Electrochemical Characterization and Rapid Voltammetric Determination of Riluzole in Pharmaceuticals and Human Serum

The electrochemical oxidation of riluzole was investigated using cyclic and linear sweep voltammetry. Under optimized conditions, current and concentration showed linear dependence in Britton Robinson buffer at pH 3.00 for boron doped diamond and pH 3.00 phosphate buffers for glassy carbon electrodes. Differential pulse and square wave voltammetry were used for the determination of riluzole levels in serum samples and pharmaceutical formulations. The limit of detections were found as 5.25 × 10^?7 M and 8.26 × 10^?8 M for glassy carbon electrode and 1.78 × 10^?7 M and 8.42 × 10^?8 M for boron-doped diamond electrodes, in serum samples, using differential pulse and square wave methods, respectively.     

Electrochemical Oxidation of Berberine and of Its Oxidation Products at a Glassy Carbon Electrode

The electrochemical behavior of berberine, an isoquinoline plant alkaloid with a wide spectrum of physiological effects, was studied at a glassy carbon electrode using cyclic, differential pulse and square‐wave voltammetry. The oxidation of berberine is a quasireversible, diffusion‐controlled process and occurred in a cascade mechanism with the formation of several oxidation products. The diffusion coefficient of berberine was calculated from cyclic voltammetry studies to be D=1.69×10^?6 cm² s^?1. The oxidation process of berberine is also pH dependent and the number of electrons and protons transferred was determined using differential pulse voltammetry. The formation of several oxidation products that adsorbed at the glassy carbon electrode surface was observed and their electrochemical behavior characterized. A mechanism for the oxidation of berberine at a glassy carbon electrode was proposed.     

Electrochemical Oxidation of Pentoxifylline and its Analysis in Pure and Pharmaceutical Formulations at a Glassy Carbon Electrode

Abstract

The oxidative behavior of pentoxifylline was studied at a glassy carbon electrode in phosphate buffer solutions using cyclic and differential-pulse voltammetry. The oxidation process was shown to be irreversible over the pH range (3.0–9.0) and was diffusion controlled. The possible mechanism of the oxidation of pentoxifylline was investigated by means of cyclic voltammetry and UV-Vis spectroscopy. An analytical method was developed for the determination of pentoxifylline in phosphate buffer solution at pH 3.0 as a supporting electrolyte. The anodic peak current varied linearly with pentoxifylline concentration in the range 2.0 × 10^?8 M to 6.0 × 10^?7 M of pentoxifylline with a limit of detection (LOD) of 4.42 × 10^?10 M. The proposed method was applied to the determination of pentoxifylline in pure and pharmaceutical formulations.     

Rapid voltammetric determination of maltol in some foods and beverages using a poly(methylene blue)/graphene-modified glassy carbon electrode

A novel poly(methylene blue)/graphene composite glassy carbon electrode was fabricated and the electrochemical behavior of maltol at the modified electrode was studied by cyclic voltammetry. In phosphate-buffered solution, the modified electrode exhibited excellent electrocatalytic activity towards the electrochemical oxidation of maltol. Under optimized conditions, the oxidation peak current showed a linear relationship with the concentrations of maltol in the ranges of 8.00?×?10^?7 to 4.00?×?10^?5 and 4.00?×?10^?5 to 5.40?×?10^?4 mol L^?1, with a detection limit of 6.50?×?10^?8 mol L^?1. The performance of the developed method was validated in terms of linearity (r?=?0.9981 and 0.9955), recovery (97.0?99.3 %), reproducibility (relative standard deviations?≤?3.1 %, n?=?6), and robustness. The method shows excellent sensitivity, selectivity, and reproducibility and has been successfully applied to analyzing maltol in a wide variety of food products.     

Glassy carbon electrodes coated with cellulose acetate for adsorptive stripping voltammetry

The utility of glassy carbon electrodes coated with cellulose acetate for adsorptive stripping voltammetry of oxidizable organic compounds is evaluated. This surface modification alleviates the co-adsorption problem commonly encountered at conventional electrodes. Interferences from electro-inactive surfactants and, in certain situations, from adsorbable electroactive substances, are minimized. Quantitation of the drugs, chlorpromazine and trimipramine, is not affected by the presence of up to 120 mg 1^?1 albumin or gelatin. The chlorpromazine response is not affected by the bilirubin or perphenazine peaks which overlap at uncoated electrodes. The adsorptive stripping response at the coated electrode is evaluated with respect to hydrolysis time, preconcentration time, concentration dependence, reproducibility, and other variables. The detection limit for chlorpromazine is 1.3 × 10^?8 M (5-min preconcentration). Applicability to assays of urine and serum samples is illustrated.     

