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.     

Comparison of Boron‐Doped Diamond and Glassy Carbon Electrodes for Determination of Procaine Hydrochloride

The electrochemical oxidation of procaine hydrochloride (PC?HCL, 2‐diethylaminoethyl 4‐aminobenzoate hydrochloride) was investigated at as‐deposited boron‐doped diamond (ad‐BDD) electrode, anodically oxidized BDD (ao‐BDD) electrode and glassy carbon (GC) electrode using cyclic voltammetry (CV). Well‐defined cyclic voltammograms were obtained for PC?HCL oxidation with high signal‐to‐background (S/B) ratio, low tendency for adsorption, good reproducibility and long‐term stability at ad‐BDD electrode, demonstrating its superior electrochemical behavior and significant advantages in contrast to ao‐BDD and GC electrode. At 100 μM PC?HCL, the voltammetric S/B ratio was nearly one order of magnitude higher at an ad‐BDD electrode than that at a GC electrode. In a separate set of experiments for oxidation of 100 μM PC?HCL, 96%, 92% and 84% of the initial oxidation peak current was retained at the ad‐BDD, ao‐BDD and GC electrode, respectively, by stirring the solution after the tenth cycle. The current response was linearly proportional to the square root of the scan rate within the range 10–1000 mV s^?1 in 10 μM PC?HCL solutions, indicating that the oxidation process was diffusion‐controlled with negligible adsorption at an ad‐BDD surface. The good linearity was observed for a concentration range from 5 to 200 μM with a linear equation of y=0.03517x+0.65346 (r=0.999), and the detection limit was 0.5 μM for oxidation of PC?HCL at the ad‐BDD electrode. The ad‐BDD electrode could maintain 100% of its original activity after intermittent use for 3 months.     

Electrochemical Behavior and Determination of Hyoscine‐N‐Butylbromide from Pharmaceutical Preparations

The electrooxidation of hyoscine N‐butylbromide (HBB) was investigated by rotating disk electrode voltammetry, cyclic voltammetry and controlled potential coulometry in 0.1 M HNO₃ and in 0.1 M tetrabutylammonium perchlorate (TBAP) solutions of acetonitrile at a platinum (Pt) electrode. Based on the results obtained, it is suggested that a bromide ion of HBB was oxidized in one reversible step in aqueous solutions and in two reversible steps in acetonitrile. A differential pulse voltammetric (DPV) method at a Pt electrode was developed for the determination of HBB in the concentration range of 1.0 × 10^?6‐1.0 × 10^?3 M. The procedure was applied to the determination of HBB in its formulations as well as its recovery from blood serum and urine samples.     

Electrocatalytic Determination of Nitrite on a Rigid Disk Electrode Having Cobalt Phthalocyanine Prepared In Situ

This work reports an in situ cobalt(II) phthalocyanine (CoPc) synthesis on a SiO₂/SnO₂ (SiSn) matrix surface obtained by the sol‐gel method and its electrocatalytic activity for oxidation of nitrite. A rigid disk electrode with SiSn/CoPc was used to study the electrooxidation of nitrite by the cyclic voltammetric, chronoamperometric techniques and differential pulse voltammetry (DPV). The adsorbed phthalocyanine electrocatalyzed nitrite oxidation at 0.73 V (versus SCE) using the DPV technique. The anodic peak current intensities, plotted from differential pulse voltammograms in 1 mol L^?1 KCl for the concentration range 0.002 to 3.85 mmol L^?1 of nitrite were linear, with a correlation coefficient of 0.998 and a detection limit of 0.95 μmol L^?1.     

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.     

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.     

Electrochemical Behaviour of Carbamazepine in Acetonitrile and Dimethylformamide Using Glassy Carbon Electrodes and Microelectrodes

The electrochemical reduction of carbamazepine in acetonitrile (ACN) and dimethylformamide (DMF) using a glassy carbon electrode and microelectrodes has been studied. The reduction process is consistent with an electrochemical‐chemical mechanism (EC) involving a two electron transfer followed by a first order reaction, as shown by the cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Half‐wave potential, number of electron transferred, diffusion coefficient and rate constant of the associated chemical reaction are reported. Limits of detection (LOD) for DPV are 0.92 and 0.76 µg mL^?1 (3.89×10^?6 mol L^?1 and 3.21×10^?6 mol L^?1) in ACN and DMF, respectively. Precision (%RSD) and recovery (%) values when pharmaceutical compounds (200mg carbamazepine tablets) and spiked plasma samples were tested ranged from 1.09 to 9.04 % and % recoveries ranged from 96 to 104.1 %.     

