Fabrication of Electrochemical Sensor Based on Layered Double Hydroxide/Polypyrrole/Carbon Paste for Determination of an Alpha‐adrenergic Blocking Agent Terazosin

New insights into the design of highly sensitive, carbon‐based electrochemical sensors are presented in this work. This was achieved by exploring the interesting properties of conductive (Mg/Al) layered double hydroxide‐dodecyl sulphate/polypyrrole nanocomposites which were synthesized by in‐situ polymerization of pyrrole during the assembly of (Mg/Al) layered double hydroxide, and by employing the anionic surfactant dodecyl sulphate as a modifier. Changes in morphology and surface area of the nanocomposites occured as a result of change in pyrrole percentage. Under optimal conditions, the modified carbon paste electrode successfully achieved detection limits of 0.057 and 0.134 nmol L⁻¹ of Terazosin hydrochloride in pharmaceutical formulation and spiked human serum fluid, respectively. Moreover, the sensors are highly stable, reusable and free of interference by other commonly present excipients in drug formulations.     

Preparation of tetraheptylammonium iodide-iodine graphite-multiwall carbon nanotube paste electrode: electrocatalytic determination of ascorbic acid in pharmaceuticals and foods

The present work describes the construction of a new modified graphite-multiwall carbon nanotube paste electrode by casting the appropriate mixture of tetraheptylammonium iodide-iodine as a new modifier. The modified paste electrode was used for the determination of ascorbic acid (AA) in a phosphate buffer solution (pH 2.0). When compared to activated carbon, a graphite and multiwall carbon nanotube paste electrode containing a new modifier, the proposed modified paste electrode not only shifted the oxidation potential of AA towards a less-positive potential but also enhanced its oxidation peak current. Further, the oxidation of AA was highly stable at the modified paste electrode. The optimum analytical conditions were sought. The current response of AA increases linearly while increasing its concentration from 5.6 × 10(-5) to 1.2 × 10(-2) M with a correlation coefficient of 0.9991; the detection limit (3σ) was found to be of 3.6 × 10(-5) M. The present modified paste electrode was also successfully used for the determination of AA in the presence of common interference compounds. The present modified electrode was successfully demonstrated towards the determination of AA in pharmaceutical and food samples.     

An Electrochemical Sensor for Determination of Ultratrace Cd,Cu and Hg in Water Samples by Modified Carbon Paste Electrode Base on a New Schiff Base Ligand

This paper describes the preparation and electrochemical application of a new chemically modified electrode for simple and highly sensitive simultaneous determination of copper, mercury and cadmium using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Firstly, a new bis‐Schiff base ligand, 2,2′‐((pyridine‐2,6‐diylbis (azanylylidene)) bis (methanylylidene))bis(4‐bromophenol) (ligand L ) has been synthesized by reaction of the 2,6‐diamino pyridine with 5‐bromo salicylaldehyde or salicylaldehyde at ethanol under refluxing. The structure of the synthesized compound resulted from the IR, ¹HNMR, MS, UV spectroscopy and elemental analysis data. Afterwards, a novel, simple and effective chemically modified carbon paste electrode with ligand L was prepared. The electrochemical properties and applications of the modified electrode, including the pH, percentage of modifier, the electron transfer, optimized conditions, linear response and detection limit were investigated. High sensitivity and reproducibility, together with the ease of preparation and regeneration of the electrode surface by simple polishing, make the electrode very suitable for the voltammetric determination of copper, mercury and cadmium in several Merck samples and water samples.     

