Direct Electrochemical Determination of Glyphosate at Copper Phthalocyanine/Multiwalled Carbon Nanotube Film Electrodes

A copper phthalocyanine/multiwalled carbon nanotube film‐modified glassy carbon electrode has been used for the determination of the herbicide glyphosate (Gly) at ?50 mV vs. SCE by electrochemical oxidation using differential pulse voltammetry (DPV). Cyclic voltammetry and electrochemical impedance spectroscopy showed that Gly is adsorbed on the metallic centre of the copper phthalocyanine molecule, with formation of Gly‐copper ion complexes. An analytical method was developed using DPV in pH 7.4 phosphate buffer solution, without any pretreatment steps: Gly was determined in the concentration range of 0.83–9.90 μmol L^?1, with detection limit 12.2 nmol L^?1 (2.02 μg L^?1).     

Electrochemical Impedance Characterization of Nafion‐Coated Carbon Film Resistor Electrodes for Electroanalysis

Carbon film disk electrodes with Nafion coatings have been characterized by electrochemical impedance spectroscopy (EIS) with a view to a better understanding of their advantages and limitations in electroanalysis, particularly in anodic stripping voltammetry of metal ions. After initial examination by cyclic voltammetry, spectra were recorded over the full potential range in acetate buffer solution at the bare electrodes, electrodes electrochemically pretreated in acid solution, and Nafion‐coated pretreated electrodes in the presence and absence of dissolved oxygen. EIS equivalent circuit analysis clearly demonstrated the changes between these electrode assemblies. In order to simulate anodic stripping voltammetry conditions, spectra were also obtained in the presence of cadmium and lead ions in solution at Nafion‐coated electrodes, both after metal ion deposition and following re‐oxidation. Permanent changes to the structure of the Nafion film occurred, which has implications for use of these electrode assemblies in anodic stripping voltammetry at relatively high trace metal ion concentrations.     

Determination of Epinephrine at Different Types of Carbon Paste Electrodes

The voltammetric behavior of epinephrine was investigated by differential pulse voltammetry (DPV) at a carbon paste electrodes (CPE) made of different carbon powders – CR-2, glassy carbon (GC) microparticles, and single-wall carbon nanotubes (SWNT). In Briton-Robinson (BR) buffer solution pH 6, the linear dependence was found for the determination of epinephrine by the given method in the concentration ranges of 1·10^?6–1·10^?4 (CR-2), 1·10^?6–1·10^?4 (GC microparticles) and 4·10^?6–1·10^?4 (SWNT) mol·dm^?3. Limits of detection were 8·10^?7, 8·10^?7, and 2·10^?6 mol·dm^?3, respectively. The best results were obtained employing CPE containing carbon paste with 50% (m/m) of SWNT, a linear dynamic range being 4·10^?7–1·10^?4 mol·dm^?3 and a limit of detection 2·10^?7 mol·dm^?3. The attempt to increase the sensitivity by adsorptive accumulation of epinephrine was not successful.     

Selective Determination of Dopamine in the Presence of Ascorbic Acid at Porous‐Carbon‐Modified Glassy Carbon Electrodes

Selective dopamine (DA) determinations using porous‐carbon‐modified glassy carbon electrodes (GCE) in the presence of ascorbic acid (AA) were studied. The effects of structure textures and surface functional groups of the porous carbons on the electrochemical behavior of DA was analyzed based on both cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements. The differential pulse voltammetry of DA on the modified GCE was determined in the presence of 400‐fold excess of AA, and the linear determination ranges of 0.05–0.99, 0.20–1.96, and 0.6–12.60 μM with the lowest detected concentrations of 4.5×10^?3, 4.4×10^?2, and 0.33 μM were obtained on the mesoporous carbon, mesoporous carbon with carboxylic and amino groups modified electrodes, respectively.     

Electroanalytical Sensor Based on Unmodified Screen‐Printed Carbon Electrode for the Determination of Levo‐Thyroxine

The electrochemical behaviour of thyroxine (T₄) is analysed using the disposable screen‐printed carbon electrode (SPCE) in the neutral phosphate buffer solution with cyclic voltammetric technique. The Differential Pulse Voltammetry and Chronoamperometry were employed for sensing of T₄. The lowest detection limit of 3 nM was obtained from the differential pulse voltammetric method without preconditioning. The Density Functional Theoretical study of T₄ was performed to elucidate the mechanism of oxidation. The analysis of the commercial pharmaceutical samples indicates the validity of the proposed method.     

