Chemiluminescent determination of glucose with a modified carbon paste electrode

A flow injection analysis detection method for glucose is presented which is based on the oxidation of glucose by glucose oxidase followed by chemiluminescent detection of hydrogen peroxide. Both glucose oxidase and hematin, a chemiluminescent reaction catalyst, were bulk-immobilized conveniently by direct mixing with carbon paste, which allows renewal of the electrode surface by simply polishing or cutting to expose a new and fully active surface in the case of fouling. Luminol in reagent solution passed through the flow cell and reacted with hydrogen peroxide produced by the enzyme reactor in the presence of the catalyst to yield light. An applied potential of -0.4 V avoided the electrode fouling effectively. The log-log plot of the emitted light intensity vs glucose concentration was linear over the range of 1-100 mmol L-1 with a correlation coefficient of 0.992. Application of this method to other chemiluminescent and bioluminescent systems is suggested. (C) 1999 Academic Press.

Lanthanide coordination polymers with dicarboxylate-like ligands: crystal structures of polymeric lanthanum(III) and terbium(III) complexes with flexible double betaines

Four novel polymeric lanthanide(III) complexes of two new double betaine derivatives have been synthesized and structurally determined. In [{La-2(L-1)(2)(H2O)(9)}(n)]Cl-6n. 2nH(2)O (1) and [{Tb(L-1)(H2O)(4)}(n)]Cl-3n. nH(2)O (2) (L-1 =4,4'-trimethylenedipyridinio-N,N'-diacetate), the lanthanide(III) ions form a two-dimensional layer in which each pair of lanthanide(III) ions is bridged by two syn-anti mu-carboxylato-O,O' groups. Adjacent layers are cross-linked through hydrogen bonds among aqua ligands, lattice water molecules and chloride ions, to form a three-dimensional network. Isomorphous [{Ln(L-1)(H2O)(4)}(n)]Cl-3n. 5nH(2)O (Ln=La, 3; Ln=Tb, 4; L-2=1,3 bis(pyridinio-4-carboxylato)-propane) each contain a centrosymmetric paddle-wheel-like dimeric unit in which each pair of adjacent metal atoms is bridged by four syn-syn mu-carboxylato-O,O' groups that are oriented nearly perpendicular to each other about the metal-metal axis. Neighboring dimeric subunits are bridged by a pair of flexible LL ligands into a polymeric chain. Adjacent chains are inter-linked by hydrogen bonds among aqua ligands, lattice water molecules and chloride ions into a three-dimensional network. (C) 1999 Elsevier Science Ltd. All rights reserved.

Thermodynamics of blends of poly(ethylene oxide) with poly(methyl methacrylate) and poly(vinyl acetate): prediction of miscibility based on Flory solution theory modified by Hamada

Flory solution theory modified by Hamada et al. (Macromolecules, 1980, 13, 729) was used to predict the miscibility of blends of poly(ethylene oxide) with poly(methyl methacrylate) (PEO-aPMMA) and with poly(vinyl acetate) (PEO-PVAc). Interaction parameters of a PEO-aPMMA blend with the weight ratio of PEO/aPMMA = 50/50 at the temperature range of 393-433 K and PEO-PVAc blends with different compositions and temperatures were calculated from the determined equation-of-state parameters based on Flory solution theory modified by Hamada ed al. Results show that interaction parameters of the PEO-aPMMA blend are negative and can be comparable with values obtained from neutron-scattering measurements by Ito et al. (Macromolecules, 1987, 20, 2213). Also, interaction parameters and excess volumes of PEO-PVAc blends are negative and increase with enhancing the content of PEO and the temperature. (C) 1998 Elsevier Science Ltd. All rights reserved.

