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Voltammograms
Kinds of Voltammograms Selected AbstractsElectrode Modified with Cobalt Cyclohexylbutyrate for the Determination of Low Molecular Weight Thiol Group Bearing Compounds Using Catalytic Stripping VoltammetryELECTROANALYSIS, Issue 3 2010Petr Jakubec Abstract Glassy carbon electrode, modified with cobalt(II) cyclohexylbutyrate monohydrate immobilized in polystyrene matrix is usable for determination of thiol group bearing compounds both in oxidized and reduced forms using catalytic stripping voltammetry. The measurements are carried out in acetate buffer (pH,4.3) containing Tween 40. After the accumulation step at ,850,mV vs. Ag/AgCl a peak at ,170,mV is observed on linear sweep voltammogram, the height of which is proportional to the concentration of added thiol. Addition of carbon nanotubes into polystyrene film enhances the sensitivity of the modified electrode. The detection limit is 1×10,6,mol dm,3 for all studied thiols. The electrode can be regenerated by exposing it to the potential between 300,600,mV. [source] Synthesis of Carbon Nanofibers for Mediatorless Sensitive Detection of NADHELECTROANALYSIS, Issue 15 2008Yang Liu Abstract Highly sensitive amperometric detection of dihydronicotinamide adenine dinucleotide (NADH) by using novel synthesized carbon nanofibers (CNFs) without addition of any mediator has been proposed. The CNFs were prepared by combination of electrospinning technique with thermal treatment method and were applied without any oxidation pretreatment to construct the electrochemical sensor. In amperometric detection of NADH, a linear range up to 11.45,,M with a low detection limit of 20,nM was obtained with the CNF-modified carbon paste electrode (CNF-CPE). Good selectivity was exhibited for the simultaneous detection of NADH and its common interferent of ascorbic acid (AA) by differential pulse voltammogram. The attractive electrochemical performance and the versatile preparation process of the CNF-CPE made it a promising candidate for designing effective NADH sensor. [source] Electrochemical Preparation of Poly(Malachite Green) Film Modified Nafion-Coated Glassy Carbon Electrode and Its Electrocatalytic Behavior Towards NADH, Dopamine and Ascorbic AcidELECTROANALYSIS, Issue 14 2007Shen-Ming Chen Abstract Poly(malachite green) film modified Nafion-coated glassy carbon electrodes have been prepared by potentiodynamic cycling in malachite green solution. The pH of polymerisation solution has only minor effect on film formation. Electrochemical quartz crystal microbalance (EQCM) was used to monitor the growth of the poly(malachite green) film. Cyclic voltammogram of the poly(malachite green) film shows a redox couple with well-defined peaks. The redox response of the modified electrode was found to be depending on the pH of the contacting solution. The peak potentials were shifted to a less positive region with increasing pH and the dependence of the peak potential was found to be 56,mV per pH unit. The electrocatalytic behavior of poly(malachite green) film modified Nafion-coated glassy carbon electrodes was tested towards oxidation of NADH, dopamine, and ascorbic acid. The oxidation of dopamine and ascorbic acid occurred at less positive potential on poly(malachite green) film compared to bare glassy carbon electrode. In the case of NADH, the overpotential was reduced substantially on modified electrode. Finally, the feasibility of utilizing poly(malachite green) film electrode in analytical estimation of ascorbic acid was demonstrated in flow injection analysis. [source] Voltammetric Elucidation of Ion Transfer Through an Extremely Thin MembraneELECTROANALYSIS, Issue 9 2004Nobuyuki Ichieda Abstract Digital simulation of the cyclic voltammogram for the ion transfer through a liquid membrane of thickness from 1,mm to 10,nm was performed. The magnitude of current and the shape of the voltammogram simulated for extremely thin membrane (10,nm thick) were similar to those observed experimentally with a bilayer lipid membrane, BLM, of about 10,nm in thick, when the diffusion coefficient of an ion in the BLM was assumed to be extraordinary small (10,13 to 10,14,cm2 s,1). [source] Complexes of glutathione with heavy metal ions as a new biochemical marker of aquatic environment pollution,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2010Jiri Baloun Abstract Reduced glutathione (GSH) plays a number of key roles in many biochemical pathways. This peptide is highly reactive and forms conjugates with other molecules via its sulfhydryl