Research on modified electrode of conducting polymer .2. Characteristics of polypyrrole film doped with heteropolyanions

Polypyrrole film electrode with Co(W2O7)(6)(10-) and CuW12O406- ions were synthesised in aqueous solutions, The electrode possesses a good stability and cyclic voltammetric behavior in weakly acidic or near neutral solutions, The redox of CuW12O406- ion can be catalysed by the polypyrrole film, The ESR measurement of the polypyrrole film with Co(W2O7)(6)(10-) and CuW12O406- ions indicates that the heteropolyanions not only play the role of neutralizing electricity in the polypyrrole film, contrasted with the film containing NO3-, but also Interact with the polypyrrole molecular chain to form some additive compound, The additive compound affects the electric structure elf the polypyrrole film and is unstable at more positive or more negative potentials.

Acetylcholinesterase amperometric detection system based on a cobalt(II) tetraphenylporphyrin-modified electrode

An acetylcholinesterase (AChE) activity detection system was fabricated based on the electrocatalysis of cobalt(II) tetraphenylporphyrin of the electrooxidation of thiocholine chloride, which is the product of the hydrolysis of acetylthiocholine chloride by AChE. A simple modified method was used to form the base electrode. AChE was cross-linked on the base electrode by glutaraldehyde. The optimum working conditions are discussed and the characteristics of the detection system are evaluated.

Determination of isoniazid and hydrazine by capillary electrophoresis with amperometric detection at a Pt-particle modified carbon fiber microelectrode

Capillary electrophoresis (CE)/electrochemical detection (EC) for the simultaneous determination of hydrazine and isoniazid has been developed. The electrochemical method uses a novel modified electrode dispersed with ultrafine platinum particles on the surface of a 30 mu m carbon fiber microelectrode. The unique characteristic of the Pt-particles modified carbon fiber microelectrode is its excellent stability. The current measurement for hydrazine is more sensitive than that of isoniazid. Selective determination of trace amount of free hydrazine in isoniazid and its formulation can be achieved at applied potential of 0.5 V.

Electrochemical preparation of microelectrodes modified with non-stoichiometric mixed-valent molybdenum oxides

A compact non-stoichiometric molybdenum (VI, V) oxide of blue film was grown on carbon fiber (CF) microelectrode surface be cycling the potential between + 0.2V and - 0.70V in a freshly prepared Na2MoO4 solution containing 5 x 10(-3) mol/L H2SO4. The quantity-of the oxide is controlled by the charge passing the electrode. The electrochemical pretreatment of CF microelectrode not only mises the deposition velocity of molybdenum oxide on CF surface, but also improves greatly the cyclic voltammetric behavior of the molybdenum oxide film prior to the electrodeposition. The cathodic processes are believed to yield the hydrogen molybdenum oxide bronzes HxMoO3(0 < x < 2), or substoichiometric lower molybdenum oxides with the formula MoO3-y(0 < y < 1). The anodic response results from the reversible oxidation of molybdenum bronze/Mo(V) centers [or perhaps Mo(IV) in more reduced coatings], to Mo(VI). Further information was gained about the chemical composition and valent state of Mo from XPS and SEM.

Improvements in the selectivity of electrochemical detectors for liquid chromatography and flow injection analysis using the self-assembled n-alkanethiol monolayer-modified au electrode

4-Aminophenol (4-AP), paracetamol (PRCT), norepinephrine (NE), and dopamine (DA) (all somewhat hydrophobic compounds) were HPLC electrochemically detected while the signals from uric acid (UA) and ascorbic acid (AA) (both hydrophilic compounds at the pH studied) were minimized, taking advantage of the permselectivity of the self-assembled n-alkanethiol monolayer (C-10-SAM)-modified Au electrodes based on solute polarity, The effects of various factors, such as the chain length of the n-alkanethiol modifier, modifying time, and pH value, on the permeability of C-10-SAM coatings were examined, The calibration curves, linear response ranges, detection limits, and reproducibilities of the EC detector for 4-AP, PRCT, NE, and DA were obtained, The result shows that the EC detector can be applied in the chromatographic detection of 4-AP, PRCT, NE, and DA in urine, effectively removing the influence of UA and AA in high concentrations existing in biological samples. As a result, a great improvement in the selectivity of EC detectors has been achieved by using Au electrodes coated with neutral n-alkanethiol monolayer.

Studies on water-swellable elastomer .1. Synthesis and characterization of amphiphilic polymer

A new amphiphilic polymer i.e., polyethylene glycol (PEG) grafted crystalline neoprene, which was used as compatibilizer to improve the compatibility of elastomer and water-absorbent resin, has been investigated. The synthesis was based on the reaction between chlorine in neoprene and sodium salts of PEG. PEGs with molecular weights of 600 and 2000 were used. The grafting percent and the PEG content were calculated through elemental analysis of chlorine in the resulted copolymers. The maximum grafting percent of copolymers was ca. 24.80%. The molecular parameters such as number-average molecular weight and the average number of grafting chains on one CR backbone were also calculated and discussed. (C) 1996 John Wiley & Sons, Inc.

