Voltammetry at microcylinder electrodes: Part I. Linear sweep voltammetry

An expression for reversible linear sweep voltammograms at stationary microcylinder electrodes is presented. From numerical calculations theoretical voltammograms are obtained for various values of the dimensionless parameter, p=(nFa²v/RTD)^{$\text{1}\text{2}$}, where a is the radius of the electrode, v the potential sweep rate and D the diffusion coefficient. The peak current and the peak potential are evaluated from the voltammograms as functions of p and are expressed by approximate equations with high precision. In order to examine the validity of the equations, an experimental study was made at platinum wire micro-electrodes (a=10?10) μm). The experimental voltammograms were in good agreement with the ones predicted theoretically for various values of the sweep rates and for several different radii of the electrodes.     

Cyclic voltammetry at microstructured electrodes

We present the theoretical treatment of cyclic voltammograms at microstructured electrodes. Calculations of voltammograms permit the determination of electrochemical parameters of redox systems in a single cell in parallel with the determinations of the spectroscopic parameters. The structural parameters of the electrode can be determined using the theoretical treatment presented if the electrochemical parameters of the redox system are known. Furthermore, lithographic-galvanic (LIGA) structures can be used as a model for microporous electrodes. Regression analysis was used to compare experimental and calculated cyclic voltammograms as well as to determine the electrochemical and spectroscopic parameters. A modified Randles-Sevčik equation has been derived to described the peak current dependence of cyclic voltammograms at micro-structured electrodes for both reversible and quasi-reversible charge transfer.     

微环电极上线性扫描伏安法准稳态可逆波理论

本文求得了适用于不同γ(式(6))和P(式(9))的最大电流表达式,并提出了准稳态的定量标准,还推导了微环电极上线性扫描伏安法准稳态可逆波方程式,经验证,理论和实验结果相符合     

Cathodic adsorption voltammetry of palladium(II)

The electrochemical behavior of palladium(II) was studied by differential pulse, linear sweep, and alternating-current square-wave voltammetry in HC1, HNO₃, H₂SO₄, and HC1O₄ solutions in the presence of dimethylglyoxime. A peak with a height linearly depending on the concentration of palladium(II) was observed in voltammograms. Typical relationships between the height and potential of a peak and pH, dimethylglyoxime concentration, the potential and time of adsorption accumulation suggested that the observed peak was due to the hydrogen liberation catalyzed by palladium(II) dimethylglyoximate adsorbed on the electrode surface. The detection limits for palladium(II) accumulated for 120 s at -0.2 V were 2 x 10^-8, 5 x 10^-9, and 8 x 10^-10 M for differential pulse, linear sweep, and alternating-current square-wave voltammetry, respectively.     

Correction to: Comments on the shape of voltammetric plots of reversible stoichiometric reactions for linear potential scan

Theoretical studies of the shape of the linear potential sweep voltammogram for a reversible electron-transfer reaction have been overviewed. Two different expressions for the current–potential dependences have been proposed therein. Our analysis has shown that this divergency originates from the implicit difference of the assumptions on the pretreatment procedure before the beginning of the potential sweep. Two principal variants of such pretreatment have been considered in detail: (1) potentiostatic exposure to the potential equal to the starting one for the subsequent sweep, E = E_i; (2) OCP (zero current) regime. In the former variant, the potentiostatic regime during the pretreatment period shifts the surface concentrations from their bulk values to the steady-state ones (dependent on E_i). It induces current passage of a diminishing amplitude due to the diffusion-layer expansion. If the pretreatment period is sufficiently long (well over 10 s in water) a time-independent distribution of the reactant and product concentrations is established across the steady-state diffusion layer accompanied by the current stabilization, i ≅ i_ss. At the starting moment of the potential sweep, t = t_i, both the potential and the surface concentrations are continuous as functions of time so that the amperometric response for t > t_i increases in time from its steady-state value, i ≅ i_ss, due to the potential sweep, with its gradual approach to a universal dependence which corresponds to the response of the system if the potential sweep starts very far from the half-wave potential where the equilibrium concentration of the reaction product is extremely low. In the latter variant of pretreatment there is a stepwise change of the potential and of the surface concentrations at t = t_i; it leads to a Cottrell-type contribution to voltammetric current which in the course of the potential sweep is supplemented by another contribution corresponding to the above universal response where the sweep starts very far from the half-wave potential. As a result, after a relatively short relaxation period the current responses in both variants approach its universal behavior. Method of a direct determination of the number of transferred electrons per consumed reactant species has been proposed. Approximate analytical expression for the dependence of current on time after passage of the current's peak has been derived. Predicted features have been verified with the use of a well-known reversible reaction: ferrocene oxidation in acetonitrile.

