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.     

Electrocatalytic Characteristics of Ferrocenecarboxylic Acid Modified Carbon Paste Electrode in the Oxidation and Determination of L‐Cysteine

The electrochemical behavior of L ‐cysteine studied at the surface of ferrocenecarboxylic acid modified carbon paste electrode (FCMCPE) in aqueous media using cyclic voltammetry and double step potential chronoamperometry. It has been found that under optimum condition (pH 7.00) in cyclic voltammetry, the oxidation of L ‐cysteine is occurs at a potential about 580 mV less positive than that 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 calibration curves were obtained in the ranges of 10^?5 M–10^?3 M and 4.1×10^?8 M–3.7×10^?5 M of L ‐cysteine concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (2δ) were determined as 2.4×10^?6 M and 2.5×10^?8 M by CV and DPV methods. This method was also examined for determination of L ‐cysteine in some samples, such as Soya protein powder, serum of human blood by using recovery and standard addition methods.     

Determination of Esomeprazole on an Electropolymerized L‐arginine and β‐cyclodextrin Modified Screen Printed Carbon Electrode

The formation of an inclusion complex of the proton‐pump inhibitor (PPI) drug esomeprazole (ESO) with ß‐cyclodextrin (ß‐CD) has been investigated and proven by cyclic voltammetry (CV). The formation constant of the complex was determined. Thereafter, an electropolymerized β‐CD and L‐arginine (L‐arg) modified screen printed carbon electrode (P‐β‐CD‐L‐arg/SPCE) was developed for the determination of ESO using differential pulse adsorptive stripping voltammetry (DPAdSV). A significant enhancement of the peak current was observed when applying an accumulation step due to the effect of adsorption. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) further indicated that the polymer of β‐CD and L‐arg efficiently improved the electron transfer kinetic between analyte and electrode surface. Under the optimized conditions, the oxidation peak current was linearly proportional to the concentration of the drug in the range of 1.0×10^?8 to 1.0×10^?5 M. The DPAdSV method was successfully used to determine the concentrations of the drug in spiked human serum samples.     

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.     

Effect of Basic Amino Acids on Nickel Ion Reduction at a Mercury Electrode

In a 0.02 M borax solution (pH 8.5), basic amino acids (arginine, lysine, and ornithine) react with Ni²⁺ to form a mono‐ligand complex that is reduced at a mercury electrode at about ?0.85 V vs. Ag|AgCl|KCl (3 M). At a long time scale (staircase voltammetry; scan rate<50 mV s^?1), the complex reduction is a catalytic (EC′) process, the rate‐determining step being the regeneration of the reducible species by the reaction of the amino acid with free Ni²⁺. At a short time scale (differential pulse voltammetry or higher scan rate staircase voltammetry), the reaction rate is controlled by the diffusion of the complex. Although the same kind of complexation occurs with either basic amino acids or glycine, the last one does not induce a similar process. The peculiar effect of basic amino acids is due to the side chain that causes the ligand molecule to adopt a favorable orientation at the electrode surface. The differential pulse voltammetry peak current is proportional to the total amino acid concentration over the concentration range from 2 to 100 μM. Hence a voltammetric method for arginine determination in nutritional supplements was developed and validated using HPLC as reference method.     

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.     

Electrochemical Analysis of D‐Penicillamine Using a Carbon Paste Electrode Modified with Ferrocene Carboxylic Acid

The electrochemical behavior of D ‐penicillamine (D ‐PA) studied at the surface of ferrocene carboxylic acid modified carbon paste electrode (FCAMCPE) in aqueous media using cyclic voltammetry and double step potential chronoamperometry. It has been found that under optimum condition (pH 7.00), the oxidation of D ‐PA at surface of such an electrode is occurred about 420 mV less positive than that an unmodified carbon paste electrode (CPE). The catalytic oxidation peak current was linearly dependent on the D ‐PA concentration and a linear calibration curve was obtained in the ranges 7.5×10^?5 M – 1.0×10^?3 M and 6.5×10^?6 M?1.0×10^?4 M of D ‐PA with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (3σ) were determined as 6.04×10^?5 M and 6.15×10^?6 M. This method was also used for the determination of D ‐PA in pharmaceutical preparation (capsules) by standard addition method.     