Electrocatalytic Oxidation and Determination of Nitrite at Multi‐walled Carbon Nanotubes Modified Carbon Ceramic Electrode

In the present work, the electrochemical oxidation of nitrite on carbon ceramic electrode (CCE) modified with multi‐walled carbon nanotubes (MWCNTs) was investigated. The modified electrode exhibited catalytic activity toward the electrooxidation of nitrite. Experimental parameters such as solution pH, scan rate, concentration of nitrite and nanotubes amount were studied. It was shown nitrite can be determined by differential pulse voltammetry (DPV) and hydrodynamic amperometry (HA) using the modified electrode. Under the optimized conditions the calibration plots are linear in the concentration ranges of 15‐220 and 50‐3000 μM with limit of detections of 4.74 and 35.8 μM for DPV and HA, respectively. The modified electrode was successfully applied for analysis of nitrite in spinach sample. The results were favorbly compared to those obtained by UV‐Visible spectrophotometric method. The results of the analysis suggest that the proposed method has promise for the routine determination of nitrite in the examined products.     

Voltammetric Determination of Trace Amounts of 2‐Methyl‐4,6‐Dinitrophenol at a Silver Solid Amalgam Electrode

The voltammetric behavior of 2‐methyl‐4,6‐dinitrophenol was investigated by differential pulse voltammetry (DPV) at a nontoxic mercury meniscus‐modified silver solid amalgam electrode (m‐AgSAE). Conditions have been found for its determination by DPV at m‐AgSAE in the concentration range of 0.2 to 1 μmol L^?1.     

Nickel oxide nanoparticles decorated graphene quantum dot as an effective electrode modifier for electrocatalytic oxidation and analysis of clozapine

In the present work, a novel, simple, and sensitive clozapine (CLZ) sensor was developed based on nickel oxide nanoparticle (NiO)-decorated graphene quantum dot (GQD)-modified glassy carbon electrode (NiO/GQD/GCE). NiO/GQD/GCE was prepared by simple electrodeposition, the electrochemical behavior of CLZ at the surface of the prepared electrode was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), and an improved reversibility and increased peak current with negative shift in the oxidation potential were observed at the proposed electrode. The effect of some experimental parameters has been examined, and based on the results, an electron transfer–chemical reaction–electron transfer mechanism has been proposed for CLZ electrooxidation. The differential pulse voltammetric response of the NiO/GQD/GCE was linear to the concentration of CLZ in the range of 3?×?10^?9 to 1?×?10^?6 M, and the detection limit was found to be 0.55 nM (S/N?=?3). The method has been successfully used for the selective determination of the CLZ amount in the pharmaceutical preparations and human serum samples with good accuracy and precision.     

Spectroelectrochemical and Voltammetric Studies of L‐DOPA

The electrooxidation of L -dopa at GC electrode was studied by in situ UV-vis spectroelectrochemistry (SEC) and cyclic voltammetry. The mechanism of electrooxidation and some reaction parameters were obtained. The results showed that the whole electrooxidation reaction of L -dopa at glassy carbon (GC) electrode was an irreversible electrochemical process followed by a chemical reaction in neutral solution (EC mechanism). The spectroelectrochemical data were treated by the double logarithm method together with nonlinear regression, from which the formal potential E⁰=228 mV, the apparent electron-transfer number of the electrooxidation reaction αn=0.376 (R=0.99, SD=0.26), the standard electrochemical rate constant k⁰=(3.93±0.12)×10⁻4 cm s⁻¹ (SD=1.02×10⁻²), and the formation equilibrium constant of the following chemical reaction k_c=(5.38±0.34)×10⁻¹ s⁻¹ (SD=1.02×10⁻²) were also obtained.     

Adsorptive Stripping Differential Pulse Voltammetric Determination of Risperidone with a Multi‐Walled Carbon Nanotube‐Ionic Liquid Paste Modified Glassy Carbon Electrode

