Home About us Contact
|
Home About us Contact | ||
|
|
||
Voltammetric Measurements (voltammetric + measurement)
Selected AbstractsAmperometric Sensor for Heparin: Sensing Mechanism and Application in Human Blood Plasma AnalysisELECTROANALYSIS, Issue 13-14 2006Jan Langmaier Abstract Voltammetric measurements of heparin at a rotating glassy carbon (GC) electrode coated with a polyvinylchloride membrane are reported. A spin-coating technique is used to prepare thin membranes (20,40,,m) with a composition of 25% (w/w) PVC, 1,1,-dimethylferrocene as a reference electron donor for the GC|membrane interface, nitrophenyl octyl ether (o -NPOE) or bis(2-ethylhexyl) sebacate (DOS) as a plasticizer, and hexadecyltrimethylammonium tetrakis(4-chlorophenyl) borate (HTMATPBCl) or tridodecylmethylammonium tetrakis(4-chlorophenyl) borate (TDMATPBCl) as a background electrolyte. It is shown that the electrodes coated with either the HTMA+/o -NPOE (DOS) or TDMA+/o -NPOE (DOS) membrane provide a comparable amperometric response towards heparin (1,10,U mL,1) in the aqueous solution of 0.1,M LiCl. However, only the membranes formulated with TDMATPBCl can be used for an amperometric assay of heparin in human blood plasma with a detection limit of 0.2,U mL,1. Effects of membrane composition, heparin concentration, rotation speed and sweep rate on the voltammetric behavior of heparin provide some insight into the sensing mechanism. Theoretical analysis of the amperometric response is outlined, and the numeric simulation of the voltammetric behavior is presented. [source] Characterization and Assessment of the Microjet Electrode as a Detector for HPLCELECTROANALYSIS, Issue 9 2004Susan Cannan Abstract The microjet electrode (MJE) is characterized as a detector for high performance liquid chromatography (HPLC). Voltammetric measurements of the oxidation of hydroquinone (HQ) allow mass transport to be determined for the MJE detector configuration, and the factors controlling the conversion efficiency of the device to be well understood. The current-time response to the flow injection analysis of volumes of solution in the 10,80,,L range has been established, and the limit of detection of this method has been determined. The latter was found to approach that of UV absorbance measurements, which is particularly encouraging, given that HQ has a relatively strong chromophore (,=2,290.8,cm,1 mol,1,L). This detection system is a robust and simple arrangement with the capability of analyzing large volumes of eluent at typical analytical HPLC flow rates. [source] Orientation Ordering of Nanoparticle Ag/Co Cores Controlled by Electric and Magnetic FieldsCHEMPHYSCHEM, Issue 7 2008Katarína Gmucová Dr. Abstract The effect of electric and magnetic fields on the sandwich structure Pt/hydrogenated amorphous silicon (a-Si:H)/stearic acid monolayer/Langmuir,Blodgett film of Ag/Co nanoparticles encapsulated in an organic envelope is studied. This structure is used as a working electrode in an electrochemical cell filled with NaCl solution (1 mM) and equipped with an Ag/AgCl reference electrode. Reversible changes in voltammograms are observed due to treatments (negative or positive bias voltage and simultaneous laser irradiation) applied to the designed structure before measurements. As an explanation of the observed phenomena we suggest that both the Co-up and Ag-up (on the a-Si:H surface) orientation orderings of nanoparticle Ag/Co cores are repeatedly reached. The role of the photovoltaic material (a-Si:H) in the observed behavior is explained. Voltammetric measurements with an applied magnetic field support our idea about the orientation ordering of nanoparticle cores. [source] Quantum-Dot-Functionalized Poly(styrene- co -acrylic acid) Microbeads: Step-Wise Self-Assembly, Characterization, and Applications for Sub-femtomolar Electrochemical Detection of DNA HybridizationADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Haifeng Dong Abstract A novel nanoparticle label capable of amplifying the electrochemical signal of DNA hybridization is fabricated by functionalizing poly(styrene- co -acrylic acid) microbeads with CdTe quantum dots. CdTe-tagged polybeads are prepared by a layer-by-layer self-assembly of the CdTe quantum dots (diameter,=,3.07,nm) and polyelectrolyte on the polybeads (diameter,=,323,nm). The self-assembly procedure is characterized using scanning and transmission electron microscopy, and X-ray photoelectron, infrared and photoluminescence spectroscopy. The mean quantum-dot coverage is (9.54,±,1.2),×,103 per polybead. The enormous coverage and the unique properties of the quantum dots make the polybeads an effective