Study of the Behavior of an EC Mechanism Using Cyclic and Derivative Chronopotentiometric Techniques with Spherical Electrodes

The theory for an EC mechanism in chronopotentiometric techniques – reversal chronopotentiometry, cyclic chronopotentiometry and reciprocal derivative chronopotentiometry – is developed. The equations of this article are valid for spherical electrodes of any size and present a compact and easy‐to‐manage form. Methods for determining kinetic parameters of the chemical reaction are proposed and the influence of the electrode radius is discussed. We conclude that large errors in the determination of these parameters are committed if electrode sphericity is neglected. Reciprocal derivative chronopotentiometry has been applied in its traditional form (dt/dE vs. E), and in a more recently proposed modality consisting of plotting dt^1/2/dE vs. E. These techniques are very convenient for studying an EC mechanism since the response is obtained in the form of peaks which are quantitatively related to the kinetic parameters of the chemical reaction. A comparison of the chronopotentiometric methods analyzed leads us to conclude that working curves based on the dt^1/2/dE vs. E curves are more suitable to obtain accurate values of the rate constants of the chemical reaction.     

Dual microband electrodes: current distributions and diffusion layer ‘titrations’. Implications for electroanalytical measurements

The simulation of transport to double microband electrodes in generator–collector mode is reported focusing especially on the ‘titration curve’ approach to electroanalysis in which a titrant is electrogenerated from a redox active precursor on the generator electrode and reacts homogeneously with the target analyte. The current on the detector electrode reflects the amount of titrant ‘surviving’ passage between the two electrodes. The form of the titration curve – plots of detector current as a function of generator current – is shown to be highly sensitive to the electrode kinetics of the redox couple driven at the generator electrode. Accordingly the naïve use of such methodology for analysis without accompanying simulation and kinetic analysis is fraught with danger. Use of the conformal mapping approach in combination with the ADI method for investigation of the ‘titration’ current distributions at the double band system gives fast and precise simulation of this and similar problems. Convergence analysis is described which allows for the automatic selection of the simulation grid size so as to obtain a chosen accuracy (for example 1%) of the current for all experimentally meaningful values of the geometrical and physico-chemical parameters of the system to be investigated.     

Evaluations of solid electrodes for use in voltammetric monitoring of heavy metals in samples from metallurgical nickel industry

Evaluation of different solid electrode systems for detection of zinc, lead, cobalt, and nickel in process water from metallurgical nickel industry with use of differential pulse stripping voltammetry has been performed. Zinc was detected by differential pulse anodic stripping voltammetry (DPASV) on a dental amalgam electrode as intermetallic Ni–Zn compound after dilution in ammonium buffer solution. The intermetallic compound was observed at –375 mV, and a linear response was found in the range 0.2–1.2 mg L^–1 (r²=0.98) for 60 s deposition time. Simultaneous detection of nickel and cobalt in the low g L^–1 range was successfully performed by use of adsorptive cathodic stripping voltammetry (AdCSV) of dimethylglyoxime complexes on a silver–bismuth alloy electrode, and a good correlation was found with corresponding AAS results (r²=0.999 for nickel and 0.965 for cobalt). Analyses of lead in the g L^–1 range in nickel-plating solution were performed with good sensitivity and stability by DPASV, using a working electrode of silver together with a glassy carbon counter electrode in samples diluted 1:3 with distilled water and acidified with H₂SO₄ to pH 2. A new commercial automatic at-line system was tested, and the results were found to be in agreement with an older mercury drop system. The stability of the solid electrode systems was found to be from one to several days without any maintenance needed.     

纳米银自组装电极的制备及对高氯酸二茂铁的电化学响应

采用自组装的方法制备了纳米银粒子修饰金电极,并运用循环伏安法、交流阻抗谱探讨了该电极的电化学特性.研究了高氯酸二茂铁在该修饰电极上的直接电化学行为.实验结果表明,高氯酸二茂铁在该修饰电极上具有良好的电流响应.用示差脉冲法测定高氯酸二茂铁,其氧化峰电流与浓度在4.0×10-6～5.0×10-4 mol/L范围呈良好线性关系,线性方程为:Ip(μA)=0.0236c(μmol/L)-0.0975,线性相关系数为0.9982,检出限为2.3×10-7 mol/L(信噪比为3).     