A new composite electrode has been fabricated based on coating multi‐walled carbon nanotubes (MWCNTs) and n‐octylpyridinum hexafluorophosphate (OPPF₆) ionic liquid composite on a glassy carbon (GC) electrode (OPPF₆‐MWCNTs/GCE). This electrode shows very attractive electrochemical performances for electrooxidation of risperidone (RIS) compared to conventional electrodes using carbon and mineral oil, notably improved sensitivity and stability. The oxidation peak potentials in cyclic voltammogram of RIS on the OPPF₆‐MWCNTs/GCE was occurred around 230 mV vs. SCE at Britton–Robinson (B–R) buffer (pH 4.0) at scan rate of 100 mV s^?1. The electrochemical parameters such as diffusion coefficient (D), charge transfer coefficient (α) and the electron transfer rate constant (k/_s) were determined using cyclic voltammetry. Under the optimized conditions, the peak current was linear to risperidone concentration over the concentration range of 10–200 nM with sensitivity of 0.016 μA/nM^?1 using differential pulse voltammetry. The detection limit was 6.54 nM (S/N = 3). The electrode also displayed good selectivity and repeatability. In the presence of clozapine (CLZ) the response of RIS kept almost unchanged. Thus this electrode could find application in the determination of RIS in some real samples. The analytical performance of the OPPF₆‐MWCNTs/GCE was demonstrated for the determination of RIS in human serum and pharmaceutical samples.     

Voltammetry as the First Method for Direct Determination of a Novel Antagonist of A2A Adenosine Receptors

In this article, for the first time, the analytical method for determination of a novel antagonist of A_2A adenosine receptors (8‐(4‐methoxyphenyl)‐4‐oxo‐4,6,7,8‐tetrahydroimidazo[2,1‐c][1,2,4]triazine‐3‐carbohydrazide, namely IMT), which can be used as a drug for liver diseases, was presented. For this purpose a commercially available boron‐doped diamond electrode (BDDE) in combination with differential pulse voltammetry (DPV) was applied. It was found by cyclic voltammetry (CV) that IMT displays at BDDE, as a sensor, two well‐defined oxidation peaks at potentials of 0.81 and 1.18 V and one reduction peak at 1.1 V vs. Ag/AgCl in 0.1 mol L^?1 acetate buffer (pH 4.5±0.1). The oxidation and reduction mechanism of IMT was proposed. The developed DPV method allowed the successful determination of IMT in the range of 0.05–50 μmol L^?1 with detection limit equal to 0.0094 μmol L^?1 and without any chemical modifications and electrochemical pretreatment of the electrode surface. The proposed procedure allows the determination of IMT in vitro directly from urine samples.     

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.     

Insights into the Oxidation Chemistry of 2‐Hydroxypurine by Electrochemical Methods

The oxidation chemistry of 2‐hydroxypurine has been investigated in phosphate containing supporting electrolytes at pH 1.4–9.8 at a pyrolytic graphite electrode by voltammetric studies, spectral studies, controlled potential electrolysis and related techniques. The kinetics of decay of the UV‐absorbing intermediate generated during electrooxidation was followed spectrophotometrically and the decay occurred in a pseudo‐first‐order reaction. The course of the electrode reaction has been deduced to involve a 6e, 6H⁺ oxidation of 2‐hydroxypurine via the formation of 2, 8‐dihydroxypurine. The electrooxidation of 2‐hydroxypurine has been found to be an EC reaction (electrode reaction followed by chemical reactions) in which charge transfer is followed by competitive chemical reactions. A detailed interpretation of the redox mechanism of 2‐hydroxypurine has been presented.     

Electroanalytical Approach for Quantification of Pesticide Maneb

For the first time, in this study electrochemical oxidation behavior of pesticide maneb is evaluated. Due to the structure electroanalytical quantification of maneb has not been exploited enough. Maneb electrochemical behavior was investigated using glassy carbon (GC), graphene modified glassy carbon (GR/GC) and boron doped diamond (BDD) electrodes. It is shown that only BDD shows satisfactory results toward maneb detection. Based on this, a simple, sensitive and selective electroanalytical method for determination of pesticide maneb using differential pulse voltammetry (DPV) is proposed, with a working linear range of 80–3000 nM and the limit of detection of 24 nM. The developed methodology has been applied for the determination of maneb in river water samples with satisfactory recovery. Additionally, this green method, being simple, fast, and free of chemical‐reduction reagents, offers several advantages over modified electrodes and expands the scope of BDD based electrochemical sensing devices, with promise for wider applications in environmental analysis.     