Electrochemical Oxidation of Tryptophan and Its Analysis in Pharmaceutical Formulations at a Poly(Methyl Red) Film-Modified Electrode

A poly(methyl red) film-modified glassy carbon electrode was fabricated and the oxidation behavior of tryptophan at the modified electrode was investigated by cyclic and linear sweep voltammetry. The oxidation peak current of tryptophan at the modified electrode increased significantly, and the oxidation process was irreversible and adsorption-controlled. An analytical method was developed for the determination of tryptophan in a phosphate buffer solution at pH 3.5. The anodic peak current varied linearly with a tryptophan concentration in the range 1.0 × 10^?7 to 1.0 × 10^?4 mol/L with a limit of detection of 4.0 × 10^?8 mol/L. The proposed method was successfully applied to determine tryptophan in composite amino acid injections.     

Self-assembling of Prussian blue nanocubic particles on nanoporous glassy carbon and its use in the electrocatalytic reduction of hydrogen peroxide

In this paper, self-assembled Prussian blue nanocubic particles on nanoporous glassy carbon was developed. The morphology of the PBNP-modified porous glassy carbon was characterized by scanning electron microscopy. The PBNP-GCE-red film-modified electrode was used for the sensitive detection of hydrogen peroxide. The electrochemical behavior of the resulting sensor was investigated using cyclic voltammetry and chronoamperometry. The value of α, k _cat, and D was calculated as 0.35, 1.7 × 10⁵ cm³ mol^?1 s^?1, and 2.6 × 10^?5 cm² s^?1, respectively. The calibration curve for hydrogen peroxide determination was linear over 0–600 μM with a detection limit (S/N = 3) of 0.51 μM.     

Electrochemical Oxidation and Determination of Theophylline at a Carbon Paste Electrode Using Cetyltrimethyl Ammonium Bromide as Enhancing Agent

Abstract

The oxidation of theophylline was studied at a carbon paste electrode in the presence of cetyltrimethyl ammonium bromide by cyclic and differential pulse voltammetry. The results indicated that the electrochemical responses of theophylline are apparently improved by cetyltrimethyl ammonium bromide, due to the enhanced accumulation of theophylline at carbon paste electrode surface. Under optimal conditions the peak current was proportional to theophylline concentration in the range of 8.0 × 10^?7 to 2.0 × 10^?4 M with a detection limit of 1.85 × 10^?7 M by differential pulse voltammetry. The proposed method was applied to the determination of theophylline in tablet and urine samples.     

Electrochemical Detection of Epinephrine Using an L-Glutamic Acid Functionalized Graphene Modified Electrode

The development and application of an L-glutamic acid functionalized graphene nanocomposite, modified glassy carbon electrode are reported for the determination of epinephrine. The properties of the nanocomposite were characterized by scanning electron microscopy, ultraviolet-visible absorption spectroscopy, infrared spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The modified electrode had high sensitivity and strongly catalytic activity for the detection of epinephrine. A linear relationship between the epinephrine concentration and the current response was obtained in the range of 1 × 10^?7 M to 1 × 10^?3 M by differential pulse voltammetry with a limit of detection of 3 × 10^?8 M. The modified electrode was employed to determine epinephrine in urine with satisfactory results.     

The Influence of Gold Nanoparticles on Simultaneous Determination of Uric Acid and Ascorbic Acid

A three-dimensional L-cysteine (L-cys) monolayer assembled on gold nanoparticles (GNP) providing simultaneous detection of uric acid (UA) and ascorbic acid (AA) was studied in this work. The cyclic voltammetry demonstrated that, at a bare glassy carbon electrode (GCE) or planar gold electrode, the mixture of UA and AA showed one overlapped oxidation peak; whereas when the electrode was modified with GNP, the oxidation peaks for UA and AA were separated. While a GNP modified electrode was further modified with L-cys monolayer (L-cys/GNP/GCE), namely, three-dimensional L-cys monolayer, a better separation for UA and AA response was obtained. Interestingly, the L-cys monolayer-modified planar gold electrode presented a block effect on the oxidation of AA, which was facilitated by the three-dimensional L-cys monolayer attributed to its distinct structure. The pH of solution presented a noticeable effect on the separation of UA and AA at GNP modified electrodes with or without L-cys monolayer. Wide concentration ranges from 2 × 10^?6?1 × 10^?3 M to UA and 2 × 10^?6?8 × 10^?4 M to AA could be obtained at L-cys/GNP/GCE.     

