Comparison of electrode materials for the detection of rapid hydrogen peroxide fluctuations using background-subtracted fast scan cyclic voltammetry

Hydrogen peroxide (H(2)O(2)) is a critically important signaling molecule. Endogenous H(2)O(2) mediates diverse physiological processes both intra- and intercellularly; and enzymatically generated H(2)O(2) is a widely used reporter molecule at biosensors that rely on enzymes to detect non-electroactive species. However, the development and application of electroanalytical methods for the direct detection of this molecule has been challenging because the electron transfer kinetics for the irreversible oxidation of H(2)O(2) are slow. We comparatively characterize the electrochemical oxidation of H(2)O(2) on bare and Nafion(?)-coated platinum and carbon-fiber microdisc electrodes using fast-scan cyclic voltammetry (FSCV). Using a waveform ranging from +0.2 to +1.3 V at 400 V s(-1), the electrocatalytic properties of the platinum surface were not readily apparent, and the carbon-fiber microelectrode demonstrated greater sensitivity and selectivity toward H(2)O(2). Nafion(?)-coating further enhanced detection on carbon electrodes. These results confirm that platinum electrodes, with or without Nafion(?), will not work acceptably with this approach, and confirm the value of carbon-fiber microelectrodes relative to more traditionally used platinum electrodes in the direct detection of rapid H(2)O(2) fluctuations using FSCV.     

Ultrafast cyclic voltammetry with asymmetrical potential scan

Based on the perfect ohmic drop compensation by online electronic positive feedback, ultrafast cyclic voltammetry with asymmetrical potential scan is achieved for the first time, with the reduction of anthracene acting as the test system. Compared with the traditional cyclic voltammetry utilizing symmetrical triangular waveform as the excitation one, the new method allows a simpler approach to mechanistic analysis of ultrafast chemical reactions coupled with a charge transfer. And perhaps more important, it also provides a way to eliminate the interference of the adsorbed product in dynamic monitoring. 2007 Zhi Yong Guo. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.     

Differential linear scan voltammetry: analytical performance in comparison with pulsed voltammetry techniques

We report here on differential linear scan voltammetry, DLSV, that combines the working principles of linear scan voltammetry, LSV, and the numerous existing pulsed voltammetry techniques. DLSV preserves the information from continuous interrogation in voltage and high accuracy that LSV provides about electrochemical processes, and the much better sensitivity of differential pulsed techniques. DLSV also minimizes the background current compared to both LSV and pulsed voltammetry. An early version of DLSV, derivative stationary electrode polarography, DSEP, had been proposed in the 1960s but soon abandoned in favor of the emerging differential pulsed techniques. Relative to DSEP, DLSV takes advantage of the flexibility of discrete smoothing differentiation that was not available to early investigators. Also, DSEP had been explored in pure solutions and with reversible electrochemical reactions. DLSV is tested in this work in more challenging experimental contexts: the measurement of oxygen with a carbon fiber microelectrode in buffer, and with a gold microdisc electrode exposed to a live biological preparation. This work compares the analytical performance of DLSV and square wave voltammetry, the most popular pulsed voltammetry technique.

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.     

The hexagonal close-packed nickel nanocrystals prepared by fast scan voltammetry

The nickel (Ni) nanocrystals (average diameter 9.7 ± 2.3 nm) were deposited onto composite graphite electrode from a plating solution of 5.0 mM NiCl₂6H₂O and 1.0 M NH₄Cl using scan rate of 6500 mV s⁻¹. The initial potential −1.5 V and final potential −0.5 V vs. Ag/AgCl with applied time 120 s were used for the whole deposition process. The variations of applied overpotentials and deposition times have affected the characteristics of Ni nanocrystals. It was found that the structural formation of Ni nanocrystals obtained were almost pure hexagonal close-packed (hcp). This study has demonstrated that the tuning of the final size, morphology and structural formation of the Ni nanocrystal were affected by control of nucleation, growth and hydrogen evolution processes in fast scan voltammetry technique used.     

Catalytic method for the determination of traces of tungsten by linear scan voltammetry

A novel, sensitive and selective catalytic method for the determination of tungsten is described, based on the W(VI-catalysed redox reaction between methyl red and Ti(III) in a hydrochloric acid medium; methyl red exhibits a sensitive oscillopolarographic wave at −0.68 V vs. SCE in NaOH solution. A calibration graph from 3.2 to 72 ng ml⁻¹ W (detection limit 1.1 ng ml⁻¹) is obtained by the fixed-reaction time procedure. The influence of 29 foreign ions on the catalytic determination of W was examined; none interfered at < 100-fold excess. The method is used to determine W in steel and ore samples, with satisfactory results.     

