A Novel Composite Electrode of Photocatalyst—TiO2／C Loading on the Surface of the Air （Oxygen） Electrode

The methods for preparing the H2O2 generating air (oxygen) electrode and the composite electrode of photocatalyst-TiO2/C loading on the surface of the air (oxygen) electrode were introduced.In the case of the composite electrode,the current efficiency of electro-generated H2O2 is higher than 80%(J≤15mA/cm^2).The degradation of aniline was used as an example to measure the influence of the composite electrode and compared with the system in which the air (oxygen) electrode and the photocatalyst-TiO2 were sqparated.The results confirmed that the composite electrode played an active role on accelerating the degradation rate of aniline.According to the measurement of the polarization curves of composite electrode and TiO2 photo anode,and of the adsorbing amount of aniline on the surface of the composite electrode,the principle of descending the recombination reta of photo-generated electron and hole and of enhancing the oxidation rate of organic molecule was described.The mechanism about the degradation of aniline was also discussed.     

超微电极技术与应用

综述超微电极的特点、分类、制备；超微电极在生物体细胞分析、单分子分析、固体电化学、化学动力学参数测定及痕量物质检测等方面的应用．     

铁氰酸钴膜电极的制备及特性

首次用电化学方法在玻碳基体上制成铁氰酸钻修饰膜电极(CHCF/GC).该电极非常稳定,可经受—1.0～0.9V(vs SCE)连续万次以上的电位扫描.讨论了CHCF膜电极的电荷传递过程,研究了影响CHCF膜电极伏安特性的各种因素和对Fe~(3+)/Fe~(2+)电对的催化作用。     

超微电极技术的发展现状

本文在阐述超微电极技术相关原理的基础上,总结了超微电极的特点、类型及研究方法,综述近十年来超微电极的制备与应用进展,并介绍了超微电极的发展现状。     

铅笔芯修饰聚苯胺制作微型复合pH电极的性能

在0.3mm直径的铅笔芯上电修饰聚苯胺,封入玻璃毛细管中,并与Ag/AgCl电极组合成复合微型pH电极.经实验测试,该电极的pH响应特性良好,在pH1～11的线性范围内,能斯特斜率为(-56.4±0.5)mV/pH,线性相关系数不小于0.996.作为参比的Ag/AgCl电极性能稳定.由于电极是复合微型化的,所以可用于活体微区测定.     

电极研究动态

2003年8月10～13日在加拿大Ottawa市召开的第39届国际纯粹化学与应用化学联合会大会的PH06专题组便是“电化学前沿”。电分析前沿是其中的一个重要组成部分，而电极的研究则是当前的热点。     

循环伏安法用于钇在钼和镍电极上的电极过程研究

使用了较为简单的数学方法,对不溶性反应产物的电极过程的循环伏安理论公式进行了推导。并将推导结果应用于LiCl—KCl—YCl_3熔盐体系,钇在钼电极上的电极过程研究,获得了很好的结果。同时还对钇在镍电极上阴极还原进行了研究,循环伏安结果表明钇和镍能够拖成金属间化合物。能谱及X射线衍射结果表明,金属间化合物的组成为Ni_2Y。     

燃料电池电极制作方法的研究

对燃料电池,性能良好的催化剂至关重要,它决定着大电流密度放电时的性能、成本和运行寿命［１］．但因电极上的反应是气、液、固三相反应,所以必须制备出高效的、结构合理的气体电极［２～３］,减小气相、液相传质阻力,提高三相接触性能,降低电极极化．Ｋ．Ｍｕｎｄ等［４～５］所制作的电极,气体扩散距离长,溶解气体的扩散电阻大．Ｒ．Ｐ．Ｉｃｚｋｏｗｓｋｉ等人［６］用ＰＴＦＥ（ｐｏｌｙｔｅｔｒａｆｌｕｏｒｏｅｔｈｙｌｅｎｅ,聚四氟乙烯）作疏水剂,在整个气体反应层制成气体扩散通道,改善了电极性能．后来,Ｓ．Ｍｏｔ…     

5—羟色胺敏感膜电极的研究 Ⅰ.离子缔合型5—羟色胺膜电极的研制

5-羟色胺(5-HT)与许多疾病的发生和发展有关。应用正交试验,研究了离子缔合型5-HT敏感膜电极的最优化膜组成。筛选了由3种定域体,7种增塑剂组成的213个配方,选定了以四苯硼-5-HT离子缔合物为活性物、磷酸三(2-乙基己基)酯为增塑剂的涂碳PVC膜电极。电极各项性能良好,其线性范围为1.00×10~(-2)～1.58×10~(-5)mol/L,检测下限为4.17×10~(-6)mol/L,斜率为59.7mV/p5-HT。电极寿命超过39天,用混合溶液法测定了体液中可能存在的17种物质的选择性系数。已用该电极测定了牛血小板中的5-HT。     