Electrodeposition of zinc oxide nanoparticles on multiwalled carbon nanotube-modified electrode for determination of caffeine in wastewater effluent

We report on the development of an electrochemical sensor based on electrodepositing zinc oxide on multiwalled carbon nanotube-modified glassy carbon electrode for the detection of caffeine in pharmaceutical wastewater effluents. The measurements were carried out using cyclic voltammetry, electrochemical impedance spectroscopy, chronoamperometry and differential pulse voltammetry (DPV). DPV measurements showed a linear relationship between oxidation peak current and concentration of caffeine in 0.1 M HClO₄ (pH 1.0) over the concentration range 0.00388–4.85 mg/L and a detection limit of 0.00194 mg/L. The diffusion coefficient and Langmuir adsorption constant for caffeine were calculated to be 3.25 × 10^?6 cm² s^?1 and 1.10 × 10³ M^?1, respectively. The sensor showed satisfactory results when applied to the detection of caffeine in wastewater effluents.     

Electrocatalytic Oxidation and Determination of Norepinephrine at Poly(Cresol Red) Modified Glassy Carbon Electrode

A glassy carbon electrode (GCE) was modified with electropolymerized films of cresol red in pH 5.6 phosphate buffer solution (PBS) by cyclic voltammetry (CV). The modified electrode shows an excellent electrocatalytic effect on the oxidation of norepinephrine (NE). The peak current increases linearly with the concentration of NE in the range of 3×10^?6–3×10^?5 M by the differential pulse voltammetry. The detection limit was 2×10^?7 M. The modified electrode can also separate the electrochemical responses of norepinephrine and ascorbic acid (AA). The separation between the anodic peak potentials of NE and AA was 190 mV by the cyclic voltammetry. And the responses to NE and AA at the modified electrode were relatively independent.     

Simultaneous voltammetric determination of uric acid and ascorbic acid using carbon paste/cobalt Schiff base composite electrode

Differential pulse and cyclic voltammetry were applied for the oxidation of mixture of uric acid and ascorbic acid at the surface of carbon paste/cobalt Schiff base composite electrode. The electrooxidation of these compounds at bare electrode is sluggish, and there is no suitable peak separation between them. However, using cobalt methyl salophen as modifier, two well-defined anodic waves with a considerable enhancement in the peak current and a remarkable peak potential separation near 315 mV are obtained. It can improve the kinetics of electron transfer for both compounds remarkably. All these improvements are created because of the electrocatalytic property of cobalt Schiff base complex. The effect of some parameters such as pH and scan rates were studied. All the anodic peak currents for the oxidation of ascorbic acid and uric acid shifted toward more negative potential with an increase in pH, revealing that protons have taken part in their electrode reaction processes. The best peak separation with appropriate current was obtained for pH 4.0. A linear range of 5.0?×?10^?4 to 1.0?×?10^?8 and 1.0?×?10^?3 to 1.0?×?10^?8 M with detection limit of 8.0?×?10^?9 and 8.0?×?10^?9 M was obtained for ascorbic acid and uric acid using differential pulse voltammetry at the surface of modified electrode, respectively. Analytical utility of the modified electrode has been examined successfully using human urine samples and vitamin C commercial tablets.     

Synthesis and characterization of activated carbon–ethylenediamine–cobalt(II) tetracarboxyphthalocyanine conjugate for catalytic oxidation of ascorbic acid

We report on the synthesis and characterization of activated carbon–ethylenediamine–cobalt(II) tetracarboxyphthalocyanine conjugate (AC–CONHCH₂CH₂NH₂–CoPc) and its electrocatalytic behavior for oxidation of ascorbic acid. Ultraviolet–visible (UV–Vis), Fourier-transform infrared (FTIR), and electrochemical impedance spectroscopies, and cyclic and square-wave voltammetry were used to characterize the electrode modifiers and modified glassy carbon electrode. The limit of detection was found to be 0.26 µm using 3δ notation. The linear dynamic range was from 1.5 × 10^?4 to 1 × 10^?2 M with electrode sensitivity of 0.01 A mol^?1 L cm^?2. A Tafel slope of 200.8 mV decade^?1 was found. The concentration of ascorbic acid in the tablet was 0.034 M. Oxalic acid showed no interference in ascorbic acid determination.     

