First Order Derivative Voltammetry on the in situ Surfactant Modified Electrode for Naringin Quantification

Carboxylated multi‐walled carbon nanotubes based glassy carbon electrodes (MWNT‐COOH/GCE) modified in situ with surfactants (sodium dodecyl sulfate (SDS), cetylpyridinium bromide (CPB) and Triton X100) have been tested for the naringin determination. The effect of surfactant nature and concentration on the voltammetric characteristics of naringin has been evaluated. Anionic 100 μM SDS shows the highest 2.7‐fold increase of the oxidation currents in comparison to MWNT‐COOH/GCE. The irreversible electrooxidation of naringin is surface‐controlled process with the one electron and one proton transfer. Under conditions of first order derivative linear sweep voltammetry in Britton‐Robinson buffer (BRB) pH 8.0, the analytical ranges of 0.75–25 and 25–100 μM with the LOD and LOQ of 0.14 and 0.46 μM, respectively, have been obtained. The electrode response is selective in the presence of ascorbic, gallic and p‐coumaric acids as well as quercetin, catechin and rutin. The method has been applied for the naringin quantification in grapefruit juices.     

Sensitive Detection of Capsaicin by Adsorptive Stripping Voltammetry at a Boron‐Doped Diamond Electrode in the Presence of Sodium Dodecylsulfate

In the present paper, a sensitive electroanalytical methodology for the determination of capsaicin using adsorptive stripping voltammetry (AdSV) at a boron‐doped diamond (BDD) electrode is presented. The voltammetric results indicate that in the presence of sodium dodecylsulfate (SDS) the BDD electrode remarkably enhances the oxidation of capsaicin which leads to an improvement of the peak current with a shift of the peak potential to less negative values. A linear working range of 0.05 to 6.0 µg mL^?1 (0.16–20 µM) with a detection limit of 0.012 µg mL^?1 (0.034 µM) has been obtained using BDD electrode by AdSV.     

Electrochemically Prepared Three‐dimensional Porous Nitrogen‐doped Graphene Modified Electrode for Non‐enzymatic Detection of Hydrogen Peroxide

A facile and green electrochemical method for the fabrication of three‐dimensional porous nitrogen‐doped graphene (3DNG) modified electrode was reported. This method embraces two consecutive steps: First, 3D graphene/polypyrrole (ERGO/PPy) composite was prepared by electrochemical co‐deposition of graphene and polypyrrole on a gold foil. Subsequently, the ERGO/PPy composite modified gold electrode was annealed at high temperature. Thus 3DNG modified electrode was obtained. Scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to characterize the structure and morphology of the electrode. The electrode exhibits excellent electroanalytical performance for the reduction of hydrogen peroxide (H₂O₂). By linear sweep voltammetric measurement, the cathodic peak current was linearly proportional to H₂O₂ concentration in the range from 0.6 μM to 2.1 mM with a sensitivity of 1.0 μA μM⁻¹ cm⁻². The detection limit was ascertained to be 0.3 μM. The anti‐interference ability, reproducibility and stability of the electrode were carried out and the electrode was applied to the detection of H₂O₂ in serum sample with recoveries from 98.4 % to 103.2 %.     

Electrochemical Determination and in silico Studies of Fludarabine on NH2 Functionalized Multiwalled Carbon Nanotube Modified Glassy Carbon Electrode

