Determination of Hydrazine Compounds by Capillary Electrophoresis with a Poly(Glutamic Acid) Modified Microdisk Carbon Fiber Electrode

ABSTRACT

Hydrazine compounds, including hydrazine (HZ), phenylhydrazine (PHZ), semicarbazide (SCZ) and isoniazid (INZ) were separated and determined by capillary electrophoresis (CE) with a poly(glutamic acid) modified microdisk carbon fiber electrode. The modified electrode exhibited highly catalytic activity for hydrazines and has good stability. Linear responses for hydrazines over 2~3 orders of magnitude were obtained. The detection limits for HZ, PHZ, SCE and INZ were 7.8, 8.0, 14.0 and 11.0 fmol, respectively.     

Sensitive Detection of NADH by Ferrocenylalkanethiol Functionalized Multiwall Carbon Nanotubes Electrodes

Abstract

The 6-ferrocenylhexanethiol (FcC₆SH) functionalized multiwall carbon nanotubes (MWNTs) modified glassy carbon electrode (FcC₆SH/MWNTs/GCE) was easily fabricated and used for the sensitive detection of NADH. Cyclic voltammetric and amperometric methods were used to study the behavior of NADH on the FcC₆SH/MWNTs/GCE. A broader linear response range to the NADH concentration from 5 µM to 1.5 mM with a correlation coefficient of 0.9982 was obtained. The detection limit was 0.54 µM. The synergetic effects of FcC₆SH and MWNTs make the modified electrode highly sensitive to NADH. In addition, the modified electrode can decrease the fouling of the electrode surface.     

Synthesis and characterisation of Ag-nanoparticles immobilised on ordered mesoporous carbon as an efficient sensing platform: application to electrocatalytic determination of hydrazine

In this study, a new strategy for the preparation of a modified glassy carbon electrode (GCE) based on a novel nano-sensing layer for the electrocatalytic oxidation of hydrazine was suggested. The suggested nano-sensing layer was prepared with the immobilisation of silver nanoparticles (AgNPs) on ordered mesoporous carbon. The morphology and properties of the prepared nanocomposite on the surface of GCE were characterised by scanning electron microscopy, transmission electron microscopy, N₂ adsorption-desorption, X-ray powder diffraction and electrochemical impedance spectroscopy. The electrochemical response characteristics of the modified electrode towards the target analyte were investigated by cyclic voltammetry. Under optimal experimental conditions, the suggested modified GCE showed excellent catalytic activity towards the electro-oxidation of hydrazine (pH = 7.5) with a significant increase in anodic peak currents in comparison with the unmodified GCE. By differential pulse voltammetry and amperometric methods, the suggested sensor demonstrated wide dynamic concentration ranges of 0.08–33.8 µM and 0.01–128 µM with the detection limit (S/N = 3) of 0.027 and 0.003 µM for hydrazine, respectively. The suggested hydrazine sensor was successfully applied for the highly sensitive determination of hydrazine in different real samples with satisfactory results.     

Electrochemical Detection of Pb(II) by Glassy Carbon Electrode Modified with Amine-Functionalized Magnetite Nanoparticles

An amine-Fe₃O₄ modified glassy carbon (GC) electrode was constructed for detecting Pb(II) ions in wastewater. The electrode was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Square wave anodic stripping voltammetry (SWASV) was used to detect the Pb(II), and the detection limit of Pb(II) was 0.15 µM. The sensitivity of the electrode to detect Pb(II) was about 10.07 µA/µM, with a correlation coefficient of 0.991, which was approximately 10 times bigger than that of a pure Fe₃O₄ modified electrode. The electrode also showed good selectivity and stability. This results indicated that the amine-magnetite material could have some potential applications in heavy metal ions detection in wastewater.     

