Electrocatalytic Oxidation and Voltammetric Determination of Hydrazine in Industrial Boiler Feed Water Using a Cobalt Phthalocyanine-modified Electrode

Abstract

A carbon paste electrode modified with cobalt phthalocyanine (CPECoPc) was developed and applied to the determination of hydrazine [N₂H₄] in industrial boiler feed water. The CPECoPc exhibited good electrocatalytical activity for hydrazine oxidation at pH 13. A linear correlation was obtained between anodic peak current (I_ap) and hydrazine concentration in the range of 1.25 × 10^?4 to 9.80 × 10^?4 mol L^?1, fit by the equation I_ap = 1.47 + 4.90 × 10⁵ [N₂H₄] with a correlation coefficient of 0.9967. A detection limit of 7.35 × 10^?5 mol L^?1 was obtained. Recovery of hydrazine from three samples ranged between 99.0% and 102.9%. The modified electrode showed no interference by cations commonly present in boiler water, such as K⁺, Na⁺, Ca²⁺, Mg²⁺, Al³⁺, Pb²⁺, and Zn²⁺. The results obtained for hydrazine in boiler water using the proposed modified electrode are in agreement with the data obtained by a standard spectrophotometric method, at the 95% confidence level.     

Electrocatalytic oxidation of methanol by ZSM-5 nanozeolite-modified carbon paste electrode in alkaline medium

Development of a novel modified electrode for electrocatalytic oxidation of methanol in order to decrease overvoltage is importance. In this paper, carbon paste electrode (CPE) was modified by ZSM-5 nanozeolite. The average diameter of used nanozeolite was 97 nm. Ni²⁺ ions were incorporated to the nanozeolite by immersion of the modified electrode in a 0.1 M nickel chloride solution. Then, electrochemical studies of this electrode were performed by using cyclic voltammetry(CV) in alkaline medium. This modified electrode was used as an anode for the electrocatalytic oxidation of methanol in 0.1 M of NaOH solution. The obtained data demonstrated that ZSM-5 nanozeolite at the surface of CPE improves catalytic efficiency of the dispersed nickel ions toward methanol oxidation. The values of electron transfer coefficient, charge-transfer rate constant, and the electrode surface coverage are obtained 0.61, 0.2342 s^?1, and 4.33 × 10^?8 mol cm^?2, respectively. Also, the mean value of catalytic rate constant between the methanol and redox sites of electrode and diffusion coefficient were found to be 2.54 × 10⁴ cm³ mol^?1 s^?1 and 1.85 × 10^?8 cm² s^?1, respectively. Obtained results from both CV and chronoamperometric techniques indicated that the electrode reaction is a diffusion-controlled process.     

Voltammetric Determination of Dopamine in Human Serum and Urine at a Glassy Carbon Electrode Modified by Cysteic Acid Based on Electrochemical Oxidation of L ‐cysteine

Abstract

The voltammetric behavior of dopamine was studied at a glassy carbon electrode modified by cysteic acid, based on electrochemical oxidation of L ‐cysteine. The modified electrode showed strong electrocatalytic activity towards dopamine and good selectivity. In a phosphate buffer solution (pH 7.4), the anodic peak current obtain from the differential pulse voltammetry of dopamine was linearly dependent on its concentration in the range of 5×10^?9 to 4.0×10^?6mol · L^?1, with a detection limit of 2×10^?9mol · L^?1. The low‐cost modified electrode had been applied to the determination of dopamine in human serum and urine samples 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.     

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.     

MCM/ZrO2 nanoparticles modified electrode for simultaneous and selective voltammetric determination of epinephrine and acetaminophen

A novel MCM/ZrO₂ nanoparticles modified carbon paste electrode (MZ-CPE) was fabricated and used to study the electro oxidation of epinephrine (EP) and acetaminophen (AC) and their mixtures by electrochemical methods. The modified electrode showed electrocatalytic activity toward EP and AC oxidation with a decrease of the overpotential by 173 mV to a less positive potential for EP at the surface of the MZ-CPE and an increase in peak current at pH 7.0. Differential pulse voltammetry peak currents of EP and AC increased linearly with their concentrations in the ranges of 1.0 × 10^?6–2.5 × 10^?3 and 1.0 × 10^?6–2.0 × 10^?3 M, respectively, and the detection limits for EP and AC were 5.0 × 10^?7 and 4.5 × 10^?7 M, respectively.     

