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Homovanillic acid (HVA) is an important biomarker for neurological disorders. Traditional methods for detection of this compound are chromatographic methods coupled with fluorescence, mass spectrometric, or electrochemical detectors. However, voltammetric methods can be useful because of their low cost, easy automation, portability, and sensitivity. 3,4-Dihydroxyphenylacetic acid (DOPAC) is formed during electrochemical oxidation of HVA. The formation of this compound could interfere with the quantification of HVA using electrochemical methods. This work aims at describing the behavior of the intermediate species generated in the oxidation of HVA using cyclic voltammetry (CV), linear staircase voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) with a glassy carbon rotating disc electrode (GC RDE). The importance and desirability of detailed investigation of surface phenomena connected with electrochemical oxidation used for electroanalytical purposes are thus clearly demonstrated. The EIS measurements indicate that the intermediate DOPAC formed by the oxidation of HVA can adsorb on the surface of a glassy carbon electrode (GCE). For the static GCE, a semi-finite linear diffusion was observed and for the GC RDE, a finite-length diffusion was verified. In the case of the semi-finite linear diffusion, EIS measurements revealed that the resistance to charge transfer decreases from 100 to 50 Ω, and the capacitance of the double layer increases from 1.44 to 1.66 μF with increasing concentration of HVA. However, LSV results showed that Levich equations for electrochemical reduction of K3[Fe(CN)6] probe in basic medium are ilim = −0.157 ω1/2 − 0.006 (R2 = 0.9999) in the absence of HVA (i.e. without DOPAC adsorption at GCE) and ilim = −0.154 ω1/2 − 0.021 (R2 = 0.9998) in the presence of HVA (i.e. with DOPAC adsorption at GCE). The small difference in these two equations proves a negligible influence of DOPAC adsorption on the quantification of HVA using stationary methods.

Cyclic staircase voltammograms of a simple, reversible oxidation on the rotating disk electrode is analysed by the digital simulation. It is demonstrated that the peak currents and potentials depend on the single dimensionless variable that considers nonlinear relationship between peak currents and the potential increment. The reverse, cathodic branch of voltammograms depends on this variable differently than the anodic one.

A voltammetric sensor has been developed based on glassy carbon electrode (GCE) modification with nanocomposite consisting of manganese-based metal-organic framework (JUK-2), multi-walled carbon nanotubes (MWCNTs), and gold nanoparticles (AuNPs) for detection of citalopram (CIT). The composition and morphology of JUK-2-MWCNTs-AuNPs/GCE were characterized by X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), energy dispersion spectroscopy (EDS), and scanning electron microscopy (SEM). The electrochemical properties investigated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) indicated that the fabricated hybrid material exhibits the properties of mixed ion-electron conductor (MIEC). Using staircase voltammetry (SCV), under optimized conditions, the fabricated sensor shows a linear response in three CIT concentration ranges, 0.05–1.0, 1.0–10.0 and 15.0–115.0 μmol L−1, with a detection limit of 0.011 μmol L−1. The JUK-2-MWCNTs-AuNPs/GCE was successfully employed for the determination of CIT in pharmaceutical, environmental waters, and biological samples with satisfactory recoveries (98.6–104.8%). Graphical abstract

This work presents a simple and low-cost strategy to obtain voltammetric tongues by using a single voltammetric sensor aided by variable selection techniques. A usual electronic tongue consists of an array of physical sensors followed by data compression before pattern recognition modeling. Alternatively, a single voltammetric sensor can also act as an array of pseudo-sensors—applied potentials in a voltammogram—that can be properly selected to perform a given discrimination. The applicability of this strategy was evaluated in the discrimination of teas. Teas prepared for immediate intake (simulating a home-made tea cup) were analyzed with staircase voltammetry at an epoxy-graphite electrode. Voltammograms were submitted to variable selection previously to linear discriminant analysis (LDA) to identify the applied potentials that improve discrimination of teas according to variety, country of origin, and manufacturer. Successive projections algorithm (SPA), genetic algorithm (GA), and stepwise (SW) formulation were the variable selection techniques evaluated. Best results were achieved with SPA/LDA models, with correct classification rates for the prediction set close to 100%.