Lead-doped carbon ceramic electrode as a renewable surface composite electrode for the preparation of lead dioxide film and detection of <Emphasis Type="SmallCaps">l</Emphasis>-tyrosine

Lead-doped carbon ceramic electrode as a new type of renewable composite electrode was prepared by mixing the lead powder with electrode matrix before gelation. Pb on the electrode surface was then converted to lead dioxide by the potential scanning of the composite electrode in 0.1 M NaOH solution in the range of ? 0.3 to 0.7 V versus SCE. The composition and morphology of the electrodes were studied by energy dispersive X-ray spectrometry, scanning electron microscopy, and atomic force microscopy techniques. Cyclic voltammetry and chronoamperometry techniques were also used to study the electrocatalytic activity of the modified electrode toward the oxidation of the l-tyrosine. The best results were obtained at a working potential of 0.45 V (vs. SCE) in 0.1 M NaOH solution. The sensor exhibited a good linear response in the range of 5–1458 µM with a coefficient of determination of 0.9963. The detection limit was 0.77 µM, and sensitivity was 37.4 μA mM^?1. In addition, the modified electrode showed high stability and interference-free response for to detection of the l-tyrosine.     

Electrocatalytic oxidation of NADH at mesoporous carbon modified electrodes

The electrochemical oxidation of β-nicotinamine adenine dinucleotide (NADH) was investigated at a glassy carbon electrode modified with carbon mesoporous materials (CMM). Due to the large surface area and electro-catalytic properties of CMM, the overpotential of the electrodes toward the oxidation of NADH is decreased by 595 mV in aqueous solution at neutral pH. The anodic peak currents increase steadily with the concentration of NADH in the range from 2 µM to 1.1 mM, the detection limit being 1.0 µM at pH 7.2 and a potential of +0.3 V vs. SCE. The apparent Michaelis-Menten constant is ～21.5 μM. The results enable NADH to be sensed at a low potential and are promising with respect to the design of dehydrogenase-based amperometric biosensors.     

Room-Temperature Ionic Liquid and Multi-Walled Carbon Nanotube Composite Modified Carbon-Ceramic Electrode as a Sensitive Voltammetric Sensor for Indomethacin

The electrochemical behavior of indomethacin on the surface of a carbon-ceramic electrode modified with multi-walled carbon nanotubes and an ionic liquid composite film is reported. The results show that the nano-structured film exhibited excellent enhancement effects on the electrochemical oxidation of indomethacin. The developed sensor presented a linear response to indomethacin over the concentration range from 1 to 50 µM with a detection limit of 0.26 µM. The proposed modified electrode was employed for the determination of indomethacin in biological and pharmaceutical samples using differential pulse voltammetry.     

Sensitive electrochemical detection of picloram utilising a multi-walled carbon nanotube/Cr-based metal-organic framework composite-modified glassy carbon electrode

This study describes the utilisation of a glassy carbon electrode modified with a composite of multi-walled carbon nanotube and Cr-based metal-organic framework (MIL-101, Cr-BDC, BDC = 1,4-benzenedicarboxylate) for the sensitive, simple and fast voltammetric determination of picloram in environmental samples. Under optimum conditions, additions of picloram using square wave voltammetry showed linear ranges of picloram concentrations from 24.15 to 3018 µg?L^?1 (0.1–12.5 μM) and from 3018 to 9658 µg?L^?1 (12.5–40 μM) with a detection limit of 14.49 µg?L^?1 (0.06 µM). The method was successfully applied to the determination of picloram in tap and river water samples spiked with picloram without any purification step by the standard addition method. The good recovery values obtained ranging from 97.5% to 105.0% revealed the reliability and accuracy of the method.     