Stripping Voltammetry of Cerium(IIl) with a Chemically Modified Carbon Paste Electrode Containing Functionalized Nanoporous Silica Gel

This research introduces the design of an adsorptive stripping voltammetric method for the cerium(III) determination at a carbon paste electrode, chemically modified with dipyridyl‐functionalized nanoporous silica gel (DPNSG‐CPE). The electroanalytical procedure comprised two steps: the Ce(III) chemical accumulation at ?200 mV followed by the electrochemical detection of the Ce(III)/dipyridyl complex, using anodic stripping voltammetry. The factors, influencing the adsorptive stripping performance, were optimized including the modifier quantity in the paste, the electrolyte concentrations, the solution pH and the accumulation potential or time. The resulting electrode demonstrated a linear response over a wide range of Ce(III) concentration (1.0–28 ng mL^?1). The precision for seven determinations of 4 and 10 ng mL^?1 Ce(III) was 3.2% and 2.5% (relative standard deviation), respectively. The prepared electrode was used for the cerium determination in real samples and very good recovery results were obtained.     

Voltammetric determination of piroxicam in micellar media by using conventional and surfactant chemically modified carbon paste electrodes

A method for piroxicam determination based on adsorptive stripping voltammetric techniques, using conventional and chemically modified carbon paste electrodes in micellar media, is described. The employed surfactants were sodium dodecyl sulfate (SDS), Triton X-100, Triton X-405, Tween 80 and Brij 30. However, the purpose of this paper is, at present, to research the use of surfactants as carbon paste modifier because one of the mechanisms of hydrophobic drugs ad-accumulation on the carbon paste electrode is based on the chemical affinity. Besides, because of the water piroxicam insolubility, a special aqueous medium, such as a surfactant solution above its c.m.c. was used, this micellar media being very advantageous in relation to the use of organic or aqueous-organic media, in order to dissolve the studied drug and to remove the problems derived from the organic solvents use. In addition, a piroxicam ad-accumulation increase, on surfactant modified carbon paste electrode, with the surfactant mass incorporated into the electrode, was observed.     

Adsorptive Stripping Voltammetric Determination of Nanomolar Concentration of Cerium(III) at a Carbon Paste Electrode Modified by N′‐[(2‐Hydroxyphenyl)Methylidene]‐2‐Furohydrazide

The aim of this work was to obtain an adsorptive stripping voltammetric method for the Ce(III) determination at a carbon paste electrode, chemically modified with N'‐[(2‐hydroxyphenyl)methylidene]‐2‐furohydrazide (NHMF). The electroanalytical procedure comprised two steps: the Ce(III) chemical accumulation at ?200 mV followed by the electrochemical detection of the Ce(III)/NHMF complex, using anodic stripping voltammetry. The factors, influencing the adsorptive stripping performance, were optimized including the modifier quantity in the paste, the electrolyte concentrations, the solution pH and the accumulation potential or time. The resulting electrode demonstrated a linear response over a wide range of Ce(III) concentration (5.0–90 nmol dm^?3). The detection limit was found to be 0.8 nmol dm^?3 on the basis of a signal to noise ratio of 3. The precision for six determinations of 10 and 55 nmol dm^?3 Ce(III) was 5.6% and 2.1% (relative standard deviation), respectively. Application of the procedure to the determination of cerium in phosphate rock and wastewater samples gave good results.     

Application of Novel Zn‐Ferrite Modified Glassy Carbon Paste Electrode as a Sensor for Determination of Cd(II) in Waste Water

This paper describes the preparation of a new sensor based on Zn‐ferrite modified glassy carbon paste electrode and its electrochemical application for the determination of trace Cd(II) ions in waste waters using differential pulse anodic stripping voltammetry (DPASV). Different Zn/Ni ferrite nanoparticles were synthesized and characterized using scanning electron microscopy (SEM) and X‐ray powder diffraction (XRPD). The prepared ferrite nanoparticles were used for the preparation of Zn‐ferrite‐modified glassy carbon paste electrode (ZnMGCPE) for determination of Cd(II) at nanomolar levels in waste water at pH 5. The different parameters such as conditions of preparation, Zn²⁺/Ni²⁺/Fe²⁺ ratio and electrochemical parameters, percentage of modifier, accumulation time, pH and accumulation potential were investigated. Besides, interference measurements were also evaluated under optimized parameters. The best voltammetric response was observed for ZnFe₂O₄ modifier, when the percentage of modifier was 3 %, accumulation time 9 min, pH of supporting electrolyte 5 and accumulation potential ?1.05 V. Thus prepared electrode displays excellent response to Cd(II) with a detection limit of 0.38 ppb, and selective detection toward Cd(II) was achieved.     