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.     

A novel palladium nanoparticles-polyproline-modified graphite electrode and its application for determination of curcumin

A novel-modified electrode has been developed, by electrodeposition of palladium nanoparticles (PdNps) on polypyroline film-coated (Poly(Pr)) graphite electrode. The modified electrode (PdNps/Poly(Pr)/GE) was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) techniques. SEM proved that the palladium nanoparticles were uniform distributed with an average particle diameter of 20–45 nm. A higher catalytic activity was obtained for curcumin oxidation using this new modified electrode (PdNps/Poly(Pr)/GE). The square wave voltammogram of curcumin in pH 2 phosphate buffer exhibited an anodic peak at 0.504 V. This oxidation peak current was found to be linearly related to curcumin concentrations in the ranges of 5.0?×?10^?9 to 1.0?×?10^?7 M with a detection limit of 1.2?×?10^?9 M. This novel-modified electrode showed excellent sensitivity, compared with the existing reports about determination of curcumin.     

Amperometric Nitric Oxide Sensor Based on Poly(Thionine)/Nafion‐Modified Electrode and Its Application in Monitoring Nitric Oxide Release from Rat Kidney

Abstract

A novel amperometric nitric oxide (NO) sensor based on a glassy carbon electrode modified with thionine and Nafion films has been developed. The oxidation peak current of NO increased significantly at the poly(thionine)/Nafion‐modified glassy carbon electrode (GCE), which can be used for the detection of NO. The oxidation peak current was linear with the concentration of nitric oxide over the range from 3.6×10^?7 to 6.8×10^?5 mol · L^?1, and the detection limit was 7.2×10^?8 mol · L^?1. This nitric oxide sensor showed high selectivity to nitric oxide determination, and some potential interference could be eliminated effectively. The nitric oxide sensor has been applied to monitor NO release from rat kidney stimulated by L‐arginine. The results indicated the applicability of the NO sensor to biomedical samples.     

Study on the Electrochemical Behavior of Melatonin with an Activated Electrode

It was found that melatonin could be incorporated and accumulated on the surface of the glassy carbon electrode which was activated electrochemically by pretreatment in sodium hydroxide solution by means of cycling the potential well into the positive limit of the solvent. In Britton‐Robinson buffer solution (pH 6.7), melatonin gave a sensitive oxidation wave at a potential of +0.65 V (vs.Ag/AgCl) by using Osteryoung square‐wave stripping voltammetry (OSWSV). The oxidation process has been shown to be irreversible and adsorption‐controlled at this electrode by means of cyclic voltammetry and linear sweep voltammetry. A chronocoulometric characterization of the adsorption characteristics of melatonin at this electrode is also presented. The factors affecting the peak current were optimized, and the dependence of peak currents on the concentration of melatonin was found to be linear in the range 8.0×10^?7?1.0×10^?5 mol L^?1. A detection limit of 5.0×10^?8 mol L^?1 was obtained (signal‐to‐noise ratio of 3). This method was applied to the assay of melatonin in tablets and capsules with good recoveries (98–100%).     

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.     

A Novel Sensitive Biosensor for Ca2+ Ion Based on Gold Nanoparticles Modified Electrode by Pulsed Electrodeposition

The work demonstrates a simple method for sensitive detection of Ca²⁺ ion by electrochemical response of alizarin red S (ARS) and Ca-ARS at a gold nanoparticle modified glassy carbon electrode (GCE). In the 0.1 M KOH, a sensitive reduction peak was observed at ?0.795 V at the gold nanoparticles modified electrode. The peak currents were proportional to the concentrations of Ca²⁺ ion in the range of 2.0 × 10^?7 M–1.2 × 10^?4 M. For the different pulse voltammetry (DPV) methods, the detection limit was 2.57 × 10^?8 M. The reaction mechanism was primarily determined by cyclic voltammetry, and the experimental results showed that the electrode processes were quasireversible responses of ARS and irreversible responses of ARS-Ca. In addition, the method was simple, fast, precise, and was used in the determination of calcium in blood serum with satisfactory results.     