Differential Pulse Voltammetric Determination of Uric Acid on Carbon‐Coated Iron Nanoparticle Modified Glassy Carbon Electrodes

A carbon‐coated iron nanoparticles (CIN, a new style fullerence related nanomaterial) modified glassy carbon electrode (CIN/GCE) has been developed for the determination of uric acid (UA). Electrochemical behaviors of UA on CIN/GCE were explored by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that the voltammetric response of UA on CIN/GC was enhanced dramatically because of the strong accumulation effect of CIN and the large working area of the CIN/GC electrode. The parameters including the pH of supporting electrolyte, accumulation potential and time, that govern the analytical performance of UA have been studied and optimized. The DPV signal of UA on CIN/GCE increased linearly with its concentration in the range from 5.0×10^?7 to 2.0×10^?5 M, with a detection limit of 1.5×10^?7 M (S/N=3). The CIN/GCE was used for the determination of UA in samples with satisfactory results. The proposed CIN/GCE electrochemical sensing platform holds great promise for simple, rapid, and accurate detection of UA.     

Voltammetric Determination of Phenoxybenzyl‐Type Insecticides at Chemically Modified Conducting Polymer‐Carbon Nanotubes Coated Electrodes

The electrochemical reduction of three common insecticides such as cypermethrin (CYP), deltamethrin (DEL) and fenvalerate (FEN) was investigated at glassy carbon electrode (GCE), multiwalled carbon nanotubes modified GCE (MWCNT‐GCE), polyaniline (herein called as modifier M₁) and polypyrrole (herein called as modifier M₂) deposited MWCNT/GCE using cyclic voltammetry. Influences of pH, scan rate, and concentration were studied. The surface morphology of the modified film was characterized by scanning electron microscopy (SEM) and X‐ray diffraction analysis (XRD). A systematic study of the experimental parameters that affect differential pulse stripping voltammetry (DPSV) was carried out and the optimized experimental conditions were arrived at. The calibration plots were linear over the insecticide's concentration range 0.1–100 mg L^?1 and 0.05–100 mg L^?1 for all the three insecticides at MWCNT‐GCE and MWCNT(M₁)‐GCE respectively. The MWCNT(M₂)‐GCE performed well among the three electrode systems and the determination range obtained was 0.01–100 mg L^?1 for CYP, DEL and FEN. The limit of detection (LOD) was 0.35 μg L^?1, 0.9 μg L^?1 and 0.1 μg L^?1 for CYP, DEL and FEN respectively on MWCNT(M₂)‐GCE modified system. Suitability of this method for the trace determination of insecticide in spiked soil sample was also determined.     

Uric Acid Determination by Adsorptive Stripping Voltammetry on Multiwall Carbon Nanotubes Based Screen‐Printed Electrodes

A sensitive electroanalytical methodology for the determination of uric acid in real samples using adsorptive voltammetry at a multiwalled carbon nanotubes (MWCNT) modified screen printed electrode (SPCE) is presented. Adsorption of uric acid takes place at open circuit potential at an optimized pH 5.0. Studies about the effect of accumulation time and scan rate on the analytical signal were developed and confirm the adsorption nature of the electrodic process. Quantitative analysis of uric acid by using its oxidation process at +0.18 V (vs. an Ag pseudoreference electrode) was carried out with an accumulation time of 5 min. Thus, a linear voltammetric based reproducible determination of uric acid (RSD 5 %) in the range 1–100 µM was obtained. The method was then successfully used for the determination of uric acid in real clinical samples of urine without detection of interferences. The proposed methodology only requires a dilution of the real sample and present advantages as low cost and easy handling for non specialized technicians.     

