ELECTROACTIVE COATINGS OF DICYANO-BIS(1,10-PHENANTHROLINE)IRON(II) ATTACHED TO NAFION POLYMER FILM-MODIFIED ELECTRODES VIA ADSORPTION

A dicyano-bis(1,10-phenanthroline)iron(II) modified elecrode was prepared. The voltammetric and the spectroelectrochemical behavior of this electrode were investigated. The influence of pH and the amount of Nafion and dicyano-bis(1,10-phenanthroline) iron(II) (DBPI) used in the electrode preparation on the electrochemical behavior is presented.

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.

ELECTROCATALYTIC OXIDATION OF REDUCED NICOTINAMIDE COENZYMES AT ORGANIC DYE-MODIFIED ELECTRODES

Chemically modified electrodes (CMEs) were prepared by adsorbing different dyes, including methylene blue (MB), toluidine blue (TB) and brilliant cresyl blue (BCB), onto glassy carbon electrodes (GCE) with anodic pretreatment. The electrochemical reactions of adsorbed dyes are fairly reversible at low coverages. The CMEs are more stable in acid solutions than in alkaline ones, which is mainly due to decomposition of the dyes in the latter media. They exhibit an excellent catalytic ability for the oxidation of nicotinamide coenzymes (NADH and NADPH). The formation of a charge transfer complex between the coenzyme and the adsorbed mediator has been demonstrated using a rotating disk electrode. The charge transfer complex decomposition is a slow step in the overall electrode reaction process. Some kinetic parameters are estimated. Dependence of the electrocatalytic activity of the CMEs on the solution pH is discussed.

DETERMINATION OF HYDRAZINES BY CAPILLARY ZONE ELECTROPHORESIS WITH AMPEROMETRIC DETECTION AT A PLATINUM PARTICLE-MODIFIED CARBON-FIBER MICROELECTRODE

A novel modified electrode dispersed with ultrafine platinum particles on the surface of a 30-mu m carbon fibre microelectrode was investigated as an amperometric detector in capillary zone electrophoresis (CEEC) for determining hydrazines. The unique cha

TRACE ANALYSIS AT A MERCAPTOACETIC ACID-MODIFIED ELECTRODE

The strong chelating ability of mercaptoacetic acid for certain metal ions is exploited for a new; kind of voltammetric sensor. Specifically, a glassy carbon electrode (GCE) surface was covalently covered br; mercaptoacetic acid. The preparation of mercap

AMPEROMETRIC DETECTION OF CATECHOLAMINES WITH LIQUID-CHROMATOGRAPHY AT A POLYPYRROLE-PHOSPHOMOLYBDIC ANION-MODIFIED ELECTRODE

A conducting polypyrrole film immobilized with PMo12O403- anion on a glassy carbon electrode was prepared by an electrochemical method. This kind of chemically modified electrode (CME) was prepared successfully by doping the polypyrrole film electrode wit

CATALYTIC-OXIDATION AND FLOW DETECTION OF ACETAMINOPHEN AT A DICYANOBIS(1,10-PHENANTHROLINE)IRON(II)-MODIFIED ELECTRODE

Dicyanobis(1,10-phenanthroline)iron(II)-modified glassy carbon electrodes were shown to exhibit an electrocatalytic response for the oxidation of acetaminophen with a decrease of 100 mV in the potential required. It can also inhibit the oxidation of ascor

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 OF REDUCED NICOTINAMIDE COENZYMES AT METHYLENE GREEN-MODIFIED ELECTRODES AND FABRICATION OF AMPEROMETRIC ALCOHOL BIOSENSORS

Chemically modified electrodes with Methylene Green adsorbed on the graphite surface and incorporated into carbon paste exhibit excellent electrocatalytic ability for oxidation of NADH. Alcohol dehydrogenase, nicotinamide adenine dinucleotide (NAD+) and m

AMPEROMETRIC DETECTION OF AMINO-ACIDS IN A FLOW-INJECTION SYSTEM WITH A NICKEL(II)-MODIFIED ELECTRODE WITH AN EASTMAN-AQ POLYMER FILM

Amperometic flow measurements were made at +0.55 V (vs. Ag/AgCl) in 0.1 mol l-1 KOH electrolyte with an Ni(II) chemically modified electrode (CME) with an Eastman-AQ polymer film. The use and characteristics of a Ni(II)-containing crystalline and polymer-modified electrode obtained by a double coating step as a detector for amino acids in a flow-injection system using reversed-phase liquid chromatography are described. The detection of these analytes is based on the higher oxidation state of nickel (NiOOH) controlled by the applied potential. The electroanalytical parameters and the detection current for a series of amines and amino acids were investigated. The use of such a CME in the flow-injection technique was found to be suitable in a solution at low pH. The linear range for glycine is 5 X 10(-6)-0.1 mol 1-1 with a detection limit of 1.0 X 10(-6) mol l-1. A 1 X 10(-4) mol 1-1 mixture of serine and tyrosine was also detected after separation on an Nucleosil C18 column.

