Studies on Zeolite Modified Electrode(Ⅰ)─Ascorbic Acid Sensor Based on Carbon Paste Electrode Containing Fe(Ⅲ)Y Zeolite

A new ascorbic acid sensor constituted of carbon paste and Fe(Ⅲ)Y zeolite was studied.The characters of the sensor such as linear range. potential window、apparen Michaelis constant、response time、stability and accuracy wee investigated. The experimental results indicate that the analytical performance of the sensor is satisfactory.

Simultaneous Determination of Dopamine and L-Ascorbic Acid by Modified Carbon Paste Electrode with Ni (II) Cyclam Complex

The electroanalysis of dopamine (DA) and ascorbic acid (AA) by square wave voltammetry has been performed at a modified carbon paste electrode with macrocyclic ligand 1, 4, 8, 11-tetraazacyclotetradecane (cyclam) and monolayer of Ni (II) cyclam. In pH 7.2 buffer solutions, the electrostatic reaction of AA with di-positive monolayer shifts the oxidation potential to less positive potential, while the electrostatic repulsion of DA with the monolayer shifts the oxidation potential of DA to more positive potential. The separation between the oxidation peaks of AA and DA at the present di-positive monolayer modified electrode (252 mV) was larger than that (187 mV) at the cyclam modified electrode. In addition, the catalytic oxidation of AA by oxidized DA has been advantageously eliminated at the modified carbon paste electrode with cyclam and Ni (II) cyclam complex. Thus, the determination of DA in the presence of an excess of AA is possible with the present modified electrodes.

VOLTAMMETRIC BEHAVIOR OF ASCORBIC ACID AT α-CYCLODEXTRIN INCORPORATED CARBON NANOTUBES-COATED ELECTRODE

制备了α -环糊精掺杂纳米碳管涂层电极并应用于抗坏血酸的电催化氧化 ,结果表明 ,氧化电位降低了 2 80mV ,电流响应明显增加。我们首次结合两种物质的特性 :纳米碳管的导电性及催化性能、α -环糊精的分子认知能力 ,对电极表面进行修饰。实验了抗坏血酸与α -环糊精超分子络合物的特性。差示脉冲技术用于定量分析抗坏血酸 ,线性范围为 2 .5× 10 -6～ 1.0× 10

Electrochemical determination of vitamin C in the presence of uric acid by a novel TiO_2 nanoparticles modified carbon paste electrode

The electrochemical behavior of vitamin C（ascorbic acid or AA） is investigated on the surface of a carbon-paste electrode modified with TiO2 nanoparticles and 2,2＇-（1,2 butanediylbis（nitriloethylidyne））-bis-hydroquinone（BBNBH）.The prepared modified electrode showed an efficient catalytic role in the electrochemical oxidation of AA,leading to remarkable decrease in oxidation overpotential and enhancement of the kinetics of the electrode reaction.This modified electrode exhibits well-separated oxidation peaks for AA and uric acid（UA）.The modified electrode is successfully applied for the accurate determination of AA in pharmaceutical preparations.

Cyclic Voltammetry Determination of Epinephrine with a Nano-gold Modified Glassy Carbon Electrode in the Presence of High Concentration Ascorbic Acid

Nano-gold (NG) modified glassy carbon electrodes (GCEs) were used for determination of epinephrine (EP) in the presence of high concentration ascorbic acid (AA) by cyclic voltammetry (CV). This modified electrode can not only catalytically oxidize EP and AA, but also separate the catalytic peak potentials of EP and AA by about 183.5 mV. In pH = 7.0 ogisogate byffer solution, the linear range of epinephrine was 5 106 ~ 1 ?10-4 mol/L.

Stripping Voltammetric Determination of Uranium in Water Samples Using Hg-Thin Film Modified Multiwall Carbon Nanotube Incorporated Carbon Paste Electrode

The variables affecting determination of ultra trace levels of uranium (VI) in aqueous samples by differential pulse cathodic stripping voltammetry were examined in detail using Hg-thin film modified carbon paste and multiwall carbon nanotube (MWCNT) incorporated carbon paste electrode. Carbon paste electrode prepared in the laboratory was modified with Hg thin film and used as the working electrode. MWCNT was incorporated into the carbon paste for enhancement in sensitivity of the measurements. Electrochemical response for the uranium (VI) reduction peak was found to be well resolved on the thin mercury film modified carbon paste surface and also with the MWCNT modification. Characteristics of the adsorption preconcentration process were investigated using electrochemical impedance measurements. Electrochemical signals were observed to be enhanced on MWCNT modification of the carbon paste.