A Novel Sensitive Electrochemical Sensor Based on Nickel Chloride Solution Modified Glassy Carbon Electrode for Curcumin Determination

In this research, the high conductivity of nickel chloride solution as well as the ability of nickel ions in establishing particular bonds with curcumin was benefited to fabricate a new electrochemical sensor based on nickel chloride solution modified glassy carbon electrode (NiCl₂/GCE) for detection and measurement of curcumin in human blood serum. Atomic force microscope (AFM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) methods indicated that using nickel chloride solution for the modification of the glassy carbon electrode (GCE) surface had a significant effect on improvement of the electrode performance. Differential pulse voltammetry (DPV) was used for quantitative measurement of curcumin, which exhibited the linear response of NiCl₂/GCE toward curcumin within the concentration range of 10–600 μM and provided the detection limit of 0.109 μM for curcumin in human blood serum.     

Determination of Impedance Spectroscopic Behavior of Triphenylphosphine on Various Electrodes

The electrochemical oxidation of triphenylphosphine (Ph₃P) was investigated by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) on glassy-carbon (GC), gold (Au) and multi-walled carbon nanotubes (MWCNT) in acetonitrile (ACN), dichloromethane (DCM), and cyclohexanone (CHN). The electron-transfer kinetics of the redox couple PPh₃/Ph₃P^·+ on various electrodes was found to increase with the order: Au < MWCNT < GC. The EIS results verify that GC provides faster charge-transfer kinetics since it affords less charge-transfer resistance and thus lower electron-transfer barrier from other electrodes tested. In DCM and CHN greater deviation from reversibility was observed which can be attributed to the poorer polarity of the solvents, which provides an additional barrier for the electron-transfer process.

[Supplemental materials are available for this article. Go to the publisher's online edition of Analytical Letters for the following free supplemental resource(s): additional tables and figures.]     

Adsorptive Stripping Voltammetric Determination of 4‐Hexylresorcinol in Pharmaceutical Products Using Multiwalled Carbon Nanotube Based Electrodes

A sensitive electroanalytical method is presented for the determination of 4‐hexylresorcinol using adsorptive stripping voltammetry (AdsSV) at a multiwalled carbon nanotube modified basal plane pyrolytic graphite electrode (MWCNT‐BPPGE). This method is also extended to the use of a MWCNT modified screen‐printed electrode (MWCNT‐SPE), thereby demonstrating that this approach can easily be incorporated into a facile and inexpensive electrochemical sensor.     

秋水仙碱的电化学性质及电分析方法研究

本文研究了抗癌药物秋水仙碱在玻碳电极上的电化学行为。在HAc NaAc缓冲溶液中,秋水仙碱在玻碳电极上产生一不可逆的氧化峰,峰电位为1.22V(vs.SCE)。用差示脉冲伏安法测定,峰电流与秋水仙碱浓度在8.00×10-7～1.00×10-5mol/L范围内有良好的线性关系,检出限达1.00×10-7mol/L。将之应用于模拟血清样品的测定,结果令人满意。同时,对电极反应机理进行了初步探讨。     

Simple,Rapid and Sensitive Electrochemical Method for the Determination of the Triketone Herbicide Sulcotrione in River Water Using a Glassy Carbon Electrode

We report a novel, simple, rapid and sensitive electrochemical method for the determination of sulcotrione, a member of the relatively new class of triketone herbicides, using differential pulse voltammetry on a glassy carbon electrode. Its electrochemical behavior including influences of electrolyte composition, pH and scan rate was studied to select optimal experimental parameters for its determination. In Britton? Robinson buffer at pH 3 sulcotrione provided a well‐defined reduction peak at ?0.84 V (vs. Ag/AgCl electrode), with good repeatability (relative standard deviation of 2.3 % for 8 measurements at 10 µM concentration level). With optimized parameters differential pulse voltammetry rendered two linear concentration ranges from 0.2 to 2 µM and from 2 to 50 µM with a detection limit of 0.05 µM. The proposed procedure was successfully applied to the determination of sulcotrione in spiked river water samples with satisfactory recoveries (93–109 %). The developed method may represent a simple, rapid and sensitive alternative to highly toxic mercury electrodes and chromatographic methods.     

