Investigation of Electrochemical Oxidation of Methanol at a Carbon Paste Electrode Modified with Ni(II)‐BS Complex and Reduced Graphene Oxide Nano Sheets

In the present research, the electro oxidation of methanol was investigated by different electrochemical methods at a carbon paste electrode (CPE) modified with bis(salicylaldehyde)‐nickel(II)‐dihydrate complex (Ni(II)‐BS) and reduced graphene oxide (RGO) (which named Ni(II)‐BS/RGO/CPE) in an alkaline solution. This modified electrode showed very efficient activity for oxidation of methanol. It was found that methanol was oxidized by NiOOH groups generated by further electrochemical oxidation of nickel (II) hydroxide on the surface of the modified electrode. The rate constant and electron transfer coefficient were calculated to be 2.18 s^?1 and 0.4, respectively. The anodic peak currents revealed a linear dependency with the square root of scan rate. This behaviour is the characteristic of a diffusion controlled process, so the diffusion coefficient of methanol was found to be 1.16×10^?5 cm² s^?1 and the number of transferred electron was calculated to be 1. Moreover, differential pulse voltammetry (DPV) investigations showed that the peak current values were proportional to the concentration of methanol in two linear ranges. The obtained linear ranges were from 0.5 to 100.0 µM (R²=0.991) and 400.0 to 1300.0 µM (R²=0.992), and the detection limit was found to be 0.19 µM for methanol determination. Generally, the Ni(II)‐BS/RGO/CPE sensor was used for determination of methanol in an industrial ethanol solution containing 4.0 % methanol.     

Differential Pulse Anodic Stripping Voltammetric Simultaneous Determination of Copper(II) and Silver(I) with Bis(2‐hydroxyacetophenone) Butane‐2,3‐dihydrazone Modified Carbon Paste Electrodes

The behavior of a modified carbon paste electrode (CPE) for simultaneous determination of copper(II) and silver(I) by anodic adsorptive stripping voltammetry (ASV) was studied. The electrode was built incorporating the bis(2‐hydroxyacetophenone) butane‐2,3‐dihydrazone (BHAB) as a complexing agent to a Nujol‐graphite base paste. The resulting electrode demonstrated linear responses over the range of Cu(II) and Ag(I) concentrations 0.1–20 and 0.01–2.0 µM respectively. The relative standard deviation (RSD) for the determination of 5.0 µM of both metal ions were 2.9 and 3.1 % for Cu(II) and Ag(I), respectively. The method has been applied to the analysis of copper in wheat and barley seed samples and silver in developed radiological film.     

Fabrication of a renewable syringe carbon paste electrode with a motor rotary blade and using for voltammetric measurement of dipyridamole

In this work, we fabricated a new renewable syringe carbon paste electrode (SCPE) equipped with a motor rotary cutting blade and used for voltammetric determination of dipyridamole (DIP) in aqueous solution, at room temperature. The cutter rotates by a small electrical motor and easily renews the surface of the carbon paste electrode by removing the spotty surface. Electrochemical performance of the constructed electrode was investigated with cyclic voltammetry (CV) and compared to some other previously reported works. The new sensor showed several advantages such as excellent repeatability, high stability, good sensitivity and easily surface renewable. The results indicated that the presence of methyltrioctyl ammonium chloride (MTOAC) could remarkably enhance the oxidation of DIP due to feasible electrical conductivity properties in a phosphate buffer solution. At optimum conditions for the new syringe CPE, the square wave voltammetry (SWV) was used to measure the concentration of DIP in a linear range of 0.08–30.0 µM and a detection limit of 0.02 µM was obtained after 100 s of accumulation time. The sensor was then tested for the simple, rapid and sensitive electrochemical determination of DIP in real samples such as pharmaceutical formulations.     