In this work, we present theoretical results in cyclic staircase voltammetry of a surface catalytic mechanism that features reversible chemical step, the so-called “surface catalytic ECrev’ mechanism”. We consider specific surface regenerative mechanism, in which both of the electro-inactive substrates are present in large excess in electrochemical cell from the beginning of the experiment. The chemical reversibility brings at this mechanism more complexity in respect to the features of well-elaborated surface catalytic EC’ mechanism coupled with chemically irreversible regenerative reaction. As we present plenty of simulated cyclic voltammograms, we also propose methods to get insight to kinetics and thermodynamics parameters relevant to chemical regenerative step. The elaboreted results can be important in analyzing the kinetics and thermodynamics of many drug-drug and drug-DNA interactions, for example. In addition, with the results reported in this work we can access relevant information about the chemistry of important lipophilic enzymes studied in protein-film voltammetry set up.

Graphene have attracted considerable attention in synthesis and electrochemical applications. In the present study, graphene paste electrode (GPE) was used to study electrochemical behavior of D-Cycloserine (DCS) using cyclic (CV), staircase (SCV) and square wave (SWV) voltammetric techniques. The electrochemical sensor showed excellent enhancement and adsorptive ability towards the electrooxidation of DCS. The electro-oxidation mechanism was proposed. Experimental parameters, such as the surface area of electrode, scan rate and pH of solution were optimized. Under the optimized conditions, the oxidation peak current was proportional to DCS concentration in the range between 1.0×10-8 - 1.5×10-7 M for SCV and 1.0×10-8 - 1.1×10-7 M for SWV and the detection limit was 2.80 nM for SCV and 3.70 nM for SWV. The proposed SCV method was observed to be simple, fast and inexpensive and hence, could be readily adopted for quality control in pharmaceutical products.

Thin-film voltammetry (TFV) has one of the simplest experimental setups for studying the electrochemical processes that take place at liquid/liquid interfaces. This is because in TFV it is possible to neglect the iR drop of the non-aqueous solvent, when it corresponds to an organic thin film attached to the working electrode. In this manuscript the theory of TFV is used for describing how the electrochemical responses of staircase cyclic voltammetry (SCV) and square-wave voltammetry (SWV) are affected by the confinement of electroactive species in a thin film that is in contact with the working electrode. The reason for comparing the responses of these two techniques is established on the different concentration profiles that the electroactive species present within the thin-film and the implications that it has on the voltammetric responses of each technique. According to our analysis, the presence of the so-called “quasi-reversible maximum” cannot be used in TFV for estimating kinetic parameters since it would lead to erroneous results. This is because both the apparent kinetic and the apparent thickness change simultaneously with the variation of the scan-rate of each technique. Instead of this, it is proposed a strategy based on the variation of the scan-rate of SCV and SWV. Thus, it is possible to obtain 2 sets of voltammograms whose peak currents and peak potentials characterize the kinetic and thickness of the system. The estimation can be made when all the peak parameters fit properly to the theoretical data provided in this manuscript. Besides, it is shown that the results of SCV and SWV complement each other providing the way for estimating the formal charge transfer rate constant and the thickness of this kind of systems.

The presence of redox reactions due to slow-moving ions at perovskite/contact interfaces is a major concern for the long-term stability of perovskite solar cells. In this work, we have evidently demonstrated the contribution of K+ ions on the removal of these non-capacitive effects that primarily accelerate the degradation mechanism in the devices. The intermittent current–voltage characteristics at the short-circuit conditions elucidate the role of K+ ions on reducing the rapid degradation at the interfaces due to the chemical reactivity of the accumulated ions by eliminating the burn-in decay in the photocurrent. Dark current–voltage measurements, time-resolved staircase voltammetry, and electrochemical impedance spectroscopy verified that both capacitive and non-capacitive currents, consequence of slow ion migration, are reduced by the incorporation of K+. Thus, this work signifies how K+ incorporation diminishes the internal degradation and enhances intrinsic stability of perovskite solar cells.

