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Vs. Ag/AgCl (vs + ag)
Selected AbstractsSeparation and Detection of Nitrophenols at Capillary Electrophoresis Microchips with Amperometric DetectionELECTROANALYSIS, Issue 2 2006Jan Fischer Abstract A miniaturized analytical system for the separation and amperometric detection of toxic nitrophenols, based on the coupling of a micromachined capillary electrophoresis (CE) chip with a glassy carbon detector is described. This microsystem enables a rapid (120,s/sample) simultaneous determination of five priority nitrophenolic pollutants (2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, and 2-methyl-4,6-dinitrophenol). These compounds can be detected down to the 1×10,5,M level using a 15,mM phosphate buffer pH,7.2 (containing 1.3,mM ,-cyclodextrin) as running solution on 77,mm long microchannel by applying a separation voltage of 3000,V and a negative potential of ,0.7,V (vs. Ag /AgCl wire). Applicability to ground water samples was demonstrated. [source] Flow injection analysis of tetracyclines using inhibited Ru(bpy)32+/tripropylamine electrochemiluminescence systemLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 1 2005Yong-Qiang Pang Abstract Tetracyclines (TCs) were found to strongly inhibit the electrochemiluminescence (ECL) from the Ru(bpy)32+,tripropylamine system when a working Pt electrode was maintained at 1.05 V (vs. Ag[sol ]AgCl) in pH 8.0 carbonate buffer solution. On this basis, a flow injection (FI) procedure with inhibited electrochemiluminescence detection has been developed for the determination of tetracycline (TC) and oxytetracycline (OTC). Under the optimized condition, the linear ranges of 2.0 × 10,8,1.0 × 10,5 and 1.0 × 10,8,1.0 × 10,5 g[sol ]mL and the detection limits of 4.0 × 10,9 and 3.8 × 10,9 g[sol ]mL were obtained for TC and OTC, respectively. The relative standard deviations (RSD) were 0.68% and 1.18% for 5.0 × 10,7 g[sol ]mL TC and OTC (n = 13), respectively. The method showed higher sensitivity than most of the reported methods. It was successfully applied to the determination of tetracycline in a Chinese proprietary medicine, Tetracyclini and Cortisone Eye Ointment, and the residues of tetracycline in honey products. The inhibition mechanism has been proposed due to an energy transfer between electrogenerated Ru(bpy)32+* and benzoquinone derivatives at the electrode surface. Copyright © 2005 John Wiley & Sons, Ltd. [source] The Influence of the Cathodic Pretreatment on the Electrochemical Detection of Dopamine by Poly(1-aminoanthracene) Modified ElectrodeELECTROANALYSIS, Issue 19 2010Estela de Pieri Troiani Abstract In this study we demonstrated the influence of the cathodic pretreatment of poly(1-aminoanthracene) (PAA) electropolymerized on a platinum electrode for determination of dopamine (DA). The DA electrochemical response was obtained after a cathodic pretreatment of the PAA electrode which consisted of applying a potential of ,0.7,V (vs. Ag/AgCl) for 3,s before each measurement. The pretreatment of the electrode changed the PAA electrocatalytic properties so that the electrode began to present electrochemical response to DA without interference of ascorbic acid (AA). The anodic peak currents determined by differential pulse voltammetry using pretreated PAA showed a linear dependence on the DA concentration from 0.56 to 100,µM with a detection limit of 0.13,µM and a correlation coefficient of 0.9986. The electrode exhibits a relative standard deviation of 1.2,% for ten successive measurements of a 0.5,mM DA solution. The analysis by scanning electron microscopy and atomic force microscopy show a homogeneous and nanostructured film with globular structures with diameter of about 20,nm. The analytical results obtained for DA determination at a pretreated PAA electrode in pharmaceutical formulation sample were in good agreement with those obtained by a comparative procedure at a 95,% confidence level. PAA electrode after the pretreatment showed electrochemical responses to DA with excellent selectivity, sensitivity, and high stability without interference of AA. [source] Direct Electrochemistry and Electrocatalysis of Myoglobin Immobilized on Gold Nanoparticles/Carbon Nanotubes Nanohybrid FilmELECTROANALYSIS, Issue 17 2008Wei Cao Abstract A novel nanohybrid material, constructed by gold nanoparticles (GNPs) and multiwalled carbon nanotubes (MWNTs), was designed for immobilization and biosensing of myoglobin (Mb). Morphology of the nanohybrid film was characterized by SEM. UV-vis spectroscopy demonstrated that Mb on the composite film could retain its native