The direct electrochemistry of cytochrome c at the nanometer-sized rare earth element oxide particle-modified gold electrodes

The direct electrochemistry of cytochrome c was studied at nanometer-sized rare earth element dioxide particle-modified gold electrodes. It was demonstrated that rare earth element oxides can accelerate the electrochemical reaction of cytochrome c and the reversibility of the electrochemical reaction of cytochrome c was related to the size of rare earth element oxide particles.

Electrochemical study of isopoly- and heteropoly-oxometallates film modified microelectrodes .6. Preparation and redox properties of 12-molybdophosphoric acid and 12-molybdosilicic acid modified carbon fiber microelectrodes

The redox behaviours of 12-molybdophosphoric acid (12-MPA) and 12-molybdosilicic acid (12-MSA) in aqueous acid media are characterized at the carbon fiber (CF) microelectrode. The preparation of CF microelectrode modified with 12-MPA or 12-MSA monolayer and the oxidation-reduction properties of the modified electrode in aqueous acid media or 50% (v/v) water-organic media containing some inorganic acids are studied by cyclic voltammetry. 12-MPA or 12-MSA monolayer modified CF microelectrode with high stability and redox reversibility in aqueous acidic media can be prepared by simple dip coating. The cyclic voltammograms of 12-MPA and 12-MSA and their modified CF microelectrodes in aqueous acid solution exhibit three two-electron reversible waves with the same half-wave potentials, which defines that the species adsorbed on the CF electrode surface are 12-MPA and 12-MSA themselves. The acidity of electrolyte solution, the organic solvents in the electrolyte solution, and the scanning potential range strongly influence on the redox behaviours and stability of 12-MPA or 12-MSA monolayer modified electrodes. On the other hand, the catalytic effects of the 12-MPA and 12-MSA and chlorate anions in aqueous acidic solution on the electrode reaction processes of 12-MPA or 12-MSA are described.

Study on the modified electrode of conducting polymers .3. Electron spin resonance characteristic of polypyrrole film electrode doped with heteropolyanions

The ESR of PPy films doped with Co (W2O7)(6)(10-) and CuW12O406- ions were reported and discussed. Results show that heteropolyanions not only play the role of neutralizing electricity in the PPy film, but also interact with the PPy molecular chain to form some adducts. The adducts affect the electronic structure of the PPy film and are unstable at more positive or more negative potentials. Dysonian ESR lineshape was recorded for the dry PPy film with CuW12O406- for the first time.

Kinetics of electrocatalytic ascorbic acid at ultramicroelectrode modified by Eastman-AQ polymer containing tris(2,2-'-bipyridine) osmium(III/II) complexes as electron-transfer centers

The theoretical model[17] of an ultramicroelectrode modified with a redox species film is used as the diagnostic tool to characterize the catalytic oxidation of ascorbic acid at carbon fiber ultramicrodisk electrodes coated with an Eastman-AQ-Os(bpy)(3)(2+) film. The electrocatalytic behavior of ascorbic acid at the ultramicroelectrode modified by an Eastman-AQ polymer containing tris(2,2'-bipyridine) osmium(III/II) as mediators is described. In order to determine the five characteristic currents quantitatively, the radius of the ultramicroelectrode and the concentration of ascorbic acid are varied systematically. The kinetic zone diagram has been used to study the electrocatalytic system. This system with 0.5-2.75 mM ascorbic acid belongs to SR + E case, and the concentration profiles of the catalyst in the film are given in detail. Finally, optimizing the design of catalytic system is discussed.

PREPARATION OF MODIFIED ELECTRODE WITH MOLYBDOPHOSPHATE ANION AND ITS ELECTROCATALYSIS FOR BROMATE REDUCTION

A molybdophosphate anion modified electrode has been prepared in 2 M sulfuric acid solution containing PMo12O403- by electrochemical cycling scan or simple adsorption on a glassy carbon electrode anodized before modification. The film electrode obtained is very stable upon potential cycling in acid solution. The catalytic effect of the film for reduction of bromate was investigated in detail.

PREPARATION AND MICROSTRUCTURAL CHARACTERIZATION OF SURFACE-MODIFIED NANOSIZED SNO2 PARTICLES

Nanosized stannic oxide particles modified with a layer of DBS were successfully prepared through the colloidal chemical method and their microstructures were characterized. FTIR and XPS were used for the determination of the main components. It can be proved that the nanosized SnO2 particles were capped by DBS. The sizes of particle were determined by TEM and XRD. By the investigation of XPS, we can conclude that there are a lot of oxygen vacancies in the surface of the nanoparticulates. Based on this conclusion, the ESR signal of the sample can be explained.