Electrochemical determination of homocysteine using carbon nanotubes modified paste electrode and isoprenaline as a mediator

Homocysteine (HCy) is an important amino acid containing thiol group and is known as a risk factor in relation to ischemic heart disease and stroke. In this study the electrochemical determination of homocysteine (HCy) has been described using isoprenaline hydrochloride (ISP) as a mediator on multiwall carbon nanotubes modified paste electrode (MWCNTPE). Electrochemical behavior of homocysteine was investigated by cyclic voltarrtmetry and chronoamperometry. The cyclic voltammograms showed that the electrocatalytic oxidation of homocysteine occurs in the presence of ISP on the surface of MWCNTPE at a potential about 640 mV. Also, results showed that the oxidatation peak current of HCy at the modified carbon nanotubes electrode was more than unmodified electrode. The diffusion coefficient and the kinetic parameters including electron transfer coefficient and rate constant of electrocatalytic reaction were determined using electrochemical approaches. Linear sweep voltammetry results showed that electrocatalytic oxidation peak current of HCy had linear dynamic range in the range of 5.0 to 800 μmol L^?1 with a detection limit of 3.3 μmol L^?1 in pH 3.5 (universal buffer).     

Electrocatalytic determination of penicillamine using multiwall carbon nanotubes paste electrode and chlorpromazine as a mediator

In this study, we describe the application of carbon paste electrode modified with multiwall carbon nanotubes as a voltammetric sensor for determination of penicillamine (PA) in the presence of chlorpromazine as a mediator. This modified electrode showed very efficient electrocatalytic activity for the anodic oxidation of PA. The peak current of linear sweep voltammograms of PA increased linearly with it’s concentration in the range of 0.5–500 μM PA. The detection limit for PA was 0.2 μM. The RSDs for 1.0 and 10.0 μM PA were 1.1 and 1.7%, respectively. The proposed sensor was successfully applied for the determination of PA in human urine and tablet.     

Voltammetric sensor for glutathione determination based on ferrocene-modified carbon paste electrode

The electrocatalytic oxidation of glutathione (GSH) has been studied at the surface of ferrocene-modified carbon paste electrode (FMCPE). Cyclic voltammetry (CV), double potential step chronoamperometry, and differential pulse voltammetry (DPV) techniques were used to investigate the suitability of incorporation of ferrocene into FMCPE as a mediator for the electrocatalytic oxidation of GSH in buffered aqueous solution. Results showed that pH 7.00 is the most suitable for this purpose. In the optimum condition (pH 7.00), the electrocatalytic ability of about 480 mV can be found and the heterogeneous rate constant of catalytic reaction was calculated as . Also, the diffusion coefficient of glutathione, D, was found to be 3.61 × 10^–5 cm² s⁻¹. The electrocatalytic oxidation peak current of glutathione at the surface of this modified electrode was linearly dependent on the GSH concentration and the linear analytical curves were obtained in the ranges of 3.2 × 10^–5 M–1.6 × 10^–3 M and 2.2 × 10^–6 M–3.5 × 10^–3 M with cyclic voltammetry and differential pulse voltammetry methods, respectively. The detection limits (3σ) were determined as 1.8 × 10^–5 M and 2.1 × 10^–6 M using CV and DPV, respectively. Finally, the electrocatalytic oxidation of GSH at the surface of this modified electrode can be employed as a new method for the voltammetric determination of glutathione in real samples such as human plasma.     

Sensitive and Selective Determination of Phenylhydrazine in the Presence of Hydrazine at a Ferrocene Monocarboxylic Acid Modified Carbon Nanotube Paste Electrode

In the present paper, the use of a carbon paste electrode modified by ferrocene monocarboxylic acid (FMC) and carbon nanotubes prepared by a simple and rapid method was described. The modified electrode showed an excellent character for electrocatalytic oxidization of phenylhydrazine (PHZ) and hydrazine (HZ) with a 300 mV separation of both peaks. Differential pulse voltammetric peak currents of PHZ and HZ increased linearly with their concentrations at the range of 0.8 µM to 700 µM and 16 µM to 800 µM and the detection limits (3σ) were determined to be 0.42 µM and 14 µM, respectively.     

