Anodic stripping voltammetry and chronopotentiometry of copper at a rotating carbosital disk electrode

The use of a new carbon material — carbosital — for electrodes is reviewed. The behaviour of copper deposited on the carbosital electrode surface in anodic stripping voltammetry and chronopotentiometry is discussed. In anodic stripping voltammetry with a rotating carbosital disk electrode, the peak current and the number of coulombs involved in stripping copper are directly proportional to the square root of the electrode rotation rate during preelectroiysis; the peak current is directly proportional to the potential scan rate during stripping. For anodic stripping voltammetry and anodic stripping chronopotentiometry, linear calibration graphs are obtained in the range 1 X 10^-3–1 x 10^-6 M copper(II). The method is applicable to analysis of high-purity cadmium for copper.     

Miniature rotating disk electrode

The dissolution and dissociation of BaCO₃ in NaAlCl₄ at 175°C have been investigated by Raman spectroscopy of CO₂ in the gas phase. It has been shown that the dissociation of CO₃^2? is complete even in basic melts. Furthermore, the acidity of Ba²⁺ has been shown, and this explains previous determinations of O^2? basicity.     

聚吖啶橙修饰电极伏安法测定黄嘌呤

报道了聚吖啶橙 (POAO)修饰电极多阶半微分伏安法测定黄嘌呤 (Xa)。在pH 5 .3的磷酸盐缓冲溶液中 ,Xa在POAO电极上于 0 .8V处产生一灵敏的氧化峰 ,峰电流与其浓度在 7.8× 1 0 - 8～ 1 .1× 1 0 - 6mol/L和 1 .1× 1 0 - 6～ 1 .0×1 0 - 5mol/L范围内呈良好的线性关系 ,检出限为 7.8× 1 0 - 9mol/L。方法可用于人尿中Xa的测定     

Determination of traces of copper by anodic stripping voltammetry at a rotating carbon paste disk electrode modified with poly(1,8-diaminonaphtalene)

In the present work, carbon paste electrodes (CPE) modified with conducting polymers 1,8-diaminonaphtalene (DAN) was developed for the voltammetric determination of Cu(II). The modified electrode exhibited a significantly increased sensitivity and selectivity for Cu²⁺ compared with a bare carbon paste electrode. Copper(II) was preconcentrated at open circuit on the modified electrode. The measurements were carried out using a rotating disk electrode (RDE) as working electrode. The experimental parameters for the determination of Cu(II) were optimized. The Cu(II) ions were chemically deposited onto the surface of poly DAN-CPE in an acidic medium. Under the optimum conditions, a linear calibration graph was obtained in the concentration range of 0.1 to 250 ppb with a correlation coefficient of 0.9998. The relative standard deviation for 6 successive determinations was 4.7%. A study of interfering substances was also performed, and the method was applied to the direct determination of copper in real samples like tap water and orange juice samples. The article is published in the original.     

气体电极反应动力学的薄膜旋转圆盘电极方法研究

薄膜旋转圆盘电极方法是一种常用的评价气体物质在纳米电催化剂上的反应活性的方法,但是在数据分析过程中经常忽视了气体反应物在催化剂层中到活性位点的传质可能对估算的反应动力学参数的影响.本文以氧电极反应为例,使用薄膜旋转圆盘电极研究了不同担载量Pt/C电极的氧还原活性.实验结果表明,根据Koutecky-Levich方程求算相同电位下的"表观动力学电流密度"(对Pt活性面积归一化的mA/cm2Pt)或比质量电流(mA/μg Pt)随Pt担载量的减小而增大,说明在估算动力学电流时不能忽略O2在催化剂层中的扩散传质,而气体在催化剂层中的传质与催化剂层的结构、厚度、纳米催化剂的分散度等密切相关.建议在使用薄膜旋转圆盘电极方法来研究纳米催化剂气体电极反应活性时,首先系统考察担载量、分散度与催化剂层厚的影响,然后根据不同担载量催化剂归一化后的动力学电流密度(或比质量电流)-电势曲线是否重合来验证得到的是否是真实的动力学电流,从而得到更为准确的评价结果.     

Development of rotating liquid membrane disk electrode and rotating liquid membrane ring-liquid membrane disk electrode and evaluation of characteristics of ion transfer reactions at the rotating aqueous/organic solution interface.

