Analytical & Bioanalytical Electrochemistry
Volume:3 Issue: 2, Apri2011

In this paper, apigenin (AG) and naringenin (NG) have been studied with the cyclic voltammetric technique using the glassy carbon (GC) electrode. The modification was carried out only in non-aqueous media, while the electrochemical characterization was done in both aqueous and non-aqueous media. 0.1 M tetrabutylammonium tetrafluoroborate (TBATFB) in acetonitrile (MeCN) was used in non-aqueous experiments, Britton-Robinson (BR) buffer solution (pH=2) and 0.1 M KCl solution were used in aqueous experiments. Surface modification experiments were performed in the +0.3 V and +2.8 V potential ranges with a scan rate of 0.1 Vs-1 and 10 cycles for two molecules. The presence of AG and NG at the GC electrode surface was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), contact angle measurement (CAM) technique and atomic force microscopy (AFM). We also investigated the electrochemical oxidation of AG and NG in non-aqueous media and propose a grafting mechanism of AG and NG to the GC electrode surface.

An attempt has been made to develop a highly selective Cr3+-ion selective PVC membrane electrode based on a 5% newly synthesized 3 aminoacetophenonethiosemicarbazone as an ionophore with 62% DBP, 30% PVC and 3% NaTPB as an anion excluder. The electrode exhibits a near Nernstian potential response of 19.7±0.2 mV per decade over a wide concentration range (1.0×10-8 M to 1.0×10-1 M) with a detection limit of 7.4×10-8 between pH 1.5-6.8 with a fast response time (10 s). The selectivity coefficient values were determined by matched potential method (MPM), indicate higher selectivity for chromium(III) ion with improved performance as compared to other carriers reported earlier. The proposed electrode exhibits an adequate shelf life (14 weeks) without any considerable divergence in potentials. Further the electrode was also successfully applied to determine the content of chromium in water samples collected from different sites of river Yamuna in Delhi.

A new chemically modified electrode was constructed based on nickel phosphate nanoparticles modified carbon paste electrode that immersed in NiCl2 solution (Ni NP/CPE). The modified electrode was employed as a sensor for electrocatalytic oxidation of paracetamol (PAR), phenylephrine hydrochloride (PHE), chlorpheniramine maleate (CLP) in aqueous solutions using differential pulse voltammetry (DPV) method in Tris-HCl buffer solution with pH 7.0. The Ni(II) ion adsorbed in nickel phosphate nanoparticles can act as catalyst to oxidize above drugs. The prepared electrode showed voltammetric responses with high sensitivity and selectivity for PAR, PHE and CLP in optimal conditions, which makes it very suitable for determination of these compounds. A linear calibration graph was obtained with concentration ranges of 0.75–7.0, 0.02–10.0 and 0.05–10.0 mM for PAR, PHE and CLP, respectively. The detection limits of PAR, PHE and CLP were obtained 0.24, 0.0064 and 0.016 mM, respectively. The proposed method was successfully applied for determination of PAR, PHE and CLP in pharmaceutical samples.

A voltammetric method using a poly(maleic acid) modified carbon paste electrode was developed for the quantification of dopamine. The modified electrode exhibited stable and sensitive current responses towards dopamine and potassium ferrocyanide. Compared with a bare CPE, the modified electrode exhibits a remarkable shift of the oxidation potentials of dopamine in the cathodic direction and a drastic enhancement of the anodic current response. The separation between anodic and cathodicpeak potentials for dopamine is 0.84 V in 0.2 M phosphate buffer solution (PBS) at pH 7. at modified carbon paste electrodes. The poly (maleic acid) CPE was also effective to simultaneously determine dopamine and uric acid in a mixture and resolved the overlapping anodic peaks of these two species into two well-defined voltammetric peaks in cyclic voltammetry. The proposed method showed excellent stability and reproducibility.

In this work, the suitability of a dioxime derivative, (2E,3E)-1,4- dihydroquinoxaline-2,3-dione dioxime (H2L), as a neutral ionophore for preparation of a PVC membrane electrode, is investigated for nickel(II) ion in solution. The prepared membrane exhibits a Nernstian response (28.2±0.1 mV decade-1) for Ni2+ ion over a wide concentration range (6.3×10-7 to 1.1×10-1 M) with a detection limit of 5.4×10-7 M. At a working pH range of 4.0–6.5, the proposed membrane electrode revealed very good selectivity for Ni2+ ion over a wide variety of other cations. Besides a relatively fast response of <60 s the sensor could be used for at least 3 months without any considerable divergence in potentials. It was successfully applied as an indicator electrode in potentiometric titration of Ni(II) ion with EDTA and in the determination of Ni2+ in some water samples.

PtPd alloy nanoparticles were electrodeposited on a multi-walled carbon nanotube (MWNT)–ionic liquid (IL, i.e., 1-octyl-3-methylimidazolium hexafluophosphate, OMIMPF6) composite film coated glassy carbon electrode. The resulting electrode (PtPd–MWNT– IL/GCE) was characterized by X-ray diffraction, scanning electron microscope and voltammetry. The influence of some parameters (e.g. electrodeposition time, electrodeposition potential and temperature) on the PtPd alloy nanoparticles was discussed and optimized. The electrocatalytic oxidation of formaldehyde on the electrode was explored, and it was found that the PtPd–MWNT–IL/GCE showed good electrochemical catalysis in H2SO4 solution. When the PtPd–MWNT–IL/GCE was used as a formaldehyde sensor, it displayed wide linear range and good stability.

In this work, for the first time a fast continuous cyclic voltammetry was used as a highly sensitive detection method for the monitoring of Folic acid in a flow-injection system. It was used for analysis of Folic acid in pure form as well as in its pharmaceutical formulations. The best performance for sensitive monitoring of Folic acid was obtained at pH 2.0, scan rate 70 Vs-1, accumulation potential 300 mV and accumulation time 0.8 s. The most advantages of the proposed detection method are, including, the removal of oxygen from the test solution is not required any more, and detection limit of the method is in sub nanomolar level. The potential waveform consisting of the potential steps for cleaning, accumulation and potential ramp was continuously applied on an Au disk microelectrode (with a 12.5 m in radius). The detection limit of the method for Folic acid was 1.45pg/ml. The relative standard deviation of the method at 2.0×10-7 M was 2.1 % for 10 runs.

In this article a new PVC based La(III) ion selective electrode based on 1, 12- diaza-5,8,13-trioxo-3(4), 9(10)-dibenzocyclotridecane(DATODBCTD) ionophore is described. This sensor has a wide linear range of concentration (3.4×10- 7-1.0×10-2) and a low detection limit of 8.0×10-7 mol L−1of La(NO3)3. It has a Nernstian response with slope of 19.4±0.4 mV decade−1 and it is applicable in the pH range of 3.5-8.0 without any divergence in potentioal. The PVC electrode has a short response time of approximately 20 s and is stable at least for 2.1 days. The electrode shows a good selectivity for La3+ ion toward a wide variety of metal ions. The proposed sensor was successfully applied for the determination of La3+ ion in different real and environmental samples and as indicator electrode for potentiometric titration of La(III) ion with EDTA.