Electrocatalytic oxidation and the mechanism of dopamine on a MWNT-modified glassy carbon electrode

The electrochemical behavior of dopamine (DA) at a MWNTs-modified glassy carbon electrode was investigated by cyclic voltammetry (CV), square wave voltammetry (SWV). The MWNTs modified electrode exhibited marked promotion of the electrochemical reaction of DA in different environments. Under optimum conditions, the peak currents of SWV of DA were increased linearly with incremental concentration of DA in the range from 5 × 10^?7 to 1 × 10^?5 mol L^?1. The limit of detection is 3 × 10^?7 mol L^?1.     

Square‐Wave Voltammetry Applied to the Analysis of the Dye Marker,Solvent Blue 14, in Kerosene and Fuel Alcohol

The purpose of this paper is to develop an electroanalytical method based on square‐wave voltammetry (SWV) for the determination of the solvent blue 14 (SB‐14) in fuel samples. The electrochemical reduction of SB‐14 at glassy carbon electrode in a mixture of Britton‐Robinson buffer with N,N‐dimethylformamide (1 : 1, v/v) presented a well‐defined peak at?0.40 V vs. Ag/AgCl. All parameters of the SWV technique were optimized and the electroanalytical method presented a linear response from 1.0×10^?6 to 6.0×10^?6 mol L^?1 (r=0.998) with a detection limit of 2.90×10^?7 mol L^?1. The developed method was successfully utilized in the quantification of the dye SB‐14 in kerosene and alcohol samples with average recovery from 93.00 to 98.10%.     

Comparative Study on Electroanalysis of Fenthion Using Silver Amalgam Film Electrode and Glassy Carbon Electrode Modified with Reduced Graphene Oxide

Oxidation and reduction processes of the insecticide fenthion was comparatively investigated at a reduced graphene oxide modified glassy carbon electrode (RGO‐GCE) and a cyclic renewable silver amalgam film electrode (Hg(Ag)FE) using square wave stripping voltammetry (SWSV). The influence of pH and SW parameters was investigated. The linear concentration ranges were found to be 1 × 10⁻⁶ – 2 × 10⁻⁵ and 1 × 10⁻⁷ – 2 × 10⁻⁵ mol L⁻¹ for Hg(Ag)FE and RGO‐GCE, respectively. The detection and quantification limits were calculated as 1.3 × 10⁻⁷ and 4.5 × 10⁻⁷ mol L⁻¹ for Hg(Ag)FE and 7.6 × 10⁻⁹ and 2.5 × 10⁻⁸ mol L⁻¹ for RGO‐GCE. Both of the developed electroanalytical methods offer rapid and simple detection of fenthion and were used on spiked tap and river water and apple juice samples. Scanning electron microscopy was used for RGO‐GCE surface characterization.     

Electrochemical Study of Moroxydine and its Voltammetric Determination with a Silver Amalgam Film Electrode

Moroxydine (Mor.) is an antiviral agent of biguanide structure. The paper presents a new silver amalgam film electrode (Hg(Ag)FE) for determination of Mor. in phosphate buffer, pH 6.2 (LOD=4×10^?9 mol L^?1, LOQ= 1×10^?8 mol L^?1) and in spiked urine using square wave adsorptive stripping voltammetry. It was found that the compound can act as an electrocatalyst not only at hanging mercury drop electrode but also at the Hg(Ag)FE. The electrode mechanism is connected with the hydrogen evolution reaction catalyzed by moroxydine. Adsorption of moroxydine at the mercury electrode was studied and special arrangements of molecules enabling electron transfer of the protonated form of moroxydine is suggested.     

Determination of 1-hydroxypyrene in human urine by a multi-wall carbon nanotubes-modified glassy carbon electrode

A multi-walled carbon nanotubes (MWNTs) modified glassy carbon electrode (MWNT-GCE) was used to study the electrochemical behaviour of1-hydroxypyrene (1-OHP) and applied to its determination. The results showed that the modified electrode had a strong adsorptive ability to 1-OHP and enhances its electrochemical signal. By square wave voltammetry, the linear relationship of 1-OHP was 6?×?10^?9???8?×?10^?7?mol?L^?1 with a linear correlation coefficient of 0.996, and the detection limit was 1?×?10^?10?mol?L^?1. Compared with other published methods, this newly proposed method possesses many advantages such as very low detection limit, fast response, low cost and simplicity. And this method was applied successfully in the determination of 1‐OHP in real human urine samples.     

