Cyclic Square Wave Voltammetry Research Articles

Adsorptive transfer cyclic square-wave voltammetry and HPLC with tandem electrochemical detection – Two novel methods for determination of chili peppers pungency

The pungency of chili peppers, the most popular hot spice used worldwide, is caused by capsaicinoids (CPDs), the content of which can vary greatly due to varietal differences and growing conditions. For the first time, a novel simple method for the fast determination of CPDs in chili peppers and chili products was developed based on adsorptive transfer cyclic square-wave voltammetry (AdTCSWV), using adsorption of lipophilic CPDs on an unmodified glassy carbon electrode surface from methanolic extracts of chili pepper samples. The CSWV is based on short oxidation of adsorbed CPDs to quinoid products, and their subsequent reduction and re-oxidation to provide specific analytical signals with a linear range from 0.05 to 1.00 mg L−1. This principle was also implemented in tandem coulometric and amperometric detection of CPDs after HPLC separation. The two-step electrochemical detection provides increased selectivity for CPDs in case of CPDs co-elution with other electrochemically oxidizable components that cannot be reversibly reduced.

A novel strategy for the simultaneous discrimination of dopamine and epinephrine by cyclic square wave voltammetry implemented with a customized potentiostat

An electrochemical strategy for the simultaneous detection of DA and EP with high sensitivity by cyclic square wave voltammetry using a modified open source potentiostat.

Cyclic voltammetry, square wave voltammetry or electrochemical impedance spectroscopy? Interrogating electrochemical approaches for the determination of electron transfer rates of immobilized redox proteins

In this article, we cross-examine three well-established electrochemical approaches, namely cyclic voltammetry (CV), cyclic square-wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) to dissect the electron transfer (ET) rate of electrostatically immobilized cytochrome c on Ag electrodes. A detailed analysis supported by simulations of redox transition provided three distinct values for the heterogeneous electron transfer (HET) rate constant of cyt c interfaced on COOH-terminated C10-long alkanethiol, i.e., kHET= 47.8 (±2,91) s−1 in CV, kHET= 64.8 (±1,27) s−1 in SWV, and kHET= 26.5 s−1 in EIS. We discuss the obtained discrepancies obtained from electrochemical methods and compare them with the data from spectro-electrochemical experiments. A comprehensive selection list is created from which the most applicable approach can be chosen for studying proteins of interest. CV is most applicable to study the interfaced proteins exhibiting kHET of ca. 0.5 - 70 s−1, SWV is suitable for a broader range of kHET of 5 – 120 s−1 and EIS for kHET of 0.5 to 5 s−1 if alkanethiols are used as immobilization strategy.

Voltammetric Determination of Glutathionein Pharmaceutical and Biological Samples Using Multiwall Carbon Nanotubes Paste Electrode in the Presence of Rutin as a Mediator.

A new sensitive and selective electrochemical sensor was developed for electrocatalytic determination of glutathione (GSH) in pharmaceutical and biological samples. GSH is a tripeptidethiol present in all eukaryotic and probiotic cells. A voltammetric study of GSH has been carried out at the surface of carbon paste electrode modified with multiwall carbon nanotubes in the presence of rutin as a mediator. The electrochemical oxidation of GSH was investigated by cyclic voltammetry, chronoamperometry and square wave voltammetry (SWV) techniques. Under the optimized conditions, the peak current was linear to GSH concentration over the concentration range of 0.3 to 180μmol L−1 using SWV. The detection limit was 0.09μmol L−1. The proposed method was successfully applied to the determination of GSH in the urine, tablet and hemolysed erythrocyte samples.

Sensitive and Selective Measurement of Serotonin in Vivo Using Fast Cyclic Square-Wave Voltammetry.

Although N-shaped fast scan cyclic voltammetry (N-FSCV) is well-established as an electroanalytical method to measure extracellular serotonin concentrations in vivo, it is in need of improvement in both sensitivity and selectivity. Based on our previous studies using fast cyclic square-wave voltammetry (FCSWV) for in vivo dopamine measurements, we have modified this technique to optimize the detection of serotonin in vivo. A series of large amplitude square-shaped potentials was superimposed onto an N-shaped waveform to provide cycling through multiple redox reactions within the N-shaped waveform to enhance the sensitivity and selectivity to serotonin measurement when combined with a two-dimensional voltammogram. N-Shaped fast cyclic square-wave voltammetry (N-FCSWV) showed significantly higher sensitivity to serotonin compared to conventional N-FSCV. In addition, N-FCSWV showed better performance than conventional N-shaped FSCV in differentiating serotonin from its major interferents, dopamine and 5-hydroxyindoleascetic acid (5-HIAA). It was also confirmed that the large amplitude of the square waveform did not influence local neuronal activity, and it could monitor electrical stimulation evoked phasic release of serotonin in the rat substantia nigra pars reticulata (SNr) before and after systemic injection of escitalopram (ESCIT, 10 mg/kg i.p.), a serotonin selective reuptake inhibitor.