New Urea Biosensor Based on Urease Enzyme Obtained from Helycobacter pylori

The urease enzyme of Helicobacter pylori was isolated from biopsy sample obtained from antrum big curvature cell extracts. A new urea biosensor was prepared by immobilizing urease enzyme isolated from Helicobacter pylori on poly(vinylchloride) (PVC) ammonium membrane electrode by using nonactine as an ammonium ionophore. The effect of pH, buffer concentration, and temperature for the biosensor prepared with urease from H. pylori were obtained as 6.0, 5 mM, and 25 °C, respectively. We also investigated urease concentration, stirring rate, and enzyme immobilization procedures in response to urea of the enzyme electrode. The linear working range of the biosensor extends from 1 × 10(-5) to 1 × 10(-2) M and they showed an apparent Nernstian response within this range. Urea enzyme electrodes prepared with urease enzymes obtained from H. pylori and Jack bean based on PVC membrane ammonium-selective electrode showed very good analytical parameters: high sensitivity, dynamic stability over 2 months with less decrease of sensitivity, response time 1-2 min. The analytical characteristics were investigated and were compared those of the urea biosensor prepared with urease enzyme isolated from Jack bean prepared at the same conditions. It was observed that rapid determinations of human serum urea amounts were also made possible with both biosensors.     

Amperometric Urea Biosensor Using Aminated Glassy Carbon Electrode Covered with Urease Immobilized Carbon Sheet,Based on the Electrode Oxidation of Carbamic Acid

A large oxidation current can be observed when ammonium carbamate aqueous solution is electrolyzed using a glassy carbon electrode (GCE) at a potential exceeding 1.0 V vs. Ag/AgCl and amino groups are introduced at the surface of the GCE. Aminated GCE exhibits the electrocatalytic activity of the oxidation of ammonium carbamate that is produced from urea as an intermediate product of urease reaction, and a distinct oxidation current is observed when the aminated GCE is used to oxidize the urea in the urease solution. A novel amperometric determination method to detect urea has been developed. This method is based on the electrooxidation of carbamic acid produced during urease reactions. Urease is immobilized to polymaleimidostyrene (PMS) coated on the insulated amorphous carbon sheet set on the aminated GCE surface. A good linear relationship is observed between urea concentration and the electrolytic current of the urease‐immobilized electrode in the concentration range from 0.5 mM to 21.0 mM. The proposed urea biosensor has an effective merit in that the interference resulting from ammonia and pH change caused by the urease reaction can be eliminated, differing from conventional urea biosensors.     

A Powder Based Polyaniline Carbon Paste Electrode for Urea Analysis

A new polyaniline carbon paste electrode prepared by mixing polyaniline (emeraldine), nafion, graphite powder and urease for urea analysis was exploited. The ratio of polyaniline, nafion, urease and graphite for the construction of the electrodes and the optimal conditions for urea determination were studied. The detection limit of this sensor for urea is 5 μM and the linearity from 5 μM to 7.5 mM is obtained in FIA. This sensor has a response time of 90s and shows good reproducibility and stability (RSD, 6.3%, n = 43). The blood samples from a patient during blood dialysis were taken and analyzed. The urea concentrations in blood obtained from this sensor are comparable with urea test kit method.     

Preparation of a potentiometric immobilized urease electrode and urea determination in serum

Polyvinylalcohol was activated with 2-fluoro-1-methylpyridiniumtoluene-4-sulphonate and urease (EC.3.5.1.5) was covalently linked to the activated matrix. PVA-urease was then immobilized on the surface of a pH glass electrode with gelatine gel and it was cross-linked using glutaraldehyde. This potentiometric membrane electrode provides a linearity to urea in the 8.910⁻⁵ to 1.110⁻³ M concentration range, but by changing the buffer concentration can be studied in the range of 10⁻⁴ to 10⁻² M urea concentration. Reproducibility experiments (n:20) were carried out with the urease enzyme electrode and with photometric methods for pooled serum sample. Average values for the two methods were 5.96 and 5.86 mM, variation coefficients were 2.5 and 3.5% respectively.     