Electrocatalytic Oxidation of Nitrite at Gold Nanoparticle-polypyrrole Nanowire Modified Glassy Carbon Electrode

A novel chemically modified electrode based on the dispersion of gold nanoparticles on polypyrrole nanowires has been developed to investigate the oxidation behavior of nitrite using cyclic voltammetry, differential pulse voltammetry and chronoamperometry techniques. The diffusion coefficient (D), electron transfer coefficient (α) and charge transfer rate constant (k) for the oxidation of nitrite were determined. The modified electrode exhibited high electrocatalytic activity toward the oxidation of nitrite. The catalytic peak current was found to be linear with nitrite concentrations in the range of 8.0×10^?7?2.5×10^?3 mol·L^?1 with a detection limit of 1.0×10^?7 mol·L^?1 (s/n=3). The proposed method was successfully applied to the detection of nitrite in water samples with obtained satisfactory results. Additionally, the sensor also showed excellent sensitivity, anti‐interference ability, reproducibility and stability properties.     

Electrochemical oxidation of thiocyanates on a boron-doped diamond electrode in acid media

The kinetics and selectivity of the oxidation of thiocyanate on a boron-doped diamond (BDD) electrode in a 0.5 M solution of H₂SO₄ were studied. An analysis of the cyclic voltammetry curves showed that the oxidation of SCN^? was irreversible and occurred with diffusion control in the range of water decomposition potentials. The obtained kinetic dependences can be described by the pseudo-first order equation. The apparent rate constant depends on the current density and initial concentration of the reagent. The main product of oxidation at low current density and high concentration of SCN^? was CN^?.     

Cu(II) Hexacyanoferrate(III) Modified Carbon Paste Electrode; Application for Electrocatalytic Detection of Nitrite

Copper hexacyanoferrate (CuHCF) film‐modified carbon paste electrode (CPE) has been prepared from various electrolytic aqueous solutions using consecutive cyclic voltammetry. The cyclic voltammograms showed the direct deposition of CuHCF films from the mixing of Cu²⁺ and Fe(CN)₆^3? ions and each time with one of the six cations: H⁺, Na⁺, K⁺, NH₄⁺, Mg²⁺, and Al³⁺. The CuHCF film showed a single redox couple that exhibited a cation effect (Na⁺, K⁺, Mg²⁺, and NH₄⁺) and anion effect (Cl^?, NO₃^?, SO₄^2?, ClO₄^?, and BrO₃^?) in the cyclic voltammograms. Voltammetric studies have indicated that in presence of nitrite, the cathodic peak current of CuHCF increases, followed by a decrease in the corresponding anodic current. This indicated that nitrite was reduced by the redox mediator immobilized on the electrode surface via an electrocatalytic mechanism. The process of reduction and its kinetics were investigated by using cyclic voltammetry, differential pulse voltammetry, chronoamperometry and chronocoulometry techniques. The electrocatalytic ability about 800 mV can be seen. The rate constant of the catalytic reduction of nitrite was found to be 7.9×10⁵ cm³ mol^?1 s^?1. Linearity range obtained was 5×10^?5?8.4×10^?3 by cyclic voltammetry and 8×10^?6?1.3×10^?3 and 4×10^?3?2×10^?2 by differential pulse voltammetry.     

Effects of covalent versus non-covalent interactions on the electrocatalytic behavior of tetracarboxyphenoxyphthalocyanine in the presence of multi-walled carbon nanotubes

Tetracarboxyphenoxy phthalocyanine was covalently linked to multi-walled carbon nanotubes and the conjugate was used for modification of glassy carbon electrodes for the detection of hydrogen peroxide. The electrocatalytic behavior was examined by cyclic voltammetry, square wave voltammetry, and rotating disk electrode. The results show that covalent linking is attractive in terms of high detecting currents, low overpotential, and high catalytic rate constants. Very low detection limits were observed with CoTCPhPc-DAMN-MWCNT(linked)-GCE at 0.33 nM. The resulting catalytic rate constant was 1.1 × 10³ M^?1s^?1.     