moiety. The interactions of the common heavy metal pollutant Cd(II) with GSH were determined by using the Brdicka reaction to evaluate whether this technique would be suitable as a biomarker. After GSH interaction with Cd(II) ions, two characteristic changes in the measured voltammogram were observed: Cat2 signal height decreased, and a new signal called P1 was found. The observed signal probably relates to the formation of a GSH,heavy metal ion complex adsorbed on the surface of the working electrode. When the interaction of GSH with cisplatin was studied, the same characteristic changes in the voltammogram were observed, which confirmed our hypothesis. Moreover, changes in the height of P1 and Cat2 signals with increasing time of GSH interaction with Cd(II) ions and/or cisplatin were also investigated. Cat2 peak height decreased proportionally with increasing time of interaction. This decrease can be explained by shielding of free sulfhydryl moiety by heavy metal ions, so it cannot catalyze the evolution of hydrogen from the supporting electrolyte. In addition, we found that, with increasing time of the interaction, the P1 signal was enhanced and shifted to more positive potentials for both Cd(II) ions and cisplatin. Environ. Toxicol. Chem. 2010;29:497,500. © 2009 SETAC [source] Dinuclear Manganese and Cobalt Complexes with Cyclic Polyoxovanadate Ligands: Synthesis and Characterization of [Mn2V10O30]6, and [Co2(H2O)2V10O30]6,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 34 2009Shinnosuke Inami Abstract An all-inorganic complex, [Mn2{(VO3)5}2]6, (1), was synthesized, and the structure determination reveals a dinuclear manganese complex coordinated by two cyclic pentavanadate ligands. The cyclic pentavanadate units sandwich the edge-sharing octahedral dimanganese core through coordination of the oxido group of the pentavanadate. A dinuclear cobalt complex with a cyclic decavanadate, [Co2(OH2)2(VO3)10]6, (2), was also synthesized. The structure analysis reveals a dinuclear cobalt complex with a macrocyclic decavanadate, which is composed of 10 VO4 units joined by the vertex sharings. The CoO6 octahedrons are edge-shared, with each cobalt octahedron coordinated to five oxido groups from the decavanadate. The remaining site is occupied by water. The coordinated water molecules are supported with hydrogen bonds in two directions. Complex 2 in acetonitrile shows no reactivity with dioxygen even at low temperature, and the cyclic voltammogram of 2 shows no redox chemistry in acetonitrile. Complex 2 exhibits chromism by water exposure both in the solid state and in acetonitrile. Complex 2 is green,yellow in color, and the addition of water causes the complex to turn brown. After heating the sample, it returns to its original color in a reversible manner. The EXAFS data in acetonitrile is also reported and is consistent with the solid-state structure. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Direct Electrochemical Preparation of NbSi Alloys from Mixed Oxide Preform Precursors,ADVANCED ENGINEERING MATERIALS, Issue 3 2009Fanke Meng A new method of preparation of NbSi alloys has been provided in this article. Electro-deoxidizing mixed Nb2O5 and SiO2 small cylindrical pellets in molten CaF2 at high temperature (1500,°C) could produce homogenous NbSi alloys. And then, the cyclic voltammogram (CV) method was used to analyze the electroreduction mechanism. This effective method could shorten procedures of production of NbSi alloys and will be promising for industrial utilization. [source] Synthesis and characterization of new blue-greenish electroluminescent materials based on 1,3,4-oxadiazole-triazolopyridinone hybridsHETEROATOM CHEMISTRY, Issue 3 2007Ming-Hsiang Shin New functionalized oxadiazole-triazolopyridinone derivatives were synthesized via arcycloaddition. With the chromophores of triazolopyridinone, the photoluminescence spectra of these compounds in dichloromethane solution showed emission peaks between 430 and 520 nm. Following the spectroscopic studies, and the measurements of cyclic voltammogram, 1,3,4-oxadiazole-triazolopyridinone hybrids possess a great potential as highly efficient, blue-greenish, organic light-emitting devices materials. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:212,219, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20285 [source] New synthesis of highly potential efficient bluish-green electroluminescent materials based on 1,3,4-oxadiazole,triazolopyridinone,carbazole derivatives for single-layer devicesHETEROATOM CHEMISTRY, Issue 2 2006Ming-Hsiang Shin New potential bluish-green electroluminescent materials of 1,3,4-oxadiazole,triazolopyridin- one,carbazole derivatives were synthesized and characterized for single-layer devices. Carbazole, pyridine, and triazolopyridinone were completely introduced into 1,3,4-oxadiazole skeletal to play assistant roles in controlling fundamental photolytic process due to the electron-donating nature, excellent photoconductivity, and flexible structure properties. Following the spectroscopic studies and the measurements of cyclic voltammogram, 1,3,4-oxadiazole,triazolopyridinone,carbazole derivatives were highly efficient bluish-green electroluminescent materials. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:160,165, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20201 [source] Voltammetric Sizing of a SphereCHEMPHYSCHEM, Issue 10 2006Nicole Fietkau Abstract The size of a glass sphere positioned in the center of a microdisk electrode is determined by using a simple electrochemical procedure and is confirmed, additionally, by a microscopical measurement of the sphere at the time of the electrochemical measurement. The cyclic voltammetric response of the naked electrode and of the electrode with the sphere positioned in its center is recorded over a wide range of scan rates (0.002,1.5 V,s,1). The size of the sphere is then determined by comparison of the experimental voltammogram with simulations for each individual scan rate. [source] Voltammetric Sizing of Inert ParticlesCHEMPHYSCHEM, Issue 7 2005Trevor J. Davies Abstract The average size of inert particles is determined using a simple electrochemical procedure. Alumina particles are deposited on an edge-plane graphite electrode, and a cyclic voltammogram is recorded. The scan rate employed varies between 0.2 and 2 V,s,1. At these scan rates the diffusion layer thickness is greater than the size of the alumina particles, minimizing the influence of the particles, height on the observed voltammetry. The average size of the particles is determined via comparison of the experimental voltammograms with simulations. [source] Li4Ti5O12 Nanoparticles Prepared with Gel-hydrothermal Process as a High Performance Anode Material for Li-ion BatteriesCHINESE JOURNAL OF CHEMISTRY, Issue 6 2010Zheng Qiu Abstract Li4Ti5O12 (LTO) nanoparticles were prepared by gel-hydrothermal process and subsequent calcination treatment. Calcination treatment led to structural water removal, decomposition of organics and primary formation of LTO. The formation temperature of spinel LTO nanoparticles was lower than that of bulk materials counterpart prepared by solid-state reaction or by sol-gel processing. Based on the thermal gravimetric analysis (TG) and differential thermal gravimetric (DTG), samples calcined at different temperatures (350, 500 and 700°C) were characterized by X-ray diffraction (XRD), field emitting scanning electron microscopy (FESEM), transmission electron microscopy (TEM), cyclic voltammogram and charge-discharge cycling tests. A phase transition during the calcination process was observed from the XRD patterns. And the sample calcined at 500°C had a distribution of diameters around 20 nm and exhibited large capacity and good high rate capability. The well reversible cyclic voltammetric results of both electrodes indicated enhanced electrochemical kinetics for lithium insertion. It was found that the Li4Ti5O12 anode material prepared through gel-hydrothermal process, when being cycled at 8 C, could preserve 76.6% of the capacity at 0.3 C. Meanwhile, the discharge capacity can reach up to 160.3 mAh·g,1 even after 100 cycles at 1 C, close to the theoretical capacity of 175 mAh·g,1. The gel-hydrothermal method seemed to be a promising method to synthesize LTO nanoparticles with good application in lithium ion batteries and electrochemical cells. [source] Square Wave Voltammetric Label-free Determination of the Natural Protein Material Silk FibroinCHINESE JOURNAL OF CHEMISTRY, Issue 11 2008Ming-Ming MA The electrochemical behavior of silk fibroin (SF) was investigated by cyclic voltammetry and square wave voltammetry in 0.01 mol/L HCl for the first time. Within the potential scan range of 0.0 to1.2 V (vs. SCE), two oxidative peaks at 0.91 V (Pa,1) and 0.43 V (Pa,2) as well as one reductive peak at 0.24 V (Pc ) were observed on cyclic voltammogram at scan rate of 0.2 V/s. The peak current of the peak Pa,1 was linear with SF concentration in the range of 5.8×10,8 to 1.1×10,6 mol/L, with the limit of detection 3.0×10,8 mol/L (S/N=3). The proposed method was of high selectivity without the