Carbon Paste Electrode Incorporating 1‐[4‐(Ferrocenyl Ethynyl) Phenyl]‐1‐Ethanone for Electrocatalytic and Voltammetric Determination of Tryptophan

A carbon paste electrode spiked with 1‐[4‐ferrocenyl ethynyl) phenyl]‐1‐ethanone (4FEPE) was constructed by incorporation of 4FEPE in graphite powder‐paraffin oil matrix. It has been shown by direct current cyclic voltammetry and double step chronoamperometry that this electrode can catalyze the oxidation of tryptophan (Trp) in aqueous buffered solution. It has been found that under optimum condition (pH 7.00), the oxidation of Trp at the surface of such an electrode occurs at a potential about 200 mV less positive than at an unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, α and rate constant for the chemical reaction between Trp and redox sites in 4FEPE modified carbon paste electrode (4FEPEMCPE) were also determined using electrochemical approaches. The electrocatalytic oxidation peak current of Trp showed a linear dependent on the Trp concentrations and linear calibration curves were obtained in the ranges of 6.00×10^?6 M–3.35×10^?3 M and 8.50×10^?7 M–6.34×10^?5 M of Trp concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods, respectively. The detection limits (3σ) were determined as 1.80×10^?6 M and 5.60×10^?7 M by CV and DPV methods. This method was also examined as a selective, simple and precise new method for voltammetric determination of tryptophan in real sample.     

Electrocatalytic Oxidation and Voltammetric Determination of Hydrazine on the Tetrabromo‐p‐Benzoquinone Modified Carbon Paste Electrode

The electrochemical properties of hydrazine studied at the surface of a carbon paste electrode spiked with p‐bromanil (tetrabromo‐p‐benzoquinone) using cyclic voltammetry (CV), double potential‐step chronoamperometry and differential pulse voltammetry (DPV) in aqueous media. The results show this quinone derivative modified carbon paste electrode, can catalyze the hydrazine oxidation in an aqueous buffered solution. It has been found that under the optimum conditions (pH 10.00), the oxidation of hydrazine at the surface of this carbon paste modified electrode occurs at a potential of about 550 mV less positive than that of a bar carbon paste electrode. The electrocatalytic oxidation peak current of hydrazine showed a linear dependent on the hydrazine concentrations and linear analytical curves were obtained in the ranges of 6.00×10^?5 M–8.00×10^?3 M and 7.00×10^?6 M–8.00×10^?4 M of hydrazine concentration with CV and differential pulse voltammetry (DPV) methods, respectively. The detection limits (3σ) were determined as 3.6×10^?5 M and 5.2×10^?6 M by CV and DPV methods. This method was also used for the determination of hydrazine in the real sample (waste water of the Mazandaran wood and paper factory) by standard addition method.     

Determination of Tyrosine in the Presence of Sodium Dodecyl Sulfate Using a Gold Nanoparticle Modified Carbon Paste Electrode

A carbon paste electrode modified with gold nanoparticles (AuMCPE) was used as a highly sensitive sensor for determination of Tyrosine (Tyr), in the presence of an anionic surfactant, sodium dodecyl sulfate (SDS), in aqueous solution. The measurements were carried out by using of differential pulse voltammetry (DPV), cyclic voltammetry (CV), amd chronocoulometry and chronoamperometry methods. The prepared electrode shows voltammetric responses with high sensitivity and selectivity for Tyr in the presence of SDS. The relationship between the oxidation peak current of Tyr and its concentration was obtained linearly and it was 1.0 × 10^?7 to 1.0 × 10^?5 M with a detection limit of 5.5 × 10^?8 M in the absence of SDS. On the other hand the oxidation peak current of Tyr increased significantly at AuMCPE in the presence of SDS and its detection limit was reduced to 2.7 × 10^?9 M. The proposed voltammetric approach was also applied to the determination of Tyr concentration in human serum.     

Voltammetric Separation and Determination of Glutathione and L‐tyrosine with Chlorogenic Acid as an Electrocatalytic Mediator

A novel and sensitive voltammetric method was proposed for separation and determination of glutathione (GSH) and L‐tyrosine (Tyr) at acetylene black and chitosan modified glassy carbon electrode (AB‐CS/GCE). By introducing chlorogenic acid (CGA) as a new electrocatalytic mediator, GSH could be detected at much lower potential with symmetric peak shape. Acetylene black and chitosan composite served as current signal amplifier for sensitive detection. The electrochemical behavior of GSH and Tyr in the presence of CGA was studied at AB‐CS/GCE and complete separation of anodic peaks was achieved. Under the optimum conditions, the electrocatalytic oxidation peak current of GSH showed a linear dependence on its concentration in the ranges of 2.0×10⁻⁷‐4.0×10⁻⁵ M with the detection limit of 5.8×10⁻⁸ M (S/N=3), while the oxidation peak current of Tyr was linear to its concentration from 2.5×10⁻⁶ to 4.3×10⁻⁴ M with the detection limit of 9.2×10⁻⁷ M (S/N=3) by differential pulse voltammetry (DPV). The established method has been applied to the simultaneous determination of GSH and Tyr in human urine with satisfactory results.     