candidate as a functionalized amplification platform for labelling of DNA or protein. Herein, as an example, the CdTe-tagged polybeads are attached to DNA probes specific to breast cancer by streptavidin,biotin binding to construct a DNA biosensor. The detection of the DNA hybridization process is achieved by the square-wave voltammetry of Cd2+ after the dissolution of the CdTe tags with HNO3. The efficient carrier-bead amplification platform, coupled with the highly sensitive stripping voltammetric measurement, gives rise to a detection limit of 0.52 fmol L,1 and a dynamic range spanning 5 orders of magnitude. This proposed nanoparticle label is promising, exhibits an efficient amplification performance, and opens new opportunities for ultrasensitive detection of other biorecognition events. [source] Electrochemical Genotyping by Using Two Ferrocene/Isoquinoline-Connected DNA Probes with Different Redox Potentials on a Single ElectrodeCHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2009Reona Ikeda A single electrode: We describe an electrochemical single-nucleotide polymorphism genotyping protocol using a single electrode that is modified with a ferrocene/isoquinoline conjugate connected to DNA probes, which possess different redox potentials. Three types of zygotes (a wild-type homozygote, a mutant homozygote, and a heterozygote) were identified by a single square wave voltammetric measurement. [source] Automatic Voltammetric System for Continuous Trace Metal Monitoring in Various Environmental SamplesELECTROANALYSIS, Issue 19-20 2007Øyvind Mikkelsen Abstract Some recent developments and results in the field of automatic monitoring of electrolabile concentration of zinc and iron in the low ,g/L range in river water, drainage water, and waste water by use of solid dental amalgam electrode (DAM) as a working electrode are reviewed for three different geographical sites representing the mentioned matrixes. At all sites, voltammetric measurements were carried out continuously every 30 or 60,minutes for periods up to 4,months, and compared with total amounts of the metals found by ICP-MS on manually collected samples. In total, the observed concentration ranges analyzed was in the ranges of sub-,g/L to approximately 30,,g/L for zinc, and from approximately 1,,g/L to 150,,g/L. for iron. Results shows good calibration curves for the metals in the different matrixes (r2avg=0.99) with standard deviation within 5%. The voltammetric system showed good stability and gave reliable results which were in a reasonable agreement with ICP-MS measurements for all analyses when comparing the concentration trends. The frequency of maintenance varied from once a week in waste water samples to once a month in river water. [source] Sensitive Adsorptive Stripping Voltammetric Methodologies for the Determination of Melatonin in Biological FluidsELECTROANALYSIS, Issue 9 2003L. Corujo-Antuña Abstract The reversible redox process that melatonin presented on carbon paste electrodes was the basis of a sensitive methodology for the determination of this hormone. From all the processes presented by this hormone, this was never used before as the basis of voltammetric measurements for melatonin determination. Therefore, parameters that affected the cyclic voltammetric signal were studied. A limit of detection as low as 9×10,11,M was obtained when optimized alternating current voltammetry was employed. The reproducibility was excellent due to an adequate pretreatment of the solid electrode (RSD=2.7%, n=10). A comparison with methodologies that employ different electrochemical techniques from the point of view of their analytical characteristics was made. This methodology has proved to be suitable for the determination of melatonin in biological fluids. [source] Voltametric and Flow Injection Determination of Oxytetracycline Residues in Food Samples Using Carbon Fiber MicroelectrodesELECTROANALYSIS, Issue 7 2003L. Agüí Abstract A voltammetric method for the determination of the antibiotic oxytetracycline (OTC) in food samples is reported. Carbon fiber microelectrodes (CFMEs), which allow voltammetric measurements to be performed in a small volume (1,mL) of the analyte extract from the samples, are employed. Repeatable electroanalytical responses were obtained with no need of applying cleaning treatments to the CFME. Under the optimized square-wave conditions, a linear calibration plot for OTC was obtained in the 1.0×10,6,1.0×10,4,mol,L,1 range, with a detection limit of 2.9×10,7,mol,L,1 (150,ng,mL,1) OTC. The determination of OTC by a flow-injection method with amperometric detection using a homemade flow cell specially