ELECTROCATALYSIS AND DETERMINATION OF HYDRAZINE COMPOUNDS IN LIQUID-CHROMATOGRAPHY AT A MIXED-VALENT COBALT OXIDE CYANOCOBALTATE FILM ELECTRODE

A glassy carbon electrode coated with an electrodeposited film of mixed-valent cobalt oxide/cyanocobaltate (Co-O/CN-Co) enabled hydrazine compounds to be catalytically oxidized at the greatly reduced overpotential and in a wide operational pH range (pH 2.0-7.0). Electrocatalytic activity at the Co-O/CN-Co modified electrode was evaluated with respect to solution pH, film thickness, supporting electrolyte ions, potential scan rate, operating potential, concentration dependence and other variables. The Co-O/CN-Co film electrode was completely compatible with a conventional reversed-phase liquid chromatographic (RP-LC) system. Practical RP-LC amperometric detection (RP-LCEC) of hydrazines was performed. A dynamic linear response range over three orders of magnitude and a detection limit at the pmol level were readily obtained. The Co-O/CN-CO film electrode exhibited excellent electrocatalytic stability in the flowing streams.

ELECTROCATALYTIC OXIDATION AND FLOW DETECTION OF HYDRAZINE COMPOUNDS IN LIQUID-CHROMATOGRAPHY AT A VITAMIN-B-12 ADSORBED GLASSY-CARBON ELECTRODE

A vitamin B-12 chemically modified electrode (CME) was constructed by adsorption of vitamin B-12 onto a glassy carbon surface. The electrode catalyzes the electrooxidation of hydrazine compounds over a wide pH range. The electrocatalytic behavior of hydrazines is elucidated with respect to the CME preparation conditions, solution pH, operating potential, mobile phase flow rate, and other variables. When applied to liquid chromatographic detection of the analytes, the vitamin B-12 CME yielded a linear response range over 2 orders of magnitude, and detection limits at the picomole level. The vitamin B-12 CME offers acceptable catalytic stability in both batch and flow systems.

Sol-gel-derived graphite organosilicate composite electrodes bulk-modified with Keggin-type alpha-germanomolybdic acid

A novel inorganic-organic hybrid material incorporating graphite powder and Keggin-type alpha -germanomolybdic acid (GeMo12) in methyltrimethoxysilane-based gels has been produced by the sol-gel technique and used to fabricate a chemically bulk-modified electrode. GeMo12 acts as a catalyst, graphite powder ensures conductivity by percolation, the silicate provides a rigid porous backbone, and the methyl groups endow hydrophobicity and thus limit the wetting section of the modified electrode. The GeMo12-modified graphite organosilicate composite electrode was characterized by cyclic and square-wave voltammetry. The modified electrode shows a high electrocatalytic activity toward the reduction of bromate, nitrite and hydrogen peroxide in acidic aqueous solution. In addition, the chemically-modified electrode has some distinct advantages over the traditional polyoxometalate-modified electrodes, such as long-term stability and especially repeatability of surface-renewal by simple mechanical polishing.

Sensitive determination of Cd and Pb by differential pulse stripping voltammetry with in situ bismuth-modified zeolite doped carbon paste electrodes

Here we investigated the analytical performances of the bismuth-modified zeolite doped carbon paste electrode (BiF-ZDCPE) for trace Cd and Pb analysis. The characteristics of bismuth-modified electrodes were improved greatly via addition of synthetic zeolite into carbon paste. To obtain high reproducibility and sensitivity, optimum experimental conditions for bismuth deposition Were Studied.

Antioxidant Sensors Based on Iron Diethylenetriaminepentaacetic Acid, Hematin, and Hemoglobin Modified TiO2 Nanoparticle Printed Electrodes

Antioxidant amperometric sensors based on iron-containing complexes and protein modified electrodes were developed. Indium tin oxide glass was printed with TiO2 nanoparticles, onto which iron-containing compounds and protein were adsorbed. When applied with negative potentials, the dissolved oxygen is reduced to H2O2 at the electrode surface, and the H2O2 generated in situ oxidizes Fe-II to Fe-III, and then electrochemical reduction of Fe-III therefore gives rise to a catalytic current. In the presence of antioxidants, H2O2 was scavenged, the catalytic current was reduced, and the decreased current signal was proportional to the quantity of existing antioxidants. A kinetic model was proposed to quantify the H2O2 scavenging capacities of the antioxidants. With the use of the sensor developed here, antioxidant measurements can be done quite simply: put the sensor into the sample solutions (in aerobic atmosphere), perform a cathodic polarization scan, and then read the antioxidant activity values. The present work can be complementary to the previous studies of antioxidant sensor techniques based on OH radicals and superoxide ions scavenging methods, but the sensor developed here is much easier to fabricate and use.