A liquid membrane disk electrode, LMDE, and a liquid membrane ring-liquid membrane disk electrode, LMRE-LMDE, were developed by placing a gelled polyvinyl chloride thin membrane impregnated with 2-nitrophenyl octyl ether, NPOE-LM, on the surface of a glassy carbon, GC, disk or ring electrode. The voltammogram for the ion transfer at the interface between an aqueous solution, W, and NPOE-LM was recorded by setting the developed electrode in W and rotating at a rate, omega, between 0 and 4000 rpm. The sensitivity of the ion-transfer current at the WINPOE-LM interface, I, was enhanced to be more than 100 times better than that at the WINPOE (solution) interface when LMDE was rotated at omega higher than 200 rpm. The reversibility of the ion transfer reaction could be evaluated based on the dependence of I on omega of LMDE, and the reaction product at LMDE could be identified at LMRE when the rotating LMRE-LMDE system was adopted.     

Electrooxidation of vanillyl alcohol in acidic aqueous solution using rotating ring-disk electrode voltammetry.

The electrooxidation of benzylic alcohol derivative in acidic aqueous solution shows an oxidation pre-peak in the cyclic voltammogram, which means that the reaction is proceeding via an ECE mechanism where the second electron transfer occurs at a less positive potential. From the result of the rotating ring-disk electrode voltammetry, the initial oxidation response of the electrode reaction can be extracted.     

Stripping voltammetry with collection at a rotating ring-disk electrode

A new electroanalytical technique is described, called "stripping voltammetry with collection." The technique involves the use of a rotating ring-disk electrode and is an improvement over traditional voltammetric stripping at a single electrode in that it is characterized by a lower limit of detection and that the period of deposition before stripping can be shorter. The use of the technique is illustrated by the determination of 10(-10)M Ag(+) in 0.1 M H(2)SO(4) by use of a ring-disk electrode having a disk electrode constructed of glassy carbon and a ring electrode constructed of platinum.     

Sinusoidal voltage modulation of a copper rotating disk electrode

An experimental and theoretical study has been made of the sinusoidal potential modulation of a copper rotating disk electrode in acidic copper sulfate solution. The mathematical model takes into account the fluctuations of the surface concentration, the effect of the double capacitance, the surface overpotential, and the ohmic resistance in the electrolyte. Numerical computations were performed to show the effect of alternating voltage (av) on the shape of direct current polarization curves, the changes in the apparent rest potential, the apparent exchange current density and the apparent Tafel slopes. The agreement between the theory and the experiment was within ±15%. At sufficiently high av frequencies, the model can be further used to predict the av modulation of a rotating hemispherical electrode.     

Determination of selenium(IV) by anodic stripping voltammetry with an in situ gold-plated rotating glassy carbon disk electrode

The application of an in situ gold-plated glassy carbon disk electrode to the determination of selenium(IV) by anodic stripping voltammetry is described. A single anodic stripping peak is obtained for solutions containing less than 1 × 10^-6 M Se(IV). The minimum concentration detected was 2 × 10^-9 M Se(IV). The determination of selenium in NBS SRM 1577 (Bovine Liver) by anodic stripping voltammetry with an in situ goldplated rotating glassy carbon electrode yielded a value of 1.14 ± 0.07 μg Se g^-1 compared with a certificate value of 1.1 ± 0.1 μg Se g^-1.     

Thin layer flow cell with a rotating disk electrode

A channel-type electrochemical flow cell with a rotating disk electrode has been constructed and characterized. The work shows that the effect of rotation is to enhance the rate of mass transport. At rotation speeds higher than 900 rpm the response becomes independent of the flow rate and channel thickness. As a result, low flow rates can be used without sacrificing the sensitivity. Analytical advantages are demonstrated using liquid chromatography, stripping analysis, stopped rotation voltammetry and flow injection analysis.     

Determination of trace amounts of dipyridamole by stripping voltammetry using a Nafion modified electrode

This paper presents a new method for determination of dipyridamole by anodic stripping voltammetry using a Nafion modified glassy carbon electrode. The stripping peak current was proportional to the concentration of dipyridamole over the range of 1.0 x 10(-9)-8.0 x 10(-8) M in (pH 1.7) BrittondashRobinson buffer with 1 min accumulation. The detection limit has been estimated as 8.0 x 10(-11) M with 4 min accumulation. The method has been successfully applied to the determination of dipyridamole in human serum.     

