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Disk Electrode (disk + electrode)
Selected AbstractsAmperometry of Heparin Polyion Using a Rotating Disk Electrode Coated with a Plasticized PVC MembraneELECTROANALYSIS, Issue 2 2006Jan Langmaier Abstract Electrochemical method of detection of heparin polyion was developed based on voltammetry of heparin on a rotating glassy carbon (GC) electrode coated with a plasticized PVC membrane. The membrane was deposited on the GC disk by spin-coating technique using a mixture of solutions of PVC in tetrahydrofuran, and 1,1,-dimethylferrocene (DMFc) and hexadecyltrimethylammonium tetrakis(4-chlorophenyl)borate (HTMATPBCl) in o -nitrophenyl octyl ether. UV/vis reflection spectrometry was used to evaluate the membrane thickness, which exhibits a linear correlation with the membrane resistance measured by impedance spectroscopy. It is shown that this electrode can be used for amperometric or coulometric detection of heparin in aqueous samples of medically relevant concentrations (1,10,U mL,1), with a detection limit of 1.4,U mL,1. Evidence is provided indicating that the current determining step is the reversible adsorption of the ion-pair of heparin polyion with HTMA+ cation at the membrane/aqueous electrolyte interface, which is driven by oxidation of DMFc at the GC/membrane interface. [source] Electrochemical Reduction of S(IV) Compounds in Water-Ethanol Solutions at Nafion/Tetraruthenated Porphyrins Glassy Carbon Modified ElectrodesELECTROANALYSIS, Issue 3 2010Karla Calfumán Abstract This work describes electrocatalytic detection of S(IV) compounds in water-ethanol solutions under acidic conditions, on a glassy carbon electrode modified with Co(II) tetraruthenated porphyrin electrostatically assembled onto a Nafion film. The Ipc current shows a linear relationship with the concentration of S(IV) oxo-anions. Controlled potential electrolysis shows that thiosulfate was detected as reaction product. Rotating disk electrode and UV-visible spectroelectrochemistry experiments showed a kinetic limitation to the electron transfer controlled by charge propagation in the film and the formation of an intermediary between Co center and S(IV) species. The reproducibility of the modification methodology presents a RSD of 4.1%. [source] Fabrication of Active Horseradish Peroxidase Micropatterns with a High Resolution by Scanning Electrochemical MicroscopyELECTROANALYSIS, Issue 16 2007Xuemei Li Abstract We used a new reactive species OH, to fabricate active horseradish peroxidase (HRP) micropatterns with a high resolution by scanning electrochemical microscopy (SECM) coupled with a carbon fiber disk electrode as the SECM tip. In this method, except for active HRP micropatterns predesigned other regions on a HRP-immobilized substrate were deactivated by OH, generated at the tip held at ,1.7,V in 1.0,mol/L KCl containing 2.0×10,3 mol/L benzoquinone (BQ) (pH,8.0). The feedback mode of SECM with a tip potential of ,0.2,V was used to characterize the active HRP micropatterns in 1.0,mol/L KCl containing 2.0×10,3 mol/L BQ and 2.0×10,3 mol/L H2O2. [source] Pulsed Amperometric Detection of Histamine at Glassy Carbon Electrodes Modified with Gold NanoparticlesELECTROANALYSIS, Issue 4 2005V. Carralero Abstract Gold nanocrystal-modified glassy carbon electrodes (nAu-GCE) were prepared and used for the determination of histamine by flow injection and high performance liquid chromatography using pulsed amperometric detection (PAD) as the detection mode. Experimental variables involved in the electrodeposition process of gold from a HAuCl4 solution were optimized. A catalytic enhancement of the histamine voltammetric response was observed at the nAu-GCE when compared with that obtained at a conventional Au disk electrode, as a consequence of the microdispersion of gold nanocrystals on the GC substrate. The morphological and electrochemical characteristics of the nAu-GCE were evaluated by SEM and cyclic voltammetry. PAD using a very simple potential waveform consisting of an anodic potential (+700,mV for 500,ms) and a cathodic potential (,300,mV for 30,ms), was used to avoid the electrode surface fouling when histamine was detected under flowing conditions. Flow injection amperometric responses showed much higher Ip values and signal-to-noise ratios at the nAu-GCE than at a conventional gold disk electrode. A limit of detection of 6×10,7,mol L,1 histamine was obtained. HPLC-PAD at the nAu-GCE was used for the determination of histamine in the presence of other biogenic amines and indole. Histamine was determined in sardine samples spiked at a 50,,g g,1 concentration level, with good results. Furthermore, the chromatographic PAD method was also used for monitoring the formation of histamine during the decomposition process of sardine samples. [source] A Lactulose Bienzyme Biosensor Based on Self-Assembled Monolayer Modified ElectrodesELECTROANALYSIS, Issue 17 2004Susana Campuzano