A novel method of electrodepositing highly dispersed nano palladium particles on glassy carbon electrode

The volumetric behavior of a chloride complex of palladium was studied at a glassy carbon electrode (GCE). The Pd-IV complex existing on the GCE surface was found, which was proposed to form an octahedral surface complex through coordination to the oxygen atom of an oxygen functional group on the pretreated GCE surface. The ferri/ferrocyanide redox couple was used as a probe to examine the activity of the GCE. X-ray photoelectron spectroscopy provided the evidence of the surface complex existing on the GCE. Highly dispersed Pd particles can be obtained when the surface complexes were reduced electrochemically to Pd atoms. The Pd particles obtained in this way were in nanometer scale and exhibit high catalytic activity towards the oxidation of hydrazine. (C) 1997 Elsevier Science Ltd.

Abnormal IR spectra of CO adsorbed on the surface of glass carbon electrode modified with polypyrrole film with platinum microparticles

Abnormal IR spectra of CO adsorbed at the surface of glass carbon electrode modified with polypyrrole film with Pt microparticles are reported.

Determination of hydroxylamine by capillary electrophoresis electrochemical detection with a palladium-particle modified carbon fiber microdisk array electrode

A highly dispersed ultramicro palladium-particle modified carbon fiber microdisk array electrode (Pd-CFE) was employed for capillary electrophoresis-electrochemical (CEEC) detection of hydroxylamine (HA). The Pd particles obtained were in the nanometer scale, had a high electrocatalytic activity towards HA and exhibited good reproducibility and stability. A linear relationship between the current and the analyte concentration was found between 5 x 10(-6) and 1 x 10(-3) mol/l of HA with a correlation coefficient of 0.9992. The detection limit was 5 x 10(-8) mol/l. The applicability of the method for the determination of HA in river water and waste water was investigated.

Electrocatalytic reduction of nitrite using Dawson-type tungstodiphosphate anions in aqueous solutions, adsorbed on a glassy carbon electrode and doped in polypyrrole film

The electrochemical behavior of Dawson-type P2W18O626- adsorbed on a glassy carbon electrode and doped in a polypyrrole film electrode was described. These modified electrodes all display catalytic activity for nitrite reduction, either in acid solutions or in pH > 4.0 solutions.

A carbon single crystal electrode for an electrochemical quartz crystal microbalance study

A highly ordered single crystal carbon material, highly oriented pyrolytic graphite (HOPG) has been successfully employed as a working electrode in an electrochemical quartz crystal microbalance study. RTV silicone rubber is selected to adhere the HOPG film onto the quartz crystal surface. Such modified quartz crystal can oscillate with stable frequency. The electrode modified in this way has good electrochemical properties.

Direct electron communication between glucose oxidase and carbon electrode covered with polypyrrole

Glucose oxidase can be effectively adsorbed onto the polypyrrole(PPy) thin film electrochemically formed on an anodized galssy carbon electrode(GCEa). Direct electron communication between the redox of GOD and the modified electrode was successfully achieved, which was detected using cyclic voltammetry. GOD entrapped in PPy film still remained its biological activity and could catalyze the oxidation of glucose. As a third generation biosensor, GOD-PPy/GCEa responded linearly up to 20 mM glucose with a wider linear concentration range.

ELECTROCATALYTIC OXIDATION AND FLOW DETECTION OF CYSTEINE AT AN AQUOCOBALAMIN ADSORBED GLASSY-CARBON ELECTRODE

A chemically modified electrode (CME) constructed by adsorption of aquocobalamin (VB12a) onto a glassy carbon electrode surface was demonstrated to catalyze the electro-oxidation of cysteine, a sulfhydryl-containing compound. The sulfhydryl oxidation occured at 0.54-0.88 V vs. Ag/AgCl depending on pH value (3.0-10.0). The electrocatalytic behavior of cysteine is elucidated with respect to solution pH, operating potential and other variables as well as the CME preparation conditions. When used as the sensing electrode in flow injection amperometric detection, the CME permitted detection of the compound at 0.8 V. The detection limit was 1.7 pmol. The linear response range went up to 1.16 nmol. The stability of the CME was shown by RSD (4.2%) over 10 repeated injections.

