Electrochemistry of triphenyltin acetate at a mercury-film glassy carbon electrode

The electrochemical behaviour of triphenyltin acetate was investigated by cyclic voltammetry, differential-pulse voltammetry and controlled potential electrolysis at a mercury-film glassy carbon electrode. Effects on the electrochemical response of the composition of supporting electrolytes, pH, electrode rotation speed and triphenyltin acetate concentration were determined. The electrochemical reduction of this compound was found to involve a preliminary adsorption process (E_peak ≈ ?0.7 V vs. SCE), the reduction of triphenyltin acetate to the triphenyltin radical (E_peak ≈ ?1.0 V) and reduction of the radical to the triphenyltin anion (E_peak ≈ ?1.4 V). A procedure for the determination of trace amounts of this compound by differential-pulse anodic stripping voltammetry in 50% (v/v) ethanol with 0.1 M acetic acid + 0.1 M ammonia solution was developed and applied to the analysis of a commercial powder formulation and water and fish samples. The limit of detection was 2.5 × 10^?9 M triphenyltin acetate.     

Electrochemistry and voltammetric determination of tannic acid on a single-wall carbon nanotube-coated glassy carbon electrode

The voltammetric behavior of tannic acid (TA) on a single-wall carbon nanotubes (SWNTs) modified glassy carbon electrode has been investigated by cyclic voltammetry. TA can generate a well-defined anodic peak on the modified electrode at around 0.42 V (vs. SCE) in 0.10 M phosphate buffer solutions (pH = 4.0). The electrochemical reaction involves 1e transfer, accompanied by one proton. The electrode process is controlled by adsorption. The parameters affecting the response of TA, such as solution pH, accumulation time and accumulation potential are optimized for the determination of TA. Under the optimum conditions, the peak current changes linearly with the TA concentration in the range of 5.0 × 10⁻⁸–1.0 × 10⁻⁶ M. The lowest detectable concentration of TA is 8.0 × 10⁻⁹ M after 180 s accumulation. This method has been successfully applied to the determination of TA in tea and beer samples. In addition, the influence of potential interferents is examined. In the presence of bovine serum albumin, the peak current of TA decreases linearly due to the formation of a super-molecular complex.     

Electrochemistry and electrocatalytic activity of polypyrrole/ferrocyanide films on a glassy carbon electrode

Functionalized polypyrrole films were prepared by incorporation of Fe(CN)₆ ³⁻ as doping anion during the electropolymerization of pyrrole at a glassy carbon electrode from aqueous solution. The electrochemical behavior of the Fe(CN)₆ ³⁻/Fe(CN)₆ ⁴⁻ redox couple in polypyrrole was studied by cyclic voltammetry. An obvious surface redox reaction was observed and dependence of this reaction on the solution pH was illustrated. The electrocatalytic ability of polypyrrole film with ferrocyanide incorporated was demonstrated by oxidation of ascorbic acid at the optimized pH of 4 in a glycine buffer. The catalytic effect for mediated oxidation of ascorbic acid was 300 mV and the bimolecular rate constant determined for surface coverage of 4.5 × 10⁻⁸ M cm⁻² using rotating disk electrode voltammetry was 86 M⁻¹ s⁻¹. Furthermore, the catalytic oxidation current was linearly dependent on ascorbic acid concentration in the range 5 × 10⁻⁴–1.6 × 10⁻² M with a correlation coefficient of 0.996. The plot of i _p versus v ^1/2 confirms the diffusion nature of the peak current i _p. Received: 12 April 1999 / Accepted: 25 May 1999     

亚硝酸根在纳米金修饰玻碳电极上的电催化氧化行为及其测定

采用直接电化学沉积法制备出纳米金修饰玻碳电极,研究了其对亚硝酸根的电催化氧化作用。结果表明,亚硝酸根在该修饰电极上于0.8 V处出现了一个良好的氧化峰。在最优实验条件下,亚硝酸根的峰电流与其浓度在2×10-6～2×10-3mol/L范围内呈一定的线性关系,检出限为6.0×10-7(S/N=3),提出了用循环伏安法测定亚硝酸根的方法。纳米金修饰电极用于东莞自来水水样中亚硝酸根的测定,回收率在98.1%～101.4%之间。对比本方法,用分光光度法对东莞自来水样中亚硝酸根进行了测定,结果满意。     

Electrocatalytic reduction of dioxygen on a glassy carbon electrode modified with adsorbed cobaloxime complex.

