Analytical & Bioanalytical Electrochemistry
Volume:4 Issue: 6, Dec 2012

The methionine modified carbon paste electrode exhibited good electrocatalytic properties towards dopamine (DA) oxidation in phosphate buffer (pH 7.0) than that of the bare electrode. The electrocatalytic response was evaluated by cyclic voltammetric technique. methionine modified carbon paste electrode has negative charge on its surface and in neutral solution DA exists as the positively charged species. In cyclic voltammetric measurements, favorable ionic interaction (i.e., electrostatic attraction) between DA and Methionine modified carbon paste electrode causes a negative shift of the oxidation potential for DA compared to that at the bare electrode. The electrode response was not affected by the oxidized product of DA. Several parameters such as scan rate variation, DA concentration and pH effect were investigated by cyclic voltammetric measurements. The peak currents were proportional to the concentration of DA with a detection limit of 1×10–6 M.

A novel sumatriptan (SUM) selective electrode was investigated with dioctyl phthalate as a plasticizer in a polymeric matrix of carboxylated polyvinyl chloride (PVCCOOH), based on the interaction between the drug solution and the dissociated COOH groups in the PVC-COOH. The sensor was fabricated by using PVC-COOH only as anionic site without incorporation of an ionophore. Linear response of SUM within a concentration range of 10-6-10-3 M with a slope of 34±1 mV/decade over pH range of 6-8 was observed. The measurement was characterized by a fast stable response within about 45 seconds.The proposed sensor was successfully applied for the selective determination of sumatriptanin the pure powder form and in its pharmaceutical formulation with naproxen without any interference. The results obtained by the proposed procedure were statistically analyzed and compared with those obtained by the U.S. Pharmacopeia method. No significant difference for either accuracy or precision was observed.

A chemically modified electrode is constructed based on multi-walled carbon nanotube modified glassy carbon electrode (MWCNTs/GCE) as a sensor for simultaneous determination of acetaminophen (ACT) and indomethacin (INDO) in phosphate buffer (pH 7) solution. The measurements were carried out using differential pulse voltammetry (DPV), cyclic voltammetry (CV) and chronoamperometry (CA) methods. DPV measurements showed that the linear relationship between oxidation peak current and concentration of ACT and INDO were in the range of 3 μM to 400 μM, and 10 μM to 330 μM, respectively. Under optimal conditions the modified electrode exhibited high sensitivity and stability for both ACT and INDO determination, making it a suitable sensor for the simultaneous submicromolar detection of ACT and INDO in solutions. The analytical performance of this sensor has been evaluated for detection of ACT and INDO in human serum, human urine and a pharmaceutical preparation with satisfactory results.

This work describes the construction and electrochemical response characteristics for three different polyvinyl chloride (PVC) membrane sensors for determination of amisulpride in presence of its degradation products and commonly used excipients. The first two sensors are based on the ion association complexes of amisulpride cation with sodium tetraphenyl borate (TPB) [sensor 1] or ammonium reineckate (R) [sensor 2] counter anions as ion exchange sites in PVC matrix. β-cyclodextrin (β-CD)-based technique with TPB as a fixed anionic site in PVC matrix was used for fabrication of the third membrane sensor [sensor 3]. The performance characteristics, sensitivity and selectivity of these electrodes in presence of amisulpride degradation products were evaluated according to IUPAC recommendations. Fast, stable and linear response was obtained for amisulpride over the concentration range 1×10-6-1×10-2 M for sensors 1 and 3 while for sensor 2 it was found to be 1×10-5-1×10-2 M. The proposed sensors showed stable Nernstian responses of 29.1, 28.2 and 31.1 mV per concentration decade with sensors 1, 2 and 3, respectively. These sensors exhibit fast response time (10-20 s) and good stability (4-6 weeks). The direct potentiometric determination of amisulpride in its pure form using the proposed sensors gave average recoveries of 99.93±0.72, 100.01±0.93 and 99.94±0.87 for sensors 1, 2 and 3, respectively. The sensors were used for determination of amisulpride, in pure form, in presence of its degradation products, in tablets and in plasma. Validation of the method shows suitability of the proposed sensors for use in the quality control assessment of amisulpride and for routine analysis as stability indicating method. The developed method was found to be simple, accurate and precise when compared with a reported RP-HPLC method.