Voltammetric behavior and quantitative determination of ambazone concentrations in urine and in a pharmaceutical formulation

The use of square wave adsorptive stripping voltammetry (SWAdSV) in conjunction with a cyclic renewable silver amalgam film electrode (Hg(Ag)FE) for the analytical determination of ambazone in urine samples and pharmaceutical formulations is described. A single reduction peak in Britton-Robinson buffer at pH 4.0 was detected at about ?1.4 V versus Ag/AgCl. Mechanistic studies have shown that the compound can act as an electrocatalyst. The method was validated. The analytical curve was linear in the concentration range from 1.0×10^?9 to 1.0×10^?7 mol L^?1. The detection and quantification limits were found to be 3.0×10^?10 mol L^?1 and 1.0×10^?9 mol L^?1, respectively. The proposed method was successfully applied to ambazone determination in real samples.      

Sensitive Determination of the Diquat Herbicide in Fresh Food Samples on a Highly Boron‐Doped Diamond Electrode

The highly boron‐doped diamond electrode (HBDD) combined with square wave voltammetry (SWV) was used in the development of an analytical procedure for diquat determination in potato and sugar cane samples and lemon, orange, tangerine and pineapple juices. Preliminary experiments realised in a medium of 0.05 mol L^?1 Na₂B₄O₇ showed the presence of two voltammetric peaks around ?0.6 V and around ?1.0 V vs. Ag/AgCl/Cl^? 3.0 mol L^?1, where the first peak could be successfully used for analytical proposes due the facility in the electrode surface renovation. After the experimental and voltammetric optimisation, the calculated detection and quantification limits were 1.6×10^?10 mol L^?1 and 5.3×10^?10 mol L^?1 (0.057 µg L^?1 and 0.192 µg L^?1, respectively), which are lower than the maximum residue limit established for fresh food samples by the Brazilian Sanitary Vigilance Agency. The proposed methodology was used to determine diquat residues in potato and sugar cane samples and lemon, orange, tangerine and pineapple juices and the calculated recovery efficiencies indicated that the proposed procedure presents higher robustness, stability and sensitivity, good reproducibility, and is very adequate for diquat determination in complex samples.     

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.     

Electrochemical Behaviors of Baicalin at an Electrochemically Activated Glassy Carbon Electrode and Its Determination in Human Blood Serum

Electrochemical behavior of baicalin (BA) at an electrochemically activated glassy carbon electrode (GCE) had been investigated in Britton‐Robinson (B‐R) buffer solution (pH = 2.87) by cyclic voltammetry (CV) and square wave voltammetry (SWV). The experimental results suggested that the electrode exhibited an electrocatalytic activity toward the redox of BA. The electron transfer coefficient (α) and the standard rate constant (k_s) of BA at the electrochemically activated glassy carbon electrode were calculated. The reaction mechanism was proposed and discussed in this work. Under the selected conditions, the reduction peak current was linearly dependent on the concentration of BA in the range of 5.0 × 10^?8 to 3.0 × 10^?6 mol L^?1 (r = 0.9990), with a detection limit of 2.0 × 10^?8 mol L^?1. The relative standard deviation (R.S.D.) for five times successful determination of 1.0 × 10^?6 mol L^?1 baicalin were 2.9%. The proposed method was also successfully applied for the determination of BA in human blood serum.     