Antioxidants are molecules that neutralize reactive oxygen species in the human body, reportedly reducing the risk of cancer and cardiovascular diseases. With multiple dietary products being advertised by their assumed high antioxidant concentration, the need for a proper way of analyzing antioxidant containing beverages becomes apparent. In this research, the antioxidant nature of teas, wines and (superfood) juices is investigated using staircase voltammetry (SV). A new parameter is proposed and evaluated to characterize the antioxidant nature, including its antioxidant capacity and activity: the Antioxidant Index (AI). AI showed green tea to have the best antioxidant nature of teas and red wine to be a better antioxidant than white wine. Superfoods did not show better antioxidant behavior than non-superfoods. AI proved to be a promising way of investigating the antioxidant nature of beverages., Food science; Food analysis; Antioxidants; Wines; Teas; Juices; Staircase voltammetry; Antioxidant index; Half wave potential.

In this work we propose the voltammetric analysis of contraceptive hormones ethinylestradiol (EE) and cyproterone acetate (CPA) using solid amalgam electrode fabricated with silver nanoparticles. To the best of our knowledge, this is the first report describing the simultaneous determination of these two compounds and also the first report of the use of amalgam electrode for analysis of EE and CPA. The voltammetric behavior of both substances was investigated by their reduction. An irreversible electrochemical process involving two protons and two electrons was found for each compound. The analytical assays were carried out using staircase voltammetry (SCV). Due to this, aiming to improve the analytical sensitivity, the cationic surfactant cetyltrimethylammonium bromide was also used. The instrumental and experimental parameters were studied and optimized to achieve the best conditions for the analysis. Under the optimum conditions, the voltammetric signals of EE and CPA showed dependence on the concentration range from 6.4 × 10−7 to 7.8 × 10−6 mol L−1 and from 1.0 × 10−6 to 1.0 × 10−5 mol L−1, respectively. The limits of detection obtained were 1.03 × 10−7 mol L−1 for EE and 2.99 × 10−7 mol L−1 for CPA. The analytical usefulness of the method was evaluated through its application on the simultaneous determination of EE and CPA in pharmaceutical formulations and urine samples. The two analytes were successfully quantified in these samples with good precision and the values found presented satisfactory concordance with the reference values, suggesting acceptable analytical efficiency for the approach described here.

We have developed theory for cyclic (staircase) voltammetry (CSCV) of a two step reversible charge transfer (EE) mechanism for redox species with unequal diffusion coefficients at rough electrodes. The various surface microscopies provide details of random morphology of the electrode which is characterized through the power spectrum in our theory. For the finite fractal electrode model, anomalous enhancement and scan rate dependence of the CSCV or CV response is caused by fractal dimension (DH), lower length scale of fractality (l), and topothesy length (lτ). The peak current corresponding to both charge transfer steps is enhanced with an increase in roughness of the fractal electrode (through increase in DH or lτ or decrease in l). The onset and offset of the anomalous regime is controlled by lτ and l, respectively. Results show that the electrode roughness has the potential to enhance the sensitivity of CSCV as an analytical technique. This is due to a decrease in the difference between the peak current...

Further analysis of staircase voltammetry for reversible and quasi-reversible metal ion deposition on a same metal electrode and on a foreign electrode is presented. Literal solutions and numerical simulation are used to quantify the electrochemical response under conditions of planar semi-infinite diffusion. Addressed topics include: consideration of the uncompensated resistance, comparison of the apparent charge found by integration of the voltammograms with the actual faradaic charge transferred, anodic dissolution of the deposit in a cyclical potential scan, properties and interest of the zero-crossing point, occurrence of 3D nucleation overvoltage.