interferences from the coexisting substances such as another natural protein material sericin and other small molecular substances. It was applied to the determination of SF in raw silk liquid samples without any pre-separation and pre-purification. [source] Electrocrystallization of Monodisperse Nanocrystal Copper on Highly Oriented Pyrolytic Graphite ElectrodeCHINESE JOURNAL OF CHEMISTRY, Issue 2 2005Huang Lin Abstract Mechanism of copper electrocrystallization on highly oriented pyrolytic graphite electrode from a solution of 1 mmol/L CuSO4 and 1.0 mol/L H2SO4 has been studied using cyclic voltammogram and chronoamperometry. The results show that in copper electrodeposition the charge-transfer step is fast and the rate of growth is controlled by the rate of mass transfer of copper ions to the growing centers. Reduction of Cu(II) ions did not undergo underpotential deposition. The initial deposition kinetics of Cu electrocrystallization corresponds to a model including progressive nucleation and diffusion controlled growth. Copper nanocrystals with size of 75.6 nm and relative standard deviation of 9% can be obtained by modulation potential electrodeposition. [source] Advances in the Study of Ion Transfer at Liquid Membranes with Two Polarized Interfaces by Square Wave VoltammetryELECTROANALYSIS, Issue 14 2010A. Molina Abstract A general analytical expression has been deduced for the I/E response of the square wave voltammetry corresponding to ion transfer processes in systems with two liquid/liquid polarized interfaces. This expression has been evaluated through the experimental study of a series of quaternary ammonium cations and metal chloro complex anions. We have found that systems with two liquid/liquid polarizable interfaces present the striking advantage that the difference between peak potentials of square wave voltammograms of cations and anions with similar standard ion transfer potential is much greater than in systems with a single polarizable one. [source] Voltammetric Determination of L -Dopa on Poly(3,4-ethylenedioxythiophene)-Single-Walled Carbon Nanotube Composite Modified MicroelectrodesELECTROANALYSIS, Issue 4 2010Jayaraman Mathiyarasu Abstract In the present communication, it is shown that platinum microelectrodes electrochemically coated with a composite of poly(3,4-)ethylenedioxythiophene and single-walled carbon nanotubes (PEDOT/SWNT) enable determinations of 3,4-dihydroxy- L -phenylalaines (L -dopa) in neutral phosphate buffer solutions containing an excess of ascorbic acid. The interpenetrated networked nanostructure of the composite was characterized by scanning electron microscope (SEM) and Raman spectroscopy. It is shown that the presence of the composite gives rise to an increase in the electroactive area of an order of magnitude in compared to the area for the bare microelectrodes. The composite film-coated microelectrode, which yielded reversible cyclic voltammograms for the ferro/ferricyanide redox couple for scan rates between 0.01 and 0.10,V s,1, also gave rise to two well-resolved oxidation peaks for L -dopa and ascorbic acid (AA). The latter effect, which was not seen in the absence of the composite, enabled differential pulse voltammetric determinations of L -dopa in the concentration range between 0.1 to 20,,M with a detection limit of 100,nM. [source] Electrocatalytic Oxidation of Glucose by the Glucose Oxidase Immobilized in Graphene-Au-Nafion BiocompositeELECTROANALYSIS, Issue 3 2010Kangfu Zhou Abstract Graphene was successfully prepared and well separated to individual sheets by introducing SO3,. XRD and TEM were employed to characterize the graphene. UV-visible absorption spectra indicated that glucose oxidase (GOx) could keep bioactivity well in the graphene-Au biocomposite. To construct a novel glucose biosensor, graphene, Au and GOx were co-immobilized in Nafion to further modify a glassy carbon electrode (GCE). Electrochemical measurements were carried out to investigate the catalytic performance of the proposed biosensor. Cyclic voltammograms (CV) showed the biosensor had a typical catalytic oxidation response to glucose. At the applied potential +0.4,V, the biosensor responded rapidly upon the addition of glucose and reached the steady state current in 5,s, with the present of hydroquinone. The linear range is from 15,,M to 5.8,mM, with a detection limit 5,,M (based on the S/N=3). The Michaelis-Menten constant was calculated to be 4.4,mM according to Lineweaver,Burk equation. In addition, the biosensor exhibits good reproducibility and long-term stability. Such impressive