Carbon ceramic electrodes bulk-modified with nanoparticles of ferrocenebutyrate-intercalated Mg-Al layered double hydroxide

Ferrocenebutyrate-intercalated layered double hydroxide (FcLDH) was prepared by the coprecipitation method and characterized by PXRD, FTIR, TEM and elemental analysis. FcLDH nanoparticles in deionized water were deposited onto the surface of graphite powder to yield graphite powder-supported FcLDH, which was subsequently dispersed into methyltrimethoxysilane-derived gels to fabricate surface-renewable, stable, rigid carbon ceramic electrodes containing the electroactive ferrocenyl group. Cyclic voltammetric study revealed that peak currents of the FcLDH-modified electrode were diffusion-con trolled in 0.1 mol l(-1) KCl aqueous solution. In addition, the formal potential of the modified electrode is related to the activity of chloride ion with a Nernst slope of 56 mV per decade.

Cupric hexacyanoferrate nanoparticle modified carbon ceramic composite electrodes

Graphite powder-supported cupric hexacyanoferrate (CuHCF) nanoparticles were dispersed into methyltrimethoxysilane based gels to produce a conducting carbon ceramic Composite, which was used as electrode material to fabricate surface- renewable CuHCF-modified electrodes. Electrochemical behavior of the CuHCF-modifled carbon ceramic composite electrodes was characterized using cyclic and square-wave voltammetry. Cyclic voltammograms at various scan rates indicated that peak currents were surface-confined at low scan rates. In the presence of glutathione, a clear electrocatalytic response was observed at the CuHCF-modified composite electrodes. In addition, the electrodes exhibited a distinct advantage of reproducible surface-renewal by simple mechanical polishing on emery paper, as well as ease of preparation, and good chemical and mechanical stability in a flowing stream.

Renewable three-dimensional Prussian blue modified carbon ceramic electrode

Prussian blue (PB) supported on graphite powder was prepared by the chemical deposition technique and subsequently dispersed into methyltrimethoxysilane-derived gels to yield a conductive graphite organosilicate composite. The composite was used as the electrode material to fabricate a three-dimensional PB-modified electrode. PB acts as a catalyst, graphite powder ensures conductivity by percolation, the silicate provides a rigid porous backbone, and the methyl groups endow hydrophobicity and thus limit the wetting section of the modified electrode. The chemically modified electrode can electrocatalyze the oxidation of hydrazine, and exhibits a distinct advantage of polishing in the event of surface fouling, as well as simple preparation, good chemical and mechanical stability and good repeatability of surface-renewal. Hydrodynamic voltammetric experiments were performed to characterize the electrode as an amperometric sensor for the determination of hydrazine. (C) 2000 Elsevier Science B.V. All rights reserved.

Electrocatalytic reduction of O-2 and H2O2 at the glass carbon electrode modified with microperoxidase-11

Electrocatalytic reduction of O-2 and H2O2 at the glass carbon electrode modified with microperoxidase-11 immobilized with Nafion film has been studied by means of cyclic voltammetry and rotating disk electrode techniques. The modified electrode shows high catalytic activity toward the reduction of both O-2 and H2O2. The rate constants of Oz and H2O2 reduction at the modified electrode have been measured and compared. It is found that O-2 undergoes a four-electron reduction at the modified electrode and the catalytic activity for the reduction of O-2 is dependent on the pH of the solutions.

Construction of a heteropolyanion-modified electrode by a two-step sol-gel method and its electro catalytic applications

The sol-gel technique was used here to construct heteropolyanion-containing modified electrodes. This involves two steps, i.e. the first forming a functionalized sol-gel thin film on the surface of the glassy carbon electrode and then immersing the electrode into a heteropolyanion solution to incorporate the heteropolyanion into the sol-gel film. Here a Dawson-type heteropolyanion, K6P2W18O62 (P2W18), was used as a representative to illuminate the behavior of the as-prepared composite film. The electrochemical performance of the P2W18-modified electrode was studied with respect to the pH effect and long-term stability. The modified electrode exhibited a high electrocatalytic response for the reduction of BrO3- and NO2-. Steady-state amperometry was applied to characterize the electrode as an amperometric sensor for the determination of NO2-. The sensor had a linear range from 0.02 to 34 mM and a detection limit of 5 x 10(-6) M. (C) 2001 Elsevier Science B.V. All rights reserved.