Machine Learning Techniques for Chemical Identification Using Cyclic Square Wave Voltammetry.

Electroanalytical techniques are useful for detection and identification because the instrumentation is simple and can support a wide variety of assays. One example is cyclic square wave voltammetry (CSWV), a practical detection technique for different classes of compounds including explosives, herbicides/pesticides, industrial compounds, and heavy metals. A key barrier to the widespread application of CSWV for chemical identification is the necessity of a high performance, generalizable classification algorithm. Here, machine and deep learning models were developed for classifying samples based on voltammograms alone. The highest performing models were Long Short-Term Memory (LSTM) and Fully Convolutional Networks (FCNs), depending on the dataset against which performance was assessed. When compared to other algorithms, previously used for classification of CSWV and other similar data, our LSTM and FCN-based neural networks achieve higher sensitivity and specificity with the area under the curve values from receiver operating characteristic (ROC) analyses greater than 0.99 for several datasets. Class activation maps were paired with CSWV scans to assist in understanding the decision-making process of the networks, and their ability to utilize this information was examined. The best-performing models were then successfully applied to new or holdout experimental data. An automated method for processing CSWV data, training machine learning models, and evaluating their prediction performance is described, and the tools generated provide support for the identification of compounds using CSWV from samples in the field.

Ionic Liquid-Modified Disposable Electrochemical Sensor Strip for Analysis of Fentanyl.

The increasing prevalence of fentanyl and its analogues as contaminating materials in illicit drug products presents a major hazard to first responder and law enforcement communities. Electrochemical techniques have the potential to provide critical information to these personnel via rapid, facile field detection of these materials. Here we demonstrate the use of cyclic square wave voltammetry (CSWV) with screen-printed carbon electrodes (SPCE), modified with the room temperature ionic liquid (RTIL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [C4C1pyrr][NTf2], toward such rapid "on-the-spot" fentanyl detection. This CSWV-based disposable sensor strip system provides an information-rich electrochemical fingerprint of fentanyl, composed of an initial oxidation event at +0.556 V (vs Ag/AgCl) and a reversible reduction and oxidation reaction at -0.235 and -0.227 V, respectively. The combined current and potential characteristics of these anodic and cathodic fentanyl peaks, generated using two CSWV cycles, thus lead to a distinct electrochemical signature. This CSWV profile facilitates rapid (1 min) identification of the target opioid at micromolar concentrations in the presence of other cutting agents commonly found in illicit drug formulations. The new protocol thus holds considerable promise for rapid decentralized fentanyl detection at the "point of need".

RECENT ADVANCES AND PROSPECTS OF SQUARE-WAVE VOLTAMMETRY

This review concerns recent methodological advances of square-wave voltammetry as one of the most sophisticatedmembers of the pulse voltammetric techniques. Besides addressing recent theoretical works and representatives ofadvanced analytical studies, an emphasis is given to a few novel methodological concepts such as kinetic analysis atconstant scan rate, cyclic square-wave voltammetry, multisampling square-wave voltammetry, and electrochemical faradaicspectroscopy. For the purpose of improving analytical performances of the technique two new methods are proposedfor the first time.

Fast Cyclic Square-Wave Voltammetry To Enhance Neurotransmitter Selectivity and Sensitivity.

Although fast-scan cyclic voltammetry (FSCV) has been widely used for in vivo neurochemical detection, the sensitivity and selectivity of the technique can be further improved. In this study, we develop fast cyclic square-wave voltammetry (FCSWV) as a novel voltammetric technique that combines large-amplitude cyclic square-wave voltammetry (CSWV) with background subtraction. A large-amplitude, square-shaped potential was applied to induce cycling through multiple redox reactions within a square pulse to increase sensitivity and selectivity when combined with a two-dimensional voltammogram. As a result, FCSWV was significantly more sensitive than FSCV ( n = 5 electrodes, two-way ANOVA, p = 0.0002). In addition, FCSWV could differentiate dopamine from other catecholamines (e.g., epinephrine and norepinephrine) and serotonin better than conventional FSCV. With the confirmation that FCSWV did not influence local neuronal activity, despite the large amplitude of the square waveform, it could monitor electrically induced phasic changes in dopamine release in rat striatum before and after injecting nomifensine, a dopamine reuptake inhibitor.

