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Vs. SCE (vs + sce)
Selected AbstractsImproved Voltammetric Response of L -Tyrosine on Multiwalled Carbon Nanotubes-Ionic Liquid Composite Coated Glassy Electrodes in the Presence of Cupric IonELECTROANALYSIS, Issue 19 2008Liqin Liu Abstract L -Tyrosine can exhibit a small anodic peak on multiwalled carbon nanotubes (MWCNTs) coated glassy carbon electrodes (GCE). At pH,5.5 its peak potential is 0.70,V (vs. SCE). When an ionic liquid (i.e., 1-octyl-3-methylimidazolium hexafluorophosphate, [omim][PF6]) is introduced on the MWCNT coat, the peak becomes bigger. Furthermore, in the presence of Cu2+ ion the anodic peak of L -tyrosine increases further due to the formation of Cu2+ - L -tyrosine complex, while the peak potential keeps unchanged. Therefore, a sensitive voltammetry based on the oxidation of Cu2+ - L -tyrosine complex on MWCNTs-[omim][PF6] composite coated electrode is developed for L -tyrosine. Under the optimized conditions, the anodic peak current is linear to L -tyrosine concentration in the range of 1×10,8,5×10,6 M, and the detection limit is 8×10,9 M. The modified electrode shows good reproducibility and stability. In addition, the voltammetric behavior of other amino acids is explored. It is found that among them tryptophan (Trp) and histidine (His) can also produce sensitive anodic peak under same experimental conditions, and their detection limits are 4×10,9 M and 4×10,6 M, respectively. [source] Amperometric Glucose Biosensors Based on Glassy Carbon and SWCNT-Modified Glassy Carbon ElectrodesELECTROANALYSIS, Issue 1 2008Irene Carpani Abstract Different carbonaceous materials, such as single-walled carbon nanotubes (SWCNTs) and glassy carbon submitted to an electrochemical activation at +1.80,V (vs. SCE) for 900,s, have been used with the aim of comparing their performances in the development of enzyme electrodes. Commercial SWCNTs have been pretreated with 2.2,M HNO3 for 20,h prior to use. The utility of activated GC as promising material for amperometric oxidase-based biosensors has been confirmed. With glucose oxidase (GOx) as a model enzyme, glucose was efficiently detected up to 1 mM without the use of a mediator. Both electrodes operated in stirred solutions of 0.1,M phosphate buffer (pH,5.5), containing dissolved oxygen, at a potential of ,0.40,V vs. SCE. Although the performances of the two carbonaceous materials were comparable, the biosensors based on activated GC were characterized by a practically unchanged response 40 days after the fabrication, a better signal to noise ratio, and a little worse sensitivity. In addition, the preparation procedure of such biosensors was more simple, rapid and reproducible. [source] Voltammetry as an Alternative Tool for Trace Metal Detection in Peloid Marine SedimentsELECTROANALYSIS, Issue 13 2007Irena Ciglene Abstract Here was demonstrated for the first time a possible application of abrasive stripping voltammetry in the direct measurement of trace metals in anoxic, sulfidic marine sediments (peloid mud) from a small and shallow (0.2,1,m) marine lagoon in Central Dalmatia, Croatia. Trace amounts of sample compounds are transferred to the graphite electrode surface and electrochemical reduction or oxidation processes are followed by the cyclic voltammetry in seawater or 0.55,M NaCl as electrolyte. After a preelectrolysis at potentials ranging from ,1.0 to ,1.5,V (vs. SCE) a well-defined anodic stripping peak corresponding to the oxidation of metal deposits generated at deposition potentials is obtained around ,0.74,V (vs. SCE). The same samples were studied by anodic stripping voltammetry at the Hg electrode and inductively coupled plasma-mass spectrometer (ICP-MS). ICP-MS showed higher concentrations of trace metals such as Al, Fe, Mo, Mn. A relatively high concentration of reduced sulfur species (RSS) (10,3 M) is determined electrochemically in porewater of the peloid mud, indicating that the magnitude of metal enrichment in the sediments is probably controlled by precipitation with sulfide. [source] Low Potential Detection of NADH at Titanium-Containing MCM-41,Modified Glassy Carbon ElectrodeELECTROANALYSIS, Issue 5 2007Zhihui Dai Abstract Titanium-containing MCM-41 (Ti-MCM-41) modified glassy carbon electrode (GCE) can exhibit an excellent electrocatalytic activity towards the oxidation of ,-Nicotinamide adenine dinucleotide (NADH). A dramatic decrease in the over-voltage of NADH oxidation reaction