Preparation and characterization of a 1,10-phenanthroline-modified glassy carbon electrode

This paper describes the grafting of 1,10-phenanthroline (P) molecules on the surface of a glassy carbon (GC) electrode. This modification was carried out in both aqueous and non-aqueous media. Britton Robinson (BR) was used in aqueous experiments at different pHs and tetrabutylammonium tetrafluoroborate (TBATFB), 0.1 M in acetonitrile (ACN) was used in non-aqueous experiments. Surface modification experiments were performed in the +1.2–2.7 V potential range with a scan rate of 100 mV/s and 30 cycles. The presence of P at the GC surface was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), contact angle measurement (CAM) and ellipsometry. The ability of the complex to modify surfaces was investigated with differential pulse voltammetry (DPV).     

Electrochemical Synthesis and Characterization of Conducting Copolymer: Poly(o-aniline-co-o-anisidine)

Copolymerization of o-anisidine and o-anisidine was achieved electrochemically in aqueous solution containing H₂SO₄ as supporting electrolyte. The copolymer compositions can be altered by varying the monomer feed ratios during electrosynthesis. The films were electropolymerized in solution containing monomers in various ratio (0.025–0.1 M) and 1 M sulphuric acid as electrolyte by applying sequential linear potential scan rate 50 mV/s between ? 0.2 to 1.0 V. versus Ag/AgCl electrode. The copolymers were characterized by cyclic voltammetric, conductivity measurement, UV-Visible spectroscopy, FT-IR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and CHN elemental analysis.     

Electrooxidation of 2,4-dichlorophenol and other polychlorinated phenols at a glassy carbon electrode

The electrooxidation of 2,4-dichlorophenol (2,4-DCP) on a rotating GC disk electrode has been studied by cyclic voltammetry and chronoamperometry at different pH values. A dual mechanism where one pathway yields a quinone-like species and the other one leads to insoluble polymers that passivate the electrode surface is proposed. From a comparative study of the electrooxidation of several DCPs at pH 2.2, it is concluded that for the same number of chlorine atoms the ortho isomer is oxidized at a lower potential than the para isomer. The anodic peak potential for electrooxidation of the chlorophenols (CPs) on glassy carbon increases with increasing pK_a, with a slope of 35 mV (pK_a unit)⁻¹, illustrating the correlation of one chemical parameter of the CPs, namely their acidity constant, with their electrochemical reactivity.     

Structural studies of electrochemically activated glassy carbon electrode: Effects of chloride anion on the redox responses of copper deposition

The redox behaviors of copper species at electrochemically activated glassy carbon electrodes have been investigated in aqueous solutions containing chloride anions. Experimental results showed that the voltammetric responses of copper species were influenced by the electrochemical activation means employed. Abnormal copper stripping was observed at electrodes obtained by cyclic polarization. Cyclic polarization would cause changes in the interwoven graphitic crystalline surface of glassy carbon, producing electrode interface with low distribution density of electron transfer sites for the early nucleation of metallic copper in the presence of chloride anion. Potentiostatic activation would generate oxygen-containing functionalities and maintain the basic surface structure of graphitic crystalline with high distribution density of electron transfer sites.     

Monolayer covalent modification of 5-hydroxytryptophan on glassy carbon electrodes for simultaneous determination of uric acid and ascorbic acid

5-Hydroxytryptophan (5-HTP) was covalently grafted on the surface of glassy carbon electrodes (GCEs) using cyclic voltammetric method in a phosphate buffer solution. The prepared electrode, denoded as 5-HTP/GCE, was characterized by X-ray photoelectron spectroscopy, cyclic voltammetry and differential pulse voltammetry (DPV). Tryptophan grafted GCE (TRP/GCE) and 5-hydroxytryptamine grafted GCE (5-HTP/GCE) were also prepared by the same method for comparison. It was found that the electrocatalytic activities toward the oxidation of uric acid (UA) and ascorbic acid (AA) was in the order of 5-HT/GCE > 5-HTP/GCE > TRP/GCE for UA oxidation and 5-HT/GCE = 5-HTP/GCE > TRP/GCE for AA oxidation. However, the CV current sensitivity was estimated as 4:2:1 for 5-HTP/GCE:5-HT/GCE:TRP/GCE. The DPV peaks for UA and AA oxidation appeared at 0.07 V and 0.34 V versus SCE, respectively, allowing simultaneous determination in mixtures. A linearly response in the range of: 5.0 × 10⁻⁷ to 1.1 × 10⁻⁵ M with the detection limit (s/n = 3) of 2.8 × 10⁻⁷ M for UA determination, and a linear response in the range of: 5.0 × 10⁻⁶ to 1.0 × 10⁻⁴ M with the detection limit of 4.2 × 10⁻⁶ M for AA determination were obtained. This electrode was used for UA and AA determinations in human urine samples satisfactorily.     