Hybrid electrochemical sensor platform for capsaicin determination using coarsely stepped cyclic squarewave voltammetry

A small, standalone electrochemical hybrid sensor platform, combining flexible electronics and screen-printed electrodes, is demonstrated in the determination of capsaicin through adsorptive stripping voltammetry. The sensing scheme was simplified to be compatible with a low-cost device. The simplification involved eliminating the need for additional modification of the electrode and employing a coarsely stepped squarewave voltammetry, a technique which is applicable with less sophisticated instrumentation. This architecture was found to be suitable for concentrations up to at least 5000 µM with a detection limit of 1.98 µM. The screen-printed carbon graphite electrodes were made reusable through an ethanol rinsing protocol. The effect of ethanol/buffer volumetric ratio in the test sample was shown to greatly influence the analytical data, and a fixed 10% (v/v) was chosen as a compromise between signal-to-noise ratio and not exceeding the solubility limit of the desired upper range.

Selective Voltammetric Measurements of Epinephrine and Norepinephrine in Presence of Common Interferences Using Cyclic Square‐voltammetry at Unmodified Carbon Electrodes

AbstractSelective electrochemical measurements of epinephrine (EP) and norepinephrine (NE) in the presence of large excess of the common interfering ascorbic acid (AA) and uric acid (UA) are accomplished using cyclic square‐wave voltammetry (C‐SWV) at unmodified carbon electrodes. Such use of bare carbon electrodes is based on monitoring the reduction peaks of the EP and NE oxidation products and relies on the reversible electrochemical behavior of these catecholamines compared to that of AA and UA and on the rich information content and high speed and sensitivity of C‐SWV. Detection limits of 3 μM EP and NE are estimated in the presence of 100 fold excess AA and UA. The C‐SWV operation at the uncoated carbon electrode facilitates also the simultaneous measurements of EP and NE. The new C‐SWV protocol enhances the resolving power of unmodified carbon electrodes and represents an extremely useful and simple addition to the arsenal of electrochemical techniques for real‐time monitoring of dynamic brain processes.

Electrochemical determination of chloramphenicol using a glassy carbon electrode modified with dendrite-like Fe 3 O 4 nanoparticles

In this study, magnetite (Fe3O4) nanoparticles were electrochemically synthesized in an aqueous electrolyte at a given potential of -1.3 V for 180 s. Scanning electron microscopy revealed that dendrite-like Fe3O4 nanoparticles with a mean size of < 80 nm were electrodeposited on a glassy carbon electrode (GCE). The Fe3O4/GCE was utilized for sensing chloramphenicol (CAP) by cyclic voltammetry and square wave voltammetry. A reduction peak of CAP at the Fe3O4/GCE was observed at 0.62 V, whereas the uncoated GCE exhibited a very small response compared to that of the Fe3O4/GCE. The electrocatalytic ability of Fe3O4 was mainly attributed to the formation of Fe(VI) during the anodic scan, and its reduction to Fe(III) on the cathodic scan facilitated the sensing of CAP. The effects of pH and scan rate were measured to determine the optimum conditions at which the Fe3O4/GCE exhibited the highest sensitivity with a lower detection limit. The reduction current for CAP was proportional to its concentration under optimized conditions in a range of 0.09-47 μM with a correlation coefficient of 0.9919 and a limit of detection of 0.09 μM (S/N=3). Moreover, the fabricated sensor exhibited anti-interference ability towards 4-nitrophenol, thiamphenicol, and 4-nitrobenzamide. The developed electrochemical sensor is a cost effective, reliable, and straightforward approach for the electrochemical determination of CAP in real time applications.

Cyclic multipulse voltammetric techniques. Part II: EC mechanism

A theoretical analysis of electrode processes controlled by kinetics of follow-up homogeneous chemical reaction under conditions of (simple) cyclic multi pulse voltammetry (CMPV), cyclic differential multi pulse voltammetry (CDMPV) and cyclic square-wave voltammetry (CSWV) is presented. The study was performed under linear diffusion conditions and for equal diffusion coefficients of all participants of the electrode process. Chemical reaction changes the shape and position of CMPV response, compared to a simple reversible electrode reaction. As the chemical process becomes faster, forward/reduction wave decreases whereas a pronounced maximum appears on it. On the other hand, the influence of following chemical reaction on the shape of CDMPV and CSWV reduction signal is not significant, while their voltammograms shifted towards more positive potentials as well. Experimentally, the rate constant of follow-up chemical reaction (kf) can be estimated from the linear dependence of limiting to maximum reduction currents ratio (il,c/imax,c) on log(tp) in CMPV, as well as of anodic to cathodic net peak currents ratio (Δip,a/Δip,c) on log(tp) in CDMPV and on log(f) in CSWV. Combination of two or more cyclic multipulse voltammetric techniques gives more information about kinetics i.e. more precise determination/estimation of the rate constant of follow-up chemical reaction, compared with application of only one technique.