Liquid chromatography amperometric detection of nitrite using a polypyrrole modified glassy carbon electrode doped with tungstodiphosphate anion

Chromatography-amperometric detection of nitrite with a polypyrrole modified glassy carbon electrode doped with tungstodiphosphate anion (Dawson-type P2W18O626-/PPy/GC electrode) based on its electrocatalytic reduction of nitrite is described. The cyclic and hydrodynamic voltammetry of nitrite at the P2W18O626-/PPy/GC electrode was studied. The factors affecting the detection of nitrite and the analytical performance of the modified electrode in flowing stream were investigated. The results show that the modified electrode has a good sensitivity (the limit of detection is 1 mu mol dm(-3)) and a satisfactory reproducibility (RSD = 3.78%, N = 21). The modified electrode was used in the chromatographic detection of nitrite spiked in the liquid from a tin of mushrooms and the mineralized spring water. It was found that the modified electrode exhibited good selectivity for nitrite.

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.

Probe beam deflection combined with cyclic voltammetry studies of C-60-modified electrode film

C-60 films, prepared by solution casting, were studied by means of in situ probe beam deflection (PBD) combined with cyclic voltammetry (CV). PBD is a powerful technique for investigation of phenomena at the electrode/electrolyte interface in acetonitrile with quaternary ammonium and alkali metal salts as supporting electrolytes. In tetra-n-butylammonium (TBA(+)) salt solution, a stable CV can be obtained during the first two reduction/reoxidation waves. On reduction, injection of cations to maintain charge balance and dissolution of small amount of C-60(-) (TEA(+)) and/or C-60(2-) (TBA(+))(2) are detected. During the reoxidation process ejection of cations and injection of anions occur simultaneously, especially for the second reoxidation wave. In the case where TBABr is the supporting electrolyte, the accompanied behavior is more complicated than in TBABF(4), TBAClO(4), and TBAPF(6) solutions. A small pair of prewaves in CV are proposed due to oxidation/reduction of C-60 domains but not dissolution/redeposition of C-60 film. Extending the potential scan range to the third reduction wave, no apparent corresponding reoxidation wave is related to the third reduction wave, the electroactivity of the film disappears rapidly and dissolution of C-60 film is observed. In tetraethylammonium (TEA(+)) and NAClO(4) solutions, the electrochemistry of the C-60 films is unstable, and potential scans lead to dissolution of flaking of the film.

Detection of hydrazine, methylhydrazine, and isoniazid by capillary electrophoresis with a palladium modified microdisk array electrode

A palladium particle-modified carbon fiber microdisk array electrode was designed and employed in capillary electrophoresis for the simultaneous detection of hydrazine, methylhydrazine, and isoniazid. The Pd-modified microdisk electrode had high catalytic ability for hydrazines and exhibited good reproducibility and stability. The response for hydrazine was linear over 3 orders of magnitude with a correlation coefficient of 0.993. The detection limits far hydrazine, methylhydrazine, and isoniazid were 1.2, 2.1, and 6.2 pg, respectively.

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.

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.

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.

SYNTHESIS OF CROSS-LINKED 2ND-ORDER NONLINEAR-OPTICAL POLYMERS WITH HIGH T-G

Synthesis and characterization of a diamino dihydroxyl azo compound were reported, The crosslinking reaction process of the diamino dihydroxyl azo compound with the biuret of hexamethylene diisocyanate was studied by FTIR, The glass transition temperatures of crosslinked polymers were measured by DSC, The orientation and oriented stability of crosslinked and poled polymers were studied by UV-Vis spectra.

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.

ELECTROCHEMICAL-BEHAVIOR OF MOLIBDOSILICIC HETEROPOLY COMPLEX WITH DYSPROSIUM AND ITS DOPED POLYPYRROLE FILM-MODIFIED ELECTRODE

In this paper, the electrochemical behaviour of molibdosilicic heteropoly complex with dysprosium K10H3[Dy(SiMo11O39)(2)]. xH(2)O [denoted as Dy(SiMo11)(2)] was studied. Voltammetric behavior of this complex was greatly influenced by pH of solutions. The polypyrrole (PPy) film doped with this complex was prepared by electropolymerization of pyrrole in the presence of Dy(SiMo11)(2) under potential cycling conditions. The microenvironment within the PPy film has an effect on the electrochemical behavior of Dy(SiMo11)(2) entrapped in the film. The film electrode can catalyze the reduction of ClO3- and BrO3-.

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