吸附/一级热解吸/气相色谱联用测定室内空气中的挥发性有机物

本文以高聚物TenaxTA动态吸附,一级热解吸/毛细管气相色谱法联用测定室内空气中的挥发性有机物。优化了热解吸温度和热解吸时间,建立了苯、甲苯、乙酸正丁酯、乙苯、对二甲苯、苯乙烯、邻二甲苯、正十一烷等8种典型有机污染物的外标定量曲线,各化合物线性范围为103,相关系数R为0.9983～0.9999,最低检出浓度可达2×10-4mg/m3;考察了方法的重复性、热解吸率和残留率,并分析了实际空气样品。     

Amperometric detection of hydrazine by cyclic voltammetry and flow injection analysis using ruthenium modified glassy carbon electrodes

Glassy carbon electrodes modified with (5-amino-1,10-phenanthroline)bis(bipyridine)ruthium(II) chloride hydrate, [(bpy)₂Ru(5-phenNH₂)]Cl₂·H₂O, are shown to oxidize hydrazine with excellent sensitivity. The presence of an amine group on the ruthenium complex facilitates electropolymerization onto the electrode surface. Using cyclic voltammetry, a large catalytic current is observed upon oxidation of hydrazine in phosphate buffer (pH 5.0), compared to the current obtained from the ruthenium-modified electrode with no hydrazine present. The sensitivity of cyclic voltammetry is sufficient for obtaining a linear calibration curve for hydrazine over the range of 10⁻⁵ to 10⁻² M. Hydrodynamic amperometry was used to determine the working potential for flow injection analysis. The limit of detection for hydrazine was determined to be 8.5 μM using FIA. The thickness of these films was shown to increase linearly with the number of electropolymerization cycles, in the range of 1000-2500 nm for 5-20 cycles, respectively, using Rutherford backscattering spectrometry (RBS). RBS analysis also suggests that the film is multilayered with the outermost layers containing a high ruthenium concentration, followed by layers where the concentration of ruthenium decreases linearly and approaches zero at the electrode surface.     

Electrochemical Response of Cobalt(II) in the Presence of Ammonia

The electrochemical oxidation of cobalt(II) at gold, boron‐doped diamond, basal and edge plane pyrolytic graphite, and highly oriented pyrolytic graphite electrodes in aqueous solutions containing NH₃ has been studied using cyclic voltammetry, with subsequent chemical and electrochemical processes explained in detail. Furthermore, the electro‐reduction of [Co(NH₃)₆]³⁺ in the presence of different electrolytes has also been studied to obtain a better understanding of the oxidation pathway of the Co(II)‐ammine complexes. In aqueous solution the mechanism can be described by the following scheme:     

Novel disposable bismuth-sputtered electrodes for the determination of trace metals by stripping voltammetry

This work describes a novel type of bismuth electrode for stripping voltammetry based on coating a silicon substrate with a thin bismuth film by means of sputtering. The bismuth-based sensors were characterized by optical methods (scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD)) and as well as by linear sweep voltammetry. Subsequently, the electrodes were tested for the detection of low concentrations of trace metals (Cd(II), Pb(II) and Ni(II)) by stripping voltammetry. Well-formed stripping peaks were observed for trace concentrations of the target analytes demonstrating “proof-of-principle” for these sensors. This type of electrochemical device, utilizing thin-film technology for the formation of the bismuth film, holds promise for future applications in trace metal analysis.     

On the selection of the optimal plasticizer for calix[n]arene-based ion-selective electrodes: Possible correlation between the ion selectivity and the ‘softness’ of the plasticizer

A criterion for the selection of a suitable plasticizer for calix[n]arene-based ion-selective electrodes is discussed. The cation selectivity of plasticized membranes without the ligand was first measured as a reference. The membranes can be roughly classified into two groups. The first group shows cation selectivity in the order Cs⁺+>K⁺>Na⁺>Li⁺. The membranes in the second group are made of phosphorus plasticizers, which show a selectivity in the reverse order. The plasticizers in the first group featured a linear relationship between the dipole moment of the plasticizer (calculated by a PM3 method) and the ratio of cesium selectivity to lithium selectivity. The linear relationship supports the view that the polar membrane which includes a soft plasticizer with a large dipole moment shows selectivity for Cs⁺, whereas the nonpolar membrane including the soft plasticizer with the small dipole moment shows much lower selectivity for Cs⁺. Next, 2-fluorphenyl-2-nitrophenyl ether (FPNPE) which showed the highest Cs⁺ selectivity and tris(2-ethylhexyl)phosphate (TEHP) which showed the highest Li⁺ selectivity were mixed in an appropriate ratio to make membranes with a different affinity for hard ions. The metal selectivities of several crown-based and calixarene-based ionophores were examined in these membranes. Although a few exceptions exist, the polar soft membrane is favorable when the interfering metal ion is hard, whereas the hard membrane is favorable when the interfering metal ion is soft.