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.     

Voltammetric determination of cysteamine at multiwalled carbon nanotubes paste electrode in the presence of isoproterenol as a mediator

A sensitive electrochemical sensor for the determination of cysteamine(CA) was developed using a modified multiwall carbon nanotube paste electrode(MWCNTPE) with isoproterenol(ISPT) as a mediator.This modified electrode showed very high electrocatalytic activity for the anodic oxidation of CA.Under the optimized conditions,the electrocatalytic peak current showed a linear relationship with CA concentration in the range of 0.3–450.0 mmol/L with a detection limit of 0.09 mmol/L CA.The modified electrode was used for the determination of CA in real samples such as urine and drug samples.     

Selective and Simultaneous Voltammetric Determination of Glutathione,Uric Acid and Penicillamine by a Modified Carbon Nanotube Paste Electrode

In this paper, the use of a carbon paste electrode (CPE) modified by (E)‐3‐((2‐(2,4‐dinitrophenyl)hydrazono)methyl)benzene‐1,2‐diol (DHB) and carbon nanotubes (CNTs) for the determination of glutathione (GSH), uric acid (UA) and penicillamine (PA) is described. Initially, cyclic voltammetry was used to investigate the redox properties of the modified electrode in phosphate buffer. Next, the electrocatalytic oxidation of GSH via EC′ mechanism at the modified electrode was described. At the optimum pH of 7.0, the oxidation of GSH occurs at a potential that is 530 mV less positive than that of an unmodified carbon paste electrode. The values of the diffusion coefficient (D=2.5×10^?6 cm² s^?1) and the catalytic rate constant (k=1.7×10³ M^?1 s^?1) were calculated for GSH, using chronoamperometry. Based on differential pulse voltammetry, the oxidation of GSH exhibited a dynamic range between 0.4 and 700.0 µM and a detection limit (3σ) of 70.0 nM. Also, simultaneous determination of GSH, UA and PA was described at the modified electrode. Finally, this method was used for the determination of these substances in synthetic solutions and blood serum samples.     

L‐Cysteine Voltammetry at a Carbon Paste Electrode Bulk‐Modified with Ferrocenedicarboxylic Acid

The electrochemical behavior of L ‐cysteine studied at the surface of ferrocenedicarboxylic acid modified carbon paste electrode (FDCMCPE) in aqueous media using cyclic voltammetry, differential pulse voltammetry and double potential step chronoamperometry. It has been found that under optimum condition (pH 8.00) in cyclic voltammetry, the oxidation of L ‐cysteine occurs at a potential about 200 mV less positive than that of an unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, α, and catalytic reaction rate constant, k_h were also determined using electrochemical approaches. The electrocatalytic oxidation peak current of L ‐cysteine showed a linear dependent on the L ‐cysteine concentration and linear analytical curves were obtained in the ranges of 3.0×10^?5 M–2.2×10^?3 M and 1.5×10^?5 M–3.2×10^?3 M of L ‐cysteine concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (3σ) were determined as 2.6×10^?5 M and 1.4×10^?6 M by CV and DPV methods.     

Determination of hydroxylamine using a carbon paste electrode modified with graphene oxide nano sheets

A carbon paste electrode that was chemically modified with 3-(4'-amino-3'-hydroxy-biphenyl-4-yl)-acrylic acid (3,4-AA) was used as a selective electrochemical sensor for the detection of hydroxylamine. Cyclic voltammetry (CV), choronoamperometry (CHA) and square wave voltammetry (SWV) were used to investigate oxidation of hydroxylamine in aqueous solution. Under optimized concentration the electrocatalytic oxidation current peak for hydroxylamine increased linearly with concentration in the range of 0.025–10.0 μM. The detection limits for hydroxylamine was 0.012 μM. Finally, the modified electrode was applied to detection hydroxylamine in water samples.     

