碳纳米管修饰电极上沙丁胺醇电催化氧化研究

将多壁碳纳米管(MWNT)分散在疏水性表面活性剂双十六烷基磷酸(DHP)溶液中形成稳定、均相的分散液,然后制备多壁碳纳米管-DHP复合膜修饰玻碳电极(MWNT-DHP/GCE).应用方波伏安法研究了沙丁胺醇在修饰电极上的电化学行为,结果表明,碳纳米管复合膜修饰电极对沙丁胺醇的氧化有良好的电催化活性,其氧化反应为一电子一质子过程,氧化电位比裸玻碳电极负移40 mV,峰电流增加了4.5倍.在最佳测试条件下,氧化峰电流与沙丁胺醇浓度在8.3×10-7~3.3×10-6mol/L范围内呈良好线性关系,开路富集2min,检出限达1.8×10-7mol/L.该修饰电极具有良好的重现性、稳定性.     

Electrochemical Characterization of Polymerized Cresol Red Film Modified Glassy Carbon Electrode and Separation of Electrocatalytic Responses for Ascorbic Acid and Dopamine Oxidation

A cresol red modified glassy carbon electrode was prepared using an electrochemical method. The cyclic voltammograms of the modified electrode indicate the presence of a couple of well-defined redox peaks, and the formal potential shifts in the negative direction with increasing solution pH. The modified electrode exhibits high electrocatalytic activity toward ascorbic acid oxidation, with an overpotential of 300 mV less than that of bare glassy carbon electrodes, and drastic enhancement of the anodic currents. The calibration graph obtained by linear sweep voltammetry for ascorbic acid is linear in the range of 50∼500 µM. The electrode markedly enhances the current response of dopamine and can separate the electrochemical responses of ascorbic acid and dopamine. The separation between the anodic peak potentials of ascorbic acid and dopamine is 190 mV by cyclic voltammetry. The linear sweep voltammetric peak currents for dopamine in the presence of 2 mM ascorbic acid vary linearly with a concentration of between 10 and 100 µM.     

Sensitive electrochemical detection of arsenic (III) using gold nanoparticle modified carbon nanotubes via anodic stripping voltammetry

Gold nanoparticles were deposited electrolessly on multiwalled carbon nanotubes (CNTs) via in situ reduction of HAuCl₄ by NaBH₄. The resulting gold covered nanotubes were immobilised onto the surface of a glassy carbon electrode via evaporation of a suspension in chloroform. Anodic stripping voltammetry was performed with the modified electrode in As(III) solutions. A limit of detection (LOD based on 3σ) of 0.1 μg L⁻¹ was obtained but more importantly a sensitivity of 1985 μA μM⁻¹ was obtained with square wave voltammetry (SWV) in an optimised system with a deposition time of 120 s. These values, particularly the high sensitivity compare favourably with previously reported methods in the area of electrochemical arsenic detection.     

A novel poly(taurine) modified glassy carbon electrode for the simultaneous determination of epinephrine and dopamine

A novel taurine modified glassy carbon electrode was prepared by electropolymerization method. The electrochemical behaviors of epinephrine (EP) and dopamine (DA) at the modified electrode were studied by cyclic voltammetry. The modified electrode exhibited enhanced sensitivity and excellent electrochemical discrimination to DA and EP. The cathodic peaks of the two species were well-separated with a potential difference of about 390 mV, so the poly(taurine) modified electrode was used for simultaneous voltammetric measurement of EP and DA by differential pulse voltammetry. Under the optimum conditions, the cathodic peak currents were linear to concentrations of EP and DA in the range of 2.0 × 10⁻⁶ to 6.0 × 10⁻⁴ mol L⁻¹ and 1.0 × 10⁻⁶ to 8.0 × 10⁻⁴ mol L⁻¹, respectively. The detection limits for EP and DA were 3.0 × 10⁻⁷ and 1.0 × 10⁻⁷ mol L⁻¹, respectively. Because the oxidation of ascorbic acid (AA) is an irreversible reaction at modified electrode, the interference of AA for determining EP and DA was eliminated. The modified electrode has been satisfactorily used for the simultaneous determination of EP and DA in pharmaceutical injections.     

