Effect of monomer molecular flow on electrode surface on the structure of poly(α-tetrathiophene) obtained by anodic polymerization

Different structures have been found for poly(α-tetrathiophene) [poly(α-4TF)] electrosynthesized on Pt by anodic oxidation of 1.0 mM monomer solutions in media such as 45:35:20 (v/v/v) acetonitrile/THF/DMF, 45:35:20 (v/v/v) acetonitrile/ethanol/DMF and 72:28 (v/v) acetonitrile/DMF containing 0.1 M LiClO₄; as well as 72:28 (v/v) acetonitrile/DMF with 0.1 M NaClO₃, under dynamic and static conditions at 25 °C. In all cases the polymer was generated by chronoamperometry at 1.000 V vs. Ag∣AgCl, corresponding to the first oxidation peak detected by cyclic voltammetry. Uniform, adherent, insoluble and black polymer films were obtained under these conditions. The resulting structures have been elucidated by combining the information of their IR spectrum, n_ox-value and doping level of the counterion. The degree of crosslinking of every polymer has been quantified and related to the molecular flow of monomer on the Pt electrode. A monomer concentration flow between 4 × 10⁻⁶ and 5 × 10⁻⁶ mmol cm⁻² s⁻¹ was determined as the limiting value below which the polymer grows with crosslinking. This value corresponds to the electropolymerization rate of α-4TF by Pt area unit at 25 °C.     

Characteristic behavior of macro-, semimicro- and microelectrodes in voltammetric and chronoamperometric measurements

The advantages of microelectrodes such as the improvement of signal-to-noise ratio, the ability to perform electrochemical measurements in high resistive solutions and small RC-time constants give the possibility of an extended use for voltammetric and chronoamperometric techniques in analytical chemistry. In this comparative study, the microelectrode properties of three selected electrodes were examined. The characterization of a RAM-microarray electrode, an epoxy-impregnated carbon electrode and a conventional glassy carbon macroelectrode was performed by cyclic voltammetry at different scan rates, by DP-voltammetric measurements using different concentrations of supporting electrolyte and by transient measurements. It could be shown, that in comparison to the microarray electrode and to the glassy carbon macroelectrode, respectively, the results obtained by using the epoxy-impregnated carbon electrode are caused by its semimicroelectrode character.     

Cathodic stripping voltammetry of trace Mn(II) at carbon film electrodes

A sensitive voltammetric method is presented for the determination of tract levels of Mn (II) using carbon film electrodes fabricated from carbon resistors of 2 Ω. Determination of manganese was made by square wave cathodic stripping voltammetry (CSV), with deposition of manganese as manganese dioxide. Chronoamperometric experiments were made to study MnO₂ nucleation and growth. As a result, it was found to be necessary to perform electrode conditioning at a more positive potential to initiate MnO₂ nucleation. Under optimised conditions the detection limit obtained was 4 nM and the relative standard deviation for eight measurements of 0.22 nM was 5.3%. Interferences from various metal ions on the response CSV of Mn(II) were investigated, namely Cd(II), Ni(II), Cu(II), Cr(VI), Pb(II), Zn(II) and Fe(II). Application to environmental samples was demonstrated.     

Xanthine Sensors Based on Anodic and Cathodic Detection of Enzymatically Generated Hydrogen Peroxide

A xanthine biosensor was fabricated by the covalent immobilization of xanthine oxidase (XO) onto a functionalized conducting polymer (Poly‐5, 2′: 5′, 2″‐terthiophine‐3‐carboxylic acid), poly‐TTCA through the formation of amide bond between carboxylic acid groups of poly‐TTCA and amine groups of enzyme. The immobilization of XO onto the conducting polymer (XO/poly‐TTCA) was characterized using cyclic voltammetry, quartz crystal microbalance (QCM), and X‐ray photoelectron spectroscopy (XPS) techniques. The direct electron transfer of the immobilized XO at poly‐TTCA was found to be quasireversible and the electron transfer rate constant was determined to be 0.73 s^?1. The biosensor efficiently detected xanthine through oxidation at +0.35 V and reduction at ?0.25 V (versus Ag/AgCl) of enzymatically generated hydrogen peroxide. Various experimental parameters, such as pH, temperature, and applied potential were optimized. The linear dynamic ranges of anodic and cathodic detections of xanthine were between 5.0×10^?6?1.0×10^?4 M and 5.0×10^?7 to 1.0×10^?4 M, respectively. The detection limits were determined to be of 1.0×10^?6 M and 9.0×10^?8 M with anodic and cathodic processes, respectively. The applicability of the biosensor was tested by detecting xanthine in blood serum and urine real samples.     