A Sensitive Electrochemical Sensor for Moxifloxacin Hydrochloride Based on Nafion/Graphene Oxide/Zeolite Modified Carbon Paste Electrode

A carbon paste electrode (CPE) modified with Nafion, Graphene oxide and zeolite has been prepared and characterized, and the resulting Nafion/Graphene oxide/Zeolite modified carbon paste electrode (N/G/Z/MCPE) has been applied to the electrochemical detection of Moxifloxacin hydrochloride (MOXI). It exhibited a good electrocatalytic activity in phosphate buffer (optimum at pH 7.4), as pointed out by cyclic voltammetry (CV), and N/G/Z/MCPE can be exploited for MOXI detection by chronoamperometry, electrochemical impedance spectroscopy and differential pulse voltammetry. This latter was the most sensitive one and gave rise to a linear calibration curve in the 0.04 to 250 μM concentration range, with limits of detection and qualification estimated at 1.0 nM and 3.3 nM, respectively. Contrary to previous electrochemical sensors for MOXI (e. g., CPE modified with metal nanoparticles), this new sensor can be used for multiple successive analyses without needing to refresh its surface.     

Fabrication of bulk-modified carbon paste electrode containing alpha-PW12O40(3-) polyanion supported on modified silica gel: Preparation, electrochemistry and electrocatalysis

Alpha-PW(12)O(40)(3-) (PW(12)) supported on the surface of silica gel derivatized by 3-aminopropyl(triethoxy)silane (devoted briefly as SiNH(3)PW(12)) was synthesized and used as bulk modifier to fabricate a renewable three-dimensional chemically modified electrode. The electrochemical behavior of the modified electrode was characterized by cyclic voltammetry. There is an ionic bonding character between PW(12) and the surface amino groups of modified silica, which greatly improves the stability of SiNH(3)PW(12)-modified carbon paste electrode due to insolubility of silica gel in water. The SiNH(3)PW(12) bulk-modified carbon paste electrode not only maintains the electrochemical activity of PW(12), but also exhibits remarkable advantages of renewability, as well as simple preparation and inexpensive material. The modified electrode offers an excellent and stable electrocatalytic response for the reduction of IO(3)(-) and hydrogen peroxide. The SiNH(3)PW(12)-CPE is successfully applied as an electrochemical detector to monitor IO(3)(-) in flow injection analysis (FIA). The catalytic peak current was found to be linear with the IO(3)(-) concentration in the range 5x10(-6) to 1x10(-3)molL(-1). The detection limit of the proposed method was found to be 3.1x10(-6)molL(-1) for IO(3)(-) determination.     

γ-Oryzanol-loaded calcium pectinate microparticles reinforced with chitosan: Optimization and release characteristics

The cationic surfactant, cetyltrimethyl ammonium bromide (CTAB) effect on accurate determination of dopamine in the presence of ascorbic acid (as natural obtrusive in determination of dopamine) using chemically modified electrode based on tin hexacyanoferrate (SnHCF) as a modifier at carbon paste electrode (CPE) is described. The electrochemical response of bare CPE and SnHCF modified electrode (ME) examined in different pHs, in absence and presence of different concentration of dopamine (DA) and ascorbic acid (AA). In addition a simple and reliable method for simultaneous electrochemical determination of AA and DA was presented. It was based on the use of the cationic surfactant CTAB that enables the separation of the oxidation peaks potential of AA and DA. The experimental results showed that DA and AA have two separate peaks. In pH 3 and at presence of 3 mM of CTAB the separation of DA and AA peaks and the eminence of them increased evidently. Good linear response to AA and DA was observed in the range of 0.4–50 and 0.2–25 mM with the correlation of 0.9912 and 0.9955, respectively.     