properties could be ascribed to the synergistic effect of graphene-Au integration and good biocompatibility of the hybrid material. [source] Kinetic Study of the Oxidation of Catechols in the Presence of Some Aza-crown Ethers by Digital Simulation of Cyclic VoltammogramsELECTROANALYSIS, Issue 9 2009Davood Nematollahi Abstract The electrochemical oxidation of catechols (1) have been studied in the presence of diaza-18-crown-6 (DA18C6) (3a), diaza-15-crown-5 (DA15C5) (3b), and aza-15-crown-5 (A15C5) (3c) as nucleophiles in aqueous solution, by means of cyclic voltammetry and controlled-potential coulometry. The results indicate the participation of electrochemically generated o -benzoquinones (2) in Michael-type reaction with aza-crown ethers (3) to form the corresponding new o -benzoquinone-aza-crown ether adducts (5). Based on ECE mechanism, the observed homogeneous rate constants (kobs) of the reaction of o -bezoquinones (2) with aza-crown ethers (3) were estimated by comparing the experimental cyclic voltammograms with the digital simulated results. The calculated observed homogeneous rate constants (kobs) was found to vary in the order DA18C6>DA15C5>A15C5. [source] Quantitative Analysis of Prometrine Herbicide by Liquid,Liquid Extraction Procedures Coupled to Electrochemical MeasurementsELECTROANALYSIS, Issue 6 2009V. Juarez Abstract A sensitive method is proposed for the preconcentration and quantification of the herbicide Prometrine (PROM) at a liquid-liquid interface employing square-wave voltammetry. The preconcentration stage was based on liquid-liquid extraction methodology and the PROM quantification was carried out from the peak current of square-wave voltammograms. Under the experimental conditions employed, linear calibration curves in the concentration range 1.0×10,6,M,5.0×10,5,M, with detection limit equal to 1.5×10,6,M were obtained without pretreatment of the samples. This linear range, as well as detection limit could be extended towards lower concentrations when a pretreatment procedure was employed. In this way, linearity of calibration curves between 8.0×10,8,M and 2.4×10,7,M and detection limit of 1.0×10,7,M, were observed. On the other hand, the standard addition method was also used as an alternative and an appropriated quantification technique for this system. A linear concentration range between 1.0×10,6,M and 2.7×10,5,M, with a correlation coefficient of 0.997, was obtained. This procedure has also a promising application in the separation of herbicides from other interferents, present in real samples, previous to their quantification. [source] Simultaneous Quantitative Determination of Cadmium, Lead, and Copper on Carbon-Ink Screen-Printed Electrodes by Differential Pulse Anodic Stripping Voltammetry and Partial Least Squares RegressionELECTROANALYSIS, Issue 23 2008Michael Cauchi Abstract Water is a vital commodity for every living entity on the planet. However, water resources are threatened by various sources of contamination from pesticides, hydrocarbons and heavy metals. This has resulted in the development of concepts and technologies to create a basis for provision of safe and high quality drinking water. This paper focuses on the simultaneous quantitative determination of three common contaminants, the heavy metals cadmium, lead and copper. Multivariate calibration was applied to voltammograms acquired on in-house printed carbon-ink screen-printed electrodes by the highly sensitive electrochemical method of differential pulse anodic stripping voltammetry (DPASV). The statistically inspired modification of partial least squares (SIMPLS) algorithm was employed to effect the multivariate calibration. The application of data pretreatment techniques involving range-scaling, mean-centering, weighting of variables and the effects of peak realignment are also investigated. It was found that peak realignment in conjunction with weighting and SIMPLS led to the better overall root mean square error of prediction (RMSEP) value. This work represents significant progress in the development of multivariate calibration tools in conjunction with analytical techniques for water quality determination. It is the first time that multivariate calibration has been performed on DPASV voltammograms acquired on carbon-ink screen-printed electrodes. [source] Electrochemistry of Mitochondria: A New Way to Understand Their Structure and FunctionELECTROANALYSIS, Issue 14 2008Jing Zhao Abstract In this article, electrochemistry of mitochondria is achieved. Cyclic voltammograms of freshly prepared mitochondria were