We develop a theory for cyclic staircase voltammetry (CSCV) of a reversible charge transfer process with unequal diffusivities on a randomly rough electrode. The roughness power spectrum based approach is developed and detailed analysis is performed for a finite fractal model. An elegant expression for the statistically averaged CSCV current is obtained in terms of single potential step current at a rough electrode. The extent of anomalous response due to finite fractal roughness is determined by scan rate. The characteristic peak current and peak to peak separation in CV are dependent on finite fractal features, namely, fractal dimension (DH), topothesy length (lτ), and finest length scale of fractality (l). Peak to peak separation is reduced while peak current is enhanced with increase in DH and lτ and decrease in l. The roughness induced anomalous regime often introduces errors in estimating diffusion coefficient from classical Randles–Secvik equation. Our theory suggests that this error can be reduce...

Pulse technologies have been widely employed in analytical electrochemistry systems. Double layer charging current has been an obstacle to the accurate measurement of faradaic current despite the theoretical and experimental efforts. Conventional pulse approaches record the current at a later pulse time for minimizing the capacitative effects and reducing the background currents. In this study, a method for extracting the quantitative information directly from the current curve data of pulse voltammetry is developed using trilinear decomposition algorithm. Feasibility of the proposed method is proved and an application study is performed for quantitative analysis of bovine serum albumin (BSA). The method can simultaneously obtain net faradaic current and double layer charging current directly from the measured signals, and the quantitative information can be obtained as well. Thus the performance of voltammetric techniques can be improved. Because the net signals are used, the sensitivities are increased by about 160%, 90% and 25% for normal pulse voltammetry, differential pulse voltammetry and staircase voltammetry, respectively. Quantitative determination of BSA in solutions was carried out with a calibration model of six samples. The recoveries are in a range from 98.1% to 102.9%, which may prove the reliability of the proposed method.

An approach for evaluating the contributions of two prominent cathodic reactions, namely the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER), to the cathodic current at various potentials, including at the corrosion potential of a Pb electrode is presented. In this approach, the capacitive charging current was eliminated using staircase voltammetry. The cathodic current was separated into the two current components arising from the ORR and HER (namely IORR and IHER), and resultant current components were assessed quantitatively by using the rotating disk electrode method together with the Koutecky-Levich equation. Additionally, the relative contributions of IORR and IHER to the cathodic current and the corrosion current in air-saturated and deaerated electrolytes at a given condition were obtained. This approach will be useful in understanding the corrosion of metals in different environments.

This work proposes a simple and inexpensive electroanalytical method to identify adulteration in hydrated ethyl alcohol fuel (HEAF) samples by using multivariate analysis. The methodology was validated in a case study with HEAF samples divided into two categories: (1) unadulterated and (2) adulterated with methanol in different concentration levels (1.0–13% m m −1 ). Staircase voltammetry was the electrochemical technique employed. Voltammograms were recorded with a copper electrode in an alkaline solution. Four different pattern recognition methods were evaluated for classification of the resulting voltammograms: partial least squares discriminant analysis (PLS-DA); linear discriminant analysis (LDA) with variable selection by the successive projections algorithm (LDA/SPA), genetic algorithm (LDA/SPA), and a stepwise formulation (LDA/SW). The best results were achieved with LDA/GA and LDA/SW models, which all prediction samples were correctly classified.

International audience; Silver ion deposition on gold and silver disc electrodes in nitrate aqueous solutions and in [EMIM][NTf 2 ] room-temperature ionic liquid were investigated by staircase voltammetry (SV) and square wave voltammetry (SWV). The kinetics of the Ag(I)/Ag couple in [EMIM][NTf 2 ] solutions prepared with AgNTf 2 depends both on their water content and the AgNTf 2 concentration. The electrochemical reaction is reversible in aqueous solutions and wet [EMIM][NTf 2 ] long exposed to the open air, while it is quasi-reversible in anhydrous [EMIM][NTf 2 ]. Silver ion deposition proceeds without 3D nucleation overvoltage only in acidic aqueous solutions and anhydrous [EMIM][NTf 2 ]. It is shown in particular that back-and-forth scans in SWV allow direct detection of relatively low nucleation overvoltage occurring in 1 M KNO 3 solution. The role of the metal-water interface was discussed, kinetic parameters for 0.1 M AgNTf 2 in anhydrous [EMIM][NTf 2 ] were determined by numerical simulation and theoretical conclusions on SV for metal ion deposition from high-resistive media previously published were checked.