Fabrication and characterization of poly 2-napthol orange film modified electrode and its application to selective detection of dopamine

The present work is based on the use of a redox mediator containing an azo group for the selective determination of dopamine in the presence of uric acid and ascorbic acid by electrochemical method. A modified electrode was prepared by electrochemical polymerization of the poly 2-napthol orange film (P2NO) on the paraffin wax-impregnated graphite electrode (PIGE) by applying potential between ?0.6 and 0.8 V at scan rate of 50 mV s^?1 for 30 segments. The modified P2NO film electrode was characterized by ATR-IR spectroscopy, FE-SEM, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), hydrodynamic voltammetry (HDV), and chronoamperometry (CA). The P2NO film modified electrode exhibited selective determination of dopamine in the presence of uric acid and ascorbic acid, and the electrocatalytic activity for oxidation of dopamine was excellent. The linear range for the determination of dopamine was 0.6 to 250 μM with a limit of detection of 0.13 μM. The modified P2NO electrode showed good stability and reproducibility. The modified electrode was used for real sample analysis such as human blood serum, rat blood serum, and pharmaceutical samples (dopamine hydrochloride injection). The results obtained were found to be satisfactory.     

Electrocatalytic Oxidation and Voltammetric Determination of L‐Cysteic Acid at the Surface of p‐Bromanil Modified Carbon Paste Electrode

The electrochemical properties of L ‐cysteic acid studied at the surface of p‐bromanil (tetrabromo‐p‐benzoquinone) modified carbon paste electrode (BMCPE) in aqueous media by cyclic voltammetry (CV) and double step potential chronoamperometry. It has been found that under optimum condition (pH 7.00) in cyclic voltammetry, the oxidation of L ‐cysteic acid at the surface of BMCPE occurs at a half‐wave potential of p‐bromanil redox system (e.g., 100 mV vs. Ag|AgCl|KCl_sat), whereas, L ‐cysteic acid was electroinactive in the testing potential ranges at the surface of bare carbon paste electrode. The apparent diffusion coefficient of spiked p‐bromanil in paraffin oil was also determined by using the Cottrell equation. The electrocatalytic oxidation peak current of L ‐cysteic acid exhibits a linear dependency to its concentration in the ranges of 8.00×10^?6 M–6.00×10^?3 M and 5.2×10^?7 M–1.0×10^?5 M using CV and differential pulse voltammetry (DPV) methods, respectively. The detection limits (2σ) were determined as 5.00×10^?6 M and 4.00×10^?7 M by CV and DPV methods. This method was used as a new, selective, rapid, simple, precise and suitable voltammetric method for determination of L ‐cysteic acid in serum of patient's blood with migraine disease.     

Determination of Some Phenothiazines Compounds in Pharmaceuticals and Human Body Fluid by Electrocatalytic Oxidation at a Glassy Carbon Electrode Using Methylene Blue as a Mediator

Abstract

A glassy carbon electrode plus Methylene blue as a mediator was employed to study and sense the electrocatalytic oxidation of phenothiazines, including chlorpromazine, perphenazine, promazine, and fluphenazine, using cyclic voltammetry and chronoamperometry as diagnostic techniques. The electron-transfer coefficient, alpha (= 0.45), for phenothiazines compounds at the surface of glassy carbon electrode was determined using a cyclic voltammetry technique. It was found that under a selected pH (8.6) the peak current due to the oxidation of Methylene blue at the surface of the electrode that occurrs at a potential of about ? 180 mV is proportional to the phenothiazines concentration. Linear analytical curves were obtained in the ranges of 1.0 × 10^?6 ? 2.1 × 10^?4 mol L^?1 for the phenothiazines compounds. The influences of potentially interfering substances on the current response of the system were examined. The method was used for the determination of phenothiazines compounds, including chlorpromazine, perphenazine, promazine, and fluphenazine in human.     

尿酸和叶酸存在下改性碳纳米管糊电极上多巴胺电催化氧化MohammadMazloum-Ardakani,MahboobeAbolhasani,Bibi-FatemehMirjalili,MohammadAliSheikh-Mohseni,AfsanehDehghani-Firouzabadi,AlirezaKhoshroo简