Simultaneous Sensitive Determination of Dopamine and Uric Acid in the Presence of Excess Ascorbic Acid with a Magnetic Chitosan Microsphere/Thionine Modified Electrode

Magnetic chitosan microspheres (MCMS) and thionine were incorporated in a modified electrode for the simultaneous sensitive determination of dopamine (DA) and uric acid (UA). Due to the unique properties of the MCMS and the electron mediation of thionine, this modified electrode showed excellent electrocatalytic oxidation toward dopamine and uric acid with a large separation of peak potentials and a significant enhancement of peak currents. However, the electrochemical behavior of ascorbic acid may be depressed at the modified electrode. Differential pulse voltammetry was used for the simultaneous sensitive determination of dopamine and uric acid in the presence of excess ascorbic acid at this modified electrode. The current responses showed excellent linear relationships in the range of 2–30 µM and 9–100 µM for dopamine and uric acid, respectively. The detection limits were estimated to be 0.5 µM and 2.3 µM for dopamine and uric acid, respectively. In addition, this modified electrode showed excellent repeatability, good stability, and satisfactory reliability, thus indicating potential for the practical applications.     

New Nanocomposite Based on Prussian Blue Nanoparticles/Carbon Nanotubes/Chitosan and Its Application for Assembling of Amperometric Glucose Biosensor

Abstract

A new nanocomposite was developed by combination of prussian blue (PB) nanoparticles and multiwalled carbon nanotubes (MWNTs) in the matrix of biopolymer chitosan (CHIT). The PB and MWNTs had a synergistic electrocatalytic effect toward the reduction of hydrogen peroxide. The CHIT/MWNTs/PB nanocomposite‐modified glassy carbon (GC) electrode could amplify the reduction current of hydrogen peroxide by ～35 times compared with that of CHIT/MWNTs/GC electrode and reduce the response time from ～60 s for CHIT/PB/GC to 3 s. Besides, the CHIT/MWNTs/PB nanocomposite‐modified GC electrode could reduce hydrogen peroxide at a much lower applied potential and inhibit the responses of interferents such as ascorbic acid (AA) uric acid (UA) and acetaminophen (AC). With glucose oxidase (GOx) as an enzyme model, a new glucose biosensor was fabricated. The biosensor exhibited excellent sensitivity (the detection limit is down to 2.5 µM), fast response time (less than 5 s), wide linear range (from 4 µM to 2 mM), and good selection.     

Determination of Rutin by a Graphene-Modified Glassy Carbon Electrode

A reduced graphene oxide-modified glassy carbon electrode for sensitive detection of rutin is reported. The modified electrode was obtained by one-step electrochemical reduction of graphene oxide on the bare glassy carbon electrode. In the presence of graphene, an enhanced electrochemical response for rutin appeared with a pair of well-defined anodic and cathodic peaks in pH 3.0 phosphate buffer. Under the optimized conditions, the anodic peak currents exhibited a linear relationship with rutin concentration from 0.1 to 2.0 µM with a detection limit of 23.2 nM. The modified electrode was employed to the analysis of tablets (with satisfactory recovery of 19.96 mg/per tablet) and Flos Sophorae. The graphene-modified electrode exhibited high sensitivity, good stability, and selectivity for the determination of rutin.     

Amperometric Biosensors for Glucose Based on Layer‐by‐Layer Assembled Functionalized Carbon Nanotube and Poly (Neutral Red) Multilayer Film

Abstract

Multiwalled carbon nanotubes (MWNTs) were treated with a mixture of concentrated sulfuric and nitric acid to introduce carboxylic acid groups to the nanotubes. Conducting polymer film was prepared by electrochemical polymerization of neutral red (NR). By using a layer‐by‐layer method, homogeneous and stable MWNTs and poly (neutral red) (PNR) multilayer films were alternately assembled on glassy carbon (GC) electrodes. With the introduction of PNR, the MWNTs/PNR multilayer film system showed synergy between the MWNTs and PNR, with a significant improvement of redox activity due to the excellent electron‐transfer ability of carbon nanotubes (CNTs) and PNR. The electropolymerization is advantageous, providing both prolonged long‐term stability and improved catalytic activity of the resulting modified electrodes. The MWNTs/PNR multilayer film modified glassy carbon electrode allows low potential detection of hydrogen peroxide with high sensitivity and fast response time. As compared to MWNTs and PNR‐modified GC electrodes, the magnitude of the amperometric response of the MWNTs/PNR composite‐modified GC electrode is more than three‐fold greater than that of the MWNTs modified GC electrode, and nine‐fold greater than that of the PNR‐modified GC electrode. With the immobilization of glucose oxidase onto the electrode surface using glutaric dialdehyde, a biosensor that responds sensitively to glucose has been constructed. In pH 6.98 phosphate buffer, nearly interference‐free determination of glucose has been realized at ?0.2 V vs. SCE with a linear range from 50 µM to 10 mM and response time <10s. The detection limit was 10 µM glucose (S/N=3).     