The preparation and electrochemical properties of a glassy carbon (GC) electrode modified with cobaloxime complex were investigated. The complex of the type [CoIII(DO)(DOH)pn)Cl2] where (DO)(DOH)pn = N2,N2'-propanediylbis-2,3-butanedione-2-imine-3-oxime) was adsorbed irreversibly and strongly on the surface of preanodized glassy carbon electrode. Electrochemical behavior and stability of modified GC electrode were investigated by cyclic voltammetry. The electrocatalytic reduction of dioxygen has been studied using this modified glassy carbon electrode by cyclic voltammetry, chronoamperometry and rotating disk electrode voltammetry as diagnostic techniques. The modified electrode showed excellent eletrocatalytic ability for the reduction of dioxygen to hydrogen peroxide in acetate buffer (pH 4.0) with overpotential 1.0 V lower than the plain glassy carbon electrode. The formal potential for this modified electrode is not shifted to more negative potentials by repeated reduction-oxidation cycles in oxygen-saturated supporting electrolyte solution. The apparent electron transfer rate constant (kS), the transfer coefficent (alpha) and the catalytic rate constant of O2 reduction at a GC modified electrode were determined by cyclic voltammetry and rotating disk electrode voltammetry and were found to be around 2.6 s(-1), 0.33 and 2.25 x 10(4) M(-1) s(-1). Based on the results, a catalytic mechanism is proposed and discussed.     

Thin layer of Ni-modified 13X zeolite on glassy carbon support as an electrode material in aqueous solutions

A new type of an electrode material, zeolite modified by the incorporation of Ni or NiO clusters into its cavities, was synthesized by multiple impregnation of zeolite 13X with a Ni-acetylacetonate solution followed by solvent evaporation and thermal degradation of the nickel compound. Samples with a Ni/13X mass ratio within the range 0.2–1.0 were synthesized. Modification by both Ni and NiO clusters, depending on whether the atmosphere was reducing (H₂) or oxidizing (air), respectively, was used to finish the sample. After modification, the zeolite kept its original crystallographic structure, as proven by X-ray diffractommetry. The dimensions of the incorporated clusters were limited by the diameter of the zeolite cavities (reaching 1.3 nm). This material, homogenized with 10 wt % of nanodispersed carbon, was bonded in the form of a thin layer to a glassy carbon disc by means of Nafion and used as an electrode material in an aqueous 0.1 M NaOH solution. The cyclovoltammograms of this thin-layer electrode resemble those of a smooth nickel electrode in alkaline solutions. The text was submitted by the authors in English.     

Electrochemistry and electrocatalytic activity of catechin film on a glassy carbon electrode toward the oxidation of hydrazine

A very stable electroactive film of catechin was electrochemically deposited on the surface of activated glassy carbon electrode. The electrochemical behavior of catechin modified glassy carbon electrode (CMGCE) was extensively studied using cyclic voltammetry. The properties of the electrodeposited films, during preparation under different conditions, and the stability of the deposited film were examined. The charge transfer coefficient (α) and charge transfer rate constant (k _s) for catechin deposited film were calculated. It was found that the modified electrode exhibited excellent electrocatalytic activity toward hydrazine oxidation and it also showed a very large decrease in the overpotential for the oxidation of hydrazine. The CMGCE was employed to study electrocatalytic oxidation of hydrazine using cyclic voltammetry, rotating disk voltammetry, chronoamperometry, amperometry and square-wave voltammetry as diagnostic techniques. The catalytic rate constant of the modified electrode for the oxidation of hydrazine was determined by cyclic voltammetry, chronoamperometry and rotating disk voltammetry and was found to be around 10⁻³ cm s⁻¹ . In the used different voltammetric methods, the plot of the electrocatalytic current versus hydrazine concentration is constituted of two linear segments with different ranges of hydrazine concentration. Furthermore, amperometry in stirred solution exhibits a detection limit of 0.165 μM and the precision of 4.7% for replicate measurements of 40.0 μM solution of hydrazine.     

Toluidine blue adsorbed on alcohol dehydrogenase modified glassy carbon electrode for voltammetric determination of ethanol