A sensitive voltammetric technique has been developed for the determination of Fludarabine using amine‐functionalized multi walled carbon nanotubes modified glassy carbon electrode (NH₂‐MWCNTs/GCE). Molecular dynamics simulations, an in silico technique, were employed to examine the properties including chemical differences of Fludarabine‐ functionalized MWCNT complexes. The redox behavior of Fludarabine was examined by cyclic, differential pulse and square wave voltammetry in a wide pH range. Cyclic voltammetric investigations emphasized that Fludarabine is irreversibly oxidized at the NH₂‐MWCNTs/GCE. The electrochemical behavior of Fludarabine was also studied by cyclic voltammetry to evaluate both the kinetic (k_s and E_a) and thermodynamic (ΔH, ΔG and ΔS) parameters on NH₂‐MWCNTs/GCE at several temperatures. The mixed diffusion‐adsorption controlled electrochemical oxidation of Fludarabine revealed by studies at different scan rates. The experimental parameters, such as pulse amplitude, frequency, deposition potential optimized for square‐wave voltammetry. Under optimum conditions in phosphate buffer (pH 2.0), a linear calibration curve was obtained in the range of 2×10^?7 M–4×10^?6 M solution using adsorptive stripping square wave voltammetry. The limit of detection and limit of quantification were calculated 2.9×10^?8 M and 9.68×10^?8 M, respectively. The developed method was applied to the simple and rapid determination of Fludarabine from pharmaceutical formulations.     

Electrochemical Behavior and Voltammetric Determination of Curcumin at Electrochemically Reduced Graphene Oxide Modified Glassy Carbon Electrode

This work presents a sensitive voltammetric method for determination of curcumin by using a electrochemically reduced graphene oxide (ERGO) modified glass carbon electrode (GCE) in 100 mM KCl‐10 mM sodium phosphate buffer solution (pH 7.40). The electrochemical behaviors of curcumin at ERGO/GCE were investigated by cyclic voltammetry, suggesting that the ERGO/GCE exhibits excellent electrocatalytic activity towards curcumin, compared with bare GCE and GO/GCE electrodes. The electrochemical reaction mechanisms of curcumin, demethoxycurcumin and bisdemethoxycurcumin at the ERGO/GCE were also investigated and discussed systematically. Under physiological condition, the modified electrode showed linear voltammetric response from 0.2 μM to 60.0 μM for curcumin, with the detection limit of 0.1 μm. This work demonstrates that the graphene‐modified electrode is a promising strategy for electrochemical determination of biological important phenolic compounds.     

Amperometric sensor for nitrite using a glassy carbon electrode modified with thionine functionalized MWCNTs/Au nanorods/SDS nanohybrids

A sensitive nitrite (NO₂^‐) biosensor was fabricated by using sodium dodecyl sulfate (SDS), Au nanorods, and thionine functionalized MWCNTs (TH‐f‐MWCNTs) nanohybrids modified glassy carbon electrode. TH was covalently immobilized on the MWCNTs via a carbodiimide reaction. Comparing with MWCNTs/GCE, TH‐f‐MWCNTs/GCE displays higher catalytic activity toward the oxidation of NO₂^‐, since TH not only promoted the electronic transmission but also could improve the concentration of NO₂^‐ at the surface of the modified electrode in acidic solutions. The Au nanorods (AuNRs) were prepared through a simple wet chemical method and were characterized by TEM. The extremely high surface‐to‐volume ratios associated with one dimension nanostructures make their electrical properties extremely sensitive to species adsorbed on surfaces and result in excellent sensitivity and selectivity. SDS displays excellent film forming ability, which made the electrode stable. Under optimal conditions, the linear range for the detection of nitrite was 0.26 to 51 μM, and the low detection limit was 20 nM. In addition, the modified electrode was successfully applied to determine nitrite in real water samples. Copyright © 2012 John Wiley & Sons, Ltd.     

Voltammetric Determinations of Thymol on an Electrode Modified by Coimmobilized Carboxylated Multiwalled Carbon Nanotubes and Surfactants