Application of a Glassy Carbon Electrode Modified with Poly(Glutamic Acid) in Caffeic Acid Determination

Glassy carbon electrodes were coated with films of poly(glutamic acid) (PG), and the modified electrode proved to be very effective in the oxidation of caffeic acid. The performance of the film was also tested with ascorbic acid, coumaric acid, ferulic acid, sinapic acid and chlorogenic acid. At pH 5.6, all the hydroxycinnamic acids yield a higher peak current intensity when oxidized after incorporation in the PG-modified electrode, and only the oxidation of ascorbic acid exhibits overpotential reduction. At pH 3.5 only caffeic and chlorogenic acid are incorporated in the modified electrode and exhibit a well-defined oxidation wave at +0.51 V and +0.48 V, which is the base for their determination. Linear calibration graphs were obtained from 9 × 10⁻⁶ mol L⁻¹ to 4 × 10⁻⁵ mol L⁻¹ caffeic acid by linear voltammetric scan and from 4 × 10⁻⁶ mol L⁻¹ to 3 × 10⁻⁵ mol L⁻¹ by square wave voltammetric scan. The method was successfully applied to the determination of caffeic acid in red wine samples without interference from other hydroxycinnamic acids or ascorbic acid.     

Electrocatalytic Behavior of Glassy Carbon Electrodes Modified with Multiwalled Carbon Nanotubes and Cobalt Phthalocyanine for Selective Analysis of Dopamine in Presence of Ascorbic Acid

This work describes the development, electrochemical characterization and utilization of a cobalt phthalocyanine modified carbon nanotube electrode for the quantitative determination of dopamine in 0.2 mol L^?1 phosphate buffer contaminated with high concentration of ascorbic acid. The electrode surface was analyzed by cyclic voltammetry and electrochemical impedance spectroscopy which showed a modified surface presenting a charge transfer resistance of 500 Ω, against the 16.46 kΩ value found for the bare glassy carbon surface. A pseudo rate constant value of 5.4×10^?4 cm s^?1 for dopamine oxidation was calculated. Voltammetric experiments showed a shift of the peak potential of DA oxidation to less positive value at 390 mV as compared with that of a bare GC electrode at 570 mV. The electrochemical determination of dopamine, in presence of ascorbic acid in concentrations up to 0.1 mol L^?1 by differential pulse voltammetry, yielded a detection limit as low as 2.56×10^?7 mol L^?1.     

Electrochemical Characterization of Pyrocatechol Sulfonephthalein-Modified Glassy Carbon Electrode and Separation of Electrocatalytic Responses for Ascorbic Acid and Dopamine Oxidation

A pyrocatechol sulfonephthalein- (PS-) modified glassy carbon (PS/GC) electrode has been prepared by adsorption of PS on a glassy carbon electrode surface. Cyclic voltammograms of the PS/GC electrode indicate the presence of a couple of well-defined redox peaks, and the formal potential shifts in the negative direction with increasing solution pH. The relation between formal potential,E^0′, and solution pH can be fit to the equationE^0′(mV) = −51.4 pH + 538.7. The PS/GC electrode shows high electrocatalytic activity toward ascorbic acid oxidation, with an overpotential ca. 380 mV less than that of the bare electrode and a drastic enhancement of the anodic currents. The electrocatalytic reaction rate constant (k), which was decreased with increasing concentration of H₂A, was determined using rotating disk electrode measurements. The values ofkwas also affected by the solution pH. The electrode can also separate the electrochemical responses of ascorbic acid and dopamine. The separation between the anodic peak potentials of ascorbic acid and dopamine is more than 50 mV by the differential pulse voltammetry.     

Electrochemical behavior and voltammetric determination of tryptophan based on 4-aminobenzoic acid polymer film modified glassy carbon electrode

Herein, a novel electrochemical method was developed for the determination of tryptophan based on the poly(4-aminobenzoic acid) film modified glassy carbon electrode (GCE). The electrochemical behaviors of tryptophan at the modified electrode were investigated. It was found that the oxidation peak current of tryptophan at the modified GCE was greatly improved compared with that at the bare GCE. The effects of supporting electrolyte, pH value, scan rate, accumulation potential and time were examined. The oxidation peak current of tryptophan was proportional to its concentration over the range from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹. The limit of detection was evaluated to be 2.0 × 10⁻⁷ mol L⁻¹. The proposed method was sensitive and simple. It was successfully employed to determine tryptophan in pharmaceutical samples.     