Square wave voltammetric quantification of folic acid,uric acid and ascorbic acid in biological matrix

Nowadays, modified electrodes with metal nanoparticles have appeared as an alternative for the electroanalysis of various compounds. In this study, gold nanoparticles（GNPs） were chosen as interesting metal nanoparticles for modifying carbon paste electrode（CPE）. GNPs and the gold nanoparticles-modified carbon paste electrode（GNPs/CPE） were characterized by UV–Vis spectroscopy, transmission electron microscopy（TEM） and scanning electron microscopy（SEM）. GNPs/CPE as a simple and sensitive electrode was used to study three important biological molecules： folic acid（FA）, uric acid（UA） and ascorbic acid（AA）. Square wave voltammetry（SWV） was used as an accurate technique for quantitative measurements. A good linear relation was observed between anodic peak current（ipa） and FA（5.2 × 10（-6）– 2.5 × 10（-5）M）, UA（1.2 × 10（-6）– 2.1 × 10（-5）M） and AA（1.2 × 10（-6）– 2.5 × 10（-5）M） concentrations in simultaneous determination of these molecules.

Determination of captopril in patient human urine using ferrocenemonocarboxylic acid modified carbon nanotubes paste electrode

In this work,we describe a new strategy for the electrochemical determination of captopril（CA） using ferrocenemonocarboxylic acid as a mediator and multiwall carbon nanotubes as sensors in aqueous solution at pH 7.0.The diffusion coefficient（D）,and the kinetic parameters such as electron transfer coefficient（α）.and heterogeneous rate constant（kh）,for CA were also determined using electrochemical approaches.Under the optimized conditions,the electrocatalytic oxidation peak current of captopril showed two linear dynamic ranges with a detection limit of 0.3×10^-6 mol L^-1 captopril.The linear calibration range was 0.8×10^（-6） to 65×10^-6 mol L^-1 using cyclic voltammetry.Finally,this modified electrode was also examined as a selective,simple and precise new electrochemical sensor for the determination of captopril in real samples such as drug and patient human urine.

A novel ZnO/reduced graphene oxide and Prussian blue modified carbon paste electrode for the sensitive determination of Rutin

A carbon paste modified sensor based on a novel composite of zinc oxide nanoparticles deposited on reduced graphene oxide(ZnO-rGrO) and Prussian blue(PB) was drop-cast(ZnO-rGrO-PB/MCPE) for the sensitive estimation of Rutin(Rtn) at pH 7.0.The high surface area of ZnO-rGrO and electrocatalytic property of PB promotes the oxidation of Rtn. Field emission scanning electron microscope(FE-SEM) and energy-dispersive X-ray spectroscopy(EDX) techniques were employed to confirm the deposition of ZnO-rGrO and PB on carbon paste electrode(CPE). The ability of ZnO-rGrO-PB/MCPE in charge transfer at the interface was investigated using electrochemical impedance spectroscopy(EIS). The heterogeneous rate constant(ks) and the charge transfer coefficient(α) have been calculated as 6.08 s^(-1) and 0.74 respectively. This sensor showed a wide linear response for Rtn from 7.0×10^(-8)to 7.0×10^(-6) M and 7.0×10^(-6) to 1.0×10^(-4) M with a limit of detection(2.05±0.04)×10^(-8) M(S/N=3). The application of ZnO-rGrO-PB/MCPE was found in the analysis of Rtn in fruit juice samples using standard addition method. This sensor showed good reproducibility, stability, selectivity and sensitivity.

A New Two Plant Tissue－based Carbon Paste Microelectrode for Neurotransmitter Detection

Presented in this paper is a biosensor constructed for the determination of neurotransmitters. It is an eggplant-banana-tissue-based carbon paste microelectrode. As oxidative enzymes in banana tissue can bio-catalytically oxidize dopamine (DA), norepinephrine(NE), L-dopa, etc, the biosensor's sensitivity is improved. Because of the ability of eggplant tissue to eliminate the oxidation of ascorbic acid (AA), the signal of AA is a steady-state response. and thereby the selectivity of the biosensor is enhanced. The effect of experimental conditions such as pH, temperature, ratio of two plant tissues, response time, and linear range were evaluated in order to optimize the analytical performance. The detection limit for DA is 3. 2 × 10-7 mol/L.Our results showed that the idea of multienzyme system is applicable to the plant tissue-based carbon paste microelectrodes.