Thymol is oxidized at glassy carbon electrodes (GCEs) modified with coimmobilized carboxylated multiwalled carbon nanotubes (MWCNT-COOH) and surfactants of various nature in a Britton–Robinson buffer solution. The effect of the nature and concentration of surfactants in the composition of the electrode surface modifier on the amperometric response of thymol was evaluated. It was found that the best voltammetric characteristics are achieved in the case of an anionic 0.10 mM sodium dodecyl sulfate (SDS) (a decrease in oxidation potential by 50 mV and an increase in oxidation currents 2.2-fold in comparison with MWCNT-COOH/GCE). The electrooxidation of thymol at MWCNT-COOH–SDS/GCE proceeds irreversibly with the participation of one electron and one proton and is controlled by the adsorption of the analyte. The electrode response is linear in the ranges 0.500–17.0 and 17.0–150 μM of thymol with the limits of detection 0.14 μM and determination 0.48 μM. The developed method is tested on thymol-containing pharmaceutical preparations. The voltammetry data are compared with the results of an independent spectrophotometric determination.     

A Simple and Novel Electrochemical Sensor Based on Phosphomolybdic‐Polypyrrole Film Modified Electrode for Highly Sensitive Detection of Cholic Acid

A simpe electrochemical sensor for detection of cholic acid (CA) was designed by modifying phosphomolybdate (PMo₁₂) doped polypyrrole (PPy) film on glassy carbon electrode (PMo₁₂‐PPy/GCE). The electrochemical behavior of CA on PMo₁₂‐PPy/GCE was investigated by cyclic voltammetry and 0.5 order differential voltammetry. The results indicated that CA had high inhibitory activity toward the peak currents of PMo₁₂‐PPy/GCE. The reduction peak currents were linearly related to the logarithmic value of the concentration of CA from 1.0×10^?7 to 1.0×10^?3 mol/L with a low detection limit of 1.0×10^?8 mol/L. The developed sensor exhibited excellent sensitivity, selectivity and stability for detection of CA, and it could be successfully applied to detect the level of CA in the urine samples. Moreover, the response mechanism of CA on the PMo₁₂‐PPy/GCE was discussed in detail.     

Sensitive voltammetric assay of etoposide using modified glassy carbon electrode with a dispersion of multi-walled carbon nanotube

A sensitive electroanalytical method for the determination of anticancer drug etoposide (ETP) using adsorptive stripping differential pulse voltammetry (AdSDPV) at a multi-walled carbon nanotube-modified glassy carbon electrode (MWCNT-modified GCE) is presented. The surface morphology of modified electrode was characterized by scanning electron microscopy. The effects of accumulation time and potential, pH, scan rate, and amount of MWCNT suspension were investigated. The calibration curve was linear in the concentration range of 2.0?×?10^?8–2.0?×?10^?6 M with the detection limit of 5.4?×?10^?9 M. The reproducibility of the peak current was found at 1.55 % (n?=?5) RSD value in pH 6.0 Britton–Robinson buffer for the MWCNT-modified GCE. The method was then successfully utilized for the determination of ETP in pharmaceutical dosage form, and a recovery of 99.55 % was obtained. The possible oxidation mechanism of ETP was also discussed. The proposed electroanalytical method using MWCNT-modified GCE is the most sensitive method for the determination of ETP with lowest limit of detection in the previously published electrochemical methods.     

Fabrication of Cu−CeO2 Coated Multiwall Carbon Nanotube Composite Electrode for Simultaneous Determination of Guanine and Adenine

A copper nano particles and cerium (IV) oxide modified carbon nanotube based composite on glassy carbon electrode (Cu−CeO₂/MWCNT/GCE) was fabricated for simultaneous determination of guanine and adenine. The surface morphology, chemistry and conductance of the prepared electrodes were characterized by scanning electron microscopy (SEM), energy dispersion X‐ray (EDX), X‐Ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The Cu−CeO₂/MWCNT/GCE improved electrochemical behaviour of guanine and adenine compared to other electrodes. The modified electrode was also used for individual and simultaneous determination of guanine and adenine. Under optimized conditions, the calibration curves were obtained linearly in the range of 0.20 to 6.00 μM for the guanine and 0.10 to 8.0 μM for the adenine by differential pulse voltammetry. The limits of detection of guanine and adenine were calculated as 0.128 and 0.062 μM, respectively. Interferences studies were also performed in the presence of inorganic and organic compounds. Moreover, the determination of guanine and adenine contents were carried out in a calf thymus DNA sample by the developed method with satisfactory results.     