A Sensitive Simultaneous Determination of Epinephrine and Piroxicam Using a Glassy Carbon Electrode Modified with a Nickel Hydroxide Nanoparticles/Multiwalled Carbon Nanotubes Composite

The electrooxidation of epinephrine (EPI) and piroxicam (PRX) has been investigated by application of nickel hydroxide nanoparticles/multiwalled carbon nanotubes composite electrode (MWCNTs‐NHNPs/GCE) using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CA) methods. The modified electrode showed suitable electrochemical responses for EPI and PRX determination. Under the optimum conditions the electrode provides a linear response versus EPI and PRX concentrations in the range of 1–220 µM and 0.7–75 µM, respectively using the DPV method. Linear responses versus EPI and PRX concentrations in the range of 1–1000 µM and 1–800 µM, respectively, were obtained using the CA method. The modified electrode was used for determination of EPI and PRX in human urine with satisfactory results.     

Determination of some β‐Blockers by Electrochemical Detection on Polycrstalline Gold Electrode after Solid Phase Extraction (SPE)

The electroanalytical characterization and determination of three selected β‐blocker agents, namely propranolol, atenolol and nadolol using cyclic voltammetry and differential pulse voltammetry (DPV) in phosphate buffer solution (pH 2.5) plus 22 % acetonitrile (ACN), was described. The analytes were characterized through their electrooxidation processes on polycrystalline gold electrodes. The analytical determination of the selected molecules was performed using the differential pulse voltammetry (DPV) at pH 2.5. Under DPV conditions, the detection limits (LODs) ranged between 5 μM and 20 μM for propranolol and atenolol, respectively. For all investigated molecules, two well‐defined ranges of linearity Ip vs analyte concentration have been identified which correspond to specific calibration parameters. Calibration graphs (Ip vs concentration) considered in the first interval of linearity, shown correlation coefficients >0.99. A solid phase extraction (SPE) procedure using a polymeric mixed‐mode cationic sorbent (Strata‐X‐C), was studied and optimized. The proposed DPV‐SPE method was successfully applied for the determination of propranolol in several pharmaceutical formulations and urine sample, with results in close agreement with those obtained using traditional liquid chromatography technique coupled with spectrophotometric detection.     

Voltammetric determination of <Emphasis Type="Italic">D</Emphasis>-penicillamine based on its homogeneous electrocatalytic oxidation with potassium iodide at the surface of glassy carbon electrode

The electrooxidation of D-penicillamine (D-PA) has been studied in the presence of potassium iodide in various buffered aqueous solutions (4.00 ≤ pH ≤ 9.00) at the surface of glassy carbon electrode using cyclic voltammetry, differential pulse voltammetry and chronoamperometry. It has been found that under optimum pH (pH 5.00) in cyclic voltammetry, the electrooxidation of D-PA in the presence of potassium iodide as a homogeneous mediator occurred at a potential about 220 mV less positive than that in absence of potassium iodide at the surface of glassy carbon electrode. The homogeneous electrocatalytic oxidation current wave of D-penicillamine was linearly dependent on the D-PA concentration and a linear calibration curve was obtained in the ranges 3.0 × 10⁻⁵−1.5 × 10⁻³ M and 9.0 × 10⁻⁶−1.2 × 10⁻⁴ M of D-PA with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods, respectively. The detection limits (2σ) were determined as 3.0 × 10⁻⁵ and 3.5 × 10⁻⁶ M with CV and DPV, respectively. This method was also used for voltammetric determination of D-PA in pharmaceutical preparation by standard addition method.     

Application of 2-(3,4-dihydroxyphenyl)-1,3-dithialone self-assembled monolayer on gold electrode as a nanosensor for electrocatalytic determination of dopamine and uric acid

The electrooxidation of dopamine (DA), uric acid (UA) and their mixture on a gold electrode modified by a self-assembled monolayer of 2-(3,4-dihydroxyphenyl)-1,3-dithialone has been studied by cyclic voltammetry (CV), chronoamperometry and differential pulse voltammetry (DPV). CV was used to investigate the redox properties of the modified electrode at various scan rates and the apparent charge transfer rate constant (k(s)), and transfer coefficient (α) were calculated. The mediated oxidation of DA at the modified electrode under the optimum condition (pH = 7.0) in CV occurs at a potential about 220 mV less positive than that of the unmodified gold electrode. The values of electron transfer coefficients (α), catalytic rate constant (k) and diffusion coefficient (D) were calculated for DA, using electrochemical methods. DPV exhibited a linear dynamic range over the concentration range of 0.2-250.0 μM and a detection limit (3σ) of 0.07 μM for DA. The modified electrode was used for simultaneous determination of DA and UA by DPV. The results showed that the electrode is highly efficient for the catalytic electrooxidation of DA and UA, leading to a remarkable peak resolution (~350 mV) for two compounds. The electrode was used for the determination of DA in an injection sample.