DETERMINATION OF CYSTEINE AND REDUCED GLUTATHIONE IN HUMAN PLASMA BY LIQUID-CHROMATOGRAPHY WITH PULSED AMPEROMETRIC ELECTROCHEMICAL DETECTION USING A PLATINUM-PARTICLES MODIFIED GLASSY-CARBON ELECTRODE

An assay procedure utilizing pulsed amperometric detection at a platinum-particles modified electrode has been developed for the determination of cysteine and glutathione in blood samples following preliminary separation by reversed-phase liquid chromatography. A chemically modified electrode (CME) constructed by unique electroreduction from a platinum-salt solution to produce dispersed Pt particles on a glassy carbon surface was demonstrated to catalyze the electo-oxidation of sulfhydryl-containing compounds: DL-cysteine (CYS), reduced glutathione (GSH). When used as the sensing electrode in flow-system pulsed-amperometric detection (PAD), electrode fouling could be avoided using a waveform in which the cathodic reactivation process occurred at a potential of - 1.0 V vs. Ag/AgCl to achieve a cathodic desorption of atomic sulfur. A superior detection limit for these free thiols was obtained at a Pt particle-based GC electrode compared with other methods; this novel dispersed Pt particles CME exhibited high electrocatalytic stability and activity when it was employed as an electrochemical detector in FIA and HPLC for the determination of those organo-sulfur compounds.

DETERMINATION OF AMINOPYRINE AND ITS METABOLITE IN BIOLOGICAL FLUID BY LIQUID-CHROMATOGRAPHY ELECTROCHEMISTRY WITH A GLASSY-CARBON ELECTRODE DISPERSED WITH ALPHA-ALUMINA PARTICLES

A sensitive high-performance liquid chromatographic method has been developed for the quantitative determination of aminopyrine (AM) and its metabolite 4-aminoantipyrine (AAN). The method utilizes reverse-phase chromatography/amperometric detection with a glassy carbon electrode dispersed with alpha-arumina particles as the working electrode, on which the oxidation of AM and AAN was greatly improved compared with that on a bare glassy carbon electrode. As a result, the detection limit was as low as 1.4 ng for AM and 0.8 ng for AAN, and the calibration plots for the above compounds have wide linear ranges from 100 ng/mL to 100 mu g/mL and 60 ng/mL to 80 mu g/mL (for AM and AAN, respectively). The above method was applied for the detection of these materials in human urine with satisfactory results.

ELECTROCATALYTIC OXIDATION AND FLOW-INJECTION DETERMINATION OF REDUCED NICOTINAMIDE COENZYME AT A GLASSY-CARBON ELECTRODE MODIFIED BY A POLYMER THIN-FILM

G chemically modified electrode (CME) was prepared by electrochemical copolymerization of pyrrole and Methylene Blue. The resulting CME exhibits effective electrocatalytic activity towards the oxidation of reduced nicotinamide coenzymes (NADH and NADPH),

ELECTROCATALYTIC OXIDATION AND AMPEROMETRIC DETERMINATION OF SULFHYDRYL COMPOUNDS AT A COPPER HEXACYANOFERRATE FILM GLASSY-CARBON ELECTRODE IN LIQUID-CHROMATOGRAPHY

Electrocatalytic oxidation of sulfhydryl compounds was effective on a copper hexacyanoferrate (CuHCF) film glassy carbon electrode, at a significantly reduced overpotential (0.55 to 0.65 V) and for a broader pH range (2.0 to 7.0). The electrocatalysis was