Carbon Composite Electrode Modified with Copper(II) Phosphate Immobilized in a Polyester Resin for Voltammetric Determination of Catechin in Teas

A carbon composite electrode modified with copper (II) phosphate immobilized in a polyester resin (Cu₃(PO₄)₂-Poly) was proposed for the voltammetric determination of catechin in teas. The modified electrode allows the determination of catechin (CAT) at lower potential than that observed at an unmodified electrode. Several parameters that can influence the voltammetric response of the proposed electrode such as carbon composite composition, pH of electrolyte, and others were investigated. The peak current was proportional to the concentration of catechin in the range from 9.9 × 10^?8 to 1.2 × 10^?6 mol L^?1, with a detection limit of 5.8 × 10^?8 mol L^?1. The stability and repeatability of the electrode for the determination of catechin were discussed, and the modified electrode was applied with success in the determination of catechin in teas.     

Voltammetric sensor based on magnetic particles modified composite electrode for determination of triamterene in biological sample

Some diuretic substances are controlled and monitored by the World Anti-Doping Agency as prohibited substances for use by athletes, such as triamterene (TRT). Thus, this work describes a voltammetric method based on graphite-epoxy composite electrode modified by tosyl-functionalized magnetic particles (GECE/MPs-To) for determination of TRT diuretic in urine sample. The TRT presented an oxidation peak at +1.24 V at GECE/MPs-To with irreversible behavior. Controlled potential electrolysis of the TRT at +1.26 V indicated the two electrons are transferred during amine group oxidation and the main product was identified by LC-MS/MS. The anodic peak current is 25 % higher at the modified electrode, suggesting that TRT is adsorbed on the magnetic particles. Using optimized conditions by using multivariate optimization of the parameters inherent of the square wave voltammetry, a calibration curve was constructed with a linear relationship for TRT from 0.500 to 99.8 μmol L^?1. The limits of detection and quantification were 1.47 and 4.91?×?10^?7 mol L^?1, respectively. The proposed method was applied to urine sample and validated by LC-MS/MS technique where the values found and compared between the two techniques showed no significant difference at 95 % confidence.     

Electrochemical Study of Interaction Between Clozapine and DNA and Its Analytical Application

Abstract

The interaction between clozapine (CLZ) as an orally administrated antipsychotic drug with double stranded calf thymus DNA (dsDNA) was investigated at electrode surface using differential pulse voltammetry (DPV). Activated carbon paste electrode (CPE) was modified with dsDNA and used for monitoring the changes of the characteristics peak of CLZ in 0.05 M acetate buffer (pH 4.3). The adsorptive stripping voltammetry on dsDNA‐modified carbon paste electrode (dsDNA‐CPE) was used for determination of very low concentration of CLZ. Under optimal conditions, the oxidation peak current is proportional to CLZ concentration in the range of 7×10^?9?1.2×10^?6 mol l^?1 with a detection limit of 1.5×10^?9 mol l^?1 for 180 s accumulation time by DPV. The proposed dsDNA‐CPE was successfully used for determination of CLZ in human serum samples with recovery of 97.0±2.5%.     

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.     

Sensitive electrochemical detection of bisphenol A with chitosan and urchinlike MnO2 microsphere modified carbon ionic liquid electrode

In this article, a carbon ionic liquid electrode (CILE) was fabricated by using ionic liquid N-hexylpyridinium hexafluorophosphate as the binder and the modifier. Then urchinlike MnO₂ microsphere and chitosan (CTS) was further casted on the CILE surface step-by-step to get a modified electrode that was denoted as CTS/MnO₂/CILE. Cyclic voltammetric studies indicated that bisphenol A (BPA) exhibited a well-defined oxidation peak at 0.486 V in 22.83 g L^?1 pH 8.0 Britton?Robinson buffer solution, which was attributed to the electro-oxidation of BPA on the modified electrode. The presence of urchinlike MnO₂ microsphere on the electrode surface could increase the oxidation peak current (I_pa) greatly, which may be due to the larger surface area that could adsorb more BPA on the electrode surface. Electrochemical parameters of BPA on the modified electrode were calculated with the electron transfer coefficient (α) as 0.66 and the apparent heterogeneous electron transfer rate constant (ks) as 0.50 s^?1. Under the optimal conditions, a linear relationship between the I_pa of BPA and its concentration was obtained in the range from 1.37 × 10^–1 mg L^?1 to 182.6 mg L^?1 with the detection limit as 7.31 × 10^–3 mg L^?1 (3σ). The CTS/MnO₂/CILE was applied to the detection of BPA content in different kinds of samples with satisfactory results.     