structure. Direct electrochemistry of Mb immobilized on the GNPs/MWNTs film was investigated. The immobilized Mb showed a couple of quasireversible and well-defined cyclic voltammetry peaks with a formal potential of about ,0.35,V (vs. Ag/AgCl) in pH,6.0 phosphate buffer solution (PBS) solution. Furthermore, the modified electrode also displayed good sensitivity, wide linear range and long-term stability to the detection of hydrogen peroxide. The experiment results demonstrated that the hybrid matrix provided a biocompatible microenvironment for protein and supplied a necessary pathway for its direct electron transfer. [source] Integrating an Enzyme-Entrapped Conducting Polymer Electrode and a Prereactor in a Microfluidic System for Sensing GlucoseELECTROANALYSIS, Issue 6 2008Po-Chin Nien Abstract In this study, the flow injection analysis was applied to the enzyme-entrapped electrode on a chip for sensing glucose. The on-chip microelectrode was fabricated by the standard photolithography in clean-room environment and the microfluidic channel height of 100,,m on the chip was formed by poly(dimethylsiloxane). The conducting polymer, poly(3,4-ethylenedioxythiophene), PEDOT, was electropolymerized to entrap the coexisting glucose oxidase (GOD) by cyclic voltammetry (CV). The amount of enzyme entrapped in the matrix measured spectroscopically was about 0.101,U/cm2. At a flow rate of 10,ml/hr, the working electrode (Pt/PEDOT/GOD, WE1) was set at 0.7,V (vs. Ag/AgCl) and sensing of H2O2 was carried out by injecting samples with various concentrations of glucose (Glu). A linear relationship between the sensing current and the glucose concentration, ranging from 1 to 20,mM, was obtained with a sensitivity of 8,nA mm,2 mM,1. The response time and the recovery time were about 30 and 230,s, respectively. For a single-potential test, the oxidation currents of 0.08,mM ascorbic acid (AA) and a blend of 0.08,mM AA and 10,mM Glu reached 31.3% and 145.5%, respectively, when compared with the oxidation current of 10,mM Glu alone. However, when a pre-reactor (WE2) was set at the same potential (0.7,V) before the main enzyme integrated electrode (WE1), the oxidation current for the above mixed solution reached 99.6% of the original one. [source] Reagentless Glucose Biosensor Based on the Direct Electrochemistry of Glucose Oxidase on Carbon Nanotube-Modified ElectrodesELECTROANALYSIS, Issue 11 2006Xiliang Luo Abstract The direct electrochemistry of glucose oxidase (GOD) was revealed at a carbon nanotube (CNT)-modified glassy carbon electrode, where the enzyme was immobilized with a chitosan film containing gold nanoparticles. The immobilized GOD displays a pair of redox peaks in pH,7.4 phosphate buffer solutions (PBS) with the formal potential of about ,455,mV (vs. Ag/AgCl) and shows a surface-controlled electrode process. Bioactivity remains good, along with effective catalysis of the reduction of oxygen. In the presence of dissolved oxygen, the reduction peak current decreased gradually with the addition of glucose, which could be used for reagentless detection of glucose with a linear range from 0.04 to 1.0,mM. The proposed glucose biosensor exhibited high sensitivity, good stability and reproducibility, and was also insensitive to common interferences such as ascorbic and uric acid. The excellent performance of the reagentless biosensor is attributed to the effective enhancement of electron transfer between enzyme and electrode surface by CNTs, and the biocompatible environment that the chitosan film containing gold nanoparticles provides for immobilized GOD. [source] A LiMn2O4 Based Electrochemical Scheme for Selective Measurement of DopamineELECTROANALYSIS, Issue 3 2006Hoang, Jyh Leu Abstract A new cathodic scheme was developed for the determination of dopamine by flow injection analysis (FIA). A mild oxidizing agent, lithium manganese (III, IV) oxide (LiMn2O4), as an upstream modifier can oxidize the dopamine to produce the dopaminequinone, and then the oxidized product is subsequently detected by the downstream detector at ,0.1,V (vs. Ag/AgCl). In this work, the significant feature of LiMn2O4 based sensing scheme possesses no interference from other tested biological amines including acetylcholine, epinephrine, glutamate, and histamine. Otherwise, there is no detectable interference from ascorbic acid, but 2% and 1% negligible interferences were found from uric acid and acetaminophen, respectively. [source] Immobilization and Electrochemistry of Negatively Charged Proteins on Modified Nanocrystalline Metal Oxide ElectrodesELECTROANALYSIS, Issue 12 2005Emmanuel Topoglidis Abstract