     

Linear sweep voltammetry at the tubular electrode

The theory of linear sweep voltammetry at the tubular electrode has been developed for reversible electrode processes. The convective diffusion differential equations have been transformed to an integral equation which is solved numerically. The theoretical current—potential curves at different velocities of the solution have been calculated. Comparison with experiments using a tubular electrode shows satisfactory agreement.     

The separation of overlapping peaks in cyclic voltammetry by means of semi-differential transformation

A method for extracting single peaks from complex linear sweep and cyclic voltamperograms is presented. Voltamperograms are transformed by means of semidifferentiation, then all undesired peaks are removed from the semiderivative curve and replaced by calculated baselines. The resulting curve is semiintegrated back, giving a voltamperogram with one peak only. Baselines in the semiderivative domain are determined by the least-squares curve-fitting of datapoints from peak border regions, using the equation that describes the semiderivative peak of a reversible electrode process. With this procedure peaks can be removed without assumptions about the mechanism of the underlying electrode reaction. Due to its design, the algorithm presented is suitable for the fully automatic processing of cyclic and linear sweep voltamperograms. Performance of the procedure was checked with generated reversible voltamperograms as well as in real experiments with both reversible and irreversible systems. The smallest distance between two peaks of equal height, for which the described method can yield correct results, has been found to be 110 mV for a reversible one-electron process at 298 K. This procedure can also be applied to the elimination of the cathodic current from the cyclic voltamperogram of a single component in order to get a pure anodic current value, free from cathodic contribution, or vice versa.     

Study on the adsorptive catalytic voltammetry of aloe-emodin at a carbon paste electrode

Recently, the studies and applications for the pola-rographic catalytic waves of organic compounds at dropping mercury electrode made considerable head-way. Tovopova et al.[1―4] reported the polarographic catalytic waves of the organic compounds containi…     

Hydrodynamic voltammetry at channel electrodes: Part IV. Theory of chronopotentiometry for reversible electrode reactions

The theory of chronopotentiometric measurements at channel electrodes is developed for reversible electrode reactions, by rigorously solving the corresponding time-dependent boundary value problem, where the non-uniform accessibility of the channel electrode surface is taken into consideration. The theoretical equations of the transition time and the potential-time curve are derived as functions of (I_d/I), where I denotes the applied current intensity and I_d the limiting diffusion current obtained at steady-state. Finally, the time variation of the current density distribution at the electrode surface is given.     

超微盘电极线性扫描准稳态可逆波及其导数波理论

提出超微盘电极线性扫描准稳态可逆波理论, 对伏安曲线性质进行了研究,利用铂超微盘电极及K~4Fe(CN)~6-KCl体系进行了验证, 此外, 还对超微盘电极线性扫描可逆波的一次, 二次, 三次微分进行了理论探讨。     

Linear-sweep voltammetry at a dropping mercury electrode in continuous flow systems

Linear-sweep voltammetry at a dropping mercury electrode is examined in flowing systems with parallel, opposite and normal mercury and fluid flow. The influence of fluid velocity (0–12 cm s^?1) on current and potential parameters of linear-sweep voltammograms is described. The ranges of fluid velocity in which current parameters are independent of flow, were determined by analysis of variance. It is shown that at certain sweep rates, the current does not depend on fluid velocity up to 12 cm s^?1.     

Comparison of fast scan voltammetry with microelectrode voltammetry of reduction of 1,4-benzoquinone

The reduction of 1,4-benzoquinone (BQ) in acetonitrile was blocked in steady-state microelectrode voltammetry although it has been believed to be a sluggish electron transfer reaction. Ferrocene was added to the BQ solution with equi-concentration in order to confirm the diffusion-control step and to evaluate accurately the kinetic effect from potential differences. Fast scan voltammograms showed the negative potential shifts both of the cathodic and the anodic peaks with an increase in the scan rate. In contrast, microelectrode voltammetry showed that the ratio of the steady-state limiting current for BQ to that for ferrocene decreased with a decrease in the electrode radii. The halfwave potential of the reduction of BQ did not vary with the radii within error. These features are largely deviated from the Butler–Volmer kinetic behavior. The electrode surface after the long term electro-reduction was coated with a precipitate. The proposed reaction mechanism is formation of films by follow-up chemical reactions of BQ associated with slight potential shift. The film blocks diffusion of BQ. This model was theoretically formulated and elucidated the experimental results.     