Differentiation of Detection of Ascorbic Acid and Dehydroascorbic Acid Using Hydrodynamic Amperometry and Anodic Stripping Voltammetry on Modified Aluminum Electrodes

An electroanalytical strategy for the simultaneous determination of ascorbic acid (AA) and dehydroascorbic acid (DHA), is described. A palladized Al electrode is used for hydrodynamic amperometry of AA. While the decrease of anodic stripping voltammetry current of the K₂UO₂[Fe(CN)₆]‐Pd/Al electrode prepared in the presence of DHA was the principal of the DHA determination. The calibration graph for both methods was linear over the concentration range 1–50 μM. The detection limit was found to be 0.5 μM. Some fresh fruit juices and vegetables of trace level of AA and DHA were analyzed as the typical example of application.     

Electrode Modified with Langmuir–Blodgett (LB) Film of Calixarenes for Preconcentration and Stripping Analysis of Hg(II)

A new type of current sensor, Langmuir–Blodgett (LB) film of calixarene on the surface of glassy carbon electrode (GCE) was prepared for determination of mercury by anodic stripping voltammetry (ASV). An anodic stripping peak was obtained at 0.15 V (vs. SCE) by scanning the potential from ?0.6 to +0.6 V. Compared with a bare GCE, the LB film coated electrode greatly improves the sensitivity of measuring mercury ion. The fabricated electrode in a 0.1 M H₂SO₄+0.01 M HCl solution shows a linear voltammetric response in the range of 0.07–40 μg L^?1 and detection limit of 0.04 μg L^?1 (ca. 2×10^?10 M). The high sensitivity, selectivity, and stability of this LB film modified electrode demonstrates its practical application for a simple, rapid and economical determination of Hg²⁺ in a water sample.     

Adsorptive Stripping Voltammetry for Trace Determination of Quinalphos Employing Silicon Carbide Nanoparticles Modified Glassy Carbon Electrode

A silicon carbide nanoparticle‐coated glassy carbon electrode (SiCNPs‐GCE) was employed for electrochemical determination of Quinalphos (QNP) using different electroanalytical techniques. QNP showed an enhancement in the reduction peak current at SiCNPs modified GCE in pH 7.0 (BR Buffer). The peak current was found to be linear with the QNP concentration in the range from 6.69×10^?9 to 1.34×10^?6 M (r=0.995) with detection limit of 1.34×10^?9 M (S/N=3). The developed sensor (SiCNPs‐GCE) was employed for QNP determination in tap water, lake water, soil, mango as well as in biological samples.     

Electroanalytical Application of Amine‐grafted Attapulgite to the Sensitive Quantification of the Bioactive Compound Mangiferin

A glassy carbon electrode (GCE) coated with a thin film of organoattapulgite was used for the voltammetric detection and quantification of mangiferin (MG), a bioactive xanthone with several therapeutic properties. The used modified attapulgite was prepared by surface grafting of [3‐(2‐aminoethylamino)propyl]trimethoxysilane. The grafted clay was characterised by SEM, CHN elemental analysis, FTIR spectroscopy and XRD techniques. The electrochemical behaviour of MG was first investigated on bare GCE by cyclic voltammetry which showed a single irreversible oxidation peak at ca 0.770 V (vs Ag/AgCl) in HCl/KCl buffer at pH 1. When the GCE was covered by the organoattapulgite, the electrode response for MG increased significantly due to favourable electrostatic interactions between MG and the protonated organoclay. A sensitive voltammetric method for the determination of MG, based on adsorptive stripping voltammetry was then developed. A linear variation of MG concentration with peak current was obtained in the range from 0.61 to 10.57 μM, with a detection limit of 2.75×10⁻⁷ M (S/N=3). Kinetic and chronocoulometric studies were also performed to characterise the diffusion of MG at the organoclay modified electrode. The interfering effect of some compounds likely to affect the stripping signal of MG was also evaluated, followed by the application of the developed method to a real biological sample.     