Electrochemical reduction of nitrite at poly-[Ru(5-NO2-phen)2Cl] tetrapyridylporphyrin glassy carbon modified electrode

This work describes the preparation of modified electrodes with Poly-tetraruthenated porphyrin. Also, a detailed Raman and electrochemical characterization of these surfaces is shown. Glassy carbon electrodes were modified with Ni (II), Zn (II) and metal free polymeric film of tetrapyridylporphyrin coordinated to four [Ru(5-NO₂-phen)₂Cl]⁺ moieties.These modified electrodes are very stable in aqueous solutions, and were evaluated for the electrochemical reduction of nitrite ion at pH = 5.9 in 0.1 M NaClO₄. When the solution contains 0.01 M nitrite, linear sweep voltammetry results, show an enhancement in the current from −0,3 V with the conducting polymers, compared to the bare electrode behavior. Analyses after controlled potential electrolysis experiments verify the production of hydrazine, hydroxylamine and ammonia. Hydroxylamine was the product of higher production among the three studied catalysts.The behavior of the modified electrodes allows predicting that the reduction process of nitrite takes place through reduced macrocycle ring. The electrocatalytic activity of the modified electrodes, measured as turn over frequency is dependent on the potential and the central ion in the cavity of the macrocycle. Finally, the modified electrode containing Ni²⁺ in the cavity of the macrocycle was used as an amperometric sensor toward nitrite detection. The results show a limit of detection of 9.37 × 10⁻⁶ M and a linear rage of concentration of 1.49 × 10⁻⁵ to 1.24 × 10⁻⁴ M.     

Electrochemical behavior and voltammetric determination of 4-aminophenol based on graphene-chitosan composite film modified glassy carbon electrode

The graphene-chitosan composite film modified glassy carbon electrode (GCE) was fabricated and used to determine 4-aminophenol (4-AP). In 0.1 M pH 6.3 phosphate buffer solution, the redox peak currents of 4-AP increased significantly and the peak-to-peak separation decreased greatly at graphene-chitosan composite film modified GCE compared with bare GCE and chitosan modified GCE, indicating that graphene possessed electrocatalytic activity towards 4-AP. The experimental conditions were optimized and the kinetic parameters were investigated. The oxidation mechanism was discussed. Under the optimal experimental conditions, the oxidation peak current was proportional to 4-AP concentration in the range from 0.2 to 550 μM with the correlation coefficient of 0.9930. The detection limit was 0.057 μM (S/N = 3). Using the proposed method, 4-AP was successfully determined in water samples and paracetamol tablets with standard addition method, suggesting that this method can be applied to determine 4-AP in environments and pharmaceuticals.     

铋膜玻碳电极阳极溶出伏安法测定异烟肼的研究

研究了异烟肼在铋膜玻碳电极上的电化学行为检测方法。在0.1mol/L pH=4.5的HAc—NaAc缓冲溶液的底液中,通过富集,用铋膜玻碳电极进行阳极溶出伏安法测定异烟肼。异烟肼的阳极峰电位为-1.02V(vs.SCE),峰电流与异烟肼的浓度在1.6×10~(-7)～8.0×10~(-5)mol/L范围内呈良好的线性关系。该方法的检出下限为8.0×10~(-8)mol/L。对异烟肼含量用本法进行了测定,获得了满意的结果。本方法的优点是成本低,操作方便,重现性好以及检测下限低。     

Synthesis and characterization of poly(N-(2-(thiophen-3-yl)methylcarbonyloxyethyl)maleimide) and its spectroelectrochemical properties