Direct electrochemical determination of carbaryl using a multi-walled carbon nanotube/cobalt phthalocyanine modified electrode

The electrochemical detection of carbaryl at low potentials, in order to avoid matrix interferences, is an important challenge. This study describes the development, electrochemical characterization and utilization of a glassy carbon (GC) electrode modified with multi-wall carbon nanotubes (MWCNT) plus cobalt phthalocyanine (CoPc) for the quantitative determination of carbaryl in natural waters. The surface morphology was examined by scanning electron microscopy, enhanced sensitivity was observed with respect to bare glassy carbon and electrocatalytic effects reduced the oxidation potential to +0.80 V vs. SCE in acetate buffer solution at pH 4.0. Electrochemical impedance spectroscopy was used to estimate the rate constant of the oxidation process and square-wave voltammetry to investigate the effect of electrolyte pH. Square-wave voltammetry in acetate buffer solution at pH 4.0, allowed the development of a method to determine carbaryl, without any previous step of extraction, clean-up, or derivatization, in the range of 0.33-6.61 μmol L⁻¹, with a detection limit of 5.46 ± 0.02 nmol L⁻¹ (1.09 ± 0.02 μg L⁻¹) in water. Natural water samples spiked with carbaryl and without any purification step were successfully analyzed by the standard addition method using the GC/MWCNT/CoPc film electrode.     

Electrochemical Investigations of the Anticancer Drug Idarubicin Using Multiwalled Carbon Nanotubes Modified Glassy Carbon and Pyrolytic Graphite Electrodes

The effect of surface modifications on the electrochemical behavior of the anticancer drug idarubicin was studied at multiwalled carbon nanotubes modified glassy carbon and edge plane pyrolytic graphite electrodes. The surface morphology of the modified electrodes was characterized by scanning electron microscopy. The modified electrodes were constructed for the determination of idarubicin using adsorptive stripping differential pulse voltammetry. The experimental parameters such as supporting electrolyte, pH, accumulation time and potential, amount of carbon nanotubes for the sensitive assay of idarubicin were studied as details. Under the optimized conditions, idarubicin gave a linear response in the range 9.36×10^?8–1.87×10^?6 M for modified glassy carbon and 9.36×10^?8–9.36×10^?7 M for modified edge plane pyrolytic graphite electrodes. The detection limits were found as 1.87×10^?8 M and 3.75×10^?8 M based on modified glassy carbon and edge plane pyrolytic graphite electrodes, respectively. Interfering species such as ascorbic acid, dopamine, and aspirin showed no interference with the selective determination of idarubicin. The analyzing method was fully validated and successfully applied for the determination of idarubicin in its pharmaceutical dosage form. The possible oxidation mechanism of idarubicin was also discussed. The results revealed that the modified electrodes showed an obvious electrocatalytic activity toward the oxidation of idarubicin by a remarkable enhancement in the current response compared with bare electrodes.     

Simultaneous Determination of Hydroquinone and Catechol at a Glassy Carbon Electrode Modified with Multiwall Carbon Nanotubes

A simply and high selectively electrochemical method for simultaneous determination of hydroquinone and catechol has been developed at a glassy carbon electrode modified with multiwall carbon nanotubes (MWNT). It was found that the oxidation peak separation of hydroquinone and catechol and the oxidation currents of hydroquinone and catechol greatly increase at MWNT modified electrode in 0.20 M acetate buffer solution (pH 4.5). The oxidation peaks of hydroquinone and catechol merge into a large peak of 302 mV (vs. Ag/AgCl, 3 M NaCl) at bare glassy carbon electrode. The two corresponding well‐defined oxidation peaks of hydroquinone in the presence of catechol at MWNT modified electrode occur at 264 mV and 162 mV, respectively. Under the optimized condition, the oxidation peak current of hydroquinone is linear over a range from 1.0×10^?6 M to 1.0×10^?4 M hydroquinone in the presence of 1.0×10^?4 M catechol with the detection limit of 7.5×10^?7 M and the oxidation peak current of catechol is linear over a range from 6.0×10^?7 M to 1.0×10^?4 M catechol in the presence of 1.0×10^?4 M hydroquinone with the detection limit of 2.0×10^?7 M. The proposed method has been applied to simultaneous determination of hydroquinone and catechol in a water sample with simplicity and high selectivity.     