A rapid scan interferometer for near millimetre wavelength radiometry

A near millimetre wavelength radiometer has been constructed, based on a rapid scan polarising interferometer. The design and procedure are described, and some results are presented.     

Carbon nanofiber electrode array for electrochemical detection of dopamine using fast scan cyclic voltammetry

A carbon nanofiber (CNF) electrode array was integrated with the Wireless Instantaneous Neurotransmitter Concentration Sensor System (WINCS) for the detection of dopamine using fast scan cyclic voltammetry (FSCV). Dopamine detection performance by CNF arrays was comparable to that of traditional carbon fiber microelectrodes (CFMs), demonstrating that CNF arrays can be utilized as an alternative carbon electrode for neurochemical monitoring.     

Intermolecular interactions in electroactive thiol monolayers probed by linear scan voltammetry

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Determination of accurate electrode contribution during voltammetry scan of electrochemical capacitors

This paper introduces the method which allows determining the accurate electrode contributions during cyclic voltammetry (CV) scan of electrochemical capacitor. As a result of theoretical considerations, a calculation method which reveals voltammetry response of both electrodes during CV of two-electrode cell with reference is developed. The technique is based on the preservation of charge neutrality where the accurate potential sweep rate of individual electrode is dynamically assigned based on its total contribution to the total two-electrode cell voltage ramp. This practice should be used in the research with CV scans of energy storage devices in order to improve their precision. The technique is not an alternative to real three-electrode measurements, where constant sweep rate of working electrode is applied and an oversized auxiliary electrode is used, but it is rather a supplement, which allows observing the true electrode behavior during operation of the capacitor. The paper provides comparison of CV scans obtained with fixed scan rates of both electrodes with dynamic CV scan for electrochemical capacitors operating in aqueous media of 1 mol L^?1 Li₂SO₄ and 7 mol L^?1 KSCN. For the first time, the simple procedure is proposed to visualize the real qualitative electrode responses.     

Reliability of background current subtraction in anodic stripping voltammetry at mercury film electrodes

The effectiveness and accuracy of the correction for background current in subtractive anodic stripping voltammetry at rotating mercury film electrodes are discussed. The effects of different experimental parameters on the subtracted baseline are examined. Long deposition periods, at extreme potentials, result in large errors in the background correction. The incomplete background correction is attributed mainly to changes in the morphology of the working electrode. Different approaches for obtaining the subtractive stripping response are compared. Errors are reduced when subtractive differential pulse stripping is used at different convection rates, resulting in a detection limit of 2 × 10^-9 M cadmium with 1-min deposition. Cadmium, lead, and zinc ions at nano molar concentrations were used as test ions.     

An analytical solution to linear scan ac voltammetry of a reversible couple

Linear scan ac voltammetry of a reversible couple has been reexamined and an analytical solution has been found without invoking the slow scan approximation. This solution is complete in the sense that it gives explicit formulae for the concentration of both oxidized and reduced species at any time and distance from the electrode. A new term appears in the current expression which mixes the ramp and ac responses. The slow scan approximation, in which the ramp or dc response is assumed to have a negligible effect on the ac response, has been tested and found to be valid at all except the lowest frequencies. For example, the error is less than 5% for a scan rate less than 20nFω/RT.     

Determination of lead in an Sb-Pb alloy by anodic linear scan voltammetry

Anodic linear scan voltammetry (ALSV) has been used to determine the content of Pb (up to 3.5 wt%) in a eutectic type of binary Sb-Pb alloy. The effect of type of electrolyte and as well as the rate of the potential change on the dissolution of Pb from this alloy were investigated by ALSV. The method can be used for the determination of low concentrations of Pb in the investigated alloy and well-defined current peaks of Pb dissolution can be detected on the voltammograms. Well-de-fined linear dependencies between the quantities of electricity under the current peak of Pb dissolution (QPb) and the respective contents of Pb (w) in the alloy, so-called "check curves", were found. The smallest ratio of Pb in Sb-Pb alloy which could be detected by ALSV was 0.45 wt%. The dissolution involves only ten atomic layers of the less precious metal (Pb) from the surface of the alloy samples.     