嵌入电极反应循环伏安曲线的理论研究

嵌入电极反应的循环伏安图一般具有氧化峰和还原峰间距很大的特点,并且往往要求采用非常低的电位扫描速度。本研究基于嵌入电极反应的热力学方程和电荷传递动力学方程,对其循环伏安曲线进行了理论处理,讨论了嵌入电极反应热力学参数b,动力学参数D和k,电位扫描速度u,及电极和溶液电阻对循环伏安曲线的影响,解释了实验得到的嵌入电极反应循环伏安曲线的特殊性。     

Reactant adsorption in cyclic staircase voltammetry on spherical microelectrodes. Reversible redox reactions

On spherical microelectrodes, cyclic staircase voltammograms of reversible redox reactions complicated by the reactant adsorption depend on lateral interactions in the monolayer. Attraction forces increase the separation between the main wave and the post-peak, while the repulsion prevents the resolution of responses of the surface and volume reactions. The theoretical relationships between the dimensionless responses and the dimensionless adsorption constant, the relative surface adsorption capacity, the Frumkin coefficient and the electrode sphericity are given.     

The behaviour of an electrochemical detector used in liquid chromatography and continuous flow voltammetry: Part III. Potential dependent current

The potential dependence of the steady-state current at a channel electrode has been calculated approximately. Six regions of behavior can be described from a consideration of the characteristic times of diffusion, fluid flow and electrochemical reaction. Wave shapes and half-wave potential shifts are as expected for amperometric cells under all values of the heterogeneous reaction rate constant, and for reversible electrochemical reactions in a coulometric cell. The wave adopts a peculiar shape for irreversible reactions at a coulometric electrode. This is caused by the inapplicability of the concept of mass transfer control in these systems.     

Paired pulse voltammetry for differentiating complex analytes

Although fast-scan cyclic voltammetry (FSCV) has contributed to important advances in neuroscience research, the technique is encumbered by significant analytical challenges. Confounding factors such as pH change and transient effects at the microelectrode surface make it difficult to discern the analytes represented by complex voltammograms. Here we introduce paired-pulse voltammetry (PPV), that mitigates the confounding factors and simplifies the analytical task. PPV consists of a selected binary waveform with a specific time gap between each of its two comprising pulses, such that each binary wave is repeated, while holding the electrode at a negative potential between the waves. This allows two simultaneous yet very different voltammograms (primary and secondary) to be obtained, each corresponding to the two pulses in the binary waveform. PPV was evaluated in the flow cell to characterize three different analytes, (dopamine, adenosine, and pH changes). The peak oxidation current decreased by approximately 50%, 80%, and 4% for dopamine, adenosine, and pH, in the secondary voltammogram compared with the primary voltammogram, respectively. Thus, the influence of pH changes could be virtually eliminated using the difference between the primary and secondary voltammograms in the PPV technique, which discriminates analytes on the basis of their adsorption characteristics to the carbon fiber electrode. These results demonstrate that PPV can be effectively used for differentiating complex analytes.     

Study of electrochemical properties of pyrrolidinofullerenes by microelectrode voltammetry

The electrochemical behavior of nine pyrrolidinofullerenes has been investigated by cyclic voltammetry on a gold microdisk electrode. Four reversible reduction peaks and two irreversible reduction peaks are observed for each fullerene derivative. The half-wave potentials of all pyrrolidinofullerenes are more negative than those of C₆₀ itself. The diffusion coefficient of these compounds is measured by their steady-state voltammograms.     

硝基化合物的吸附伏安法研究 I: 5-硝基-1, 10-邻菲咯啉的吸附伏安特性

本文用线性扫描技术对氨性溶液中, 低浓度, 5-硝基-1,10-邻菲咯啉的吸附伏安特性进行了研究.     

Voltammetry at microcylinder electrodes: Part IV. Normal and differential pulse voltammetry

Expressions for reversible normal pulse (NP) and differential pulse(DP) voltammograms at microcylinder electrodes, which are powerful and convenient tools in in vivo measurements, were derived in connection with the effects of successive pulse electrolysis. These expressions were computed numerically, varying the pulse interval, τ, and the pulse width, δ. Consequently, it was found that the use of τ>10δ for NP and τ>5δ for DP did not distort the well-known shapes of the voltammograms. By choosing τ=10δ for NP voltammetry or τ=5δ for DP voltammetry, the analysis time was greatly reduced. Methods of analysing reversible NP and DP waves are presented. NP and DP measurements were carried out at platinum and carbon fiber microcylinder electrodes for various values of τ and δ. The minimum values of δ for undistorted voltammograms found experimentally were τ = 5δ for NP voltammetry and τ = 2δ for DP voltammetry.