Amperometric Detection of Morphine at Preheated Glassy Carbon Electrode Modified with Multiwall Carbon Nanotubes

A highly sensitive and fast responding sensor for the determination of morphine is described. The multiwall carbon nanotubes immobilize on preheated glassy carbon electrode (5 min at 50 °C) by gently rubbing of electrode surface on a filter paper supporting the carbon nanotubes.The results indicated that carbon nanotubes(CNTs) modified glassy carbon electrode exhibited efficiently electrocatalytic oxidation for morphine with relatively high sensitivity, stability and long life. Under conditions of cyclic voltammetry, the potential for oxidation of morphine is lowered by approximately 100 mV and the current is enhanced significantly (10 times) in comparison to the bare glassy carbon electrode at wide pH range (2–9). The electrocatalytic behavior is further exploited as a sensitive detection scheme for morphine determination by hydrodynamic amperometry. Under the optimized conditions the calibration plots are linear in the concentration range 0.5–150 μM with the calculated detection limit (S/N=3) of 0.2 μM and sensitivity of 10 nA/μM and a relative standard deviation (RSD) of 2.5% (n=10). The amperometric response is extremely stable, with no loss in sensitivity over a continual 30 min operation. Such attractive ability of multiwall carbon nanotubes (MWCNTs) modified GC electrode, suggests great promise for a morphine amperometric sensor. Finally the ability of the modified electrode was evaluated for simultaneous determination of morphine and codeine.     

苦参碱在多壁碳纳米管修饰玻碳电极上的电催化氧化及其电分析方法

研究了苦参碱(Matrine, MT) 在多壁碳纳米管修饰玻碳电极(MWCNT/GCE)上的电化学行为. 与GCE相比, MT在MWCNT/GCE上峰电位负移120 mV, 峰电流增大约2.5倍, 表明MWCNT/GCE对MT的电化学氧化具有良好的催化作用. 同时测定并计算了MT在MWCNT/GCE上的电极过程动力学参数: 电子转移系数α、电极反应速率常数ks、扩散系数D. 运用差分脉冲伏安法对苦参碱样品含量进行测定, 相对标准偏差为0.12%～2.9%, 加标回收率为98.4%～99.0%. 该方法可用于MT的电化学定量测定.     

Modified glassy carbon electrode by electropolymerization of tetrakis-(2-aminopheny)porphyrin for the determination of norepinephrine in the presence of ascorbic acid

A glassy carbon electrode (GCE) was modified with electropolymerization of meso-tetrakis(2-aminophenyl)porphyrin (TAPP) in acetonitrile by cyclic voltammetry (CV). The voltammetric behavior of norepinephrine (NE) in the presence of excess ascorbic acid (AA) was investigated at the modified electrode by cyclic and square wave voltammetry (SWV) in phosphate buffer solution. The modified electrode gave higher selectivity and highly effective electroactivity to NE oxidation in voltammetric measurements of NE in the presence of AA and epinephrine. In pH 7.4 phosphate buffer solution, the peak current increased linearly with the concentration of NE in two concentration ranges of 1.0×10⁻⁶ to 5.0×10⁻⁵ mol dm⁻³.     

The NADH Electrochemical Detection Performed at Carbon Nanofibers Modified Glassy Carbon Electrode

In this work, the capability of carbon nanofibers to be used for the design of catalytic electrochemical biosensors is demonstrated. The direct electrochemistry of NADH was studied at a glassy carbon electrode modified using carbon nanofibers. A decrease of the oxidation potential of NADH by more than 300 mV is observed in the case of the assembled carbon nanofiber‐glassy carbon electrode comparing with a bare glassy carbon electrode. The carbon nanofiber‐modified electrode exhibited a wide linear response range of 3×10^?5 to 2.1×10^?3 mol L^?1 with a correlation coefficient of 0.997 for the detection of NADH, a high specific sensitivity of 3637.65 (μA/M cm²), a low detection of limit (LOD=3σ) of 11 μM, and a fast response time (3 s). These results have confirmed the fact that the carbon nanofibers represent a promising material to assemble electrochemical sensors and biosensors.     

Covalent modification of a glassy carbon electrode with penicillamine for simultaneous determination of hydroquinone and catechol

A simple and highly selective electrochemical method has been developed for the simultaneous determination of hydroquinone (HQ) and catechol (CC) at a glassy carbon electrode covalently modified with penicillamine (Pen). The electrode is used for the simultaneous electrochemical determination of HQ and CC and shows an excellent electrocatalytical effect on the oxidation of HQ and CC upon cyclic voltammetry in acetate buffer solution of pH 5.0. In differential pulse voltammetric measurements, the modified electrode was able to separate the oxidation peak potentials of HQ and CC present in binary mixtures by about 103 mV although the bare electrode gave a single broad response. The determination limit of HQ in the presence of 0.1 mmol L⁻¹ CC was 1.0 × 10⁻⁶ mol L⁻¹, and the determination limit of CC in the presence of 0.1 mmol L⁻¹ HQ was 6.0 × 10⁻⁷ mol L⁻¹. The method was applied to the simultaneous determination of HQ and CC in a water sample. It is simple and highly selective.     