Staircase voltammetry as a rapid detection method for anodic stripping determination of lead

Rapid-scan staircase voltammetry is used to strip lead plated on a rotating mercury film electrode. With potential steps of 10 mV every 64 μs, the entire stripping of the metals is made in only 4 ms. Noise is reduced by averaging several current measurements on each step. The method allows quantification of 0.1 μg l^?1 lead within a total time to less than 4 min. Because of the rapid scan, the rotation of the electrode can continue during the stripping step. Oxygen does not affect the measurements although a small decrease in current is observed. The method is tested on a sample of sea water. Some results are also given for cadmium.     

A rapid version of standardless stripping voltammetry for determining mercury in aqueous solutions

It was shown that mercury(II) in aqueous solutions can be determined by standardless stripping voltammetry based on the determination of the coulometric constant of the electrochemical cell. This approach considerably reduces the analysis time in comparison to the known analogs. The coulometric constants were found for electrochemical cells with a gold and a gold-graphite film electrodes in solutions of different volumes. The optimum time of preelectrolysis was determined for measurements using the proposed method.     

Microcells for voltammetry and stripping voltammetry

The designs and applications of "non-flow" microcells in voltammetry and stripping voltammetry for samples with volumes from sub-microliters to 5 ml are reviewed. The analysis of microcell designs was carried out on the basis of their classification: (i) microcells with a static sample, including thin-layer microcells with a static sample; (ii) microcells with forced convection of the sample; and (iii) microcells for batch injection of samples. Two working electrode types (the usual state and inverted state) are discussed. The use of working micro- and mercury-film electrodes and of the accelerated removal of dissolved oxygen are also considered in detail.     

Theory of reverse scan square-wave voltammetry influenced by the kinetics of reactant adsorption

A model of electrode reaction complicated by slow adsorption of the reactant is developed for square-wave voltammetry with inverse scan direction. The relationship between the dimensionless net peak current and the logarithm of dimensionless rate constant of adsorption is a curve with a minimum and a maximum. For this reason the ratio of real net peak current and the square-root of frequency is a non-linear function of the logarithm of frequency and exhibits either a maximum or a minimum. The frequency of extreme serves for the estimation of the rate constant: log(k _ads /D ^1/2 ) = log(k* _ads )_crit + 0.5 log f _crit , where (k* _ads ) _crit is a critical dimensionless rate constant of adsorption. Square-wave voltammetry is sensitive to the kinetics of adsorption if k _ads < 10² cm s⁻¹      

Signal-to-noise considerations for rapid scan atomic spectrometry with an inductively coupled plasma

The blank photon flux from an ICP is measured with a conventional 1-m spectrometer for the spectral region from 200 to 450 nm. This flux is then used to calculate the minimum integration time required before quantum noise (shot noise from the photon flux) becomes significant under various conditions. The calculations demonstrate that blank integration times may be much shorter than the times spent integrating either samples or standards without degradation of the total measurement. Comparison to extrapolated values for a high resolution spectrometer configuration indicate that minimum integration times requirements will vary drastically with wavelength, slit width and spectrometer configuration. The data demonstrates that integration times may be as short as l ms under certain circumstances indicating that very rapid scan data acquisition is feasible for ICP-AES if done with intelligent interactive control.     

A rapid method of sample preparation for determining arsenic in water by stripping voltammetry

A procedure was developed for sample preparation for the further determination of arsenic in potable and natural water and process solutions by stripping voltammetry (SV). To minimize the losses and simplify the procedure, arsenic(III) was oxidized by the ozonation or UV irradiation of the solution in the presence of sulfite, chloride, or hydroxide ions, which increased the oxidation efficiency. The time required for 100% oxidation does not exceed 60 s for an arsenic concentration of no more than 1 mg/L. The reduction to arsenic(III) was performed photochemically in the presence of sodium sulfite for 5 min. Further stripping voltammetric determination was performed in the same solution using a gold-plated carbon electrode. The developed procedure is rapid, simple, and easy-to-automate.     

A rapid procedure for obtaining hydrodynamic voltammetry plots for electrochemical detectors in high-pressure liquid chromatography systems

The construction of relatively simple and inexpensive apparatus for the determination of the operating conditions for electrochemical detectors in high-pressure liquid chromatography systems is described. A procedure has been developed for the characterization of electrochemically active compounds.