obtained by immobilizing mitochondria together with glutaraldehyde and bovine serum albumin on the surface of a pyrolytic graphite electrode. Two pairs of redox peaks could be observed which were ascribed to the electron transfer reactions of cytochrome c and FAD/FADH2. Study of submitochondrial particles was also conducted, which could confirm the results of the study of the entire mitochondria. The redox wave of NADH could be obtained due to the destruction of the membrane of mitochondria. We have also checked the function of succinate in mitochondria by employing the electrochemical method. This work is not only the first to be able to obtain the direct electrochemistry of mitochondria, but is also beneficial to the further understanding of the structure and function of mitochondria in vitro. [source] Zinc Oxide/Zinc Hexacyanoferrate Hybrid Film-Modified Electrodes for Guanine DetectionELECTROANALYSIS, Issue 18 2007Hung-Wei Chu Abstract An electroactive polynuclear hybrid films of zinc oxide and zinc hexacyanoferrate (ZnO/ZnHCF) have been deposited on electrode surfaces from H2SO4 solution containing Zn(NO3)2 and K3[Fe(CN)6] by repetitive potential cycling method. Simultaneous cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) measurements demonstrate the steady growth of hybrid film. There are two redox couples present in the voltammograms of hybrid film and it is obvious in the case of pH,2. Surface morphology of hybrid film was investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Energy dispersive spectrometer (EDS) data confirm existence of zinc oxide in the hybrid film. The effect of type of monovalent cations on the redox behavior of resulting film was investigated. In pure supporting electrolyte, electrochemical responses of modified electrode resemble with that of a surface immobilized redox couple. The electrocatalytic activity of ZnO/ZnHCF hybrid film was investigated towards guanine using cyclic voltammetry and rotating disc electrode (RDE) techniques. Finally, feasibility of using ZnO/ZnHCF hybrid film-coated electrodes for guanine estimation in flow injection analysis (FIA) was also investigated. [source] A Versatile System for Arbitrary Function Large-Amplitude Fourier Transformed VoltammetryELECTROANALYSIS, Issue 13 2007Lishi Wang Abstract A novel low-cost instrument for arbitrary function large-amplitude Fourier transformed voltammetry was developed. Description of both hardware and software was given in detail in this paper. A micro-control-unit (MCU) in combination with a field programmable gate array (FPGA) was designed to act as the controller of the instrument. Profiting from the built-in USB2.0 standard interface of the MCU, vast amount of data to/from the high resolution digital-to-analog converter (DAC)/analog-to-digital converter (ADC) then could be exchanged with computer in real-time, instead of being temporarily stored at the capacity limited memory of the instrument which always restricted the length of sampling time and the size of the collected data set. In the [Fe(CN)6]4+/3+ system, by superimposing a sinusoidal waveform with an amplitude of 120,mV onto a triangular potential and then applying to a macro electrode through the instrument, voltammograms up to the eighth harmonic could be well resolved by FT-IFT method. Excellent agreement was attained with Bond's similar experiment [Anal. Chem. 76 (2004) 3619] in respect of the shape and relative peak height of each harmonic. With the simply structured instrument, stable performance, flexible and versatile function was achieved. Arbitrary forms of AC perturbation which may not necessarily be sinusoidal or square-wave or other regular formed periodic signal could be synthesized and superimposed onto a DC potential as the excitation signal with this instrument. Some more useful electrode process information was expected to unveil by utilizing the FT-IFT algorithm to dissect the response signal. [source] Electrocatalytic Oxidation of Sulfur Containing Amino Acids at Renewable Ni-Powder Doped Carbon Ceramic Electrode: Application to Amperometric Detection L -Cystine, L -Cysteine and L -MethionineELECTROANALYSIS, Issue 21 2006Abdollah Salimi Abstract A sol-gel technique was used here to prepare a renewable carbon ceramic electrode modified with nickel powder. Cyclic voltammograms of the resulting modified electrode show stable and a well defined redox couple due to Ni(II)/Ni(III) system with surface confined characteristics. The modified electrode shows excellent catalytic activity toward L -cystine, L -cysteine and L -methionine