Docosyltrimethylammonium chloride modified glassy carbon electrode for simultaneous determination of dopamine and ascorbic acid

A glassy carbon electrode (GCE) modified with docosyltrimethylammonium chloride (DCTMACl) is used for simultaneous determination of dopamine (DA) and ascorbic acid (AA) using differential pulse voltammetry (DPV) technique in 0.10 mol·L^?1 phosphate buffer solution of pH 5.0. The cationic surfactant DCTMACl modified film has a positive charge. DA exists as the positively charged species, whereas AA is the negatively charged one in the solution. Thus, at DCTMACl film-modified GCE, the oxidation peak potential of AA shifts toward less negative potential and the peak current of AA increases a little, while the oxidation peak potential of DA shifts toward more positive potential and peak current decreases greatly in comparison with that on bare electrode. The two anodic peaks are separated around 200 mV. Under optimal conditions, the catalytic peak currents obtained from DPV increase linearly with concentrations of DA and AA in the ranges of 1.0?×?10^?5 to 1.0?×?10^?3?mol·L^?1. This electrode has good reproducibility, high stability in its voltammetric response, and low detection limit (micromolar) for both AA and DA. The modified electrode has been applied to the determination of DA and AA in injection.     

Synthesis and characterisation of a novel bi-nuclear copper2+ complex and its application as electrode-modifying agent for simultaneous voltammetric determination of dopamine and ascorbic acid

A new binuclear complex of copper²⁺, [LCu²⁺(CH₃COO)₂Cu²⁺L](CH₃COO)₂ where L is N,N-bis(phthalimide)ethylenediamine, was synthesised and characterised. The complex ion [LCu²⁺ (CH₃COO)₂Cu²⁺L]²⁺ was encapsulated into ZSM-5 zeolite and used to modify the surface of the glassy carbon electrode. This modified electrode, in a phosphate buffer solution at pH 7.0, exhibited an oxidation potential for dopamine (DA) and ascorbic acid (AA) at electrode potentials of 0.230 V and ?0.090 V vs. Ag/AgCl respectively, a separation of 0.320 V. The electro-oxidation of DA or AA on the modified electrode is independent of each other. No interference was observed from Na⁺, K⁺, Cl^?, SO ₄ ^2? , Mg²⁺, Ca²⁺, Zn²⁺, Fe²⁺, and glucose. The detection limits obtained were 2.91 × 10^?7 M for DA and 3.5 × 10^?7 M for AA.     

Electrochemical Behavior of Hydroquinone at Poly (Acridine Orange)–Modified Electrode and Its Separate Detection in the Presence of o‐Hydroquinone and m‐Hydroquinone

Abstract

Poly (acridine orange) (PAO) film–modified electrode was prepared by the electrooxidation of Acridine orange on a glassy carbon electrode (GCE) for the detection of hydroquinone in the presence of o‐hydroquinone and m‐hydroquinone. The electrochemical behavior of hydroquinone on the modified electrode was investigated with respect to different solution acidity, scan rate, and accumulation time. A pair of sharp and well‐defined peaks was obtained at 0.45 and 0.42 V [vs. a saturated calomel electrode (SCE)] at the PAO film–modified electrode. The potential difference between this pair of cathodic and anodic peaks was decreased to only 30 mV as compared to the 241 mV that was obtained on the bare glassy carbon electrode (GCE). As to o‐hydroquinone and m‐hydroquinone, their corresponding oxidation peaks appeared at 0.55 V and 0.89 V (vs. SCE), respectively. The oxidation potential differences between these three isomers enabled the separate detection of hydroquinone. Under the optimum experimental situation, the oxidation peak current of hydroquinone was proportional to the concentration at the range of 6.8×10^?7–9.6×10^?5 M. The detection limit was been estimated as 3×10^?7 M with 130 s accumulation. This method was applied to the hydroquinone detection in tap water samples.