A new monomer; N-(2-(thiophen-3-yl)methylcarbonyloxyethyl) maleimide (NMT) was synthesized. The chemical structure of the monomer was characterized by Nuclear Magnetic Resonance (¹H-NMR) and Fourier Transform Infrared (FTIR) Spectroscopy. Electrochemical polymerization of NMT was performed in acetonitrile (AN)/borontrifloride ethylether (BFEE) solvent mixture (1:1, v/v) where tetrabutylammonium tetrafluoroborate (TBAFB) was utilized as the supporting electrolyte. The resulting conducting polymer was characterized by Fourier Transform Infrared (FTIR) Spectroscopy, thermal analyses and Scanning Electron Microscopy (SEM). Electrical conductivity was measured by the four-probe technique. The spectroelectrochemical behavior and switching ability of P(NMT) film were investigated by UV–Vis spectrophotometry. P(NMT) revealed color changes between yellow and blue in the reduced and oxidized states respectively.     

Ion-exchange adsorption of copper(II) ions on functionalized single-wall carbon nanotubes immobilized on a glassy carbon electrode

The cation-exchange property of oxidatively treated carbon nanotubes (CNTs) is newly reported. Single-wall carbon nanotubes (SWNTs), which were oxidatively treated, were immobilized on a glassy carbon surface and, on this CNT-modified electrode, Cu(II) ions were spontaneously adsorbed and their redox waves electrochemically measured. It is suggested that the adsorption of the cationic Cu(II) ions occurs by their electrostatic interaction with the negatively charged carboxylic anions on the CNTs after the ion-exchange with protons. The surface coverage of the adsorbed Cu(II) ions depending on the dipping time, the amount of immobilized CNTs, and the Cu(II) concentration was estimated from the electrochemical chronocoulometric measurements. The effect of the ionic strength on the adsorption of the Cu(II) ions was investigated and the adsorption strengths of various alkali metal cations and protons were compared. It is hoped that this new cation-exchange property of CNT-modified electrodes may extend their range of electrochemical applications.     

Electrocatalytic reduction of dioxygen by cobalt porphyrin-modified glassy carbon electrode with single-walled carbon nanotubes and nafion in aqueous solutions

Cobalt porphyrin (CoP)-modified glassy carbon electrode (GCE) with single-walled carbon nanotubes (SWNTs) and Nafion demonstrated a higher electrocatalytic activity for the reduction of dioxygen in 0.1 M H₂SO₄ solution. Cyclic and hydrodynamic voltammetry at the CoP-SWNTs/GCE-modified electrodes in O₂-saturated aqueous solutions was used to study the electrocatalytic pathway. Compared with the CoP/GCE-modified electrodes, the reduction potential of dioxygen at the CoP-SWNTs/GCE-modified electrodes was shifted to the positive direction and the limiting current was greatly increased. Especially, the Co(TMPP)-SWNTs/GCE-modified electrode was catalyzed effectively by the 4e⁻ reduction of dioxygen to water, because hydrodynamic voltammetry revealed the transference of approximately four electrons for dioxygen reduction and the minimal generation of hydrogen peroxide in the process of dioxygen reduction.     

Study of nimesulide and its determination using multiwalled carbon nanotubes modified glassy carbon electrodes

A new method for the determination of nimesulide was established based on the multiwalled carbon nanotubes (MWCNTs) modified glassy carbon electrode (MWCNTs/GCE). In 0.2 M PBS (pH 6.6) buffer solution, the MWCNTs/GCE showed a remarkable catalytic and enhancement effect on reduction of the nimesulide. The reduction peak potential of nimesulide shifted positively from −0.665 V at bare GCE to −0.553 V at MWCNTs/GCE, and the sensitivity increased ca. 7 times. A linear dynamic range of 3.2 × 10⁻⁷-6.5 × 10⁻⁵ M (R = 0.9992) with a detection limit of 1.6 × 10⁻⁷ M was obtained. The electrochemical behaviors of nimesulide were studied and electron-transfer coefficient (α = 0.45), proton number (X = 1) and electron-transfer number (n = 2) have been determined. This method has been used to determine the content of nimesulide in medical tablets. The recovery was determined to be 93.2-106.2% by means of standard addition method. Compared with UV-vis spectrometry, the method was not remarkable difference.     