Abstract A bienzyme biosensor in which the enzymes ,-galactosidase (,-Gal), fructose dehydrogenase (FDH), and the mediator tetrathiafulvalene (TTF) were coimmobilized by cross-linking with glutaraldehyde atop a 3-mercaptopropionic acid (MPA) self-assembled monolayer on a gold disk electrode, is reported. The working conditions selected were Eapp=+0.10,V and (25±1),°C. The useful lifetime of one single TTF-,-Gal-FDH-MPA-AuE was surprisingly long, 81,days. A linear calibration plot was obtained for lactulose over the 3.0×10,5,1.0×10,3,mol L,1 concentration range, with a limit of detection of 9.6×10,6,mol L,1. The effect of potential interferents (lactose, glucose, galactose, sucrose, and ascorbic acid) on the biosensor response was evaluated. The behavior of the SAM-based biosensor in flow-injection systems in connection with amperometric detection was tested. The analytical usefulness of the biosensor was evaluated by determining lactulose in a pharmaceutical preparation containing a high lactulose concentration, and in different types of milk. Finally, the analytical characteristics of the TTF-,-Gal-FDH-MPA-AuE are critically compared with those reported for other recent enzymatic determinations of lactulose. [source] Using the Aggregation of Latex Polymers in the Fabrication of Reproducible Enzyme ElectrodesELECTROANALYSIS, Issue 17 2003Wibowo Rahmat Abstract An enzyme electrode for glucose is described as a model system to demonstrate a fabrication method using latex aggregation and entrapment of enzyme. Electrosterically-stabilized latex particles synthesized by emulsion polymerization in batch from acrylic acid, methyl methacrylate and butyl acrylate, and glucose oxidase were coagulated together at pH,5.5 with ethanol. A platinum disk electrode dipped in the solution becomes coated with latex/enzyme. The relative thickness of the film and relative amount of enzyme may be controlled by the time the electrode is in contact with the solution. The enzyme was then immobilized by covalent attachment of amine groups to carboxylic moieties in the polymer using 1-ethyl-3(3-dimethylaminopropyl)-carbodiimide hydrochloride and N -hydroxysuccinimide. Five minutes contact with the latex/enzyme solution and subsequent amide coupling, gave electrodes with a reproducibility of 5.7% RSD, a wide dynamic range (0,100,mM) and good storage properties. [source] Simulation of nerve bundle activation by simultaneous multipoint extracellular stimulation with surface electrodesELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 6 2009Hirokazu Takahashi Abstract Neural prostheses for restoring lost functions can benefit from selective activation of nerves. We previously proposed a multipoint gating stimulation, which can selectively activate a desired portion of a nerve bundle, regardless of the density of the electrode. In this paper, we discuss the design of an electrode array and effective strategies to determine the stimulus parameters. Large electrodes were less affected by the relative location of the electrodes and the nodes of Ranvier, suggesting that a rectangular electrode, whose long side along a nerve bundle is longer than the internodal distance (i.e., on the order of 1 mm), would be more effective than a disk electrode. We were able to estimate an appropriate current at each electrode on the basis of a blocking threshold, above which no spike propagation was permitted. For lateral gating stimulation, the gate current should be set above the threshold, while for depthwise gating stimulation, the gate current should be set below the threshold. The spatial resolutions of lateral and depthwise gating stimulation were theoretically estimated to be at least 50 ,m when the grid spacing of the array was 1.2 mm. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(6): 31,40, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10064 [source] Determination of Bioactive Components in Polygonum perfoliatum L. by Capillary Electrophoresis with Electrochemical DetectionCHINESE JOURNAL OF CHEMISTRY, Issue 4 2009Shuping JIN Abstract The major bioactive components in a Chinese herb named Polygonum perfoliatum L. including ferulic acid, vanillic acid, quercetin, caffeic acid and protocatechuic acid were simultaneously determined by capillary electrophoresis with electrochemical detection (CE-ED) in this paper. The effects of working electrode potential, pH and concentration of running buffer, separation voltage, and injection time on CE-ED were investigated. Under the optimum conditions, the five analytes could be separated within 17 min at a separation voltage of 18 kV in 10 mmol· L,1 phosphate buffer (pH 9.2). A 300 µm diameter carbon disk electrode generated good responses at +0.95 V (vs. SCE) to the five analytes. The response was linear over three orders of magnitude with detection limits (S/N=3) ranging from 7.1×10,8 to 9.3×10,8 g·mL,1 for the analytes. This proposed method could be successfully applied