DETERMINATION OF CATECHOL DERIVATIVES ON PRETREATMENT AND COPOLYMER COATED GLASSY-CARBON ELECTRODE

A glassy carbon electrode was pretreated electrochemically and was coated with a copolymer of maleic acid anhydride attached with Eastman-AQ55D (MA/AQ). The voltammetric behavior of a series of biologically important compounds, such as dopamine, L-DOPA, D

RAPID-DETERMINATION OF KINETIC-PARAMETERS FOR THE ELECTROCATALYTIC REDUCTION OF DIOXYGEN BY VITAMIN-B12 ADSORBED ON GLASSY-CARBON ELECTRODE

In this paper, the electrochemical behavior of vitamin B-12, ie cyanocobalamin (abbr. VB12) in a weak acidic aqueous solution and adsorbed on glassy carbon (GC) surface (abbr. VB12(ad)/GC) in different pH buffer solutions have been described by using cyclic voltammetry (cv). It is found that VB12 and VB12(ad)/GC exhibit catalytic activity for the electroreduction of O2 according to two reduction peaks at -0.50 and -1.00 V vs. sce; but their electrocatalytic activity is very unstable. Based on the method of hydrodynamic amperometry [B. Miller and S. Bruckenstein, J. electrochem. Soc. 117, 1033 (1970)], some kinetic parameters for the electrocatalytic reduction of O2 by VB12(ad)/GC have been determined rapidly by using a linear rotation-scan method [Rongzhong Jiang and Shaojun Dong, Electrochim. Acta 35, 1451 (1990)]. These kinetic parameters indicate that the reduction of O2 on VB12(ad)/GC gives water predominantly in both potential ranges which correspond to those two reduction peaks. Possible reaction mechanisms have been suggested.

FLOW-INJECTION ANALYSIS OF GLUCOSE AT AN AMPEROMETRIC GLUCOSE SENSOR-BASED ON ELECTROCHEMICAL CODEPOSITION OF PALLADIUM AND GLUCOSE-OXIDASE ON A GLASSY-CARBON ELECTRODE

A glassy carbon electrode (GCE) modified with palladium provides excellent electrocatalytic oxidation of hydrogen peroxide. When the electrolyte contains palladium chloride and glucose oxidase, the GCE can be modified by electrochemical codeposition at a given potential. The resulting modified surface was coated with a thin film of Nation to form a glucose sensor. Such a glucose sensor was successfully used in the flow-injection analysis of glucose with high stability and anti-poisoning ability. It gave a detection limit of 1 X 10(-7) M injected glucose, with a linear concentration range of 0.001-8 mM. There is no obvious interference from substances such as ascorbate and saccharides.

REDOX THERMODYNAMICS OF CYTOCHROME-C AT THE BARE GLASSY-CARBON ELECTRODE

Investigation of the redox thermodynamics of horse heart cytochrome c at bare glassy carbon electrodes has been performed using cyclic voltammetry with a nonisothermal electrochemical cell. The thermodynamic parameters of the electron-transfer reaction of cytochrome c have been estimated in different component buffer solutions. The change DELTAS(re)-degrees in reaction center entropy and the formal potential E-degrees' (at 25-degrees-C, vs. standard hydrogen electrode (SHE)) for cytochrome c are found to be -64.1 J K-1 mol-1 and 0.251 V in phosphate buffer, -64.8 J K-1 mol-1 and 0.257 V in Tris + HCl buffer, -65.6 J K-1 mol-1 and 0.261 V in Tris+CH3COOH buffer (pH 7.0, ionic strength 100 mM). The temperature dependence of the formal potential obtained in phosphate buffer with or without NaCl in the range 5-55-degrees-C shows biphase characteristics in an alkaline solution with an intersection point at ca. 44-degrees-C or 42-degrees-C, which should be due to a structural change in the protein moiety of cytochrome c. However, in acidic and neutral solutions only a monotonic relationship between E-degrees' and temperature is observed. The effect of the buffer component on E-degrees' for cytochrome c is also discussed.