is observed at 0.28,V (vs. SCE). The modified electrode is found to be stable and reproducible. The electrode shows a linear response for a wide range of 10,1200,,M NADH and the detection limit is 8.0,,M. Ti-MCM-41 mesoporous molecular sieves provide an efficient matrix for development of NADH biosensors and the prepared electrode not only can be used to detect the concentration of NADH in biochemical reaction, but also as the potential matrix of the construction of dehydrogenases biosensor. [source] Photoelectrocatalytic Oxidation of NADH with Electropolymerized Toluidine Blue OELECTROANALYSIS, Issue 2-3 2007Yusuf Dilgin Abstract A poly(Toluidine Blue O) (poly-TBO) modified electrode was successfully prepared by repeated sweeping the applied potential from ,0.6 to +0.8,V (vs. SCE) on a glassy carbon electrode (GCE) in borate buffer solution at pH,9.1,containing 0.1,M NaNO3 and 0.4,mM Toluidine Blue O (TBO). The poly-TBO modified GCE shows electrocatalytic activity toward NADH oxidation in phosphate buffer solution at pH,7.0, with an overpotential of ca. 350,mV lower than that at the bare electrode. The photoelectrocatalytic oxidation of NADH at this electrode was also successfully investigated by using cyclic voltammetry and amperometry at constant potential. When the modified electrode surface was irradiated with a 250,W halogen lamp, a photoelectrocatalytic effect was observed for NADH oxidation and the current was increased about 2.2 times. The applied potential was selected at +100,mV for amperometric and photoamperometric detection of NADH. A linear calibration graph for NADH was obtained in the range between 1.0×10,5 and 1.0×10,3 M and between 5.0×10,6 and 1.0×10,3 M for amperometric and photoamperometric studies, respectively. The effect of some interfering compounds, such as ascorbic acid and dopamine on the electrocatalytic and photoelectrocatalytic oxidation of NADH was tested. [source] The Solid State Electrochemistry of Dysprosium(III) Hexacyanoferrate(II)ELECTROANALYSIS, Issue 17 2005Ping Wu Abstract A new electroactive polynuclear inorganic compound of rare earth metal hexacyanoferrate, dysprosium hexacyanoferrate (DyHCF), was prepared chemically and characterized using techniques of FTIR spectroscopy, thermogravimetric analysis (TGA), UV-vis spectrometry and X-ray photoelectron spectroscopy (XPS) etc. The cyclic voltammetric behavior of DyHCF mechanically attached to the surface of graphite electrode was well defined and exhibited a pair of redox peaks with the formal potential of 217,mV (vs. SCE) at a scan rate of 100,mV/s in 0.2,M NaCl solution and the redox peak currents increased linearly with the square root of the scan rates. [source] Electrochemical Overoxidation of Polyindole and Its Cation-Permselective BehaviorELECTROANALYSIS, Issue 12 2004Mihaela Ghita Abstract Polyindole films prepared by potentiostatic growth in dichloromethane solution were subjected to overoxidation studies in aqueous media. Overoxidation at potentials greater than 1.1,V (vs. SCE) in 0.1,M KNO3 or 0.1,M H2SO4 was possible. Overoxidation in 0.1,M NaOH resulted in mechanically unstable films which were not adherent to the electrode surface. The overoxidation process in 0.1,M KNO3 involved removal of one electron per four indole monomer moieties in the polymer film. Nucleophilic attack led to introduction of carboxylate functionality and to cation permselective behavior, as tested by cyclic voltammetry and hydrodynamic voltammetry of hexamminoruthenium(III) and hexacyanoferrate(III). Such films may be useful in various electrochemical sensor applications. [source] The Electrochemical Behavior of ,-Ketoglutarate at the Hanging Mercury Drop Electrode in Acidic Aqueous Solution and Its Practical Application in Environmental and Biological SamplesELECTROANALYSIS, Issue 12 2004Li Yang Abstract The voltammetric behavior of ,-ketoglutarate (,-KG) at the hanging mercury drop electrode (HMDE) has been investigated in acetate buffer solution. Under the optimum experimental conditions (pH,4.5, 0.2,M NaAc-HAc buffer solution), a sensitive reductive wave of ,-KG was obtained by linear scan voltammetry (LSV) and the peak potential was ,1.18,V (vs. SCE), which was an irreversible adsorption wave. The kinetic parameters of the electrode process were ,=0.3 and ks=0.72,1/s. There was a linear relationship between peak current ip, ,-KG and ,-KG concentration in the range of 2×10,6,8×10,4,M ,-KG. The detection limit was 8×10,7,M and the