Electrocatalytic Determination of Ascorbic Acid at the Surface of 2,7‐Bis(ferrocenyl ethyl)fluoren‐9‐one Modified Carbon Paste Electrode

A chemically modified carbon paste electrode with 2,7‐bis(ferrocenyl ethyl)fluoren‐9‐one (2,7‐BFEFMCPE) was employed to study the electrocatalytic oxidation of ascorbic acid in aqueous solution using cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The diffusion coefficient (D=1.89×10^?5 cm² s^?1), and the kinetic parameter such as the electron transfer coefficient, α (=0.42) of ascorbic acid oxidation at the surface of 2,7‐BFEFMCPE was determined using electrochemical approaches. It has been found that under an optimum condition (pH 7.00), the oxidation of ascorbic acid at the surface of such an electrode occurs at a potential about 300 mV less positive than that of an unmodified carbon paste electrode. The catalytic oxidation peak currents show a linear dependence on the ascorbic acid concentration and linear analytical curves were obtained in the ranges of 8.0×10^?5 M–2.0×10^?3 M and 3.1×10^?5 M–3.3×10^?3 M of ascorbic acid with correlation coefficients of 0.9980 and 0.9976 in cyclic voltammetry and differential pulse voltammetry, respectively. The detection limits (2δ) were determined to be 2.9×10^?5 M and 9.0×10^?6 M with cyclic voltammetry and differential pulse voltammetry, respectively. This method was also examined for determination of ascorbic acid in pharmaceutical preparations.     

纳米碳管电极上氧的电催化还原

以聚四氟乙烯为粘结剂制成了多壁纳米碳管（MWNT）电极.采用恒电位阶跃法和循环伏安法研究了MWNT电极在碱性溶液中的电化学行为，并对碱性溶液中溶解氧在该电极上的电化学还原行为进行了研究.实验结果表明： MWNT电极具有比石墨电极更高的孔隙率和电化学表面积；MWNT电极上O2还原成的反应为准可逆过程；在5～50 mV•s－1的扫描速率范围内，阴极峰电流与扫描速度成线性关系，表明MWNT电极上O2还原成的反应受吸附控制；对碱性溶液中的氧还原反应， MWNT比石墨具有更高的催化活性.     

The electrocatalytic examination of cephalosporins at carbon paste electrode modified with CoSalophen

The electrocatalytic oxidation of cephalexin and cefazolin has been studied at a carbon paste electrode modified with cobalt salophen (CoSal) by cyclic voltammetry. The selectivity of the carbon paste modified with CoSal in detecting cephalexin and cefazolin was examined. To suggest the electrocatalytic mechanism for electro-oxidation of cefazolin, the electrochemical behavior of ceftriaxone was investigated which has a thiol group out of the beta lactam ring. The electrocatalytic oxidation of these antibiotics is shown to be irreversible at the CoSal modified electrode. Scan rate dependence of cefazolin, which is a sulfur-containing compound, has been examined. The results indicated that the electrocatalytic oxidation of the compounds is diffusion controlled. The responses of the modified electrode were compared with those of unmodified electrode and it has shown that the modified electrode has better sensitivity than unmodified electrode to the detection of cefazolin. The overall number of electrons contributed to the oxidation of cefazolin is obtained 1 by chronoamperometry; the number of electron involved in the rate-determining step was 1. The results of differential pulse voltammetry (DPV) using the modified electrode with high sensitivity were applied for the determination of cefazolin in human synthetic serum samples. The linear range was obtained from 1 × 10⁻⁵ to 1 × 10⁻³ M for DPV determination of cefazolin in buffered solutions (pH 3.0).     

