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.     

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.     

Electrochemical Studies and Selective Detection of Thioridazine Using a Carbon Paste Electrode Modified with ZnS Nanoparticles and Simultaneous Determination of Thioridazine and Olanzapine

A novel ZnS nanoparticle‐modified carbon paste electrode (ZnSNP‐MCPE) was fabricated and used to study the electrooxidation of thioridazine (TR) using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The determination conditions, such as accumulation time, pH of solution, and modifier amount were optimized. The mechanism of the electrooxidation process on the surface of the modified electrode was studied electrochemically. A linear range of 0.1–36.0 µM with detection limit of 65.0 nM was obtained for TR. In a mixture containing TR and olanzapine (OLZ), the DPV peaks of two compounds can be well separate from each other with a potential difference of 425 mV. Finally, this method was successfully applied to determinate the TR content in real samples.     

A New Sensor for Simultaneous Determination of Tyrosine and Dopamine Using Iron(III) Doped Zeolite Modified Carbon Paste Electrode

A new chemically modified electrode is constructed based on iron(III) doped zeolite modified carbon paste electrode (Fe³⁺Y/ZMCPE). The new sensor could be used for the simultaneous determination of the biologically important compounds dopamine (DA) and tyrosine (Tyr). The measurements are carried out using differential pulse voltammetric (DPV) method. The prepared modified electrode shows voltammetric responses of high sensitivity, selectivity and stability for DA and Tyr under optimal conditions, which makes it a suitable sensor for simultaneous trace detection of DA and Tyr in solution. Application of the DPV method demonstrates that in the Briton Robinson buffer solutions (pH=5) containing 50 µmol/L Tyr, there is a linear relationship between the oxidation peaks and the concentrations of DA over the range of 0.1–200 µmol/L, with a detection limit of 0.05 µmol/L (S/N=3). For Tyr a linear correlation between oxidation peak current and concentration of Tyr over the range of 0.5–200 µmol/L (containing 50 µmol/L DA), with a detection limit of 0.08 µmol/L is obtained. The analytical performances of this sensor are evaluated for the detection of DA and Tyr in human serum and a medicine.     

Differential Pulse Voltammetric Determination of Montelukast in Tablets and Human Plasma by Using Chitosan Modified Carbon Paste Electrode

Electrochemical reduction and determination of montelukast (MKS) was studied in methanol – 0.1 M HCl solution (1 : 1, v/v) by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at chitosan modified carbon paste electrode. The linear range was 1.70×10^?7–1.83×10^?5 M for DPV analysis. Limit of detection (LOD) and limit of quantification (LOQ) were 5.32×10^?8 M and 1.61×10^?7 M, respectively. The developed method was successfully applied to the determination of MKS in tablets and spiked human plasma. The results obtained were in good agreement with those obtained using a reported spectrofluorimetric technique.     

Polyfurfural-Electrochemically Reduced Graphene Oxide Modified Glassy Carbon Electrode for the Direct Determination of Nitrofurazone

An electrochemical sensor based on a polyfurfural-electrochemically reduced graphene oxide modified glassy carbon electrode has been developed for the sensitive and rapid determination of nitrofurazone. The morphologies and properties of the sensor were characterized by electrochemical impedance spectroscopy, scanning electron microscopy, cyclic voltammetry, and differential pulse voltammetry (DPV). In pH 7.0 Britton–Robinson buffer solution, the as-prepared polyfurfural-electrochemically reduced graphene oxide modified glassy carbon electrode shows excellent electrocatalytic performance for the electrochemical reduction of nitrofurazone, and the reduction peak current is about 9.45, 1.31, and 1.25 times higher than that of the bare glassy carbon electrode, polyfurfural modified glassy carbon electrode, and electrochemically reduced graphene oxide modified glassy carbon electrode, respectively. The DPV determination of nitrofurazone indicates that the linear range and detection limit of nitrofurazone are 1–50 and 0.25?µmol/dm³, respectively. In addition, this sensor exhibits high selectivity, reproducibility, stability, and also was successfully used to directly determine nitrofurazone in the commercial antibacterial lotion with comparative sensitivity to high-performance liquid chromatography, showing its promising application prospects.     