oxidation at reduced overpotential in alkaline solutions. In addition the antifouling properties at the modified electrode toward the above analytes and their oxidation products increases the reproducibility of results. L -cystine, L -cysteine and L -methionine were determined chronoamperometricaly at the surface of this modified electrode at pH range 9,13. Under the optimized conditions the calibration curves are linear in the concentration range 1,450,,M, 2,90,,M and 0.2,75,,M for L -cystine, L -methionine and L -cysteine determination, respectively. The detection limit and sensitivity were 0.64,,M, 3.8,nA/ ,M for L -cystine, 2,,M, 5.6,nA/ ,M for L -methionine and 0.2,,M and 8.1,nA/,M for L -cysteine. The advantageous of this modified electrode is high response, good stability and reproducibility, excellent catalytic activity for oxidation inert molecules at reduced overpotential and possibility of regeneration of the electrode surface by potential cycling for 5,minutes. Furthermore, the modified electrode has been prepared without using specific reagents. This sensor can be used as an amperometric detector for disulfides detection in chromatographic or flow systems. [source] Electrochemical Approach to the Radical Anion Formation from 2,-Hydroxy Chalcone DerivativesELECTROANALYSIS, Issue 5 2006P. Quintana-Espinoza Abstract Three 2,-hydroxy chalcone derivatives were electrochemically reduced to the radical anion by a reversible one-electron transfer followed by a chemical dimerization reaction. Under suitable conditions of the medium, the one-electron reduction produces very well resolved cyclic voltammograms due to the formation of the radical anion. By using appropriately the wide versatility of the cyclic voltammetric technique, was possible to study the generation of the radical anion and its stability. [source] Electrochemical Reduction of 4,4,-(2,2,2-Trichloroethane-1,1-diyl)- bis(chlorobenzene) (DDT) and 4,4,-(2,2-Dichloroethane-1,1-diyl)- bis(chlorobenzene) (DDD) at Carbon Cathodes in DimethylformamideELECTROANALYSIS, Issue 4 2006Mohammad Abstract In dimethylformamide containing tetramethylammonium tetrafluoroborate, cyclic voltammograms for reduction of 4,4,-(2,2,2-trichloroethane-1,1-diyl)bis(chlorobenzene) (DDT) at a glassy carbon cathode exhibit five waves, whereas three waves are observed for the reduction of 4,4,-(2,2-dichloroethane-1,1-diyl)bis(chlorobenzene) (DDD). Bulk electrolyses of DDT and DDD afford 4,4,-(ethene-1,1-diyl)bis(chlorobenzene) (DDNU) as principal product (67,94%), together with 4,4,-(2-chloroethene-1,1-diyl)bis(chlorobenzene) (DDMU), 1-chloro-4-styrylbenzene, and traces of both 1,1-diphenylethane and 4,4,-(ethane-1,1-diyl)bis(chlorobenzene) (DDO). For electrolyses of DDT and DDD, the coulometric n values are essentially 4 and 2, respectively. When DDT is reduced in the presence of a large excess of D2O, the resulting DDNU and DDMU are almost fully deuterated, indicating that reductive cleavage of the carbon,chlorine bonds of DDT is a two-electron process that involves carbanion intermediates. A mechanistic scheme is proposed to account for the formation of the various products. [source] Voltammetric Assay of Naproxen in Pharmaceutical Formulations Using Boron-Doped Diamond ElectrodeELECTROANALYSIS, Issue 11 2005V. Suryanarayanan Abstract The electrooxidation of naproxen was studied, for the first time, using boron-doped diamond (BDD) electrode by cyclic and differential pulse voltammetry (CV and DPV) in nonaqueous solvent supporting electrolyte system. The results were also compared with glassy carbon electrode (GC) under the same conditions. Naproxen undergoes one electron transfer resulting in the formation of cation radical for the first electrooxidation step, which follows other chemical and electrochemical steps such as deprotonation, removal of another electron and the attack of nucleophile (ECEC mechanism). BDD electrode provided higher signal to background ratio, well resolved and highly reproducible cyclic voltammograms than the GC electrode. With a scan rate of 50,mV s,1 and pulse height of 50,ms, respectively, the DPV technique was able to determine the naproxen concentrations in the range of 0.5 to 50,,M with a detection limit of 30,nM. The influence of interference compounds namely 2-acetyl-6-methoxy naphthalene (AMN) on naproxen oxidation can also be followed successfully. Moreover, the percentage of AMN present in the standard chemical form of a mixture containing naproxen can be found accurately. Rapidity, precise and good selectivity were also found for the determination