Theory of a.c. voltammetry at a rotating disk electrode: Part II. Quasi-reversible and irreversible redox-electrode reactions

Alternating current response at a rotating disk electrode to a small a.c. potential wave superimposed on the slowly changing d.c. potential is theoretically treated for an quasireversible and an irreversible redox-electrode process. Expressions for alternating current-d.c. potential curves are given for three types of a.c. signals, i.e., sinusoidal, rectangular and triangular waves. It is shown that the effect of the coupling of the diffusion layers due to hydrodynamics and a.c. polarization can be expressed in terms of a parameter which is defined by the ratio of the frequency of a.c. wave to that of the rotation of the electrode and Schmidt number.     

A study of corrosion on a rotating iron disk electrode

Corrosion of iron in slightly acidified sodium sulphate solutions (mainly pH 4.5) in the open air was studied with a rotating disk electrode method at room temperature.Microscopic observations of corroded iron disk surfaces in the pH 4.5 solution revealed that iron initially corrodes locally with the formation of round pits of 10–30 μm in diameter and of(0.6–1.3) × 10³ in number per apparent square centimetre followed by the U-shaped brown protective wall formation of precipitates (rust) outside the pits. Each protective wall is formed along the lines of flow of the solution adjacent to the iron surface and each pit is located near the upstream end of the wall. Steady state of corrosion sets in when the parts of surface area surrounded by the wall are completely covered with a microscopically non-porous rust film.The amount of iron in the rust film and the total amount of corrosion of iron including that in the film increase parabolically with the increase in the time of immersion. The amount of iron in the film increases in proportion to the total amount of corrosion independently of the speed of rotation of the disk electrode even in the steady state.The fraction of area of iron surface not covered with the film decreases with time and reaches a certain fixed value in the steady state: the value is smaller at higher rotational speed. The corrosion rate is proportional to the uncovered area, as the corrosion is near the steady state. The pH of the bulk solution increases as corrosion progresses.The corrosion rate of iron can be well interpreted by assuming that the rate is controlled by the diffusion of oxygen from the bulk solution to the surface of iron and that the rust film on iron impedes the diffusion of oxygen.     

Gold nanoparticle included graphene oxide modified electrode: Picomole detection of metal ions in seawater by stripping voltammetry

We obtained a gold nanomaterial/graphene oxide-modified glassy carbon electrode and characterized it using transmission electron microscope, scanning electron microscope, cyclic voltammetry (CV), and X-ray photoelectron spectroscopy techniques. A response of the electrode using square wave anodic stripping voltammetry for Pb²⁺, Cu²⁺, and Hg²⁺ was found linear in the range from 1 × 10^–7 to 1 × 10^–11 M. The detection limits of Pb²⁺, Cu²⁺ and Hg²⁺ were 0.14, 0.5 and 1.2 pM, respectively. The method was applied to the simultaneous determination of Pb²⁺, Cu²⁺ and Hg²⁺ in seawater samples from a coastal region of Anatolia, and the results corresponded well with the values obtained by inductively coupled plasma-optical emission spectroscopy.     

On the steady-state assumption and its application to the rotating disk voltammetry of adsorbed enzymes

Rotating disk voltammetry is routinely used to study electrochemically driven enzyme catalysis because of the assumption that the method produces a steady-state system. This assumption is based on the sigmoidal shape of the voltammograms. We have introduced an electrochemical adaptation of the King-Altman method to simulate voltammograms in which the enzyme catalysis, within an immobilized enzyme layer, is steady-state. This method is readily adaptable to any mechanism and provides a readily programmable means of obtaining closed form analytical equations for a steady-state system. The steady-state simulations are compared to fully implicit finite difference (FIFD) simulations carried out without any steady-state assumptions. On the basis of our simulations, we conclude that, under typical experimental conditions, steady-state enzyme catalysis is unlikely to occur within electrode-immobilized enzyme layers and that typically sigmoidal rotating disk voltammograms merely reflect a mass transfer steady state as opposed to a true steady state of enzyme intermediates at each potential.     

Using the rotating disk electrode for evaluating film porosity of conductive polymers

Conductive polymer (poly-o-phenylenediamine and poly-3-methylthiophene) films were synthesized on a rotating disk electrode. Dependences of the limiting penetration currents on the nature of the polymer and film thickness were obtained in solutions containing electroactive substances (hydroquinone, quinone) reducing or oxidiring at redox potentials beyond the range of polymer electroactivity (selected by adjusting the pH value). The transport of hydroquinone and quinone test species through the pores in polymer films was examined based on the results of these studies, and the degree of film porosity was evaluated.