A novel toluidine blue O (TBO) adsorbed alcohol dehydrogenase (ADH) biocomposite film have been prepared through simple adsorption technique with the help of electrostatic interaction between oppositely charged layers. Nafion (NF) coating was made on top of the biocomposite film modified glassy carbon electrode (GCE) to protect ADH from leaching. The fabricated ADH/TBO/NF biocomposite electrode remains highly stable in the pH range from 4 to 13. More facile electron transfer process occurs at ADH/TBO/NF biocomposite than at TBO/NF film, which is obvious from the six folds increase in k_s value. Maximum surface coverage concentration (Γ) of TBO is noticed at ADH/TBO/NF film, which is 82% higher than at TBO/NF and 15% higher than at ADH/TBO film modified GCEs. Electrochemical impedance spectroscopy studies reveal that ADH has been well immobilized in the biocomposite film. Scanning electron microscopy studies confirm the discriminate surface morphology of various components present in the biocomposite film. Cyclic voltammetry studies validate that ADH/TBO/NF biocomposite film exhibits excellent electrocatalytic activity for ethanol oxidation at low over potential (I_pa = −0.14 V). The same studies show biocomposite film possesses a good sensitivity of 7.91 μA M⁻¹ cm⁻² for ethanol determination. This above sensitivity value is 17.40% higher than the sensitivity obtained for TBO/NF film (6.74 μA M⁻¹ cm⁻²). Further, using differential pulse voltammetry, a sensitivity of 1.70 μA M⁻¹ cm⁻² has been achieved for ADH/TBO/NF biocomposite film.     

Electrochemistry of a lithium electrode in lithium polysulfide solutions

The effect of lithium polysulfides on the cycling of a lithium electrode and the corrosion rate of lithium cathodic deposits in sulfolane electrolytes is studied. Lithium polysulfides are found to affect the shape of polarization curves, the overpotential of electrode processes, and the cycling time. The presence of lithium polysulfides in electrolyte systems increases the cycling time of a lithium electrode and positively affects the quality of lithium cathodic deposits. A suggested reason for the positive effect of lithium polysulfides is the appearance of a surface film on metallic lithium: this film has quite high protective properties but does not inhibit electrochemical processes.     

Electrocatalytic oxidation and flow detection of cysteine at an aquocobalamin adsorbed glassy carbon electrode

A chemically modified electrode (CME) constructed by adsorption of aquocobalamin (VB12a) onto a glassy carbon electrode surface was demonstrated to catalyze the electro-oxidation of cysteine, a sulfhydryl-containing compound. The sulfhydryl oxidation occurred at 0.54-0.88 V vs. Ag AgCl depending on pH value (3.0-10.0). The electrocatalytic behavior of cysteine is elucidated with respect to solution pH, operating potential and other variables as well as the CME preparation conditions. When used as the sensing electrode in flow injection amperometric detection, the CME permitted detection of the compound at 0.8 V. The detection limit was 1.7 pmol. The linear response range went up to 1.16 nmol. The stability of the CME was shown by RSD (4.2%) over 10 repeated injections.     

Cathodic reduction of coenzyme Q10 on glassy carbon electrode in acetic acid-acetonitrile solutions

The electrochemical reduction of coenzyme CoQ(10) and CoQ(0) on glassy carbon (GC) has been investigated in mixed solvent containing 80 vol.% acetic acid and 20 vol.% acetonitrile. A combination of cyclic voltammetry (CV) and rotating disk electrode technique (RDE) was employed to elucidate the mechanism of electrode processes. The results obtained were interpreted in terms of an E(r)E(q) mechanism involving the inverted ordering of formal potentials, i.e. E(2)(0')>E(1)(0'). The cathodic processes of both compounds consist of two successive one-electron one-proton steps, whereas the second electron transfer is thermodynamically more facile than the first. The processes occur with the generation of unstable semiquinone radicals as primary products. The results presented can help in explanation of the biochemical properties of CoQ(10) in the living cell.     

Electrochemistry of a carbon microfiber adsorbed by cobalt nanoparticles.

The adsorption of cobalt nanoparticles on a carbon microfiber surface has been electrochemicaly detected. The redox processes observed in an electrochemical cell filled with redistilled water and equipped with the carbon fiber microelectrode modified by cobalt nanoparticles have been compared to those observed in an aqueous solution of Co2+ cations. The movement of the adsorbed nanoparticles has been demonstrated by the feedback capacitance-potential method.     

Electrocrystallizations of copper on glassy carbon in CuCl2 silica sol and aqueous solutions

Electrocrystallizations of copper from both CuCl₂ silica sol and aqueous solutions were studied by the chronoamperometry technique.It was found that current density contributions of the double-layer charging（iDL） in current-time transients（CTTs） from both of the solutions were large.An adsorption-nucleation based model was proposed to analyze quantitatively the CTTs,by which copper electrocrystallization mechanism was characterized as progressive nucleation with 3D growth（3DP） under diffusion control.The diffusion coefficient of copper ions and the AN_∞products in aqueous solutions were larger than that in silica sols, which indicated that copper nucleation was inhibited in sol solution.The large iDL may be resulted from the adsorption of chloride ions on the electrode surface.     