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.     

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.     

A Glassy Carbon Electrode Modified with Multiwalled Carbon Nanotube/Chitosan Composite as a New Sensor for Simultaneous Determination of Acetaminophen and Mefenamic Acid in Pharmaceutical Preparations and Biological Samples

A new chemically modified electrode is constructed based on multiwalled carbon nanotube/chitosan modified glassy carbon electrode (MWCNTs‐CHT/GCE) for simultaneous determination of acetaminophen (ACT) and mefenamic acid (MEF) in aqueous buffered media. The measurements were carried out by application of differential pulse voltammetry (DPV), cyclic voltammetry (CV) and chronoamperometry (CA) methods. Application of DPV method showed that the linear relationship between oxidation peak current and concentration of ACT and MEF were 1 μM to 145 μM, and 4 μM to 200 μM, respectively. The analytical performance of this sensor has been evaluated for detection of ACT and MEF in human serum, human urine and a pharmaceutical preparation with satisfactory results.     

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.     

Evaluation of the Potentialities of a Carbon Nanotubes/Silicone Rubber Composite Electrode in the Determination of Hydrochlorothiazide

A multiwall carbon nanotube/silicone rubber (MWCNT/SR) composite electrode has been used for the determination of hydrochlorothiazide (HCTZ) in pharmaceutical formulations by differential pulse voltammetry (DPV). The electro-oxidation process was evaluated by cyclic voltammetry, from which it was observed that HCTZ presents an irreversible oxidation peak at 0.82 V vs. saturated calomel electrode (SCE) in the potential range from 0.5 to 1.1 V, in Britton-Robinson buffer pH 7.0 at MWCNT/SR. HCTZ was determined by DPV using a MWCNT/SR 70% (MWCNT, m/m) composite electrode after the optimization of the experimental parameters. The linear range was from 5.0 to 70.0 µ mol L^?1, with a limit of detection (LOD) of 2.6 µ mol L^?1. The HCTZ was determined in pharmaceutical formulations using the proposed composite electrode and the results agreed with those from the official high performance liquid chromatography (HPLC) method within 95% confidence level, according to the t-Student test.     

Carbon Nanotube Based Sensor for Simultaneous Determination of Acetaminophen and Ascorbic Acid Exploiting Multiple Response Optimization and Measures in the Presence of Surfactant

A simple procedure for the simultaneous determination of acetaminophen (AC) and ascorbic acid (AA) by differential pulse voltammetry (DPV) using a carbon nanotube paste electrode exploiting measures in cetylpyridinium bromide (CPB) medium is described. Under the best instrumental parameters of DPV, optimized by means of factorial design, the calibration plots in the range 100.0–700.0 µmol L^?1 (r=0.993) and 39.4–146.3 µmol L^?1 (r=0.995) with limits of detection of 7.1 and 2.1 µmol L^?1, were achieved for AA and AC, respectively. The developed method was successfully applied for the AC and AA determination in pharmaceutical formulations, whose accuracy was attested by comparison with HPLC method.     

Simultaneous Sensitive Determination of Dopamine and Uric Acid in the Presence of Excess Ascorbic Acid with a Magnetic Chitosan Microsphere/Thionine Modified Electrode

Magnetic chitosan microspheres (MCMS) and thionine were incorporated in a modified electrode for the simultaneous sensitive determination of dopamine (DA) and uric acid (UA). Due to the unique properties of the MCMS and the electron mediation of thionine, this modified electrode showed excellent electrocatalytic oxidation toward dopamine and uric acid with a large separation of peak potentials and a significant enhancement of peak currents. However, the electrochemical behavior of ascorbic acid may be depressed at the modified electrode. Differential pulse voltammetry was used for the simultaneous sensitive determination of dopamine and uric acid in the presence of excess ascorbic acid at this modified electrode. The current responses showed excellent linear relationships in the range of 2–30 µM and 9–100 µM for dopamine and uric acid, respectively. The detection limits were estimated to be 0.5 µM and 2.3 µM for dopamine and uric acid, respectively. In addition, this modified electrode showed excellent repeatability, good stability, and satisfactory reliability, thus indicating potential for the practical applications.     