relative standard deviation was 2.0% (C,-KG=8×10,4,M, n=10). Applications of the reductive wave of ,-KG for practical analysis were addressed as follows: (1) It can be used for the quantitative analysis of ,-KG in biological samples and the results agree well with those obtained from the established ultraviolet spectrophotometric method. (2) Utilizing the complexing effect between ,-KG and aluminum, a linear relationship holds between the decrease of peak current of ,-KG ,ip and the added Al concentration C in the range of 5.0×10,6,2.5×10,4,M. The detection limit was 2.2×10,6,M and the relative standard deviation was 3.1% (C=4×10,5,M, n=10). It was successfully applied to the detection of aluminum in water and synthetic biological samples with satisfactory results, which were consistent with those of ICP-AES. (3) It was also applied to study the effect of AlIII on the glutamate dehydrogenase (GDH) activity in the catalytically reaction of ,-KG+NH+NADH,L -glutamate+NAD++H2O by differential pulse polarography (DPP) technique. By monitoring DPP reductive currents of NAD+ and ,-KG, an elementary important result was found that Al could greatly affect the activity of GDH. This study could be attributed to intrinsic understanding of the aluminum's toxicity in enzyme reaction processes. [source] Potential-resolved electrochemiluminescence of Ru(bpy)32+/C2O42, system on gold electrodeLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 2 2002Feng Li Abstract The electrogenerated chemiluminescence of Ru(bpy)32+/C2O42, system on a pre-polarized Au electrode was studied using a potential-resolved electrochemiluminescence (PRECL) method. Two anodic ECL peaks were observed at 1.22,V (vs. SCE) (EP1), 1.41,V (vs. SCE) (EP2), respectively. The effects of the concentration of oxalate and Ru(bpy)32+, adsorbed sulphur, CO2, O2, pH of the solution and pretreatment of the Au electrode on the two PRECL peaks were examined. The surface state of the pre-oxidized gold electrode was also studied using the X-ray photoelectron spectroscopy (XPS) technique. Moreover, comparative studies on i,E and I,E curves were carried out and a possible mechanism involving both the catalytic and the direct electro-oxidation pathways was proposed for the ECL of Ru(bpy)32+/C2O42, system. EP1 is attributed to the Ru(bpy)32/3+ reaction catalysed by C2O42, to generate Ru(bpy)32+*. EP2 is likely because C2O42, was oxidized at the electrode to form CO2,·, followed by reaction with Ru(bpy)33+ to generate Ru(bpy)32+*. Copyright © 2002 John Wiley & Sons, Ltd. [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] 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] 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] Electrochemical Preparation and Characterization of Lanthanum Hexacyanoferrate Modified ElectrodeCHINESE JOURNAL OF CHEMISTRY, Issue 2 2005Wu Ping Abstract An electroactive polynuclear inorganic compound of rare earth metal hexacyanoferrate, lanthanum hexacyanoferrate (LaHCF), was prepared by electrochemical deposition on the surface of a glassy carbon electrode with a potential cycling procedure. The cyclic voltammogram of LaHCF exhibits a pair of well-defined redox peaks with the formal potential of 208 mV (vs. SCE) at a scan rate of 100 mV/s in 0.2 mol/L NaCl solution and the redox peak currents increase linearly with the square root of the scan rate up to 1000 mV/s. The effects of the concentration of supporting electrolyte on the electrochemical characteristics of LaHCF were studied by voltammetry. LaHCF was also characterizated by scanning electron microscope (SEM), FTIR and XPS techniques. [source] Electrochemical study on interaction of vincristine with tubulinCHINESE JOURNAL OF CHEMISTRY, Issue 11 2001Yong Yu Abstract In Tris (0.005 mol/L)-NaCl (0.05 mol/L) buffer solution (pH = 7.10), keeping temperature at 37°C, a highly sensitive reduction peak of the antitumor agent was obtained by linear sweep voltammetry. The peak potential is-1.56 V (vs. SCE). The peak current is proportional to the concentration of vincristine over the range of 2.1 ± 10,7 -4.2 ± 10,6 mol/L with the detection limit of 1.0 ± 10,7 mol/L. The behavior of the binding of vincristine to tubulin was studied. The results showed that the reaction of tubulin dimer with vincristine formed an electrochemically active complex to be 1:2. Its stability constant is 2.5 ± 1014. The reduction process of the complex is irreversible with adsorptive characteristics. [source] | ||||||||||