修饰的多壁碳纳米管糊电极用于生物与制药样品中苄丙酮香豆素电催化氧化和测定

采用一种简单灵敏的方法开发了在多壁碳纳米管修饰的ZnCrFeO4糊电极(MWCNTs/ZnCrFeO4/CPE)表面测定苄丙酮香豆素的新型传感器.运用循环伏安法、差示脉冲伏安法、计时电流法和电化学阻抗谱考察了该化学修饰电极上苄丙酮香豆素的电化学性能.结果表明,MWCNTs/ZnCrFeO4/CPE电极对苄丙酮香豆素氧化表现出较高的电催化活性,在pH=4时,产生峰值氧化电流约0.97 vs Ag/AgCl参比电极.当苄丙酮香豆素浓度在0.02-920.0 μmol/L范围内,该峰电流与其呈线性关系,检测极限(3σ)为0.003 μmol/L.另外,运用差示脉冲伏安法测定了MWCNTs/ZnCrFeO/CPE电极上苄丙酮香豆素的催化反应速率常数和扩散系数.     

β‐Cyclodextrin Incorporated Carbon Nanotube Paste Electrode as Electrochemical Sensor for Nifedipine

In this work a carbon paste electrode modified with multiwalled carbon nanotubes/β‐cyclodextrin (MWCNTs/β‐CD) was constructed and applied to the determination of nifedipine. The electrochemical behavior of nifedipine at this electrode was investigated using cyclic voltammetry and differential pulse voltammetry. Characterization of the modified electrode was conducted with electrochemical impedance spectroscopy and scanning electron microscopy. After adsorption of nifedipine on the MWCNTs/β‐CD paste electrode at 0.0 V for 6 min, a well defined reduction peak was produced in sodium hydroxide of 0.05 M. The calibration curve was linear from 7.0×10^?8 to 1.5×10^?5 M. The detection limit was obtained as 2.5×10^?8 M. The results demonstrated that this electrochemical sensor has excellent sensitivity and selectivity. This sensor was applied for determination of nifedipine in drug dosage and blood serum with excellent recoveries.     

碳纳米管阵列电极的构建及电化学研究

本文提出一种改进的氧化铝模板法制备碳纳米管阵列电极:首先结合气相化学沉积和磁控溅射在氧化铝模板中制得碳纳米管阵列电极,然后用HF溶液将沉积了碳纳米管的氧化铝模板阻挡层除去,控制溶出时间即可得到不同溶出长度的碳纳米管阵列电极.循环伏安测试表明,锂离子在该阵列电极中的嵌入脱出反应主要发生在碳纳米管的端口处.此外,还应用固定频率交流阻抗法,研究了不同溶出时间的碳纳米管阵列电极的电容性质.     

Electroanalytical Study of the Antioxidant and Antitumor Agent Curcumin

Curcumin (CU) shows a wide range of pharmacological properties including antioxidant, anti‐inflammatory, and antitumor effects. In order to understand the chemical basis of different activities of curcumin, we have studied the oxidation and reduction of curcumin. Based on cyclic and differential pulse voltammetric methods, using carbon paste and hanging mercury drop electrodes, in the present study we tested different parameters to optimize the conditions for the determination of curcumin and its electrochemical characteristics. Better results were obtained via differential pulse voltammetry using carbon paste electrode. Curcumin yields well‐defined differential pulse voltammetric responses with well‐defined oxidation (in the potential region of 0.3–0.6 V, vs. Ag/AgCl) and reduction (at 0.3 V) peaks using carbon paste electrode.     

碳纳米管膜电极的制备及其分析应用

本文详细介绍了碳纳米管的特性,并就碳纳米管在电分析化学中的应用情况进行了全面的综述,重点介绍了各种碳纳米管膜电极的制备及其应用。     

Facile Fabrication of Zirconia Modified Screen‐Printed Carbon Electrodes for Electrochemical Sensing of Phosphate

We report here a facile method to immobilize zirconia nanoparticles on a disposable screen‐printed carbon electrode (designated as ZrO₂‐SPCE) for phosphate sensor application. Simply by ultrasonicating a bare SPCE in a ZrO₂ slurry, ZrO₂ nanoparticles can be immobilized effectively on the electrode surface as verified by surface characterization evidences. Using ferricyanide as a redox probe, an increase in the charge transfer resistance (R_ct) of ferricyanide upon adsorption of phosphate on ZrO₂ is used for the determination of phosphate. This ZrO₂‐SPCE phosphate sensor shows a wide linear range up to 1 mM and a detection limit of 1.69 µM (S/N=3). Practical applicability of the ZrO₂‐SPCE is demonstrated by detecting phosphate content in human blood samples.