The modulation of a ramped potential applied to a voltammetric electrode evokes two responses: a quasiperiodic 'ac' current of the same periodicity as the modulation, and a perturbation of the underlying dc current. The latter is the subject of this article. Reasoning by analogy with an analytical result for reversible square-wave-modulated linear-potential-scan voltammetry, a sequence of credible arguments has allowed prediction of the dc current for modulations of any waveform and of any amplitude. Applications to staircase voltammetry and to modulated cyclic voltammetry are included. © 2001 Elsevier Science B.V. All rights reserved.

The use of staircase voltammetry for the measurement of reversible diffusional redox species under a linear mass-transport regime leads to significant suppression of the peak currents (up to 20% for larger step sizes) and an increase in the peak-to-peak separation (cf. ∆ E pp ~ 70 mV at the reversible limit as opposed to 57 mV). These discrepancies between the voltammetric results of a staircase and true analogue voltammogram may lead to mis-interpretation of data. This work provides an overview of the differences between the two techniques in the macro-electrode reversible limit and provides new expressions which allow the peak current of a staircase voltammogram to be quantitatively analysed. Moreover, clear guidance is provided about which conditions the application of the provided equation is valid in the terms of mass-transport edge effects to the macro-electrode.

Protein-film voltammetry (PFV) is a versatile tool designed to provide insight into the enzymes physiological functions by studying the redox properties of various oxido-reductases with suitable voltammetric technique. The determination of the thermodynamic and kinetic parameters relevant to protein's physiological properties is achieved via methodologies established from theoretical considerations of various mechanisms in PFV. So far, the majority of the mathematical models in PFV have been developed for redox proteins undergoing a single-step electron transfer reactions. However, there are many oxido-reductases containing quinone moieties or polyvalent ions of transition metals like Mo, Mn, W, Fe or Co as redox centers, whose redox chemistry can be described only via mathematical models considering successive two-step electron transformation. In this work we consider theoretically the protein-film redox mechanisms of the EE (Electrochemical–Electrochemical), ECE (Electrochemical–Chemical–Electrochemical), and EECat (Electrochemical–Electrochemical–Catalytic) systems under conditions of cyclic staircase voltammetry. We also propose methodologies to determine the kinetics of electron transfer steps by all considered mechanisms. The experimentalists working with PFV can get large benefits from the simulated voltammograms given in this work.

General analytical and explicit equations for the transient and stationary I–E responses of electrocatalytic process of soluble solution species at mediator modified electrodes, valid for any reversibility degree of the charge transfer and for any multipotential pulse technique, are presented. These expressions have been applied to staircase voltammetry (SCV) and linear sweep voltammetry (LSV), and also to their corresponding differential and derivative modalities. The value of the chemical rate constant can be easily obtained from a cathodic plateau of the SCV curves under transient and stationary conditions. Easy methods for determining other characteristic parameters of the process are proposed. The theoretical predictions have been experimentally tested.

The comparison between the response corresponding to a simple charge transfer taking place at an electroactive monolayer with that of an electrocatalytic process at a modified electrode are presented by using the multipulse potential techniques cyclic staircase voltammetry (CSCV) and cyclic square wave voltammetry (CSWV). General analytical and explicit equations for the IE responses have been tested by means of the study of the reduction of azobenzene monolayer at mercury electrode. The value of the chemical rate constant ( k c ' = 40 M  1 s  1 ) has been easily obtained from the cathodic plateau of the CSCV curves and from the best fitting between theoretical and experimental CSWV curves.