Enzyme coated glass pH-electrode: Its fabrication and applications in the determination of urea in blood samples

A new enzyme coated electrode for the determination of urea in blood samples has been developed. It is based on the encapsulation of urease enzyme in the porous silicate matrix by the sol-gel technique on a glass electrode for the purpose of sensing urea in blood samples. Various parameters like the effect of pH, selection of a suitable buffer of appropriate concentration and interference of common substances in blood samples have been evaluated to optimize the conditions for the determination of urea. The electrode can be used for the determination of urea in the concentration range 0.03-30.0 mM in a solution. The detection limit of the present enzyme-coated electrode is found to be 52 μg/ml of urea. The relative standard deviation for the electrode-to-electrode reproducibility is found to be 2.4% for the determination of 0.1 mM of urea (six replicate electrodes). Sol-gel matrix containing immobilized enzyme was stable for about 25 days at ∼4 °C with 80% urease activity. Urea content in various clinical blood samples has been estimated using this electrode and the results are found to be in good agreement with the standard clinical methods as reported in the literature.     

Tungsten electrode for urea

Tungsten electrodes for urea were prepared via covalent linking of urease on oxidized metal surfaces in different ways. The most stable electrodes were obtained when tungsten was silanized and activated by glutaraldehyde or hexamethylene diisocyanate. The electrode with urease coupled via glutaraldehyde was tested for optimum conditions of use. The nature of the buffer and its concentration and ionic strength are particularly important.     

An amperometric urea biosensor based on covalent immobilization of urease on copolymer of glycidyl methacrylate and vinylferrocene

A unique urea biosensor construction based on the direct covalent attachment of urease onto a polymeric electron transfer mediator, poly(glycidyl methacrylate-co-vinylferrocene)-coated electrode is described. Amperometric response was measured as a function of urea concentration, at a fixed potential of +0.35 V vs. Ag/AgCl in phosphate-buffered saline (pH 7.0). Covalent immobilization of the urease directly to the functionalized ferrocene copolymer surface produced biosensors with a short response time (about 3 s) and provided low detection limits. The stability, reusability, pH, and temperature response of the biosensor, besides its kinetic parameter, were also studied.     

A Novel Bioelectrochemical Sensor Based on Immobilized Urease on the Surface of Nickel Oxide Nanoparticle and Polypyrrole Composite Modified Pt Electrode

Nickel oxide nanoparticle (NiO?NP) and polypyrrole (PPy) composite were deposited on a Pt electrode for fabrication of a urea biosensor. To develop the sensor, a thin film of PPy?NiO composite was deposited on a Pt substrate that serves as a matrix for the immobilization of enzyme. Urease was immobilized on the surface of Pt/PPy?NiO by a physical adsorption. The response of the fabricated electrode (Pt/PPy?NiO/Urs) towards urea was analyzed by chronoamperometry and cyclic voltammetry (CV) techniques. Electrochemical response of the bio‐electrode was significantly enhanced. This is due to electron transfer between Ni²⁺ and Ni³⁺ as the electro‐catalytic group and the reaction between polypyrrole and the urease‐liberated ammonium. The fabricated electrode showed reliable and demonstrated perfectly linear response (0.7–26.7 mM of urea concentration, R²= 0.993), with high sensitivity (0.153 mA mM^?1 cm^?2), low detection of limit (1.6 μM), long stability (10 weeks), and low response time (～5 s). The developed biosensor was highly selective and obtained data were repeatable and reproduced using PPy‐NiO composite loaded with immobilized urease as urea biosensors.     

Metal-metal oxide enzyme electrodes for the determination of urea

Enzyme electrodes for urea assay based on metal-metal oxide (Sb, Bi, W, Ti + RuO₂) with urease immobilized in gelatin gel were examined. It was shown that the best electrodes were obtained for tungsten. The urea response of the electrodes was influenced by the pH and concentration of the buffer used. Increasing additions of inert salt (potassium chloride) change the pH characteristic of the tungsten electrode and buffer capacity, thus influencing the urea response of the electrode.     

A coated-metal enzyme electrode for urea determinations

A potentiometric enzyme electrode is reported in which an enzyme immobilized in polyvinyl chloride is used to coat an antimony metal electrode to detect changes in pH when the electrode is immersed in a solution of the enzyme substrat. As an example, urea is determined in solution by using immobilized urease on an antimony electrode, giving a linear concentration range of 5.0 × 10^-4–1.0 × 10^-2 M urea with a slope of 44 mV per decade change in urea concentration. The response slope is stable for about 1 week, with response times in the range 1–2 min, but with absolute potential changes occurring from day to day.