Electrocatalytic and Simultaneous Determination of Ascorbic Acid,Nicotinamide Adenine Dinucleotide and Folic Acid at Ruthenium(II) Complex‐ZnO/CNTs Nanocomposite Modified Carbon Paste Electrode

This paper describes the development a novel ruthenium(II) complex‐ZnO/CNTs modified carbon paste electrode (Ru(II)/ZnO/CNTs/CPE) for the electrocatalytic determination of ascorbic acid (AA). The objective of this novel electrode modification was to seek new electrochemical performances for the detection of AA, nicotinamide adenine dinucleotide (NADH) and folic acid (FA). The peak potentials recorded were 170, 500 and 830 mV vs. Ag/AgCl/KCl_sat for AA, NADH and FA, respectively. The peak currents were linearly dependent on AA, NADH and FA concentrations using square wave voltammetry (SWV) method at the ranges of 0.008–251, 1.0–650, and 3.0–700 µmol L^?1, with detection limits of 0.005, 0.5, and 1.0 µmol L^?1, respectively.     

Nanocrystalline Metallosilicate Modified Electrodes for the Simultaneous,Sensitive, and Selective Determination of Riboflavin,Rutin, and Pyridoxine

Nanocrystalline metallosilicate modified glassy carbon electrodes were fabricated for the simultaneous determination of vitamins. Among these, nanocrystalline zirconosilicate exhibited the highest activity with a linear range from 30 nM–500 µM for riboflavin and 120 nM–600 µM for rutin and pyridoxine. Sensitivity values of 2.8, 1.49, and 1.13 µA/µM cm² and lower detection limits of 5 nM, 30 nM, and 30 nM for riboflavin, rutin, and pyridoxine, respectively, were found. The proposed sensor is stable and reproducible (RSD<3.5 %). The analytical performance of this sensor was demonstrated in the pharmaceutical preparations (multivitamin tablets) with satisfactory recovery (97–103 %).     

Investigation of Methanol Behavior at the Designed Electrochemical Sensor based on Ni(II) Complex and Graphene Nanosheets

In this work, the electrochemical oxidation of methanol was investigated by different electrochemical methods at a carbon paste electrode (CPE) modified with (N‐5‐methoxysalicylaldehyde, N´‐2‐hydroxyacetophenon‐1, 2 phenylenediimino nickel(II) complex (Ni(II)–MHP) and reduced graphene oxide (RGO), which is named Ni(II)‐MHP/RGO/CPE, in an alkaline solution. This modified electrode was found to be efficient for the oxidation of methanol. It was found that methanol was oxidized by the NiOOH groups generated by further electrochemical oxidation of nickel(II) hydroxide on the surface of the modified electrode. Under optimum conditions, some parameters of the analyte (MeOH), such as the electron transfer coefficient (α), the electron transfer rate constant) k_s), and the diffusion coefficient of species in a 0.1 M solution (pH = 13), were determined. The designed sensor showed a linear dynamic range of 2.0–100.0 and 100.0–1000.0 μM and a detection limit of 0.68 μM for MeOH determination. The Ni(II)‐MHP/RGO/CPE sensor was used in the determination of MeOH in a real sample.     

Development of a Carbon Paste Electrode Modified with Reduced Graphene Oxide and an Imidazole Derivative for Simultaneous Determination of Biological Species of N‐acetyl‐L‐cysteine,Uric Acid and Dopamine

In this work, the modified carbon paste electrode (CPE) with an imidazole derivative 2‐(2,3 dihydroxy phenyl) 4‐methyl benzimidazole (DHPMB) and reduced graphene oxide (RGO) was used as an electrochemical sensor for electrocatalytic oxidation of N‐acetyl‐L‐cysteine (NAC). The electrocatalytic oxidation of N‐acetyl‐L‐cysteine on the modified electrode surface was then investigated, indicating a reduction in oxidative over voltage and an intensive increase in the current of analyte. The scan rate potential, the percentages of DHPMB and RGO, and the pH solution were optimized. Under the optimum conditions, some parameters such as the electron transfer coefficient (α) between electrode and modifier, and the electron transfer rate constant) k_s) in a 0.1 M phosphate buffer solution (pH=7.0) were obtained by cyclic voltammetry method. The diffusion coefficient of species (D) 3.96×10^?5 cm² s^?1 was calculated by chronoamperometeric technique and the Tafel plot was used to calculate α (0.46) for N‐ acetyl‐L‐cysteine. Also, by using differential pulse voltammetric (DPV) technique, two linear dynamic ranges of 2–18 µM and 18–1000 µM with the detection limit of 61.0 nM for N‐acetyl‐L‐cysteine (NAC) were achieved. In the co‐existence system of N‐acetyl‐L‐cysteine (NAC), uric acid (UA) and dopamine (DA), the linear response ranges for NAC, UA, and DA are 6.0–400.0 µM, 5.0–50.0 µM and 2.0–20.0 µM, respectively and the detection limits based on (C=3s_b/m) are 0.067 µM, 0.246 µM and 0.136 µM, respectively. The obtained results indicated that DHPMB/RGO/CPE is applicable to separate NAC, uric acid (UA) and dopamine (DA) oxidative peaks, simultaneously. For analytic performance, the mentioned modified electrode was used for determination of NAC in the drug samples with acceptable results, and the simultaneous determination of NAC, UA and DA oxidative peaks was investigated in the serum solutions, too.     