In a 0.02 M borax solution (pH 8.5), basic amino acids (arginine, lysine, and ornithine) react with Ni2+ to form a mono-ligand complex that is reduced at a mercury electrode at about −0.85 V vs. Ag|AgCl|KCl (3 M). At a long time scale (staircase voltammetry; scan rate

Voltammetric methods use a constant sweep rate during the course of a scan. This paper reports a study of the influence of a nonconstant sweep rate on the voltammetric response. In this approach, either continuously increasing or continuously decreasing potential scan rates can be employed, unlike presently available methods which rely on a constant sweep rate. The voltammetric response of potassium ferrocyanide at a glassy carbon electrode was used as a model system to test the new method. The responses obtained using traditional staircase voltammetry (linear staircase voltammetry) and the new approach (nonlinear staircase voltammetry) were compared by experiment and by simulation. The new approach offers capability for signal enhancement, whereby enhanced current or enhanced peak shape can be obtained by choice of appropriate waveform parameters.

Mathematical models under conditions of cyclic staircase voltammetry and electrochemical impedance spectroscopy (EIS), which consider the kinetic effects due to the complexation reaction by the facilitated transfer of metal ions at polarized interfaces, are presented. Criteria for qualitative recognition of these kinetic effects from the features of simulated cyclic voltammograms are given. In case of the existence of these effects, only the EIS can bring access to the thermodynamics and kinetics of the complexation chemical reaction. Analytical equations for estimating the thermodynamic parameters by such systems under EIS conditions are evaluated. The theoretical results are compared with the experimental results of the facilitated Cu 2+ transfer at the polarized water-1,2-dichlorethane interface, assisted by two phenanthroline-containing macrocycles. In the experimental case where kinetic effects due to the complexation step exist, we show how elegantly EIS can be used as a tool for estimation of the complexation constant of Cu 2+ and 5-oxo-2,8-dithia [9],(2,9)-1,10-phenanthrolinophane (PhenOS2).

Several multipotential step techniques such as staircase voltammetry (SCV), additive differential staircase voltammetry (ADSCV) and cyclic voltammetry (CV) have been applied to the study of the reversible reduction/oxidation of molecules with multiple redox centers (interacting or not) using spherical electrodes of any size. The theoretical predictions have been tested with two experimental systems: quinizarine in acetonitrile and pyrazine in aqueous acid media, founding an excellent agreement between theory and experiments. A critical analysis of the response with each technique allows us to conclude that, although all of them are powerful qualitative tools, ADSCV, proposed in this paper, is the most suitable technique to study such multistep processes quantitatively, and it can be used to determine the formal potentials easily for any number of electrochemical steps in the case of molecules with strongly interacting centers, and also in the case of molecules with two redox centers whatever the interaction degree between them. The formal potentials for the systems mentioned above have been evaluated with this technique. The advantages of using microelectrodes in order to obtain characteristic parameters of the system are also discussed.

Simple, analytical and fully explicit expressions for the I–E curves of a charge transfer process of a diffusionless system corresponding to staircase voltammetry (SCV) are presented. We have analyzed the reversibility influence and our results indicate that SCV curves obtained at different sampled times tend to coincide as the rate constant decreases. Moreover, the current–potential SCV response converts to that corresponding to linear sweep voltammetry (LSV) when the pulse amplitude ΔE0. We have also obtained the theoretical expression for the response of differential staircase voltammetry (DSCV) which presents two peaks and a cross potential at which ΔI=0.

In this paper, a novel method for detection of formaldehyde (HCHO), based on its electrocatalytic oxidation of HCHO at a nickel electrode, is reported. The mechanism of electrocatalytic oxidation and quantification of HCHO have been investigated by cyclic and staircase voltammetry, respectively. The electrocatalytic oxidation peak potential of HCHO is at about 475 mV vs. Ag/AgCl electrode; the peak current responds proportionally to concentrations of HCHO in alkaline solution. The linear range of detection is from 46.8 to 1640 μg/L (1.56 × 10−6 to 5.46 × 10−5 M) with a correlation coefficient of 0.996 and a detection limit of 23.4 μg/L (7.80 × 10−7 M). The relative standard deviation (RSD) is less than 6% (n = 5), and the recovery is in the range 98–106% for real samples. The result is consistent with that from the spectrophotometry.