Voltammetric Determination of Folic Acid Using Adsorption of Methylene Blue onto Electrodeposited of Reduced Graphene Oxide Film Modified Glassy Carbon Electrode

This work presents a sensitive voltammetric method for determination of folic acid by adsorbing methylene blue onto electrodeposited reduced graphene oxide film modified glassy carbon electrode (MB/ERGO/GCE) in 100 mM KCl‐10 mM sodium phosphate buffer solution (pH 7.40). The surface morphology of the MB/ERGO/GCE modified electrode was characterized using scanning electron microscopy, displays that both MB and ERGO distributed homogeneously on the surface of GCE. The MB/ERGO/GCE modified electrode shows more favorable electron transfer kinetics for potassium ferricyanide and potassium ferrocyanide probe molecules, which are important electroactive compounds, compared with bare GCE, MB/GCE, and ERGO/GCE. The electrochemical behaviors of folic acid at MB/ERGO/GCE were investigated by cyclic voltammetry, suggesting that the modified electrode exhibited excellent electrocatalytic activity towards folic acid compared with other electrodes. Under physiological condition, the MB/ERGO/GCE modified electrode showed a linear voltammetric response from 4.0 μM to 167 μM for folic acid, and with the detection limit of 0.5 μM (S/N=3). The stability, reproducibility and anti‐interference ability of the modified electrode were examined. The developed method has been successfully applied to determination of FA in tablets with a satisfactory recovery from 96 % to 100 %. The work demonstrated that the electroactive MB adsorbing onto graphene modified electrode showed an enhanced electron transfer property and a high resolution capacity to FA.     

Carbon‐Based Electrodes for Sensitive Electroanalytical Determination of Aminonaphthalenes

The electroanalytical performance of bare glassy carbon electrodes (GCE) for the determination of 1‐aminonaphthalene (1‐AN) and 2‐aminonaphthalene (2‐AN) was compared with GCE modified by a Nafion permselective membrane or multiwalled carbon nanotubes and with other types of carbon‐based materials, carbon film and boron doped diamond. Nafion‐modified GCE gave the highest sensitivity and lowest detection limit (0.4 µmol L^?1) for differential pulse voltammetric determination of 1‐AN. Electrochemical impedance spectroscopy gave information about the processes at the electrode surface. Simultaneous determination of 1‐AN and 2‐AN in a mixture at GCE and their determination in model samples of river water is presented.     

Highly Sensitive Amperometric Sensor for Eugenol Quantification Based on CeO2 Nanoparticles and Surfactants

Amperometric sensor for eugenol based on glassy carbon electrode (GCE) modified with CeO₂ nanoparticles dispersed in surfactant was fabricated. The effect of surfactant nature (sodium dodecylsulfate, cetylpyridinium bromide (CPB) and Brij® 35) on eugenol voltammetric behaviour was tested. In comparison to CeO₂‐H₂O/GCE, CeO₂‐CPB/GCE showed 2.8‐fold increased current and 70 mV cathodic shift of potential in the diffusion‐controlled irreversible electrooxidation. The electrodes were characterized with SEM and EIS. CeO₂‐CPB/GCE showed significantly lower charge transfer resistance (2.6±0.3 kΩ vs. 20±1 kΩ for CeO₂‐H₂O/GCE and 173±9 kΩ for GCE). Under conditions of DPV, the sensor linear dynamic range is 0.075‐75.0 μM of eugenol with the limits of detection (LOD) and quantification (LOQ) of 19.1 and 63.8 nM, respectively. The sensor exhibited high sensitivity, selectivity, good reproducibility and fast response and was applied for the real samples analysis (essential oils and clove spices). The results obtained correspond well to the data of spectrophotometric method.     