Cyclic multipulse voltammetric techniques. Part I: Kinetics of electrode processes

A comparative, theoretical and experimental, analysis of reversible and kinetically controlled electrode reactions by cyclic multi pulse voltammetry (CMPV), cyclic differential multi pulse voltammetry (CDMPV) and cyclic square-wave voltammetry (CSWV) is presented. The cyclic multipulse voltammetric techniques enable faster and more complete characterization of the electrode processes, comparing with classical multipulse voltammetric techniques. Electron transfer coefficients (α and β), i.e. symmetry of the electron transfer reaction can be estimated by visual inspection of the proper cyclic multipulse voltammogram. Their values, as well as the standard rate constant of a simple electrode reaction Ox+ne−⇄ Red, can be determined from the slopes of linear dependences of characteristic (half wave or peak) cathodic and anodic potentials on the logarithm of pulse duration in CMPV and CDMPV, or logarithm of frequency in CSWV. The criteria for recognition of kinetically controlled electrode reactions by cyclic multipulse voltammetric techniques are given.

A study of sodium diethyldithiocarbamate oxidation at glassy carbon electrode in water and water-organic mixtures

The oxidation of sodium diethyldithiocarbamate at a glassy carbon electrode in water and water-organic mixtures in the presence of KCl and NaOH is investigated. Using cyclic square-wave voltammetry and rotated electrode voltammetry it is shown that, in water and water-ethanol mixtures, the electrode reaction is irreversible. In the case of KCl water solution, the oxidation reaction involves one electron. In the case of KCl in a water-ethanol mixture, two electrons are involved. The possible oxidation mechanism is discussed.

Simultaneous electrochemical measurement of metal and organic propellant constituents of gunshot residues

The simultaneous electrochemical measurement of heavy-metal and organic propellants relevant to gunshot residues (GSRs) is demonstrated. Cyclic voltammetry (CV) and cyclic square-wave stripping voltammetry (C-SWV) are shown to detect, in a single run, common propellants, such as nitroglycerin (NG) and dinitrotoluene (DNT), along with the heavy metal constituents of GSR, antimony (Sb), lead (Pb), zinc (Zn) and barium (Ba). The voltammetric detection of the stabilizer diphenylamine (DPA) along with inorganic constituents has also been examined. The resulting electrochemical signatures combine -in a single voltammogram- the response for the various metals and organic species, based on the reduction and oxidation peaks of the constituents. Cyclic square-wave voltammetry at the glassy carbon electrode (GCE), involving an intermittent accumulation at the reversal potentials of -0.95 V (for Sb, Pb, DNT and NG) and -1.3 V (for Sb, Pb, Zn and DPA) is particularly useful to offer distinct electrochemical signatures for these constituents of GSR mixtures, compared to analogous cyclic voltammetric measurements. Simultaneous voltammetric measurements of barium (at thin-film Hg GCE) and DNT (at bare GCE) are also demonstrated in connection to intermittent accumulation at the reversal potential of -2.4 V. Such generation of unique, single-run, information-rich inorganic/organic electrochemical fingerprints holds considerable promise for 'on-the-spot' field identification of individuals firing a weapon, as desired for diverse forensic investigations.

Study of the Electrocatalytic Reaction of Hydrogen Peroxide Mediated by Azobenzene Monolayer with Several Multipotential Pulse Techniques

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.

Cyclic Square Wave Voltammetry: Theory and Experimental

Abstract The voltage wave form of cyclic square wave voltammetry (CSWV) and its theory are presented, and experimental verification of theoretical work for CSWV is given. Indications are that the peak potential difference, Ep, of the differential current between the forward sweep and the reverse sweep is zero. Their peak heights have the same value for a reversible electrode reaction, zero, a different value for a reversible electrode reaction with stripping process, not zero, and the same value for a quasi-reversible electrode reaction. According to this property, the reversibility of an electrode reaction can be easily determined.