Voltammetric Study and Detection of Methane on Nickel Hydroxide–Modified Nickel Electrode

Abstract

The nickel hydroxide–modified nickel (NMN) electrode was prepared by cyclic voltammetry. The modified electrode exhibited better catalytic effect toward electrochemical oxidation of methane in 1.0 mol · L^?1 NaOH solution. The catalytic activation of nickel hydroxide on the nickel electrode surface was investigated in different supporting electrolyte solutions by the cyclic voltammetry method in detail, and the related electrochemical oxidation of methane at the NMN electrode was first proposed by amperometric i‐t curve method under the experiment conditions. The results indicated that in the 1.0 mol · L^?1 NaOH solution, the anodic peak current increased with the increased concentration of methane.     

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).     

Comparison Between a Charge Transfer Process and an Electrocatalytic Process in Cyclic Voltammetry and Cyclic Voltcoulommetry. Application to the Oxidation of Ferrocyanide at a Ferrocene‐Monolayer Modified Gold Electrode

Ferrocyanide oxidation catalyzed by a ferrocene‐alkylthiolate monolayer at gold electrodes has been investigated by using cyclic voltammetry (CV) and cyclic voltcoulommetry (CVC). The voltammetric current‐potential curves obtained present a stationary sigmoidal feature which points out to a very high rate constant for the chemical step, whereas the charge‐potential curves do not reach an stationary behavior in any case. Simple expressions are presented for the characterization of the CV and CVC curves under Nernstian conditions for the charge transfer step. From these expressions, a value for the chemical rate constant 2.5×10⁴ M^?1 s^?1 has been easily obtained from an anodic plateau of the CV curves or from the linear anodic region of the CVC curves.     

Electrocatalytic reduction of oxygen on the surface of glassy carbon electrodes modified with plumbagin

The preparation and electrochemical characterization of glassy carbon electrodes modified with plumbagin were investigated by employing cyclic voltammetry, chronoamperometry and rotating disc electrode techniques. The cyclic voltammograms of the electroreduction of oxygen showed an enhanced current peak at approximately −0.289 V in air-saturated phosphate buffer pH = 7 and scan rate 10 mV s⁻¹. The thermodynamic and kinetic parameters of the reduction of oxygen at glassy carbon have been evaluated using cyclic voltammetry. The experimental parameters were optimized and the mechanism of the catalytic process was discussed. The obtained values of E°′ (V vs. Ag/AgCl), the apparent electron transfer rate constant k_s (s⁻¹), heterogeneous rate constant for the reduction of O₂ at the surface of the modified electrode k_h (M⁻¹ s⁻¹) and α (charge transfer coefficient of oxygen) were as follows: −0.146, 23.4, 9.9 × 10³ and 0.57, respectively. In addition, plumbagin exhibited strong catalytic activity toward the reduction of H₂O₂.     

Electrocatalytic Determination of Ampicillin Using Carbon-Paste Electrode Modified with Ferrocendicarboxylic Acid

Abstract

A carbon-paste electrode spiked with ferrocenedicarboxylic acid (FDCMCPE) was constructed by incorporation of ferrocenedicarboxylic acid in a 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 ampicillin (AMPC) in aqueous buffered solution. It has been found that under the optimum condition (pH 10.0) in cyclic voltammetry, the oxidation of AMPC occurred at a potential of about 480 mV on the surface of the modified carbon-paste electrode. The kinetic parameters such as electron-transfer coefficient, α, and rate constant for the chemical reaction between AMPC and redox sites in FDCMCPE were also determined using electrochemical approaches. Under the optimized conditions, the electrocatalytic oxidation peak current of AMPC showed two linear dynamic ranges with a detection limit of 0.67 µmol L^?1 AMPC. The linear calibration was in the range of 2.34–30 µmol L^?1 and 40–700 µmol L^?1 AMPC using the differential pulse voltammetric method. Finally, this method was also examined as a selective, simple, and precise electrochemical sensor for the determination of AMPC in real samples such as drugs and urine.     