The immobilization of two acidic, low isoelectric point proteins, green fluorescence protein and ferredoxin (FRD) is investigated on nanocrystalline, mesoporous TiO2 and SnO2 electrodes. Modification of these electrodes with a cationic polypeptide (poly- L -lysine) or an aminosilane prior to protein immobilization is found to enhance protein binding at least ten fold, attributed to more favorable protein/electrode electrostatic interactions. Cyclic voltammetry studies of FRD-modified SnO2 electrodes indicate reversible protein electrochemistry with a midpoint potential of ,0.59,V (vs. Ag/AgCl) and an interfacial electron transfer rate constant of 0.45,s,1. [source] Simultaneous Determination of Hydroquinone and Catechol at a Glassy Carbon Electrode Modified with Multiwall Carbon NanotubesELECTROANALYSIS, Issue 10 2005Honglan Qi Abstract A simply and high selectively electrochemical method for simultaneous determination of hydroquinone and catechol has been developed at a glassy carbon electrode modified with multiwall carbon nanotubes (MWNT). It was found that the oxidation peak separation of hydroquinone and catechol and the oxidation currents of hydroquinone and catechol greatly increase at MWNT modified electrode in 0.20,M acetate buffer solution (pH,4.5). The oxidation peaks of hydroquinone and catechol merge into a large peak of 302,mV (vs. Ag/AgCl, 3,M NaCl) at bare glassy carbon electrode. The two corresponding well-defined oxidation peaks of hydroquinone in the presence of catechol at MWNT modified electrode occur at 264,mV and 162,mV, respectively. Under the optimized condition, the oxidation peak current of hydroquinone is linear over a range from 1.0×10,6,M to 1.0×10,4,M hydroquinone in the presence of 1.0×10,4,M catechol with the detection limit of 7.5×10,7,M and the oxidation peak current of catechol is linear over a range from 6.0×10,7,M to 1.0×10,4,M catechol in the presence of 1.0×10,4,M hydroquinone with the detection limit of 2.0×10,7 M. The proposed method has been applied to simultaneous determination of hydroquinone and catechol in a water sample with simplicity and high selectivity. [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] Fast Mapping of Gunshot Residues by Batch Injection Analysis with Anodic Stripping Voltammetry of Lead at the Hanging Mercury Drop ElectrodeELECTROANALYSIS, Issue 2 2005Adriana De, Donato Abstract The forensic analysis of lead in gunshot residues (GSR) sampled on the hands of potential shooters is rendered faster, simpler and less expensive by a new batch injection analysis (BIA) method, based on differential pulse anodic stripping voltammetry (DPASV). A simple "J" shaped adaptor was designed to direct the flux of the analyte injected with a micropipettor onto the hanging mercury drop electrode of any commercial electrode stand. Sampling methods for GSR were compared and lifting with adhesive tape was elected for field use. The tapes are glued on polyethylene screens and stored in capped vials. Sampling with multiple strips provides coarse mapping of the distribution of lead on the shooter's hands. After a dissolution/extraction step with chloroform/aqueous 0.10,mol,L,1 HCl, 100,,L of the aqueous phase are injected during 25,s for accumulation of lead on the HMDE at ,0.60,V (vs. Ag/AgCl). A detection limit of 20,ng/mL of Pb(II), outreaching for GSR analysis, is reached without oxygen removal, at a frequency of 20 injections per hour. Results for sequences of shootings with a revolver and a pistol are presented. [source] Amperometric Detection of Catecholamine Neurotransmitters Using Electrocatalytic Substrate Recycling at a Laccase ElectrodeELECTROANALYSIS, Issue 2 2005Yvonne Ferry Abstract An enzyme electrode based on the coimmobilization of an osmium redox polymer and laccase on glassy carbon electrodes has been applied to ultra sensitive amperometric detection of the catecholamine neurotransmitters dopamine, epinephrine and norepinephrine, resulting in nanomolar detection limits, as low as 4,nM for dopamine. The sensitivity of the electrode is due to signal amplification via oxidation of the catecholamine by the immobilized laccase, which is regenerated by concomitant reduction of oxygen to water, coupled to the electrocatalytic re-reduction of the oxidized catecholamine by the osmium redox complex: electrocatalytic substrate recycling. In addition because the sensor can be operated in reductive mode at ,0.2,V (vs. Ag/AgCl), noise and interferences are diminished. Combined with its high sensitivity this enzyme electrode also exhibited excellent selectivity allowing the detection of catecholamines in the