of naproxen in pharmaceutical formulations. [source] Electroconductive Hydrogels: Electrical and Electrochemical Properties of Polypyrrole-Poly(HEMA) CompositesELECTROANALYSIS, Issue 7 2005Sean Brahim Abstract Composites of inherently conductive polypyrrole (PPy) within highly hydrophilic poly(2-hydroxyethyl methacrylate)-based hydrogels (p(HEMA)) have been fabricated and their electrochemical properties investigated. The electrochemical characteristics observed by cyclic voltammetry suggest less facile reduction of PPy within the composite hydrogel compared to electropolymerized PPy, as shown by the shift in the reduction peak potential from ,472,mV for electropolymerized polypyrrole to ,636,mV for the electroconductive composite gel. The network impedance magnitude for the electroconductive hydrogel remains quite low, ca. 100,,, even upon approach to DC, over all frequencies and at all offset potentials suggesting retained electronic (bipolaronic) conductivity within the composite. In contrast, sustained application of +0.7 V (vs. Ag/AgCl, 3,M Cl,) for typically 100,min. (conditioning) to reduce the background amperometric current to <1.0,,A, resulted in complete loss of electroactivity. Nyquist plots suggest that sustained application of such a modest potential to the composite hydrogel results in impedance characteristics that resembles p(HEMA) without evidence of the conducting polymer component. PPy composite gels supported a larger ferrocene monocarboxylate diffusivity (Dappt=7.97×10,5,cm2,s,1) compared to electropolymerized PPy (Dappt=5.56×10,5,cm2,s,1), however a marked reduction in diffusivity (Dappt=1.01×10,5,cm2,s,1) was observed with the conditioned hydrogel composite. Cyclic voltammograms in buffer containing H2O2 showed an absence of redox peaks for electrodes coated with PPy-containing membranes, suggesting possible chemical oxidation of polypyrrole by the oxidant [source] Supramolecular Derivatives of 9,10-Anthraquinone.ELECTROANALYSIS, Issue 5-6 2003Complexing Properties, Electrochemistry at Regular-, Low Ionic Strength Abstract Three newly synthesized polyanthraquinone derivatives: 7,13-bis(9,10-dioxo-1-anthryl)-1,4,10-trioxa-7,13-diazacyclopentadecane, (AQ)A215C5, 7,16-bis(9,10-dioxo-1-anthryl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, (AQ)A218C6, and tris[(9,10-diokso-1-antryl)-aminoethyl]amine, (AQNet)3N, were examined by cyclic and normal pulse voltammetry. All anthraquinone groups in these compounds were electroactive and formed the radicals and dianions similarly to simple anthraquinone. The differences between the voltammograms obtained in the absence and presence of supporting electrolyte are discussed, and the diffusion coefficients of the compounds and the rates of the chemical reactions following the first reduction step were evaluated. (AQNet)3N appears to be a good model compound for multi electron transfers in aprotic solvents. It offers two consecutive nearly reversible 3-electron redox systems: 0/,3 and ,3/,6. The interactions of the radicals and dianions of the above compounds with alkali metal cations were examined. [source] Integration of a carbon microelectrode with a microfabricated palladium decoupler for use in microchip capillary electrophoresis/ electrochemistryELECTROPHORESIS, Issue 1 2005Michelle L. Kovarik Abstract A method to integrate a carbon microelectrode with a microfabricated palladium decoupler for use in microchip capillary electrophoresis (CE) is detailed. As opposed to previous studies with decouplers for microchip CE, the working electrode material, which is made by micromolding of a carbon ink, is different from the decoupling electrode material (palladium). The manner in which the working electrode is made does not add additional etching or lithographic steps to the fabrication of the glass electrode plate. The hybrid poly(dimethylsiloxane)/glass device was characterized with fluorescence microscopy and by monitoring the CE-based separation of dopamine. Hydrodynamic voltammograms exhibited diffusion-limited currents occurring at potentials above +1.0 V. It was also shown that the half-wave potential does not shift as the separation potential is changed, as is the case in nondecoupled systems. Gated injections of dopamine in a 25 mM boric acid buffer (pH 9.2) showed a linear response from 200 to 5 ,M (r2 = 0.9992), with a sensitivity of 5.47 pA/,M and an estimated limit of detection of 2.3 ,M (0.621 fmol, S/N = 3). This is the first report of coupling a carbon electrode with a decoupler in microchip CE. [source] | ||||||||||||||||||||||||||||