Zn-Co, Zn-Fe and Zn-Co-Fe coatings were electrodeposited on mild steel from an acid sulphate bath, using thiamine hydrochloride (THC) and citric acid (CA) as additives. Bath constituents and operating parameters were optimized by standard Hull cell method, for peak performance of the coatings against corrosion. The effect of current density (c.d.), pH on the deposit characters, such as corrosion resistance, hardness, thickness, partial current density and CCE were studied and discussed. Corrosion resistances were evaluated by Potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) method. Corrosion resistance of the Zn-Co-Fe coating under optimal c.d. (3.0 A dm-2) was found due to its inherent high dielectric barrier, evidenced impedance signals. High partial current density for zinc in Zn-Co-Fe alloy coating supports the possibility of a synergistic catalytic effect of Co on Fe and vice versa. X-ray diffraction study clearly indicates that a drastic change in corrosion resistance of ternary alloy is due to the change in the phase structure of the coatings, compared to binary alloys. Surface morphology and composition of the coatings were examined by using Scanning Electron Microscopy (SEM), interfaced with Energy Dispersive X-ray Analysis (EDXA) facility, respectively.

Combination of the exceptional properties of graphene oxide with the selectivity of lead porphyrin leads to fabricate a novel cysteine-selective sensor. The electrode made of 30% PVC, 53% NPOE, 2% NaTPB and 15% GO-PP was found to show the most favorable behavior. The sensor shows a Nernstian response (58.8 mV decade-1) in the concentration window of 5.0×10-7-5.0×10-1 M with detection limit of 8.0×10-8 M. The graphene oxide-lead porphyrin composite based sensors displayed a fast and selective response towards cysteine which was successfully applied to the determination of cysteine in real sample (human serum).

An experimental attempt was made to characterize A new composite fast ionic systems, [Ag2CdI4:0.x AgI] (x=0.2, 0.4, 0.6 mol. wt. %), were prepared, using [Ag2Cd 4] mixed composite system as the host. [Ag2CdI4] compound belongs to the fast ion conductors of A2BX4 (A=Ag, Cu, B=Hg, Cd, Zn, Pb and others. The compound [Ag2CdI4] becomes superionic near 388K as the crystal lattice changes from a tetragonal to a hexagonal structure. Near 445 K, [Ag2CdI4] is replaced by an equilibrium mixture of α-AgI and CdI2. At each of these phase transition, ionic conductivity increases by an order of magnitude or more. The substitution of Cd2+ from Ag+ in [Ag2CdI4] is accompanied by a slight increase in the room temperature conductivity, as a result of either increased crystalline defects or an increased Ag+ substitution also characterized. X-ray powder diffraction, FTIR and Thermal (DTA, DSC, TGA) analyses were performed to confirm the formation of fast ion conductors [Ag2CdI4:0.x AgI].

In this work, interaction study of metal ions with quercetin, the secondary metabolite of plants was investigated by conductometric method and fluorescence spectroscopy. The conductometric study was done in acetonitrile solution. The conductance of the solution is measured after each addition of the quercetin to the cation solution. The fluorescence spectrum of quercetin was recorded in presence and absence of metal ions at maximum wave length (481 nm) upon excitation at 425 nm. Among the many cations titrated with quercetin, Mg2+, Al3+, Pb2+ and Zn2+ enhanced the intrinsic fluorescence of the quercetin while Cu2+, Ni2+ and Co2+ ions quench the intrinsic fluorescence emission of the quercetin solution. These different phenomena are observed due to the different release of absorbed energy in formed complex. The ability of quercetin molecule to form a complex with metal ions may be has an effect in quercetin anti-oxidative properties.