to the analysis of the real samples with relatively simple extraction procedures and satisfactory results. [source] Analysis of Trace Ingredients in Green Tea by Capillary Electrophoresis with Amperometric DetectionCHINESE JOURNAL OF CHEMISTRY, Issue 3 2008Ping LI Abstract In this paper, four trace ingredients (rutin, gallic acid, quercetin, chlorogenic acid) in green tea were simultaneously determined by capillary electrophoresis coupled with amperometric detection (CE-AD). Effects of several important factors such as the pH and concentration of running buffer, separation voltage, injection time and detection potential were investigated to acquire the optimum conditions. Under the optimum conditions, the analytes could be separated within 20 min at a separation voltage of 18 kV in a 60 mmol/L borate buffer (pH 8.7). A 300 µm diameter carbon disk electrode generated good responses at 950 mV (vs. SCE) for all analytes. The relationship between the peak currents and concentrations of the analytes was linear over about three orders of magnitude with detection limits (S/N=3) ranging from 1.0×10,7 to 1.0×10,4 g·mL,1 for all the analytes. This proposed method demonstrated long-term stability and reproducibility with relative standard deviations less than 3% for both migration time and peak current (n=7), which could be successfully used for the determination of the analytes in green tea with satisfactory assay results. [source] Disposable Gold Electrodes with Reproducible Area Using Recordable CDs and Toner MasksELECTROANALYSIS, Issue 1 2006Denise Lowinsohn Abstract The fabrication and characterization of very cheap disposable gold disk electrodes with reproducible area is reported. The innovation of the proposed procedure is the use of toner masks to define reproducible areas on uniform gold surfaces obtained from recordable compact disks (CD-R). Toner masks are drawn in a laser printer and heat transferred to gold surfaces, defining exactly the electrodes area. The electrochemical behavior of these disposable electrodes was investigated by cyclic voltammetry in Fe(CN)64, solutions. The relative standard deviation for signals obtained from 10 different gold electrodes was below 1 %. The size of the disk electrodes can be easily controlled, as attested by voltammetric responses recorded by using electrodes with radii varying from 0.5 to 3.0,mm. The advantages of using this kind of electrode for analytical measurements of substances that strongly adsorb on the electrode surface such as cysteine are also addressed. [source] Electrochemical Impedance Characterization of Nafion-Coated Carbon Film Resistor Electrodes for ElectroanalysisELECTROANALYSIS, Issue 7 2005Carla Gouveia-Caridade Abstract Carbon film disk electrodes with Nafion coatings have been characterized by electrochemical impedance spectroscopy (EIS) with a view to a better understanding of their advantages and limitations in electroanalysis, particularly in anodic stripping voltammetry of metal ions. After initial examination by cyclic voltammetry, spectra were recorded over the full potential range in acetate buffer solution at the bare electrodes, electrodes electrochemically pretreated in acid solution, and Nafion-coated pretreated electrodes in the presence and absence of dissolved oxygen. EIS equivalent circuit analysis clearly demonstrated the changes between these electrode assemblies. In order to simulate anodic stripping voltammetry conditions, spectra were also obtained in the presence of cadmium and lead ions in solution at Nafion-coated electrodes, both after metal ion deposition and following re-oxidation. Permanent changes to the structure of the Nafion film occurred, which has implications for use of these electrode assemblies in anodic stripping voltammetry at relatively high trace metal ion concentrations. [source] Ni(II)cyclam Catalyzed Reduction of CO2 , Towards a Voltammetric Sensor for the Gas PhaseELECTROANALYSIS, Issue 18 2003P. Jacquinot Abstract The detection of CO2 in the gas phase is possible in presence of oxygen with an amalgamated Au-poly(tetrafluoroethylene) gas diffusion electrode and an internal electrolyte solution containing Ni(II)cyclam. For concentrations between 0.1 to 1% the electrochemical cell has a sensitivity of 3.58 mA %,1 and the detection limit is 500,ppm. In preliminary experiments at rotating disk electrodes the optimum pH-range was found to be between 3.5 to 6 and a selectivity ratio of the catalyst for CO2/H+ of 5,:,1 could be determined. The relationship between reduction current and the square root of the angular speed is linear, indicating that the electrochemical process is limited by diffusion of CO2. Tl and Pb are presented as alternative electrode materials at which the Ni(II)cyclam catalyzed reduction of CO2 can be observed. Problems arise from fouling effects at the sensing electrode and a non-linearity of the calibration plot at higher concentrations. [source] | ||||||||||