Investigation of oxygen- and hydrogen peroxide-reduction on platinum particles dispersed on poly(o-phenylenediamine) film modified glassy carbon electrodes

Composite membrane modified electrodes were prepared by electrochemical deposition of platinum particles in a poly(o-phenylenediamine) (PPD) him coated on glassy carbon (GC) electrodes. The modified electrodes showed high catalytic activity towards the reduction of oxygen and hydrogen peroxide. A four-electron transfer process predominated the reduction process. The pH dependence and the stability of the electrodes were also studied.

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.

DIRECT ELECTROCHEMISTRY AND SURFACE CHARACTERIZATION OF GLUCOSE-OXIDASE ADSORBED ON ANODIZED CARBON ELECTRODES

The glassy carbon electrode (gce) and highly oriented pyrolytic graphite (hopg) were electrochemically anodized at a potential of +2.0 V (vs. Ag/AgCl) to create active sites and to improve the adsorption of glucose oxidase (GOD) and flavin adenine dinucle

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

化学修饰铋膜电极检测重金属镉

随着我国工业的快速发展，环境污染日益严重，其中重金属已经成为最主要的污染物 之一。重金属具有分布广泛、半衰期长等特点，因而对人们的生产生活危害巨大。镉作为 一种常见的重金属污染物，它能够引发废用性萎缩、肾功能衰竭和感染等疾病，因此对环 境中存在的痕量镉的进行检测显得极为重要。传统的痕量分析方法包括光谱分析法和色谱 分析法，但这两方法所使用的仪器比较笨重，操作过程复杂，因而不适于在线分析。电化 学分析方法因其快速、便携、价格低廉、灵敏度高等特点而受到了人们的广泛关注，其中 较为常用的阳极溶出伏安法已经在镉离子等重金属离子的现场快速高灵敏检测中发挥了 重要作用。然而传统阳极溶出法中使用的汞电极因具有毒性而被许多国家禁止使用，所以 寻找汞电极的替代电极成为近年来的阳极溶出技术的研究热点。铋膜电极因具有类似汞电 极的分析性能且环境友好而受到了广泛重视，特别是各种化学修饰方法使得铋膜电极的性 能得到了显著提高。但是目前铋膜电极仍存在稳定性低、抗干扰能力差等问题，这些不足 严重制约了该类电极在重金属的阳极溶出分析中的应用。本文旨在通过新的化学修饰方法 解决铋膜电极应用中的瓶颈问题，发展具有优异分析性能的化学修饰铋膜电极应用于镉离 子等重金属离子的阳极溶出分析。本文的主要研究内容包括： l）以阳极溶出法测定镉离子为例，研究了化学修饰铋膜电极的响应特性，考察了富 集时间、富集电位、铋离子浓度、离子载体浓度和Nafion 浓度等实验条件对检测灵敏度的 影响。 2）将离子载体引入铋膜电极与Nafion 结合使用，研究了镉离子在该电极上的阳极溶 出响应，并探讨了铜、铅、铟三种金属离子对镉离子检测选择性的影响。将这种改良后的 化学修饰铋膜电极用于实际海水样品的检测，所得结果与ICP-MS 的测量结果基本一致。 3）将四氟硼酸钠引入铋膜电极与离子载体、碳纳米管结合使用，研究了镉离子在该 电极上的阳极溶出响应，考察了铜、铅、铟离子对镉离子测定的影响。 4）考察了电解富集和开路电位富集两种富集方式对电极灵敏度和选择性的影响。 实验表明：通过预富集，在未除氧的溶液中即可得到显著的镉离子溶出电流峰，且背 景噪音低；加入离子载体后，电极对目标金属有良好的选择性，可以在复杂基体条件下测 定重金属离子镉；电解富集条件下电极的的灵敏度较高，而开路电位富集条件下电极的选 择性较好。这种环保的无汞化学修饰电极为海水中重金属污染物的检测提供了新的手段。