Electrochemical Behavior and Ultrasensitive,Simple and Effective Voltammetric Determination of Acetaminophen Using Modified Glassy Carbon Electrode Based on 4-Hydroxyquinoline-3-carboxylic Acid

An electrochemical oxidation of acetaminophen (ACOP) has been successfully performed by using glassy carbon electrode covered with 4-hydroxyquinoline-3-carboxylic acid (4HQ3CA) to reinforce electrode's feature. To characterize the modified electrode (4HQ3CA/GC), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and Fourier transform infrared spectroscopy (FT-IR) techniques were used. The finding optimum conditions (supporting electrolyte, pH) and the electrochemical determination studies were performed with differential pulse voltammetry (DPV). It was decided that the supporting electrolyte medium suitable for ACOP determination was Britton-Robinson (BR) buffer and the effect of pH change on the oxidation peak of ACOP in this media was investigated. The effect of changing scan rate on the oxidation peak of ACOP was examined and this study showed that the oxidation process of ACOP on the 4HQ3CA/GC modified electrode surface was diffusion and adsorption controlled process. A wide concentration range from 0.0025 μM to 141 μM with a limit of detection (LOD) of 5.98×10⁻¹⁰ M (3 s/m) was obtained. This prepared sensor was carried out for the determination of ACOP in pharmaceutical sample.     

Simultaneous Determination of Isoproterenol,Acetaminophen and Folic Acid Using a Novel Nanostructure‐Based Electrochemical Sensor

In this study, a carbon paste electrode modified with (E)‐2‐((2‐chlorophenylimino)methyl)benzene‐1,4‐diol (CD) and titanium dioxide nanoparticles (TiO₂) was used to prepare a novel electrochemical sensor. The objective of this novel electrode modification was to seek new electrochemical performances for the detection of isoproterenol (IP) in the presence of acetaminophen (AC) and folic acid (FA). Initially, cyclic voltammetry (CV) was used to investigate the redox properties of this modified electrode at various scan rates. In the following, the mediated oxidation of IP at the modified electrode was described. The results showed an efficient catalytic activity of the electrode for the electrooxidation of IP, which leads to a reduction in its overpotential by more than 235 mV. The value of the electron transfer coefficient (α), catalytic rate constant (k_h) and diffusion coefficient (D) were calculated for IP, using electrochemical approaches. Based on differential pulse voltammetry (DPV), the oxidation of IP exhibited a dynamic range between 0.5 and 1000 µM and a detection limit (3σ) of 0.47 µM. DPV was used for simultaneous determination of IP, AC and FA at the modified electrode. Finally, this method was used for the determination of IP in real samples, using standard addition method.     

A Sensitive Simultaneous Determination of Adrenalin and Paracetamol on a Glassy Carbon Electrode Coated with a Film of Chitosan/Room Temperature Ionic Liquid/Single‐Walled Carbon Nanotubes Nanocomposite

The present work demonstrates that simultaneous determination of adrenalin (AD) and paracetamol (PAR) can be performed on single‐walled carbon nanotube/chitosan/ionic liquid modified glassy carbon electrode (SWCNT‐CHIT‐IL/GCE). The electro‐oxidations of AD and PAR were investigated with cyclic voltammetry (CV), differential pulse voltammetry (DPV) and also chronoamperometry (CA) methods. DPV experiments showed that the oxidation peak currents of AD and PAR are proportional to the corresponding concentrations over the 1–580 μmol/L and 0.5–400 μmol/L ranges, respectively. The RSD at a concentration level of 15 μmol/L AD and 15 μmol/L PAR were 1.69% and 1.82%, respectively. Finally the modified electrode was used for simultaneous determination of AD and PAR in real samples with satisfactory results.     