Simultaneous determination of cysteamine and folic acid in pharmaceutical and biological samples using modified multiwall carbon nanotube paste electrode

A carbon paste electrode（CPE） chemically modified with multiwall carbon nanotubes and ferrocene（FC） was used as a selective electrochemical sensor for the simultaneous determination of trace amounts of cysteamine（CA） and folic acid（FA）.This modified electrode showed very efficient electrocatalytic activity for the anodic oxidation of CA.The peak current of differential pulse voltammograms of CA and FA increased linearly with their concentration in the ranges of 0.7-200μmol/L CA and 5.0- 700μmol/L FA.The detection limits for CA and FA were 0.3μmol/L and 2.0μmoI/L,respectively.The diffusion coefficient（D） and transfer coefficient（α） of CA were also determined.These conditions are sufficient to allow determination of CA and FA both individually and simultaneously.

四氰基醌二甲烷修饰碳糊电极电催化氧化测定抗坏血酸

本文用四氰基醌二甲烷(Tetracyanoquinodimethane)(TCNQ)作价体,制成 TCNQ-碳糊电极,研究了该电极的性能。电极对水溶液中的抗坏血酸(AH_2)在较宽的PH和浓度范围内均有良好的电催化氧化作用,电极的稳定性良好,在AH_2浓度5.0×10(-5)～5.0×10～(-2)mol/L范围内,催化峰电流与AH_2浓度呈线性关系,响应时间小于 30s。

羧基化碳纳米管嵌入石墨修饰电极对多巴胺和抗坏血酸的电催化

采用涂层和嵌入修饰法 ,将羧基化多层碳纳米管制成两种修饰电极。以多巴胺 (DA)和抗坏血酸(AA)为模型化合物 ,研究了两种修饰电极对DA和AA共存时的电催化作用。结果表明 :嵌入的方式比涂层的方式显示了更多的优点。嵌入修饰电极不仅使峰电流增加 ,并且使两者共存时的氧化峰位分离达 16 0mV ,同时 ,该电极对DA的响应灵敏于AA ,这有利于在大量的AA存在下实现对DA的测定。在 1× 10 - 3 mol/L的AA的存在下 ,还原电流的一阶导数与DA浓度在 5× 10 - 7～ 1× 10 - 4 mol/L范围内呈良好的线性关系 ;检测下限达 1× 10 - 7mol L。

碳纳米管修饰电极的孔性界面对电分离多巴胺和抗坏血酸的影响

制备了碳纳米管修饰电极 (镶嵌、涂层 ) ,并研究了电分离多巴胺 ( DA)和抗坏血酸 ( AA)的机理 .结果表明 ,该电极的表面有一个多孔性的立体界面层 ,不仅对 DA和 AA具有较强的电催化作用 ,而且二者的氧化峰电位差 (ΔEpa)达 2 5 0 m V以上 .用循环伏安法和差示脉冲伏安法研究了影响ΔEpa的因素 .分散剂的种类对 ΔEpa有很大的影响 ;多层碳纳米管的管径对 ΔEpa的影响较小 ,碳纳米管的种类 (单层、多层、螺旋型多层 )则有一定的区别 ;同一种碳纳米管经不同氧化强度的酸截短后 ,对 ΔEpa产生了明显影响 .这说明修饰电极的界面性质对电分离 DA和 AA有较大的影响 .

碳纳米管修饰电极对多巴胺和抗坏血酸的电催化氧化

研究了碳纳米管修饰玻碳电极 (NTCME)的制备方法及对多巴胺 (DA)和抗坏血酸 (AA)的电催化氧化作用。在磷酸盐缓冲溶液 (PBSpH 7.4)中 ,以NTCME为工作电极时 ,DA与AA的氧化电位分别为 0 .2 6和 0 .0 1V(vs.SCE) ,比在裸玻碳电极 (GC)上分别降低了 0 .0 7和 0 .6 2V。NTCME能消除DA与AA共存时测定的相互干扰。利用二阶导数卷积伏安法测定 ,DA与AA分别在 2 .0 0× 10 - 6～ 3.84× 10 - 4 和 7.99× 10 - 5～ 3.6 6× 10 - 3 mol L浓度范围内 ,峰高与浓度呈线性关系 ;检出限分别为 1.90× 10 - 7和 5 .96× 10 - 5mol L。