Fuel-Cell Type Ceramic-Carbon Oxygen Sensors

Several classes of sol-gel derived, fuel-cell-type gas sensors are described. The electrochemical sensors are comprised of a hydrophobically modified silicate network and a dispersion of carbon powder and inert metal (palladium or platinum in the zero valent state) or organometallic (e.g., cobalt porphyrin) catalyst modifier.The carbon powder provides conductivity, the Ormosil network assures high porosity, which is pertinent for gas permeation through the back of the electrodes, and the hydrophobic functional group assures that only a thin layer at the outermost section of the electrode is wetted by the electrolyte, thus providing fast dynamic response.     

Carbon paste-based electrochemical detectors for microchip capillary electrophoresis/electrochemistry

The first reported use of a carbon paste electrochemical detector for microchip capillary electrophoresis (CE) is described. Poly(dimethylsiloxane) (PDMS)-based microchip CE devices were constructed by reversibly sealing a PDMS layer containing separation and injection channels to a separate PDMS layer that contained carbon paste working electrodes. End-channel amperometric detection with a single electrode was used to detect amino acids derivatized with naphthalene dicarboxaldehyde. Two electrodes were placed in series for dual electrode detection. This approach was demonstrated for the detection of copper(II) peptide complexes. A major advantage of carbon paste is that catalysts can be easily incorporated into the electrode. Carbon paste that was chemically modified with cobalt phthalocyanine was used for the detection of thiols following a CE separation. These devices illustrate the potential for an easily constructed microchip CE system with a carbon-based detector that exhibits adjustable selectivity.     

Graphite Based Microsensors Developed for the Electrochemical Determination of L‐Tyrosine from Pharmaceutical Samples

Two electrochemical sensors were proposed for the determination of L‐tyrosine from pharmaceutical capsules. The electrochemical sensors were based on plain graphite paste and chitosan modified graphite paste. Working conditions, e. g. pH, supporting electrolytes have been optimized. The results revealed for both electrodes very low limits of quantification (LOQ) (0.18 mg L^?1 and 0.0018 mg L^?1) for plain graphite paste based sensors and for chitosan modified paste sensors respectively. A higher sensitivity of 7.95×10^?10 A mg L^?1 was obtained for the sensor based on plain graphite paste (G). The uniformity content test showed that L‐Tyrosine can be recovered in pharmaceutical capsules with an average value higher than 98.00 % and a relative standard deviation (RSD%) value less than 1.00 % (N=5).     

用对氨基苯酚改性的碳纳米管糊电极同时测定羟胺和苯酚(英文)

A carbon paste electrode that was chemically modified with multiwall carbon nanotubes and p-aminophenol was used as a selective electrochemical sensor for the simultaneous detection of hydroxylamine (HX) and phenol. Cyclic voltammetry, double potential-step chronoamperometry, square wave voltammetry (SWV), and electrochemical impedance spectroscopy were used to investigate the use of p-aminophenol in the carbon nanotubes paste matrixes as a mediator for the electrocatalytic oxidation of HX and phenol in aqueous solution. The coefficient of electron transfer and catalytic reaction rate constant were determined using the electrochemical methods. Under optimized conditions, the electrocatalytic oxidation current peaks for HX and phenol increased linearly with concentration in the range of 0.5-180.0 and 10.0-650.0 μmol/L for HX and phenol, respectively. The detection limits for HX and phenol were 0.15 and 7.1 μmol/L, respectively. The anodic potential peaks of HX and phenol were separated by 0.65 V in SWV. Because of good selectivity and sensitivity, the present method provides a simple method for the selective detection of HX and phenol in practical samples such as water samples.     