Voltammetric Determination of Acibenzolar‐S‐Methyl Using a Renewable Silver Amalgam Film Electrode

Acibenzolar‐S‐methyl (ASM) is a novel fungicide applied for crop protection. A renewable silver amalgam film electrode was used for the determination of ASM in pH 3.4 Britton? Robinson buffer using square wave adsorptive stripping voltammetry (SW AdSV). The parameters of the method were optimized. The electroanalytical procedure made possible to determine ASM in the concentration range of 5×10^?8–3×10^?7 mol L^?1 (LOD=4.86×10^?9, LOQ=1.62×10^?8 mol L^?1). The effect of common interfering pesticides and heavy metal ions was checked. The validated method was applied in ASM determination in spiked water 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 Benzene,Toluene and Xylenes (BTX) in Water Using a Cathodically Pre‐treated Boron‐doped Diamond Electrode

An electrochemical method for the simultaneous determination of benzene, toluene and xylenes (BTX) in water was developed using square‐wave voltammetry (SWV). The determination of BTX was carried out using a cathodically pre‐treated boron‐doped diamond electrode (BDD) using 0.1 mol L^?1 H₂SO₄ as supporting electrolyte. In the SWV measurements using the BDD, the oxidation peak potentials of the total xylenes‐toluene and toluene‐benzene couples, present in ternary mixtures, display separations of about 100 and 200 mV, respectively. The attained detection limits for the simultaneous determination of benzene, toluene and total xylenes were 3.0×10^?7, 8.0×10^?7 and 9.1×10^?7 mol L^?1, respectively. The recovery values taken in ternary mixtures of benzene, toluene and total xylenes in aqueous solutions are 98.9 %, 99.2 % and 99.4 %, respectively.     

Square‐Wave Voltammetric Determination of Paraquat at Carbon Paste Electrode Modified with Hydroxyapatite

The voltammetric behavior of paraquat was investigated at hydroxyapatite‐modified carbon paste electrode HAP‐CPE in K₂SO₄. A method was developed for the detection of the trace of this herbicide, based on their redox reaction. The reduction peaks of paraquat were observed around ?0.70 V and ?1.00 V (vs. SCE) in square‐wave voltammetry. Experimental conditions were optimized by varying the accumulation time, apatite loading and measuring solution pH. Calibration plots were linear under the optimized parameters over the herbicide's concentration range 8–200×10^?7 mol L^?1, with a detection and quantification limits about 1.5×10^?8 mol L^?1 and 6.4 10^?8 mol L^?1, respectively.     

Response surface methodology for optimisation of 4,6-Dinitro-o-cresol quantification using hanging mercury drop electrode

A method for the pesticide DNOC (4,6-Dinitro-o-cresol) quantification using hanging mercury drop electrode (HMDE) and stripping square wave voltammetry (SSWV) optimisation is proposed. As a continuous cathodic current decrease was observed during the experiments, a waiting time, together with solution pH and SWV instrumental variables were optimised by factorial designs. From the two reduction current peaks values, only one was considered as dependent variable in the optimisation process. While the cathodic current peak and standard deviation were used in the waiting time and solution pH optimisation process, the instrumental parameters for SWV were optimised by using only current peak values. With the optimal parameters, a calibration curve from (0.01–0.55) × 10^?6 mol L^?1 with LOD of 2 × 10^?8 mol L^?1 was obtained. The proposed method was checked for DNOC quantification in different water samples obtained from Cordoba area and very good results, with recovery values around 102% were observed.     

Adsorptive stripping voltammetry of nickel at a bare glassy carbon electrode

A bare glassy carbon electrode is applied to nickel determination by adsorptive stripping voltammetry in the presence of dimethylglyoxime as a complexing agent. A procedure of nickel determination and electrode regeneration was proposed. The calibration graph for Ni(II) for an accumulation time of 120?s was linear from 2?×?10^?9 to 1?×?10^?7?mol?L^?1. The detection limit was 8.2?×?10^?10?mol?L^?1. The relative standard deviation for a solution containing 2?×?10^?8?mol?L^?1 of Ni(II) was 4.1%. The proposed procedure was applied for Ni(II) determination in certified water reference materials.     

Electrochemical Behavior of 8‐Azaguanine at DNA Langmuir–Blodgett Modified Glassy Carbon Electrode and Its Analytical Application

A highly sensitive electrochemical biosensor for the detection of trace amounts of 8‐azaguanine has been designed. Double stranded (ds)DNA molecules are immobilized onto a glassy carbon electrode surface with Langmuir–Blodgett technique. The adsorptive voltammetric behaviors of 8‐azaguanine at DNA‐modified electrode were explored by means of cyclic voltammetry and square wave voltammetry. Compared with bare glassy carbon electrode (GCE), the Langmuir–Blodgett film modified electrode can greatly improve the measuring sensitivity of 8‐azaguanine. Under the optimum experimental conditions, the Langmuir–Blodgett film modified electrode in pH 3.0 Britton–Robinson buffer solutions shows a linear voltammetric response in the range of 5.0×10^?8 to 1.0×10^?5 mol L^?1 with detection limit 9.0×10^?9 mol L^?1. The method proposed was applied successfully for the determination of 8‐azaguanine in diluted human urine with wonderful satisfactory.     