Electrochemical properties and the determination of nicotine at a multi-walled carbon nanotubes modified glassy carbon electrode

Electrochemical properties of nicotine at the glassy carbon electrode modified with multi-walled carbon nanotubes were explored. Nicotine underwent irreversible reduction at the modified electrode, which was an adsorption-controlled process with two protons and two electrons. The reductive peak current of nicotine significantly increased at the modified electrode compared with the bare glassy carbon electrode, suggesting that the multi-walled carbon nanotubes can enhance the electron transfer rate. The current was proportional to the concentration of nicotine over two line ranges, and the detection limit was 9.3 µM (at S/N?=?3). For ten parallel detections of 0.62 mM nicotine, the relative standard deviation was 2.67%, suggesting that the film modified electrode had excellent reproducibility. The modified electrode was applied to the direct determination of nicotine in tobacco samples with good sensitivity, selectivity and stability.     

Electrodeposition of silver nanoparticles on a zinc oxide film: improvement of amperometric sensing sensitivity and stability for hydrogen peroxide determination

A strategy to fabricate a hydrogen peroxide (HP) sensor is developed by electrodepositing silver nanoparticles (Ag NPs) on a modified glassy carbon electrode (GCE) with a zinc oxide (ZnO) film. The Ag NPs/ZnO/GCE has been characterized by scanning electron microscopy, cyclic voltammetry, and chronoamperometry. It has been found that the Ag NPs synthesized in the presence of ZnO film provide an electrode with enhanced sensitivity and excellent stability. The sensitivity to HP is enhanced 3-fold by using Ag NPs/ZnO/GCE compared to Ag NPs/GCE. The HP sensor exhibits good linear behavior in the concentration range 2 µM to 5.5 mM for the quantitative analysis of HP with a detection limit of 0.42 µM (S/N?=?3).     

Electrochemical Detection of Persulfate at the Modified Glassy Carbon Electrode with Nanocomposite Containing Nano‐Ruthenium Oxide/Thionine and Nano‐Ruthenium Oxide/Celestine Blue

The present study describes the fabrication of a sensitive amperometric sensor for the determination of persulfate. The immobilization surface was prepared by modifying a glassy carbon (GC) electrode with a nanocomposite containing ruthenium oxide (RuOx) nanoparticles and thionine (TH) or celestin blue (CB). The modified electrodes indicated excellent electrocatalytic activity toward persulfate reduction at a potential of +0.1 V. The proposed sensor showed detection limits of 1.46 µM for the GC/RuOx/TH modified electrode and 2.64 µM for the GC/RuOx/CB modified electrode. The sensitivities were obtained as 3 nA µM^?1 at a concentration range of 10 µM to 11 mM for the GC/RuOx/TH modified electrode and 1 nA µM^?1 at a concentration range of 10 µM to 6 mM for the GC/RuOx/CB modified electrodes.     

Direct electrochemical behavior of hemoglobin at surface of Au@Fe3O4 magnetic nanoparticles

Nanoparticles (NPs) consisting of an Fe₃O₄ core and a thin gold shell (referred to as Au@Fe₃O₄ NPs) were self-assembled on the surface of a glassy carbon electrode modified with ethylenediamine. Following adsorption of hemoglobin, its interaction with the NPs was studied by UV–Vis spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. Stable and well-defined redox peaks were observed at about ?350 mV and ?130 mV in pH 6.0 buffer. The modified electrode was used as a mediator-free sensor for hydrogen peroxide (H₂O₂), with a linear range from 3.4 µM to 4.0 mM of H₂O₂, and with a 0.67 µM detection limit (at an S/N of 3). The apparent Michaelis-Menten constant is 2.3 mM.     