presence of ascorbic acid. However, differentiation between the current responses achieved for the three catecholamines is not possible. The effective mode of constant recycling, resulting in amplification of the current response, of the laccase enzyme electrode sensor combined with the inherent advantages of using electrochemical techniques holds great promise for the future of catecholamine detection and monitoring. [source] A Tubulin-Based Quantitative Assay for Taxol (Paclitaxel) with Enzyme Channeling SensingELECTROANALYSIS, Issue 8 2004Shin-ichiro Suye Abstract We report the development and characterization of a biosensor for sensitive and rapid determination of the anticancer agent Taxol (paclitaxel). The sensor is based on the interaction of Taxol with its receptor protein tubulin in conjunction with the separation-free immunosensor technique of enzyme channeling. The sensor system consisted of a three electrode electrochemical cell containing a graphite carbon electrode modified with glucose oxidase and tubulin as working electrode poised at +40,mV (vs. Ag/AgCl). Addition of Taxol, horseradish peroxidase labeled Taxol, glucose and potassium iodide to the cell generated a cathodic current response that was proportional to the concentration of Taxol in the range of 10 to 1,000,pM. [source] Development of a new method for analysis of Sudan dyes by pressurized CEC with amperometric detectionELECTROPHORESIS, Issue 11 2007Shaofeng Liu Abstract A new analytical method, pressurized CEC (pCEC) with amperometric detection (AD) using 1.5,,m RP nonporous silica packed columns has been developed for the rapid separation and determination of four Sudan dyes in hot chilli. The influence of several experimental parameters on the retention behavior has been investigated. The electrochemical oxidation of Sudans I,IV separated by pCEC can be reliably monitored with a carbon electrode at +0.95,V (vs. Ag/AgCl). Fast and efficient separation of the analytes was achieved within 7,min by pCEC under the optimum conditions with an ACN/water (95:5%) mobile phase containing formic acid (pH,4.3), 5% acetone and 0.002% triethylamine using a separation voltage of 12,kV. The detection limits for four Sudan dyes ranged from 8.0,×,10,7 to 1.2,×,10,6,mol/L. To evaluate the feasibility and reliability of this method, the proposed pCEC-AD method was further demonstrated with hot chilli samples spiked with Sudan dyes. [source] Microchip capillary electrophoresis with a cellulose-DNA-modified screen-printed electrode for the analysis of neurotransmittersELECTROPHORESIS, Issue 15 2005Muhammad Johirul Abstract A microfluidic chip based on capillary electrophoresis coupled with a cellulose-single-stranded DNA (cellulose-ssDNA) modified electrode was used for the simultaneous analysis of dopamine (DA), norepinephrine (NE), 3,4-dihydroxy- L -phenylalanine (L -DOPA), 3,4-dihydroxyphenylacetic acid (DOPAC), and ascorbic acid (AA). The modification of the electrode improved the electrophoretic analysis performance by lowering the detection potential and enhancing the signal-to-noise characteristic without surface poisoning of the electrode. The sensitivity of the modified electrode was about 12 times higher than those of the bare ones. The test compounds were separated using a 62,mm long separation channel at the separation field strength of +200,V/cm within 220,s in a 10,mM phosphate buffer (pH,7.4). The most favorable potential for the amperometric detection was 0.7,V (vs. Ag/AgCl). A reproducible response (relative standard deviation of 1.3, 1.3, 2.1, 3.1, 3.4% for DA, NE, L -DOPA, DOPAC, and AA, respectively, for n,=,9) for repetitive sample injections reflected the negligible electrode fouling at the cellulose-ssDNA modified electrode. Square-wave voltammetric analyses reflected the sensitivities of the modified electrode for DA, NE, L -DOPA, DOPAC, and AA which were 1.78, 0.82, 0.69, 2.45, and 1.23,nC/µM with detection limits of 0.032, 0.93, 1.13, 0.31, and 0.62,µM, respectively. The applicability of this microsystem to real sample analysis was demonstrated. [source] Divanadium(V) and Trapped Valence Linear Tetravanadium(IV,V,V,IV) ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 35 2009Anindita Sarkar Abstract In an acetonitrile/water mixture, reactions of the N,N,-bis(diacetyl)hydrazine (H2diah), bis(acetylacetonato)oxidovanadium(IV) [VO(acac)2] and monodentate N -coordinating heterocycles (hc) in a 1:2:2 mol ratio provide yellow divanadium(V) complexes of formula [(hc)O2V(,-diah)VO2(hc)] (1, hc = imidazole; 2, hc = pyrazole; 3, hc = 3,5-dimethyl pyrazole). On the other hand, in the same