Modification of glassy carbon electrodes by 4-chloromethylphenyl units and d-glucosaminic acid

The present work is dealing with the attachment of d-glucosaminic acid (D-GA) on glassy carbon electrode by two different methods. Firstly, the electrode was modified by chloromethylphenyl groups by reduction of 4-chloromethylphenyldiazonium cations followed by the nucleophilic substitution of the chlorine by the amine functionality of D-GA and secondly by the direct immobilization of the amine terminated molecule. The generality of the nucleophilic substitution reaction and the direct immobilization of an amine were also demonstrated with reactants bearing an electroactive ferrocene moiety; 4-nitrophenylferrocene (NFc) and 4-ferrocenylaniline (FcA). The surfaces modified with FcA and NFc were investigated by cyclic voltammetry, and the D-GA modified electrodes were characterized by X-ray photoelectron spectroscopy. A preliminary evaluation of the efficiency of these surface modifiers to prevent protein adsorption was realized by scanning electron microscopy.     

Modification of glassy carbon electrodes by 4-chloromethylphenyl units and d-glucosaminic acid

The present work is dealing with the attachment of d-glucosaminic acid (D-GA) on glassy carbon electrode by two different methods. Firstly, the electrode was modified by chloromethylphenyl groups by reduction of 4-chloromethylphenyldiazonium cations followed by the nucleophilic substitution of the chlorine by the amine functionality of D-GA and secondly by the direct immobilization of the amine terminated molecule. The generality of the nucleophilic substitution reaction and the direct immobilization of an amine were also demonstrated with reactants bearing an electroactive ferrocene moiety; 4-nitrophenylferrocene (NFc) and 4-ferrocenylaniline (FcA). The surfaces modified with FcA and NFc were investigated by cyclic voltammetry, and the D-GA modified electrodes were characterized by X-ray photoelectron spectroscopy. A preliminary evaluation of the efficiency of these surface modifiers to prevent protein adsorption was realized by scanning electron microscopy.     

Electrochemical polymerization of water-soluble and insoluble monomers in supercritical carbon dioxide-in-water emulsion

Dense carbon dioxide is an environmentally benign solvent, but its non-polarity limits the use of carbon dioxide as a reaction medium for electrochemical reactions. We have previously reported that the electrochemical polymerization in a carbon dioxide-in-water (C/W) emulsion proceeds to form conductive polypyrrole films [Jikei M, Saitoh S, Yasuda H, Itoh H, Sone M, Kakimoto M, et al. Polymer 2006;47:1547-54]. In this study, the effect of reaction conditions of the electrochemical polymerization on the resulting polypyrrole films was systematically investigated in order to reveal the features, flexibility and limitations of the C/W emulsion as a medium for electrochemical reactions. Other monomers, such as aniline and 3,4-ethylenedioxythiophene, were also examined for the electrochemical polymerization in the C/W emulsion. We have found that water-soluble monomers, such as pyrrole and aniline, are suitable for the electrochemical polymerization in the C/W emulsion that form films with a fine uneven texture.     

Electrogenerated chemiluminescence of ruthenium (II) bipyridyl complex directly immobilized on glassy carbon electrodes

Ru(bpy)₃Cl₂ was used to modify the glass carbon electrodes (GCE) by oxidation and co-deposition on the electrode surface. The modified electrodes were characterized by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). About 2.2 × 10⁻⁹ mol Ru(bpy)₃ ²⁺ was immobilized on the GCE surface (ϕ = 4 mm). The modified GC electrodes showed stable electrochemiluminescence with tripropylamine (TPrA) as the co-reactant with a linear range from 10 to 500 μM (R ² = 0.999). Among the 10 amino acids tested, the modified electrode system showed selective response to arginine and lysine, indicating that the molecular structure played an important role as co-reactant. This simple and sensitive electrode modifying method when combined with flow-injection or liquid chromatography systems has the potential for amino acid analyses.     