Electrocatalytic Determination of Ascorbic Acid at the Surface of 2,7‐Bis(ferrocenyl ethyl)fluoren‐9‐one Modified Carbon Paste Electrode

A chemically modified carbon paste electrode with 2,7‐bis(ferrocenyl ethyl)fluoren‐9‐one (2,7‐BFEFMCPE) was employed to study the electrocatalytic oxidation of ascorbic acid in aqueous solution using cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The diffusion coefficient (D=1.89×10^?5 cm² s^?1), and the kinetic parameter such as the electron transfer coefficient, α (=0.42) of ascorbic acid oxidation at the surface of 2,7‐BFEFMCPE was determined using electrochemical approaches. It has been found that under an optimum condition (pH 7.00), the oxidation of ascorbic acid at the surface of such an electrode occurs at a potential about 300 mV less positive than that of an unmodified carbon paste electrode. The catalytic oxidation peak currents show a linear dependence on the ascorbic acid concentration and linear analytical curves were obtained in the ranges of 8.0×10^?5 M–2.0×10^?3 M and 3.1×10^?5 M–3.3×10^?3 M of ascorbic acid with correlation coefficients of 0.9980 and 0.9976 in cyclic voltammetry and differential pulse voltammetry, respectively. The detection limits (2δ) were determined to be 2.9×10^?5 M and 9.0×10^?6 M with cyclic voltammetry and differential pulse voltammetry, respectively. This method was also examined for determination of ascorbic acid in pharmaceutical preparations.     

Hemin Modified Carbon Fat Electrode for Analyzing Antimalarial Endoperoxide Artemisinin in Artemisia annua

A hemin bulk modified carbon electrode with Adeps neutralis (solid fat) as binder was developed for the determination of antimalarial endoperoxide artemisinin in plant matrix. The hemin modified electrode showed significant catalytic activity for the electrochemical reduction of artemisinin at about ?380 mV vs. Ag/AgCl in phosphate buffer solution of pH 7 by using cyclic and differential pulse voltammetry. Under optimized conditions strict linearity between artemisinin concentration and height of the cathodic catalytic current peak was observed in 4.8×10^?6–7.8×10^?5 M concentration range (R=0.9991) when using differential pulse voltammetry. The detection limit was calculated as 1.4×10^?6 M of artemisinin. The developed electroanalytical device is suitable for the determination of artemisinin in Artemisia annua extracts.     

A new voltammetric sensor for the determination of sulfite in water and wastewater using modified-multiwall carbon nanotubes paste electrode

The electrochemical response of a modified-carbon nanotubes paste electrode with p-aminophenol was investigated as an electrochemical sensor for sulfite determination. The electrochemical behaviour of sulfite was studied at the surface of the modified electrode in aqueous media using cyclic voltammetry and square wave voltammetry. It has been found that under the optimum condition (pH 7.0) in cyclic voltammetry, the oxidation of sulfite occurs at a potential about 680?mV less positive than that of an unmodified-carbon nanotubes paste electrode. Under the optimized conditions, the electrocatalytic peak current showed linear relationship with sulfite concentration in the range of 2.0?×?10^?7–2.8?×?10^?4?mol?L^?1 with a detection limit of 9.0?×?10^?8?mol?L^?1 sulfite. The relative standard deviations for ten successive assays of 1.0 and 50.0?µmol?L^?1 sulfite were 2.5% and 2.1%, respectively. Finally, the modified electrode was examined as a selective, simple and precise new electrochemical sensor for the determination of sulfite in water and wastewater samples.     

Rutin as an Electrochemical Mediator in the Determination of Captopril using a Graphite Paste Electrode

A simple, rapid and sensitive cyclic voltammetry method is described for the determination of the antihypertensive drug captopril in aqueous solution using a graphite paste electrode with rutin as mediator. The catalytic role of rutin in the oxidation of captopril was confirmed by the increase observed in anodic peak current at+0.44 V vs. SCE in the presence of the mediator. Anodic peak current varied linearly with the concentration of captopril in the dynamic range 0.2 to 1.0 mmol L^?1. The method exhibited a limit of detection of 89.4 μmol L^?1 and a reproducibility of 1 %, values that are comparable with those exhibited by other methodologies employing electrodes without any modification. The recovery rate for the determination of captopril in a pharmaceutical sample was good (91.21 %) suggesting that the described analytical technique would be effective in industrial applications whilst offering a number of advantages over published cyclic voltammetric methods.