Selective Simultaneous Determination of Paracetamol and Uric Acid Using a Glassy Carbon Electrode Modified with Multiwalled Carbon Nanotube/Chitosan Composite

A multiwalled carbon nanotube/chitosan modified glassy carbon electrode (MWCNTs‐CHT/GCE) has been used for simultaneous determination of paracetamol (PAR) and uric acid (UA). The measurements were carried out using differential pulse voltammetry (DPV), cyclic voltammetry (CV) and chronoamperometry (CA). DPV measurements showed a linear relationship between oxidation peak current and concentration of PAR and UA in phosphate buffer (pH 7) over the concentration range 2 µM to 250 µM, and 10 µM to 400 µM, respectively. The analytical performance of this sensor has been evaluated for detection of PAR and UA in human serum and human urine with satisfactory results.     

Chemically Modified Carbon Paste Electrode for Determination of Sulfate Ion by Potentiometric Method

Four Schiff base complexes of different metal ions, M=Cr(III), Mn(III), Fe(III), and Co(III), were studied to characterize their ability as sulfate ion carriers in carbon paste electrode (CPE). The modified CPE electrode with Schiff base complex of Cr(III), N,N′‐ethylenebis(5‐hydroxysalicylideneiminato) chromium(III) Chloride, showed good response characteristics to SO₄^2? ion. The proposed electrode exhibits a Nernstian slope of 28.9±0.4 mV per decade for SO₄^2? ion over a wide concentration range from 1.5×10^?6?4.8×10^?2 M, with a detection limit of 9.0×10^?7 M. The CPE electrode manifested advantages of relatively fast response time, suitable reproducibility and life time and, most important, good potentiometric selectivity relative to a wide variety of other common inorganic anions. The potentiometric response of the electrode is independent of the pH of the test solution in the pH range 4.0–9.0. The proposed electrode was used as an indicator electrode in potentiometric titration of sulfate with Ba²⁺ ion, the determination of zinc in zinc sulfate tablet and also determination of sulfate content of a mineral water sample.     

An electrochemical sensor based on CuO nanoparticle for simultaneous determination of hydrazine and bisphenol A

In the present research, the direct electrochemical oxidation of hydrazine in the presence of bisphenol A was investigated at a copper oxide nanoparticles/ionic liquid/carbon paste electrode (CuO NPs/IL/CPE). The combination of the good conductive 1-hexyl-3-methylimidazolium hexafluorophosphate and CuO nanoparticles resulted in an electrode with attractive properties for the determination of hydrazine in the presence of bisphenol A. The linear dynamic ranges were obtained in the ranges of 0.05–150 and 0.2–175 µM with the detection limits (3sb/m) 0.03 and 0.1 µM for HY and BPA, respectively. High stability, sensitivity, selectivity and reproducibility, fast response, the ease of preparation, and surface renewal made the sensor well suitable for the determination of hydrazine in the presence of bisphenol A, which are important pollutants in the environment. Finally, this new sensor was used for the determination of HY and BPA in some water samples such as river water and wastewater.     