ELECTROCHEMICAL CATALYSIS AT AN ULTRAMICROELECTRODE MODIFIED WITH REDOX SPECIES

General equations of the electrocatalytic reaction at an ultramicroelectrode modified with redox species have been described according to the Andrieux Saveant model. The electrocatalytic kinetic process has been discussed for the whole set of cases, ie (R), (R + S), (SR) (SR + E), (E), (R + E), (ER), (S), (ER + S) and (S + E) limiting situations. The effect of gamma on the catalytic steady state current shows that the higher the value of gamma, the lower the catalytic current. The kinetic process shifts rapidly from R to E with increasing values of gamma. It is favorable for catalysis only when gamma is very low. Therefore, the redox species modified ultramicroelectrode with thin film is utilized for electrocatalysis, and the larger the radius of ultramicroelectrode, the higher the catalytic efficiency.

FLOW-INJECTION AMPEROMETRIC DETECTION OF HYDRAZINE BY ELECTROCATALYTIC OXIDATION AT A PRUSSIAN BLUE FILM-MODIFIED ELECTRODE

A Prussian Blue-modified glassy carbon electrode prepared by simple adsorption exhibited excellent electrocatalytic activity in the oxidation of hydrazine in acidic media. A film of the perfluorosulphonic acid polymer Nafion coated on top of the Prussian Blue-modified glassy carbon electrode can improve the mechanical stability of the Prussian Blue layer in the flow stream. Hydrazine was detected by flow-injection analysis at the modified electrode with high sensitivity. The limit of detection was 0.6 ng.

AMPEROMETRIC FLOW-INJECTION ANALYSIS OF HYDRAZINE BY ELECTROCATALYTIC OXIDATION AT COBALT TETRAPHENYLPORPHYRIN MODIFIED ELECTRODE WITH HEAT-TREATMENT

Chemically modified electrodes prepared by treating the cobalt tetraphenylporphyrin modified glassy-carbon electrode at 750-degrees (HCME) are shown to catalyze the electrooxidation of hydrazine. The oxidation occurred at +0.63 V vs. Ag/AgCl (saturated potassium chloride) in pH 2.5 media. The catalytic response is evaluated with respect to solution pH, potential scan-rate, concentration dependence and flow-rate. The catalytic stability of the HCME is compared with that of the cobalt tetraphenylporphyrin adsorbed glassy-carbon electrode. The stability of the HCME was excellent in acidic solution and even in solutions containing organic solvent (50% CH3OH). When used as the sensing electrode in amperometric detection in flow-injection analysis, the HCME permitted sensitive detection of hydrazine at 0.5 V. The limit of detection was 0.1 ng. The linear range was from 50 ng to 2.4-mu-g. The method is very sensitive and selective.

ELECTROCHEMICAL STUDY OF ISOPOLYOXOMETALLATES AND HETEROPOLYOXOMETALLATES FILM MODIFIED MICROELECTRODES .1. PRETREATMENT AND MODIFICATION OF THE MO80-26(4-) MODIFIED CARBON-FIBER MICROELECTRODE

In this paper the preparation of isopoly- and heteropolyoxometallates (IPA and HPA) thin film modified carbon fiber (CF) microelectrodes and the factor that influences the modification of IPA and HPA films are described. IPA and HPA film modified CF microelectrodes can all be prepared by cyclic potential scan and simple dip coating. The modified electrodes prepared are very stable and reversible in acidic solution with monolayer characteristics. The electrochemical pretreatment of CF microelectrodes plays an important role in the modification of IPA and HPA film. The absorption of IPA and HPA film on electrode surfaces has been discussed on the basis of surface conditions of the CF microelectrode and the structure of IPA and HPA.

EASTMAN-AQ/NIII MODIFIED ELECTRODE CHARACTERIZATION AND APPLICATION IN FLOW-INJECTION DETERMINATION OF CARBOHYDRATES AND AMINO-ACIDS

A novel Eastman-AQ/Ni(II) chemically modified electrode (CME) produced by "double coating step" deposition of a poly(ester sulphonic acid) polymer film and Ni2+-containing crystalline species onto glassy carbon instead of a metallic nickel electrode exhibited stable electrocatalytic oxidation of numerous alpha-hydrogen compounds including carbohydrates, amines and amino acids. In cyclic voltammetry, the electrocatalysis appeared with an irreversible anodic wave at +0.55 V (vs. Ag/AgCl). The CME was adapted for constant-potential amperometric detection of these compounds in flow injection analysis. Using the CME, the linear response concentration range was between 1.0 x 10(-5) and 5.0 x 10(-2) mol/l and the detection limit was 5.0 x 10(-6) mol/l for glucose. The stability of the CME was adequate for routine quantitative application.