Electrochemical Behavior of Polyaniline,Poly(o-Anisidine) and Their Copolymer Thin Films in Inorganic and Organic Supporting Electrolytes

Abstract

The influence of inorganic and organic supporting electrolytes on electrochemical, optical, and conducting properties of polyaniline, poly(o-anisidine), and poly(aniline-co-o-anisidine) thin films were investigated. Homo- and copolymer thin films were synthesized electrochemically, under cyclic voltammetric conditions in aqueous solutions of inorganic acids, viz., H₂SO₄, HCl, HNO₃, H₃PO₄, and HClO₄ and organic acids, viz., benzoic acid, cinnamic acid, oxalic acid, malonic acid, succinic acid, and adipic acid, at room temperature. The films were characterized by cyclic voltammetry, ultraviolet (UV)–Visible spectroscopy, and conductivity measurements using four probe technique. The optical absorption spectra indicated that the formation of the conducting emeraldine salt (ES) phase took place in all the inorganic supporting electrolytes used whereas, inorganic supporting electrolytes ES phase formed only with oxalic acid. It was also observed that the current density and conductivity of thin films are greatly affected by the nature and size of the anion present in the electrolyte. The formation of copolymer has also been confirmed by differential scanning calorimetry.     

碳糊电极和化学修饰碳糊电极制备及应用综述

综述了碳糊电极及化学修饰碳糊电极的发展、制备及表征,概括了近年来化学修饰碳糊电极在食品分析、药物分析、环境监测等领域的应用,并展望了其发展前景。     

Synthesis, characterization and electrochromic properties of a near infrared active conducting polymer of 1,4-di(selenophen-2-yl)-benzene

A novel selenophene-based monomer, 1,4-di(selenophen-2-yl)-benzene (DSB), was synthesized via Stille coupling reaction of 1,4-dibromobenzene and tributyl(2-selenophenyl)stannane. Conducting polymer (PDSB) was prepared electrochemically in the presence of tetrabutylammonium hexafluorophosphate (TBAPF₆) as the supporting electrolyte in dichloromethane (DCM). The resulting conducting polymer was characterized by Cyclic Voltammetry, Fourier Transform Infrared and Ultraviolet-visible spectroscopy. Spectroelectrochemistry analysis and kinetic studies of PDSB revealed a π-π^∗ transition at 340 nm with a striking and rapid (0.6 s) transmittance change (35%), at near infrared region (1250 nm), indicating that PDSB is a very suitable near infrared electrochromic material.     

Modification of glassy carbon electrode with multi-walled carbon nanotubes and iron(III)-porphyrin film: Application to chlorate, bromate and iodate detection

In this study, multi-wall carbon nanotubes (MWCTs) is evaluated as a transducer, stabilizer and immobilization matrix for the construction of amperometric sensor based on iron-porphyrin. 5,10,15,20-Tetraphenyl-21H,23H-porphine iron(III) chloride (Fe(III)P) adsorbed on MWCNTs immobilized on the surface of glassy carbon electrode. Cyclic voltammograms of the Fe(III)P-incorporated-MWCNTs indicate a pair of well-defined and nearly reversible redox couple with surface confined characteristics at wide pH range (2-12). The surface coverage (Γ) and charge transfer rate constant (k_s) of Fe(III)P immobilized on MWCNTs were 7.68 × 10⁻⁹ mol cm⁻² and 1.8 s⁻¹, respectively, indicating high loading ability of MWCNTs for Fe(III)P and great facilitation of the electron transfer between Fe(III)P and carbon nanotubes immobilized on the electrode surface. Modified electrodes exhibit excellent electrocatalytic activity toward reduction of ClO₃⁻, IO₃⁻ and BrO₃⁻ in acidic solutions. The catalytic rate constants for catalytic reduction of bromate, chlorate and iodate were 6.8 × 10³, 7.4 × 10³ and 4.8 × 10² M⁻¹ s⁻¹, respectively. The hydrodynamic amperometry of rotating-modified electrode at constant potential versus reference electrode was used for detection of bromate, chlorate and iodate. The detection limit, linear calibration range and sensitivity for chlorate, bromate and iodate detections were 0.5 μM, 2 μM to 1 mM, 8.4 nA/μM, 0.6 μM, 2 μM to 0.15 mM, 11 nA/μM, and 2.5 μM, 10 μM to 4 mM and 1.5 nA/μM, respectively. Excellent electrochemical reversibility of the redox couple, good reproducibility, high stability, low detection limit, long life time, fast amperometric response time, wide linear concentration range, technical simplicity and possibility of rapid preparation are great advantages of this sensor. The obtained results show promising practical application of the Fe(III)P-MWCNTs-modified electrode as an amperometric sensor for chlorate, iodate and bromate detections.