Carbon Paste Electrode Plated with Lead Film. Voltammetric Characteristics and Application in Adsorptive Stripping Voltammetry

A lead film plated in situ at a carbon paste support was tested as a novel, potential electrode for adsorptive stripping voltammetric determination of cobalt traces in an ammonia buffer solution. To show the practical applicability of the new electrode, a catalytic adsorptive Co system in a supporting electrolyte containing 0.1 M ammonia buffer, 5×10^?4 M nioxime and 0.25 M nitrite was selected and investigated as a model solution. Pb and Co ions were simultaneously accumulated in situ on the electrode surface: Pb ions electrochemically at ?1.3 V) and then at ?0.75 V, at which potential the Co(II)‐nioximate complex was also pre‐concentrated via adsorption. Instrumental parameters, such as the time of nucleation and formation of Pb film deposits, the time of accumulation of the Co‐nioxime complex at the PbF/CPE, and the procedures of electrode regeneration, were optimized to obtain good reproducibility and sensitivity of the Co response. The optimized procedure yields favorable and highly stable stripping responses with good precision (RSD=3% for a 5×10^?8 M Co) and good linearity (up to 5×10^?7 M, coefficient of determination, R=0.996). The detection limit was 4×10^?10 M Co (0.023 μg L^?1) for an accumulation time of 120 s. The method enables the determination of Co in the presence of high excesses of Ni or Zn. The voltammetric data were correlated with the structural characterization by scanning electron microscopy (SEM) and X‐ray fluorescence spectroscopy (XRF).     

A Selective Simultaneous Determination of Levodopa and Serotonin Using a Glassy Carbon Electrode Modified with Multiwalled Carbon Nanotube/Chitosan Composite

A glassy carbon electrode (GCE) modified with carbon nanotube/chitosan (MWCNTs‐CHT/GCE) was used for the sensitive voltammetric determination of levodopa (Lev) and serotonin (Ser). The measurements were carried out using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CA). Under the optimum conditions the electrode provides a linear response versus Lev and Ser concentrations in the range of 2.0–220.0 µM and 0.5–130.0 µM, respectively, using DPV. The modified electrode was satisfactorily used for determination of Lev and Ser in human serum and urine with satisfactory results.     

Determination of Cysteine at Bismuth Nanostructure – Carbon Ionic Liquid Electrode by Square Wave Voltammetry

Bismuth nanostructure‐carbon ionic liquid electrode has been employed for sensitive determination of cysteine (Cys). Bismuth nanostructure was incorporated into the carbon ionic liquid electrode (CILE) and applied for determination of cysteine. An interaction was taking place between bismuth nanostructure and the thiol group of cysteine. The bismuth cysteinate complex oxidation potential occurred at more negative potential compared to the cysteine oxidation peak obtained at bare carbon ionic liquid electrode (CILE). Square wave voltammetry (SWV) was used for the determination of the cysteine and satisfactory results were obtained. The calibration curve was linear in the concentration range of 1 to 500 µM and 0.5–2 mM of Cys. A low detection limit of 0.5 µM was achieved for Cys. The electrode showed a good selectivity for determination of cysteine in the presence of other amino acids. The proposed electrode was satisfactory applied for the determination of cysteine in human serum plasma sample.     

Utilization of Carbon Paste Electrodes for the Voltammetric Determination of Chlortoluron

Conventional (CPE) and miniaturized (m‐CPE) carbon paste electrodes consisting of a carbon paste filled capillary were used for differential pulse voltammetric determination of chlortoluron in samples of river water and soil, in the latter case after the extraction by methanol. Britton‐Robinson buffer pH 3 with low content of methanol was found to be optimal for the determination. The achieved determination limits were 2.8 µmol L^?1 and 0.34 µmol L^?1 in river water, and 3.1 and 4.3 µg g^?1 in soil, using CPE and m‐CPE, respectively.     

Palladium Paste Nanocomposite Electrode as a New Metallic Electrocatalyst for Ethanol Oxidation and Nonenzymatic Amperometric Sensor in Alkaline Medium

Palladium paste nanocomposite electrode was employed as an efficient electrocatalyst for ethanol oxidation and nonenzymatic amperometric ethanol sensor, in alkaline media. The combined application of unique properties of nanomaterials and ionic liquids results in electrodes with interesting advantages compared to the conventional Pd disk electrodes. High tolerance towards accumulation of carbonaceous species (CO‐like intermediates) and poisoning by strongly adsorbed species suggests this electrode suitable for many applications. The sensor has the advantages of high sensitivity, low detection limit (20.0 µM), wide linear range (30.0 µM–1.6 M), ease of renewing the electrode surface, good long‐term stability and reproducibility for ethanol determination.     