聚多巴胺/多壁碳纳米管/玻璃碳电极上多巴胺的电分析

基于多巴胺（DA）在多壁碳纳米管（MWCNTs）修饰玻璃碳（GC）电极上的电聚合,制得聚多巴胺(PDA)/MWCNTs/GC电极,并对该修饰电极进行了电化学阻抗谱 (EIS)和循环伏安法(CV)表征。 在该修饰电极上,DA呈现良好的电化学行为。在pH=7.4磷酸缓冲溶液中其氧化电流显著高于在裸电极上的响应,且能有效地抑制2.0 mmol/L抗坏血酸(AA)或K4Fe(CN)6的直接电化学响应,表明MWCNTs可增敏信号,且阳离子选择透过性PDA膜可抑制阴离子的电化学干扰。 采用CV实验检测DA,DA氧化的半微分伏安峰高(ipa-sd)与多巴胺浓度在0.08～1.76 μmol/L范围内呈线性关系,在无抗坏血酸和有0.5 mmol/L抗坏血酸共存时的线性回归方程分别为ipa-sd(μA/s1/2)=0.107+0.405c(μmol/L)（r2=0.986）和ipa-sd(μA/s1/2)=0.628+0.649c(μmol/L)(r2=0.992),检测限均为8.0×10-8 mol/L(S/N=3)。 该法用于盐酸多巴胺注射液中多巴胺的快速测定,结果满意。     

对乙酰氨基酚在多壁碳纳米管修饰电极上的电化学行为

制备了多壁碳纳米管修饰玻碳电极,研究了对乙酰氨基酚在多壁碳纳米管修饰电极上的循环伏安行为,并建立了测定对乙酰氨基酚含量的电化学分析方法。在pH为6.89的磷酸盐缓冲液中,多壁碳纳米管修饰电极对对乙酰氨基酚有明显的电催化作用,其氧化峰电流与对乙酰氨基酚浓度在1.0×10-6～1.0×10-4mol·L-1范围内呈良好的线性关系,检测限为2.0×10-7mol·L-1。     

Electrochemical behaviors of ofloxacin and its voltammetric determination at carbon nanotubes film modified electrode

A multi-wall carbon nanotubes (MWNTs)-Nafion film-coated glassy carbon electrode (GCE) was fabricated and the electrochemical behavior of ofloxacin on the MWNTs-Nafion film-coated GCE were investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The oxidation peak current of ofloxacin increased significantly on the MWNTs-Nafion film modified GCE compared with that using a bare GCE. This nano-structured film electrode exhibited excellent enhancement effects on the electrochemical oxidation of ofloxacin. A well-defined oxidation peak attributed to ofloxacin was observed at 0.97 V and was applied to the determination of ofloxacin. The oxidation peak current was proportional to ofloxacin concentration in the ranges 1.0 × 10⁻⁸ to 1.0 × 10⁻⁶ mol/L and 1.0 × 10⁻⁶ to 2.0 × 10⁻⁵ mol/L. A detection limit of 8.0 × 10⁻⁹ mol/L was obtained for 400 s accumulation at open circuit (S/N = 3). This method for the detection of ofloxacin in human urine was satisfactory. __________ Translated from Chinese Journal of Applied Chemistry, 2007, 24(5): 540–545 [译自: 应用化学]     

A New Indirect Electrochemical Method for Determination of Ozone in Water Using Multiwalled Carbon Nanotubes

A new electrochemical methodology has been developed for the detection of ozone using multiwalled carbon nanotubes (MWCNT). The method presented here is based on the reaction of ozone with indigo blue dye producing anthranilic acid (ATN). The electrochemical profile of ATN on an electrode of glassy carbon (GC) modified with MWCNT showed an oxidation peak potential at 750 mV vs. Ag/AgCl. An analytical method was developed using differential pulse voltammetry (DPV) to determine ATN in a range of 50–400 nmol L^?1, with a detection limit of 9.7 nmol L^?1. Ozonated water samples were successfully analyzed by GC/MWCNT electrode and the recovery procedure yielded values between of 96.5 and 102.3 %.