介孔硅修饰碳糊电极制备及其对DA、UA、AA混合样品的电化学响应

以离子液体化学修饰介孔硅(MCF-IL)为掺杂,制备出一种新型的碳糊电极(MCFIL/CPE),并研究了多巴胺(DA)、尿酸(UA)和抗坏血酸(AA)在该碳糊电极上的电化学行为。结果表明,DA、UA和AA在MCF-IL/CPE电极上分别表现出良好的电化学响应,而且三者的电化学信号互相不干扰,为三者的同时测定奠定基础,并进一步探究了DA、UA和AA在MCF-IL/CPE的电化学响应,确定了MCF-IL与石墨粉的最佳比例。结果表明,MCF-IL用量为17%和25%时,DA、UA和AA具有良好的电化学响应信号。在同时测定DA、UA和AA时,可以将MCF-IL用量固定为17%或25%。

固体石蜡碳糊硅钼酸电极的研制及应用

固体石蜡作粘合剂的碳糊电极在１０－４ｍｏｌ／Ｌ硅钼杂多酸溶液中活化后，其表面形成了杂多酸薄膜。电极对浓度为２．０×１０－５～１.０×１０－２ｍｏｌ／Ｌ范围的硅钼杂多酸有能斯特响应；斜率为２９．０ｍＶ，从而可间接测定硅。该电极选择性、稳定性较好，响应快，已用于矿泉水样中偏硅酸含量测定。

蒙脱石修饰碳糊电极测定氨基酸的研究 Ⅱ.酪氨酸的测定

本文报道蒙脱石修饰碳糊电板测定酪氨酸,在0.001 mol/L KCl-HCl(pH=2.0)溶液中开路富集,介质交换后微分脉冲阳极溶出伏安法测定,在0.5～2.5 μg/ml范围内有线性,检测限为63ng/ml。可避免其他氨基酸、微量元素和常量金属元素的干扰,直接用于氨基酸药物样品的分析,获得了满意的结果。还对酪氨酸在电极上的反应机理进行了探讨。

抗坏血酸在多壁碳纳米管修饰玻碳电极上的催化氧化

多壁碳纳米管(MWNTs)在质量分数为36%的HCl中超声纯化后于2.2mol/L的HNO3中超声氧化处理。处理好的MWNTs分散于N,N-二甲基甲酰胺(DMF)后滴加在玻碳电极表面制得MWNTs修饰电极(MWNTs/GCE),此电极对抗坏血酸(AA)有显著电催化氧化作用。在pH=4.0的B-R缓冲溶液中首次得到AA有2个分离良好的氧化峰,其电位分别在0.187和0.452V(vs.SCE)。根据AA分子与表面羧基化的MWNTs相结合后的电子传递性质对AA的2个氧化峰进行了初步解释。AA在MWNTs/GCE上的氧化为吸附控制的不可逆过程,其在电极表面的吸附量为1.02×10-9mol/cm2,2个氧化峰的电极反应标准速率常数分别为1.03×10-2和3.94×10-3s-1。应用MWNTs/GCE对AA的电催化氧化性质以微分脉冲伏安法对AA进行测定,在最佳实验条件下其线性范围为5.0×10-7～5.0×10-2mol/L,检测限为5.0×10-8mol/L(S/N=3)。

纳米金修饰玻碳电极在抗坏血酸共存下选择性测定多巴胺

利用电沉积的方式制备了纳米金 ( Nano- gold,NG)修饰玻碳电极 ( GCE)。该电极对多巴胺 ( DA)和抗坏血酸 ( AA)均有催化作用 ,且多巴胺在纳米金修饰玻碳电极上有较强的吸附作用。同时研究了磷酸缓冲溶液的 p H值和离子强度对 DA的电化学行为的影响。纳米金修饰玻碳电极在 DA和 AA的混合溶液中的循环伏安图上可观察到两个明显分开的氧化峰 ,峰电位差达到 1 5 0 m V。据此 ,提出了两种利用该电极在抗坏血酸共存下选择性测定多巴胺的方法 ,线性范围分别为 3.0× 1 0 - 6 ～1 .0× 1 0 - 4mol/ L和 1 .2 5× 1 0 - 6 ～ 1 .0× 1 0 - 4mol/ L。