A Sensitive Electrochemical Sensor Based on Graphene Oxide Nanosheets Decorated by Fe3O4@Au Nanostructure Stabilized on Polypyrrole for Efficient Triclosan Sensing

Triclosan is broadly utilized as preservative or antiseptic in various cosmetic and personal care products. It becomes hazardous for environmental safety and human health more than a certain concentration. In this research, graphene oxide (GO) nanosheets were prepared by composing Fe₃O₄@Au nanostructure decorated GO together with polypyrrole (PPy) (Fe₃O₄@Au‐PPy/GO nanocomposite) in a facile way. The composite excellent increased the electrochemical response, presenting a high sensitive electrochemical method for triclosan detection. The synthesized Fe₃O₄@Au‐PPy/GO nanocomposite was characterized for its morphological, magnetically and structural properties by FESEM‐mapping, TEM, and XRD. The Fe₃O₄@Au‐PPy/GO nanocomposites modified glassy carbon electrodes (GCE), Fe₃O₄@Au‐PPy/GO GCE, showed a higher sensitivity good stability, reproducibility, lower LOD (2.5×10^?9 M) and potential practical application in electrochemical detection of triclosan under optimized experimental conditions.     

A Self‐assembled L‐Cysteine and Electrodeposited Gold Nanoparticles‐reduced Graphene Oxide Modified Electrode for Adsorptive Stripping Determination of Copper

Glassy carbon electrode (GCE) modified with L‐cysteine and gold nanoparticles‐reduced graphene oxide (AuNPs‐RGO) composite was fabricated as a novel electrochemical sensor for the determination of Cu²⁺. The AuNPs‐RGO composite was formed on GCE surface by electrodeposition. The L‐cysteine was decorated on AuNPs by self‐assembly. Physicochemical and electrochemical properties of L‐cysteine/AuNPs‐RGO/GCE were characterized by scanning electron microscopy, atomic force microscopy, energy dispersive spectroscopy, Raman spectroscopy, X‐ray diffraction, cyclic voltammetry and adsorptive stripping voltammetry. The results validated that the prepared electrode had many attractive features, such as large electroactive area, good electrical conductivity and high sensitivity. Experimental conditions, including electrodeposition cycle, self‐assembly time, electrolyte pH and preconcentration time were studied and optimized. Stripping signals obtained from L‐cysteine/AuNPs‐RGO/GCE exhibited good linear relationship with Cu²⁺ concentrations in the range from 2 to 60 μg L⁻¹, with a detection limit of 0.037 μg L⁻¹. Finally, the prepared electrode was applied for the determination of Cu²⁺ in soil samples, and the results were in agreement with those obtained by inductively coupled plasma mass spectrometry.     

Development of an Electrochemical Sensor to Detect Dopamine and Ascorbic Acid Based on Neodymium (III) Oxide and Chitosan

Neodymium (III) oxide (Nd_Ox) was dispersed in chitosan dissolution and deposited on a glassy carbon electrode (chitosan‐Nd_Ox/GCE). The surface properties of the chitosan‐Nd_Ox/GCE were evaluated with FeCN₆⁻³ solution using cyclic voltammetry and electrochemical impedance spectroscopy. The modified electrode was used in the determination of individual dopamine (DP) and ascorbic acid (AA) with square wave adsorptive voltammetry. Under optimal parameters (pH 4.0; accumulation time; t_ACC 60s and accumulation potential; E_ACC 0.10 V) for DP and (pH 3,0; t_ACC 60s and; E_ACC −0.20 V) for AA, anodic peak currents were proportional to the concentration of DP and AA between 0.90 and 17.0 μmolL⁻¹, with detection limit of 0.079 μmolL⁻¹ for DP and 0.12 μmolL⁻¹ for AA. The sensor was used in the determination of DP and AA in human urine samples and vitamin C tablets with consistent results. The new sensor is easy to develop. In addition, the sensitivity in particular for AA was improved compared with previous work.