An Electrochemical Sensor Based on Nitrogen‐doped Carbon Nanofiber for Bisphenol A Determination

In this paper, bisphenol A was determined by electrochemical method at a nitrogen‐doped carbon nanofiber modified carbon paste electrode (NCNF/CPE) with high sensitivity and good selectivity. NCNF was obtained by a simple electrospinning followed by carbonization procedure, in which polyacrylonitrile (PAN) as precursor and nitrogen doping was realized by re‐utilizing the tail gas that produced in the thermal pretreatment process. Good reproducibility and high stability were obtained for BPA detection at NCNF modified CPE. Current response plotted with BPA concentration was linear in the range of 0.1–60 μM with LOD of 0.05 μM. The proposed electrochemical sensor was employed for BPA determination with satisfactory recoveries for real water samples, indicating the practical applicability of NCNF/CPE.     

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.     

Catalytic Adsorptive Stripping Chronopotentiometry of Co(II)‐DMG‐Bromate System at an In Situ Plated Lead Film Electrode

A novel catalytic adsorptive stripping chronopotentiometric (CC‐CAdSCP) procedure for the determination of Co(II) traces was developed using a lead film electrode (PbFE). The PbFE was generated in situ on a glassy carbon support from a 0.1 M ammonia buffer containing 1×10^?5 M Pb(II), 6.5×10^?5 M DMG and the target metals. An addition of 0.2 M NaBrO₃ to the solution yielded an 11‐fold catalytic enhancement of chronopotentiometric response of the Co(II)‐DMG complex. The CC‐CAdSCP curves were well‐developed, sharp and reproducible (RSD 5.0 % for 5×10^?9 M Co(II)). The limit of detection for Co(II) for 210 s of accumulation time was 4×10^?10 M (0.024 µg L^?1). In addition, the elaborated method allowed the simultaneous quantification of Co(II) and Ni(II) simultaneously.     

Highly Selective Sensing Platform Utilizing Graphene Oxide and Multiwalled Carbon Nanotubes for the Sensitive Determination of Tramadol in the Presence of Co‐Formulated Drugs

Novel insights into the strategy of highly precise, carbon‐based electrochemical sensors are presented by exploring the excellent properties of graphene oxide (GO) and multiwalled carbon nanotube composites (GO‐MWCNTs/CPE) for the sensitive determination of tramadol hydrochloride (TRH). Cyclic voltammetry, differential pulse voltammetry, chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) scanning electron microscopy, and X‐ray diffraction (XRD) techniques were used to characterize the properties of the sensor. The linear response obtained for TRH using the GO‐MWCNTs/CPE was found to be over the range of 2.0x10⁻⁹ to 1.1x10⁻³ M with a good linearity and high correlation (0.9996). The limits of detection and quantification were found to be 1.50x10⁻¹⁰ M and 4.99 x 10⁻¹⁰ M, respectively. The proposed sensor was applied for determination of TRH in the presence of presence of co‐formulated drugs ketorolac tromethamine (KTM) and paracetamol (PAR). The sensor was shown to successfully apply to the determination of TRH in plasma as real samples. Satisfactory recoveries of TRH from samples clearly revealed that the proposed sensor can be applied into clinical analysis, quality control and a routine determination of drugs in pharmaceutical formulations.     

Electrochemical Determination of Phenolic Acids at a Zn/Al Layered Double Hydroxide Film Modified Glassy Carbon Electrode

A stable sensor for the determination of gallic acid (GA) and caffeic acid (CA) was fabricated by electrodeposition of Zn‐Al‐NO₃ layered double hydroxide film on a glassy carbon electrode (LDHf/GCE). A sensitive electrochemical method was achieved for the determination of GA and CA in a phosphate buffer solution (pH 3). The differential pulse voltammetry response of the LDHf/GCE to GA has a linear concentration range from 4 µM to 600 µM with a correlation coefficient of 0.9985 and the calculated detection limit of 1.6 µM at a signal‐to‐noise ratio of 3. The differential pulse voltammetry response of the LDHf/GCE to CA has a linear concentration range from 7 µM to 180 µM with a correlation coefficient of 0.9969 and the calculated detection limit of 2.6 µM at a signal‐to‐noise ratio of 3. The constructed sensor was applied to the determination of GA in commercial green tea samples.