Simultaneous Voltammetric Determination of Captopril and Hydrochlorothiazide on a Graphene/Ferrocene Composite Carbon Paste Electrode

In this work, a voltammetric method has been developed for the simultaneous determination of captopril (CPT) and hydrochlorothiazide (HCT) in pharmaceutical combinations and clinical samples using a graphene/ferrocene composite carbon paste (GR/Fc/CP) electrode. The electrochemical behaviors of CPT and HCT were individually and simultaneously investigated at the surface of the GR/Fc/CP electrode. In differential pulse voltammetric (DPV) mode and under optimized experimental conditions, CPT and HCT gave linear responses over the concentration ranges 1.0–430 µM and 0.5–390 µM (r²>0.99), respectively. The prepared electrode could be used for simultaneous determination of CPT and HCT in some real samples.     

Room-Temperature Ionic Liquid and Multi-Walled Carbon Nanotube Composite Modified Carbon-Ceramic Electrode as a Sensitive Voltammetric Sensor for Indomethacin

The electrochemical behavior of indomethacin on the surface of a carbon-ceramic electrode modified with multi-walled carbon nanotubes and an ionic liquid composite film is reported. The results show that the nano-structured film exhibited excellent enhancement effects on the electrochemical oxidation of indomethacin. The developed sensor presented a linear response to indomethacin over the concentration range from 1 to 50 µM with a detection limit of 0.26 µM. The proposed modified electrode was employed for the determination of indomethacin in biological and pharmaceutical samples using differential pulse voltammetry.     

Electropolymerization of Thin Film Conducting Polymer and Its Application for Simultaneous Determination of Ascorbic Acid,Dopamine and Uric Acid

In this paper electropolymerization of a thin film of para‐phenylenediamine (PPD) is studied at glassy carbon electrode (GCE) in sulfuric acid media by cyclic voltammetry. The results showed that this polymer was conducting and had a reproducible redox couple in the potential region from 0.0 to 0.4 V in phosphate buffer solution. This modified GCE (p‐PPD‐GCE) was applied for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) using differential pulse voltammetry (DPV). The p‐PPD‐GCE in 0.1 M phosphate buffer solution (pH 5.0) separated the DPV signals of AA, DA and UA with sufficient potential differences between AA–DA and DA–UA and also enhanced their oxidation peak currents. The oxidation currents were increased from 2.0 to 2000.0 µM for AA, 10.0 to 1250.0 µM for DA and 50.0 to 1600.0 µM for UA. The detection limits were evaluated as 0.4, 1.0 and 2.5 µM for AA, DA and UA, respectively (S/N=3).     

Voltammetric measurement of trace amount of glutathione using multiwall carbon nanotubes as a sensor and chlorpromazine as a mediator

In this work, we propose chlorpromazine as a new mediator for the rapid, sensitive, and highly selective voltammetric determination of glutathione (GSH) using multiwall carbon nanotubes paste electrode (MWCNTPE). The experimental results showed that the carbon nanotubes paste electrode has a highly electrocatalytic activity for the oxidation of GSH in the presence of chlorpromazine as a mediator. Cyclic voltammetry, double potential step chronoamperometry, and differential pulse voltammetry (DPV) are used to investigate the suitability of chlorpromazine at the surface of MWCNTPE as a mediator for the electrocatalytic oxidation of GSH in aqueous solutions. It is shown that chlorpromazine can catalyze the oxidation of GSH in an aqueous buffer solution to produce a sharp oxidation peak current at about +0.70 versus Ag/AgCl as a reference electrode. Kinetic parameters such as electron transfer coefficient and catalytic reaction rate constant, k/h, are also determined. Using DPV and under the optimum conditions at pH 4.0, the electrocatalytic oxidation peak current of GSH shows a linear dependence on GSH concentration in the GSH concentration range of 0.3 to 18.3 µM. The detection limit (3σ) is determined to be 0.16 µM. The relative standard deviation for 1.5 and 5.0 µM GSH are found to be 3.7% and 2.5%, respectively. The proposed method may, thus, also be used as a novel, selective, simple, and precise method for the voltammetric determination of GSH in such real samples as hemolyzed erythrocyte.