Measurement of Dissolved Oxygen in Biological Fluids by Using a Modified Carbon Paste Electrode

A modified carbon paste electrode was constructed for the determination of dissolved oxygen using diamino‐o‐benzoquinone (DABQ) as the modifier. The electrochemical behavior of the electrode in citrate buffer (pH 2.0) was studied. In the presence of dissolved oxygen (DO) both cathodic and anodic peak currents decreased, indicating a chemical reaction between modifier and O₂. The decrease in peak current was linearly proportional to the amount of dissolved oxygen in the concentration range of 252–1260 μM of DO. The electrode was utilized in the determination of DO in urine samples. The relative error and RSD of the method were 1.6% and 4.1%, respectively. The electrode was applied more than two months for the determination of DO without any significant divergence in its voltammetric response.     

A New Chemically Modified Carbon Paste Electrode Derived from Aloe Vera Xanthate Nanoparticles to Detect Mercury Ions

This environmentally benign work describes a simple electrochemical sensor constructed with a chemically modified carbon paste electrode (CMCPE) using aloe vera xanthate nanoparticles to detect mercury ions. The characterization and morphology of nanoparticles were thoroughly investigated using modern techniques. The CMCPE efficiently senses the mercury ions. The limit of detection of mercury ions wasexcellent to the order of 0.231 μg mL⁻¹. Real-time sample analysis showed promising results. The recovery range was between 99.4 % and 101.7 %. The activity of CMCPE was commendable even after fifty days.     

Comparison of different carbon nanostructures influence on potentiometric performance of carbon paste electrode

Recently, different carbon nanomaterials were introduced for construction of electrochemical sensors. In this study, the influence of carbon nanomaterial on performance of carbon paste potentiometric electrode was investigated. In this manner, different kinds of carbon nanomaterial, i.e., graphene, graphene oxide and carbon nanotube (CNT) were used as a conduction phase in carbon paste electrode. Then, potentiometric characteristics of the corresponding paste electrodes such as calibration slope, linear range, detection limit, response time and stability were compared with each other. The results appeared comprehensive findings about the role of electrode’s content in electrochemical performance.     

脱氧核糖核酸在硬脂酸铝离子膜上固定杂交及BAR基因片段检测

将石墨粉、固体石蜡和硬脂酸按一定比例混合制得表面富含羧基的碳糊电极,然后在电极表面组装荷正电的铝离子膜。在硬脂酸铝离子膜上进行DNA探针的固定和与目标基因的杂交。以亚甲蓝为杂交指示剂,用循环伏安法优化了DNA的固定和杂交条件。应用该电化学生物传感器以微分脉冲伏安法对转基因玉米外源BAR基因片段进行了检测,结果令人满意。     

Electrochemical Determination of Dopamine Using a Novel Perylenediimide-Derivative Modified Carbon Paste Electrode

A novel perylenediimide derivative, N,N′-bis(4-{2-[2-(2-methoxyethoxy ethoxy]ethoxy}phenyl)-3,4:9,10-perylene tetracarboxydiimide, was utilized for the modification of a carbon paste electrode to develop a practical and sensitive electrochemical sensor for dopamine detection. The effects of experimental parameters (modifier amount, pH, and scan rate) on the dopamine peak current were examined. The performance of the modified carbon paste electrode was evaluated under optimum conditions and 4.6-fold increase in the peak current was obtained compared to an unmodified carbon paste electrode. The linear range was between 1 and 100?µM dopamine and the limits of detection and quantification were 0.011 and 0.036?µM, respectively. The developed sensor was also applied for the quantitative determination of dopamine in injections and promising results were obtained.     

碳糊电极和化学修饰碳糊电极的制备及性能综述

碳糊电极在电化学研究中起着非常重要的作用．从电极材料选用和修饰剂选择方面综述了碳糊电极和化学修饰碳糊电极制备的几种方法,分析了碳糊电极和化学修饰碳糊电极制备技术存在的主要问题及其原因,评价了碳糊电极和化学修饰碳糊电极的表征技术、性能以及影响电极性能的因素．概括了近年来本课题组在碳糊电极研究中的一些结果．