in 0.1M phosphate buffer solution (PBS) at pH 7.0. The effect of pH, scan rate, concentration of Terazosin were studied by using congo red modified CPE. The modified electrode showed a good detection limit of 7.3 µM over the linear dynamic range of 1.76×10-5 M to 3.33×10-5 M, which is better than many reported methods in the literature. The prepared poly (CR) modified electrode exhibited good stability, high sensitivity, better reproducibility, low detection limit towards the determination of Terazosin(TR). Finally, the electrochemical oxidation of TR at the surface of poly CR/ CPE was employed for the determination of TR in real sample analysis.

Among Ni-base alloys, Alloy 22 is one the most important alloys because of its corrosion response under both oxidizing and reducing solutions. In this paper, passive and electrochemical response of Alloy 22 was investigated in alkaline solutions with focus on the variation of passive film stability with KOH concentrations. The resistance, capacitance and thickness of the passive film were measured by electrochemical impedance spectroscopy (EIS). Moreover, the semiconducting properties were evaluated from Mott–Schottky (M–S) tests. M–S plots depicted that this Ni-base alloy in KOH solutions behave as p-type semiconductor. Also, these tests indicated that defect (acceptor) density is in the range 1022 cm-3 and increased with solution concentration. In conclusion, all electrochemical results revealed that dilute KOH solutions offer better conditions of the passive film formation on this Ni-base alloy than concentrated KOH solutions. Finally, scanning electron microscope micrographs revealed that Alloy 22 is well passivated even in concentrated KOH solutions.

The focus of this work is on the preparation of a Cu2 all-solid-state ion selective electrode (ASS-ISE) to be used in the analysis of copper ions in complex samples. The ASSISE was composed of a conductive substrate of graphite-epoxy resin on a copper wire. This conductive substrate was further coated with a layer of Cu2+selective PVC membrane, comprising 32% of PVC, 57% of nitrobenzene (NB) as the plasticizing solvent, 2% of an ionic additive (i.e. sodium tetraphenyl borate (NaTPB)), and 9% of an organic ligand named 3-(2-methyl-2,3-dihydrobenzothiazol-2-yl)-2H-chromen-2-one (L) as the selective ionophore. The device with the optimal composition had a Nernstian response of 29.3±0.3 mV/decade from 1.0×10-8 M to 1.0×10-3 M of the analyte and its lower detection limit was estimated at be 4.0×10-9 M. The ASS-ISE showed excellent selectivity for the target ion in the presence of various common interfering ions, and was found to be satisfactorily applicable to the analysis of copper electroplating waste water samples.

Sodium dodecyl sulfate surfactant modified graphene paste electrode (SDSMGPE), prepared by electrochemical immobilization of the Sodium dodecyl sulfate surfactant (SDS) on a graphene paste electrode, was applied for simultaneous determination of dopamine (DA) in the existence of ascorbic acid (AA) and uric acid (UA) through cyclic voltammetry(CV) and differential voltammetry(DPV). The modified electrode shows strong electrocatalytic function for the oxidation of DA, AA and UA and three well-defined voltammetric peaks of about 167 mV, 12 mV and 303 mV by CV method. A linear response in the range of (1×10-5)-(1×10-3) M with a detection limit of 4.7×10-6 M and limit of quantification limit 15×10-6 M for DA was obtained. This SDSMGPE indicated a potent and persistent electron mediating behavior bring up by adequately separated oxidation peaks of DA, AA and UA. The bare graphene paste electrode (BGPE) and SDSMGPE were characterized using Energy-dispersive X-ray spectroscopy (EDX) and Field emission scanning electron microscopy (FESEM) were used to check the electrochemical efficiency of electrodes. The effects of graphene paste constitution, concentration, surfactant, pH, and scan rate were investigated. The modified electrode is highly stable and can be used to the determination of DA in injection samples. The proposed method is simple, fast, sensitive, selective, stable, reproducible and accurate.

The electrochemical behavior of four biologically active cycloalkane espirohydantoins with 5-, 6-, 7-, and 8-membered rings: 1,3-diazaspiro[4.4] nonane-2,4-dione (CSH(5)); 1,3-diazaspiro[4.5]decane-2,4-dione (CSH(6)); 1,3-diazaspiro[4.6]undecane-2,4dione (CSH(7)); and 1,3-diazaspiro[4.7]dodecane-2,4-dione (CSH(8)) has been investigated at the pH range 1.81-12 by modern electrochemical techniques as cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV). The electrochemical studies were carried out on a hanging mercury drop electrode (HMDE) at room temperature. CSH(5) and CSH(6) at pH 5.50 and 7.63 and CSH(7) at pH 5.50 showed a single quasireversible peaks. For CSH(7) at pH 7.63 and CSH(8) at two pH values the irreversible nature of the electrode process was proved. The effect of scan rate, pH and concentration on peak current and peak potential was investigated. Physical parameters like diffusion coefficient and heterogeneous electron transfer rate constant were determined from scan rate and concentration effects. The number of proton transfer in the electrochemical reaction was determined from the peak potential shift as a function of pH and a mechanism of cycloalkanespiro-5-hydantoins derivatives on the basis of CV, SWV and DPV results was proposed. The proposed mechanisms of the cited cycloalkane spiro-5-hydantoins could be essential in regard to the hidden pathways by which such compounds exert their biochemical actions.

Granisetron content of some pharmaceutical tablets was determined using a novel all-solid-state polymeric-membrane-electrode (ASS-PME) having a sensing element functioning based on an ion-exchange mechanism. The best results were observed with ASSPMEs containing 8% GST-tetrakis (p-chlorophenyl) borate as the ion-pair, 56% of dibutyl phthalate, 31% of poly(vinyl chloride), 3% of an ionic liquid and 2% of KpClTPB. The ASS element of the device was a conductive composite of graphite, MWCNTs, and an epoxy resin coated on a copper wire, and the PVC membranes were coated on the ASS. The ASS-PME showed a Nernstian response of 58.1±0.2 mV/decade over the range of 1.0×10-6 to 1.0×10-3 M. The application of the device was validated and the method was found to be applicable in the analysis of Granisetron hydrochloride in pharmaceutical formulations.

The inhibition effect of Curcumine Longa (CUR) on the corrosion of aluminum in presence of 1 M HCl solution was studied by weight loss, Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), quantum chemical calculations and SEM techniques. Weight loss and electrochemical results showed that inhibition efficiency of CUR increases with increase in the concentration and attained a maximum value of 89.60% at 100 ppm concentration. Polarization study revealed that CUR acts as mixed type inhibitor whereas EIS study showed that the CUR inhibits aluminum corrosion by getting adsorbed at metal/ electrolyte interfaces which followed the Langmuir adsorption isotherm. SEM study confirmed the film forming ability of CUR on the aluminum surface. Quantum chemical calculations study was performed to provide insight into adsorption behavior of CUR on the aluminum surface. Experimental and theoretical results were in good agreement and well complimented to each other.