Effect of Pulse Width of Square Potential to Remove Silver Interference in the Determination of Mercury(II)

A graphite electrode modified with silver (Ag‐CPE) has been applied to detect mercury(II) using differential pulse voltammetry (DPV). Under optimized conditions, the calibration curve is linear in the range from 5.0×10^?8 mol L^?1 to 1.0×10^?4 mol L^?1 of mercury(II). The detection limit was found to be 3.38×10^?8 mol L^?1 with a relative standard deviation (RSD) of 2.25 % (n=8). The proposed method was successfully applied for the detection of mercury(II) in leachate samples. The Ag‐CP composites were characterized using X‐ray diffraction (XRD), BET adsorption analysis and scanning electron microscopy (SEM).     

Development and application of the tartrazine voltammetric sensors based on molecularly imprinted polymers

A modified glassy carbon electrode was prepared as an electrochemical voltammetric sensor based on molecularly imprinted polymer film for tartrazine (TT) detection. The sensitive film was prepared by copolymerization of tartrazine and acrylamide on the carbon nanotube-modified glassy carbon electrode. The performance of the imprinted sensor was investigated by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy in detail. Under the optimum conditions, two dynamic linear ranges of 8?×?10^?8 to 1?×?10^?6?mol?L^?1 and 1?×?10^?6 to 1?×?10^?5?mol?L^?1 were obtained, with a detection limit of 2.74?×?10^?8?mol?L^?1(S/N?=?3). This sensor was used successfully for tartrazine determination in beverages.     

A Novel Strategy for Simultaneous Determination of Dopamine and Uric Acid Using a Carbon Paste Electrode Modified with CdTe Quantum Dots

A novel CdTe quantum dots‐modified carbon paste electrode (QDMCPE) was fabricated and used to study the electrooxidation of dopamine and uric acid and their mixtures by electrochemical methods. Using square wave voltammetry (SWV), a highly sensitive and simultaneous determination of dopamine and uric acid was explored at the modified electrode. SWV peak currents of dopamine and uric acid increased linearly with their concentrations in the ranges of 7.5×10^?8–6.0×10^?4 M, and 7.5×10^?6–1.4×10^?3 M, respectively. Finally this new sensor was used for determination of dopamine and uric acid in some real samples.     

Direct Electroanalytical Determination of Fluvastatin in a Pharmaceutical Dosage Form: Batch and Flow Analysis

Abstract

The reduction of luvastatin (FLV) at a hanging mercury-drop electrode (HMDE) was studied by square-wave adsorptive-stripping voltammetry (SWAdSV). FLV can be accumulated and reduced at the electrode, with a maximum peak current intensity at a potential of approximately ?1.26 V vs. AgCl/Ag, in an aqueous electrolyte solution of pH 5.25. The method shows linearity between peak current intensity and FLV concentration between 1.0 × 10^?8 and 2.7 × 10^?6 mol L^?1. Limits of detection (LOD) and quantification (LOQ) were found to be 9.9 × 10^?9 mol L^?1 and 3.3 × 10^?8 mol L^?1, respectively.

Furthermore, FLV oxidation at a glassy carbon electrode surface was used for its hydrodynamic monitoring by amperometric detection in a flow-injection system. The amperometric signal was linear with FLV concentration over the range 1.0 × 10^?6 to 1.0 × 10^?5 mol L^?1, with an LOD of 2.4 × 10^?7 mol L^?1 and an LOQ of 8.0 × 10^?7 mol L^?1. A sample rate of 50 injections per hour was achieved.

Both methods were validated and showed to be precise and accurate, being satisfactorily applied to the determination of FLV in a commercial pharmaceutical.