电化学预处理玻炭电极上的电催化

用循环伏安法、计时电流法、计时库仑法和X射线光电子能谱法研究了恒电流法电化学预处理玻炭电极上的表面性质及其对抗坏血酸、儿茶酚和对苯二酚的电催化效应。讨论了电催化机理, 证明电极表面吸附及表面功能团的催化是发生电催化的主要原因。儿茶酚、对苯二酚和抗坏血酸的混合物的预处理电极上的波峰明显分开, 有可能应用于儿茶酚和抗坏血酸的同时测定。     

Raman spectra of glassy aqueous solutions

The Raman spectra of glassy LiCl and LiBr aqueous solutions are obtained in the OH (OD) stretching vibrational region. Spectral features are discussed in conjunction with those of amorphous ice and liquid water.     

A study on the electroanalytical performance of a bismuth film-coated and Nafion-coated glassy carbon electrode in alkaline solutions

Bismuth film electrodes are widely used for determination of heavy metal ions in acidic solutions, while alkaline solutions are rarely employed. We have compared the deposition of Bi(III) and Pb(II) on a Nafion-coated glassy carbon electrode in alkaline and acidic solutions. The results indicate that both Bi(III) and Pb(II) can be deposited in either alkaline or acidic solution, but the quantity of Pb(II) deposited in alkaline solution is less than that in acidic solution. The modified electrode was used to determine heavy metal ions in both alkaline and acidic solutions, and the results of the method agree well with those of atomic absorption spectroscopy.     

Redox behavior of biofilm on glassy carbon electrode

Marine and freshwater biofilm usually shift the open circuit potential (OCP) of stainless steel towards the electropositive direction by + 450 mV vs SCE. The nature of oxide film and bacterial metabolism were also correlated with ennoblement process by various investigators. Glassy carbon electrode (GCE) was used in the present study and a shifting of potential in the positive side (+ 450 mV) was noticed. It indicates that biofilm contributes to the ennoblement process without any n/p-type semiconducting oxide film. The nature of the cathodic curve for the biofilm covered GCE is compared with the previous literature on the electrochemical behavior of stainless steel. The present study explains the oxidation and reduction peaks of biofilm covered GCE by cyclic voltammetry. Electrochemical impedance result reveals the diffusion process within the manganese biofilm. The present study confirms the previous investigations that the manganese biofilm rules the electrochemical behavior of materials and suggests that oxide film is not necessary to assist the ennoblement process.     

邻仲丁基苯酚在玻碳电极上的电化学行为

通过循环伏安法(CV)研究了玻碳电极上邻仲丁基苯酚(OSBP)的电化学行为.结果显示:在pH=8.0的磷酸盐缓冲液中,OSBP在玻碳电极上发生的氧化反应是受扩散控制的不可逆等电子、质子转移过程,且氧化产物部分被还原.氧化峰电流与浓度在5.0×10~(-6)～2.0×10~(-4)mol·L~(-1)之间呈良好的线性关系,检出限(S/N=3)为6.60×10~7mol·L~(-1).重复测定的相对标准偏差(RSD)为4.48%(n=7),加标回收率为86.2%～100.5%.结果令人满意.     

Amperometric detection of indapamide on glassy carbon electrode

This work describes the development of a fast, precise and reliable voltammetric method for the quantification of indapamide, an orally active diuretic sulfonamide used for hypertensive treatment. This compound acts inhibiting sodium reabsorption and increasing the elimination of water. This characteristic was responsible for its banishment by the International Olympic Committee since 1999. The study begins by finding an adequate potential range (−0.20 to 0.30 V) to avoid poisoning the working glassy carbon electrode (GCE) in phosphate buffer 0.10 mol L⁻¹ (pH=12.0). Utilizing flow injection analysis, linear responses between 2.0 × 10⁻⁶ mol L⁻¹ to 2.5 × 10⁻⁵ mol L⁻¹ of indapamide (R²=0.995), and detection limit (LOD) 3.0 × 10⁻⁷ mol L⁻¹ were obtained. This method was applied for the quantification of indapamide in tablets and in synthetic urine. The same flow system was used for the analysis of commercial drugs and the response obtained corresponded to 98 % of the concentration indicated on the drug label. These tablets were also analyzed by high performance liquid chromatography (HPLC), obtaining a recovery of 103 % and LOD 4.0 × 10⁻⁷ mol L⁻¹. The velocity of analysis using flow methods compares advantageously to the classical chromatographic methods. For synthetic urine, linear responses were obtained in samples spiked in the region from 5.0 × 10⁻⁶ mol L⁻¹ to 30 × 10⁻⁶ mol L⁻¹ (R²=0.991) and LOD 3.0 × 10⁻⁷ mol L⁻¹.