solvent mixture reactions of the same reagents in a 1:4:2 mol ratio produce green linear tetravanadium(IV,V,V,IV) complexes of formula [(acac)2OV(,-O)VO(hc)(,-diah)(hc)OV(,-O)VO(acac)2] (4, hc = imidazole; 5, hc = pyrazole; 6, hc = 3,5-dimethyl pyrazole). The complexes 1,6 have been characterized by elemental analysis, magnetic susceptibility, and various spectroscopic and electrochemical measurements. The X-ray crystal structures of 1, 3 and 6 have been determined. In all three structures, the diazine ligand diah2, is in trans configuration. Metal-centred bond parameters are consistent with the localized electronic structure of the two trans -bent {OV(,-O)VO}3+ cores present in 6. The pentavalent metal centres in 1, 3 and 6 are in a distorted trigonal-bipyramidal N2O3 coordination environment, while the terminal tetravalent metal centres in 6 are in a distorted octahedral O6 coordination sphere. The eight-line EPR spectra of the tetravanadium species (4,6) in dimethyl sulfoxide at ambient temperature indicate the rare valence localized electronic structure in the fluid phase. All the complexes are redox active and display metal-centred electron transfer processes in dimethyl sulfoxide solution. A reduction within ,0.78 to ,0.94 V (vs. Ag/AgCl) is observed for the divanadium(V) species 1,3, while a reduction and an oxidation are observed in the potential ranges ,0.82 to ,0.90 V and 0.96 to 1.12 V (vs. Ag/AgCl), respectively, for the tetravanadium species 4,6. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Electrodeposited CuGa(Se,Te)2 thin-film prepared from sulfate bathPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006Yusuke Oda Abstract CuGa(Se,Te)2 (CGST) thin films were prepared on a soda-lime glass substrate sputter coated with molybdenum by electrodeposition. The aqueous solution which contained CuSO4 -5H2O, Ga2(SO4)3 -19.3H2O, H2SeO3, H6TeO6, Li2SO4 and gelatin was adjusted to pH 2.6 with dilute H2SO4 and NaOH. It has been observed that (i) a crack-less and smooth CGST film with a composition close to the stoichiometric ratio was deposited at -600 mV (vs. Ag/AgCl) when Te was hardly included in the film and (ii) cracks and products on the surface increased with increasing Te content in the film. Annealing at 600 °C for 10 min improved the crystallinity of the as-deposited films. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electrochemical Evaluation of Nucleoside Analogue Lamivudine in Pharmaceutical Dosage Forms and Human SerumELECTROANALYSIS, Issue 20 2005Burcu Dogan Abstract Lamivudine (LAM) is a synthetic nucleoside analogue with activity against human immunodeficiency virus-type 1 (HIV-1) and Hepatitis B virus (HBV). The aim of this study was to determine LAM levels in serum and pharmaceutical formulations, by means of electrochemical methods using hanging mercury drop electrode (HMDE). On this electrode, LAM undergoes irreversible reduction at the peak potential near Ep,1.26,V (vs. Ag/AgCl/3,M KCl). Reduction LAM signals were measured by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square-wave voltammetry (OSW). DPV and OSW techniques for the determination of LAM in acetate buffer at pH,4.5, which allows quantitation over the 4×10,6 to 1×10,4,M range in supporting electrolyte for both methods, were proposed. The linear response was obtained in acetate buffer in the ranges of 2×10,6 to 2×10,4,M for spiked serum samples at pH,4.5 for both techniques. The repeatability and reproducibility of the methods for all media were determined. The standard addition method was used in serum. Precision and accuracy were also checked in all media. No electroactive interferences from the endogenous substances were found in serum. With respect to side effects of high doses and short half-life of LAM, a fast and simple detection method is described in this study. [source] Electrochemical Detection of Cadmium and Lead Complexes with Low Molecular Weight Organic AcidsELECTROANALYSIS, Issue 3-5 2009Jaklová Dytrtová Abstract The Cd and Pb complexes with oxalic (OA) and citric acid (CA) were detected in model and soil solutions using cyclic and stripping voltammetry. A mixed complex consisting of Cd, Pb, and OA was found; its peak potential varied from ,582.0 to ,542.5,mV (vs. Ag/AgCl/KCl(3,mol L,1)). For mixed complex formation, the presence of PbOH+ species and Cd2+ in oxalic acid solution was necessary. Only the ,simple' complexes of CA with Pb and Cd were found in the model solution. The existence of all investigated metal complexes is confined to neutral pH range. The mixed complex was also found in real soil solutions. [source] | ||||||||||