A chemically modified carbon paste electrode (CPE), consisting of 2,2''-[(1E)-(1,2-phenylenebis(azanylylidene)] bis(methanylylidene)]bis(benzene-1,4-diol) (PBD) and multiwalled carbon nanotubes (CNTs), was used to study the electrocatalytic oxidation of dopamine using cyclic voltammetry, chronoamperometry, and differential pulse voltammetry (DPV). First, the electrochemical behavior of the modified electrode was investigated in buffer solution. Then the diffusion coefficient, electrocatalytic rate constant, and electron-transfer coefficient for dopamine oxidation at the surface of the PBD-modified CNT paste electrode were determined using electrochemical approaches. It was found that under optimum conditions (pH = 7.0), the oxidation of dopamine at the surface of such an electrode occurred at about 200 mV, lower than that of an unmodified CPE. DPV of dopamine at the modified electrode exhibited two linear dynamic ranges, with a detection limit of 1.0 μmol/L. Finally, DPV was used successfully for the simultaneous determination of dopamine, uric acid, and folic acid at the modified electrode, and detection limits of 1.0, 1.2, and 2.7 μmol/L were obtained for dopamine, uric acid, and folic acid, respectively. This method was also used for the determination of dopamine in a pharmaceutical preparation using the standard addition method.     

Acetylferrocene Modified Carbon Paste Electrode; A Sensor for Electrocatalytic Determination of Hydrazine

The electrocatalytic oxidation of hydrazine at a carbon paste electrode spiked with acetylferrocene as a mediator was studied by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. In contrast to other ferrocenic compounds, acetylferrocene exhibits a chemical irreversible behavior, but it can act as an effective mediator for electrocatalytic oxidation of hydrazine, too. The heterogeneous electron transfer rate constant between acetylferrocene and the electrode substrate (carbon paste) and the diffusion coefficient of spiked acetylferrocene in silicon oil were estimated to be about 3.45×10^?4 cm s^?1 and 4.45×10^?9 cm² s^?1, respectively. It has been found that under the optimum conditions (pH 7.5) the oxidation of hydrazine occurs at a potential of about 228 mV less positive than that of an unmodified carbon paste electrode. The catalytic oxidation peak current of hydrazine was linearly dependent on its concentration and the obtained linear range was 3.09×10^?5 M–1.03×10^?3 M. The detection limit (2σ) has been determined as 2.7×10^?5 M by cyclic voltammetry. Also, the peak current was increased linearly with the concentration of hydrazine in the range of 1×10^?5 M–1×10^?3 M by differential pulse voltammetry with a detection limit of 1×10^?5 M. This catalytic oxidation of hydrazine has been applied as a selective, simple, and precise new method for the determination of hydrazine in water samples.     

Sodium dodecyl sulfate modified carbon nanotubes paste electrode as a novel sensor for the simultaneous determination of dopamine,ascorbic acid,and uric acid

A novel modified multiwall carbon nanotubes paste electrode with sodium dodecyl sulfate as a surfactant (SDS) has been fabricated through an electrochemical oxidation procedure and was used to electrochemically detect dopamine (DA), ascorbic acid (AA), uric acid (UA), and their mixture by cyclic voltammetry (CV) and differential voltammetry (DPV) methods. Several factors affecting the electrocatalytic activity of the hybrid material, such as the effect of pH, of the scan rate and of the concentration were studied. The bare carbon nanotubes paste electrode (BCNTPE) and SDS-modified carbon nanotubes paste electrode (SDSMCNTPE) were characterized using Field Emission Scanning Electron Microscopy (FESEM) and Energy-Dispersive X-ray spectroscopy (EDX). Using the CV procedure, a linear analytical curve was observed in the 1 × 10⁻⁶–2.8 × 10⁻⁵ M range with a detection limit at 3.3 × 10⁻⁷ M in pH 6.5, 0.2 M phosphate buffer solutions (PBS).     

Electrodeposited acetaminophen as a bifunctional electrocatalyst for simultaneous determination of ascorbic acid, glutathione, adrenaline and tryptophan

In this study, an acetaminophen-modified glassy carbon electrode (ACMGCE) was fabricated for the purpose of investigating its electrochemical behavior by cyclic voltammetry (CV). ACMGCE serves as an excellent bifunctional electrocatalyst for the oxidation of ascorbic acid (AA) and glutathione (GSH) in a phosphate buffer solution (pH 7.0). The kinetic parameters such as the electron transfer coefficient, α, and the heterogeneous electron transfer rate constant, k', for the oxidation of AA and GSH at the ACMGCE surface were determined by CV. In addition, detection limits of 3.89 μM for AA and 0.37 μM for GSH were obtained at the ACMGCE using a differential pulse voltammetric (DPV) method. In DPV, the bifunctional modified electrode could separate the oxidation peak potentials of AA, GSH, adrenaline (AD) and tryptophan (Trp) present in the same solution, though the peak potentials were indistinguishable at a bare GCE. Finally, the modified electrode was successfully applied to the determination of AA in a pharmaceutical preparation and GSH in a human plasma sample.