Electrochemical Behavior of Hydrogen Peroxide at a Glassy Carbon Electrode Modified with Nickel Hydroxide–Decorated Multiwalled Carbon Nanotubes

Abstract

The multiwalled carbon nanotube–nickel hydroxide composite film used to modify glassy carbon electrode was prepared and confirmed by transmission electron microscopy and cyclic voltammetry. The process and mechanism of film formation were discussed in detail. The electrode modified with the composite film exhibited good catalytic activity toward electrochemical oxidation of hydrogen peroxide in 0.1 mol/L sodium hydroxide solution. Various factors affecting the electrocatalytic activity of nickel hydroxide film were investigated. The anodic peak current increased with the increased concentration of hydrogen peroxide. The linear range for the determination of hydrogen peroxide was from 1.5 × 10^?6 mol/L to 2.5 × 10^?3 mol/L with the detection limit 6.1 × 10^?7 mol/L (S/N = 3). And the proposed method was applied to the determination of hydrogen peroxide in disinfector with higher sensitivity and lower detection limit.     

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.     

Comparison of Boron-Doped Diamond and Glassy Carbon Electrodes for Determination of Terbinafine in Pharmaceuticals Using Differential Pulse and Square Wave Voltammetry

This paper examines the electrochemical oxidation of terbinafine with the boron doped diamond and glassy carbon electrodes. The studies were performed by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and square-wave voltammetry (SWV). The supporting electrolytes, solution pH, the range of potentials, and the scan rates were optimized. Terbinafine was irreversibly oxidized in all electrolytes, yielding well-defined peaks in the positive potential range. The peak potential shifted towards less positive values as the solution pH increased. Voltammetric determination of terbinafine was performed under the optimized conditions. Using the boron doped diamond electrode, a linear relationship between current and concentration was obtained between 5.44 × 10^?7 and 5.18 and 10^?6 mol/L with SWV and between 7.75 · 10^?7 and 8.55 · 10^?6 mol/L by DPV. At the glassy carbon electrode, a linear relationship between 7.75 · 10^?7 and 8.55 · 10^?6 mol/L was obtained by SWV and between 7.75 · 10^?7 and 1.05 · 10^?5 mol/L by DPV. The sensitivity, precision, and selectivity of the procedures were evaluated. In order to check the practical application of the developed methods, the concentration of terbinafine was determined in pharmaceutical preparations.     

Electrochemical Oxidation of Phenothiazine Derivatives at Glassy Carbon Electrodes and Their Differential Pulse and Square‐wave Voltammetric Determination in Pharmaceuticals

Abstract

Three 2,10‐disubstituted phenothiazines—chlorpromazine hydrochloride (CPM), thioridazine hydrochloride (TR) and propericiazine (PRC)—were electrochemically studied in various buffer systems at different pH values, using a glassy carbon electrode. The substances were electrochemically oxidized at potential range 0.55–0.75 V. The oxidation was reversible and exhibited diffusion‐controlled process. The mechanism of the oxidation process is discussed. According to the linear relation between peak current and concentration, differential pulse voltammetry (DPV) and square wave voltammetry (SWV) methods for quantitative determination of chlorpromazine and propericiazine in 0.1 M HClO₄, and thioridazine in pH 2 phosphate buffer, was applied. Both the repeatability and reproducibility of the methods were also determined for all studied substances. The developed procedures were successfully applied to the determination of chlorpromazine and thioridazine in pharmaceutical dosage forms.     

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.     

Simultaneous determination of dopamine, uric acid and ascorbic acid with LaFeO3 nanoparticles modified electrode

LaFeO₃ nanoparticles of approximately 22 nm in size were synthesized and characterized by XRD and TEM. A novel glassy carbon electrode modified with LaFeO₃ nanoparticles was constructed and characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The modified electrode exhibited strong promoting effect and high stability toward the electrochemical oxidation of dopamine (DA), which gave reversible redox peaks with a formal potential of 0.145 V (vs. Ag/AgCl) in pH 7.0 phosphate buffer solution. The anodic peak current (measured by constant potential amperometry) increased linearly with the concentration of dopamine in the range from 1.5?×?10^?7 to 8.0?×?10^?4 M. The detection limit was 3.0?×?10^?8 M. The relative standard deviation of eight successive scans was 3.47% for 1.0?×?10^?6 M DA. The interference by ascorbic acid was eliminated efficiently. The method was used to determine DA in dopamine hydrochloride injections and showed excellent sensitivity and recovery.