Determination of kinetic parameters of the FeCl3/FeCl2 systemvia a novel treatment of chronoamperometric data

Summary Computer based methods for the processing of chronoamperometric datavia convolutions are discussed. On the example of the quasi-reversible Fe³⁺/Fe²⁺ couple, their application for data acquisition and determination of the heterogeneous electrochemical parameters is demonstrated. The plot of Q/i vs. t/i is superior to that employingi/I ₁, being less sensitive to distortions by charging currents once these have died away and by the effects of damping on the initially rapidly varying currents. Cyclic voltammetry is often combined with convolution or deconvolution, and digital simulation studies are also frequently performed to confirm the results.

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Bestimmung kinetischer Parameter des Systems FeCl₃/FeCl₂ mittels einer neuen Verarbeitung chronoamperometrischer Daten

Zusammenfassung Computerunterstützte Verfahren zur Verarbeitung chronoamperometrischer Daten mittels Faltungsintegralen werden diskutiert. Am Beispiel des quasireversiblen Systems Fe³⁺/Fe²⁺ wird die Anwendung der neuen Methoden zur Datenerfassung und zur Bestimmung der heterogenen elektrochemischen Parameter gezeigt. Der Plot von Q/i gegen t/i ist dem voni/I ₁ überlegen, da er durch Ladeströme und Dämpfung der ursprünglich stark variierenden Ströme weniger stark beeinflußt wird. Cyclische Voltammetrie wird häufig im Zusammenhang mit Konvolutions- und Dekonvolutionsmethoden angewandt; digitale Simulation zur Überprüfung der Ergebnisse wird ebenfalls oft eingesetzt.

     

Synthesis, characterization and application of monocarboxy-phthalocyanine-single walled carbon nanotube conjugates in electrocatalysis

In this paper we report on the synthesis, characterization and use of monocarboxy-phthalocyanine-single walled carbon nanotube conjugates in the electrocatalysis of amitrole and diuron. UV-Vis, FTIR and XRD spectroscopies were used in the characterization of cobalt(II)-tris(benzyl-mercapto)-mono(carboxyphenoxy)-phthalocyanine conjugates (CoMCPc-PA-SWCNT(linked)), while AFM was used to show changes in surface morphologies of the modified electrodes. Cyclic voltammetry and chronoamperometry were used for the electrocatalytic oxidation of amitrole and diuron on the modified glassy carbon electrode. The catalytic rate constants for amitrole and diuron were found to be 1.83 × 10⁶ and 1.99 × 10⁶ M⁻¹ s⁻¹, respectively. The linear range for both was 1.0 × 10⁻⁵-2.0 × 10⁻⁴ M, with sensitivities of 5.10 and 3.70 A mol⁻¹ L cm⁻² for amitrole and diuron, respectively. The limits of detection were estimated to be 0.14 and 0.20 μM for amitrole and diuron, respectively, using the 3δ notation.     

Electrochemical behavior of some triazine derivatives at glassy carbon electrode in non-aqueous media

Electroreduction of 4-amino-6-methyl-3-thio-1,2,4-triazine-5-one (I), 6-methyl-3-thio-1,2,4-triazine-5-one (II), and 2,4-dimethoxy-6-methyl-1,3,5-triazine (III) in dimethylformamide was investigated. Electrochemical techniques including differential pulse voltammetry (DPV), cyclic voltammetry (CV), chronoamperometry, and coulometry were employed to study the mechanism of the electrode process. From the analysis of the voltammetric and spectroscopic experiments a mechanism was proposed for the electroreduction of thio-triazine and triazine compounds. Compounds I and II having thiol groups exhibited similar redox behavior. Both compounds displayed two cathodic peaks, whereas the third compound (III), with no thiol group, showed only one cathodic peak in the same potential range as the second peak of compounds I and II.The results of this study show that in the former wave, the one electron reduction of thiol led to a dimer (disulfide) species and in the latter, the triazine ring was reduced in a two-electron process. The effects of various physical and electrochemical parameters were studied and the electrochemical behavior of the monomers was reported as a function of these parameters. A completely irreversible behavior was observed from cyclic voltammograms obtained under different conditions. Furthermore, in this study some numerical constants, such as diffusion constant, transfer coefficient, and rate constant of coupled chemical reaction were determined.