designed to work with CFMEs, was also evaluated using pure acetonitrile as the carrier. The SW voltammetric method was applied to the determination of OTC in spiked milk and eggs samples, at 100,ng,mL,1 and 200,ng g,1 levels, respectively. The procedure involved the extraction of the analyte in ethyl acetate, evaporation of the solvent and reconstitution of the residue in acetonitrile ,5.0×10,4,mol,L,1 tetrabutylammonium perchlorate medium. Recoveries of 96±8 and 91±8% were obtained for milk and eggs, respectively, by applying the standard additions method. [source] Ultrasonically Enhanced Voltammetric Analysis and Applications: An OverviewELECTROANALYSIS, Issue 5-6 2003Craig Abstract Ultrasonically enhanced voltammetric measurements have been successfully applied for the detection of a wide range of trace metals. These are reviewed and the beneficial effects of power ultrasound applied to electroanalysis highlighted, most notably the possibility for quantitative analysis in otherwise highly passivating media, where classical electrochemical techniques often fail. [source] Electron Transfer Kinetics of Ferrocene at Microcrystalline Boron-Doped Diamond Electrodes: Effect of Solvent and ElectrolyteELECTROANALYSIS, Issue 4 2003Shannon Haymond Abstract Cyclic voltammetric measurements were made using well-characterized microcrystalline boron-doped diamond thin-film electrodes to test the material's responsiveness for ferrocene as a function of scan rate, solvent, and electrolyte composition. Apparent heterogeneous electron transfer rate constants, k°app, of 0.042±0.015, 0.048±0.015, and 0.008±0.002,cm/s were observed in 0.1,M NaClO4/CH3CN, 0.1,M TBAClO4/CH3CN, and 0.1M TBAClO4/CH2Cl2, respectively. These rate constants, obtained using electrodes without any type of pretreatment, are similar to those observed for freshly polished glassy carbon. The results demonstrate that boron-doped diamond is a viable material for the electrochemical analysis of nonaqueous analytes. [source] Voltammetric Study of Nitro Radical Anion Generated from Some Nitrofuran Compounds of Pharmacological SignificanceELECTROANALYSIS, Issue 1 2003S. Bollo Abstract The electrochemical behavior of 2-(5-amino- 1,3,4-oxadiazolyl)-5-nitrofuran (NF359) and its comparison with well-known drugs such as nifurtimox (NFX) and nitrofurazone (NFZ) in protic, mixed and aprotic media by cyclic voltammetry, tast and differential pulse polarography was studied. All the compounds were electrochemically reducible in all media being the reduction of the nitrofuran group the main voltammetric signal. The one-electron reduction couple due to the nitro radical anion formation was visualized in mixed (for NF359 and NFZ) and aprotic media (for all compounds). By applying a cyclic voltammetric methodology we have calculated the decay constants (k2) of the corresponding nitro radical anions in mixed and aprotic media. In mixed medium data fit well with a disproportionation reaction of the nitro radical anion but in aprotic medium fit better with a dimerization reaction. Also, considering cyclic voltammetric measurements in aprotic media we have estimated the reduction potential of the RNO2/RNO2., couple in aqueous medium, pH 7 (E17 values) finding very good correlation with E17 values obtained by pulse radiolysis. Furthermore we have calculated the equilibrium constants from the electron transfer from nitro radical anion to oxygen (kO2) finding that nitro radical anion from NF359 is thermodynamically favored to react with oxygen in respect to both NFZ and NFX. [source] Oxidative polymerization of N -vinylcarbazole in polymer matrixPOLYMER INTERNATIONAL, Issue 6 2001Belkis Ustamehmeto Abstract A new class of soluble conductive poly(N -vinylcarbazole) (PVCz) compounds has been developed by oxidative matrix polymerization of N -vinylcarbazole (NVCz) by Ce(IV) in the presence of poly(ethylene glycol) (PEG). PEG was found to be a more suitable matrix with which to obtain a stable homogenous ternary complex solution when compared with poly(acrylic acid) (PAA) and poly(vinylpyrrolidone) (PVP). The role of PEG, NVCz and Ce(IV) concentration, order of component addition, the structure of the polymer matrix, molecular weight of polymer and the effect of solvent have been investigated. Obtaining soluble PEG,Ce(III),PVCz ternary complexes was shown by cyclic voltammetric measurements, and the initial rate of formation NVCz cation radicals as calculated using UV,visible spectrophotometry. Advantageously with these soluble complexes, conductivities could be measured both in solution and in the solid state. © 2001 Society of Chemical Industry [source] | |||||||||||||