Simultaneous determination of dopamine and serotonin using a carbon nanotubes-ionic liquid gel modified glassy carbon electrode

An electrochemical sensor based on carbon nanotubes (CNTs)-ionic liquid (IL) composite has been developed for the simultaneous determination of serotonin (5-HT) and dopamine (DA). The CNTs-IL composite modified electrode presents excellent selectivity and sensitivity towards 5-HT and DA and eliminates the interference of ascorbic acid. The parameters which influence the determination of 5-HT and DA have been investigated. Under optimized conditions, linear calibration graphs were obtained in the range from 20 nM to 7 µM, with a detection of limit of 8 nM, for 5-HT, and in the range from 0.1 to 12 µM, with a detection of limit of 60 nM, for DA. The electrode has been applied to the assay of 5-HT and DA in human blood serum with good results.     

Solidified floating organic drop microextraction for determination of trace amounts of zinc in water samples by flame atomic absorption spectrometry

A glassy carbon electrode was prepared that was coated with a composite film containing electropolymerized poly(amidosulfonic acid) and multi-walled carbon nanotubes. It was used to study the electrochemical response of procaine by differential pulse voltammetry. The results indicate that the electrode exhibits a remarkable improvement in the oxidation peak of procaine, and this led to a simple and sensitive method for the electroanalytical determination of procaine. The peak current is proportional to the concentration of procaine from 80 nM to 1.0 µM. The detection limit is 25 nM (S/N?=?3). The modified electrode was successfully applied to the direct determination of procaine in pharmaceutical formulations.     

Synergistic Effect of Graphene and Multiwalled Carbon Nanotubes on a Glassy Carbon Electrode for Simultaneous Determination of Uric Acid and Dopamine in the Presence of Ascorbic Acid

A poly(diallyldimethylammonium chloride)-graphene-multiwalled carbon nanotube modified glassy carbon electrode was fabricated and evaluated by cyclic voltammetry and differential pulse voltammetry. The modified electrode offered high sensitivity, selectivity, excellent long-term stability, and electrocatalytic activity for uric acid and dopamine. This sensor showed wide linear dynamic ranges of 5.0 to 350.0 µmol L^?1 for uric acid and 10.0 to 400.0 µmol L^?1 for dopamine in the presence of 500 µmol L^?1 ascorbic acid. The limits of detection were 0.13 for uric acid and 0.55 µmol L^?1 for dopamine. This functionalized electrode has potential application in bioanalysis and biomedicine.     

Application of multivariate optimization method in nanomolar simultaneous determination of morphine and codeine in the presence of uric acid using a glassy carbon electrode modified with a hydroxyapatite-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticle/multiwalled carbon nanotubes composite

The electrochemical oxidation of morphine (MO) and codeine (COD) has been investigated by the application of a novel glassy carbon electrode modified with a hydroxyapatite-Fe₃O₄ nanoparticles/multiwalled carbon nanotubes composite (HA-FeNPs-MWCNTs/GCE). The modified electrode worked as an efficient sensor for simultaneous determination of MO and COD in the presence of uric acid. Response surface methodology was utilized to optimize the voltammetric response of the modified electrode for the determination of MO and COD. The amount of HA-FeNPs in the modifier matrix (%HA-FeNPs), the solution pH and the accumulation time were chosen as the three important operating factors through the experimental design methodology. The central composite design as a response surface approach was applied for obtaining the optimum conditions leading to maximum oxidation peak currents for MO and COD. The differential pulse voltammetry results showed that the obtained anodic peak currents were linearly proportional to concentration in the range of 0.08–32 µM with a detection limit (S/N = 3.0) of 14 nM for MO and in the range of 0.1–28 µM and with a detection limit of 22 nM for COD. The proposed method was successfully applied to determine these compounds in human urine and blood serum samples.