Advances in Derivative Voltammetry - A Search for Diagnostic Criteria of Several Electrochemical Reaction Mechanisms

New methods for analysis of current-potential curves in terms of their derivatives are presented for studying various types of electrode processes – such as simple electron transfer reactions (reversible, quasi-reversible, and irreversible electron transfer) as well as chemically coupled electron transfer reactions along with a diagnostic scheme for differentiating these various types of electrochemical reaction mechanisms. Expressions for first- and higher order derivatives are derived from theoretical analytical solutions for currents for the different types of electrode mechanisms. The derivative curves are analyzed in terms of various parameters which characterize peak shape or peak symmetry with an emphasis on the second derivatives with well-defined anodic and cathodic peaks. Second derivatives can yield, in a simpler manner, the symmetry ratios; i.e., a ratio of anodic to cathodic peak-currents (ipa/ipc), and a ratio of anodic to cathodic peak-widths (Wpa/wpc) and a ratio of anodic to cathodic peak potential differences (ΔEpa/ΔEpc) or a peak separation (Epa-Epc) are evaluated, and these ratio can be related to kinetic parameters associated with a particular types of electrode mechanisms. Peaks are found to be symmetrical for a simple reversible electron transfer process (Er). However, peaks become asymmetrical when the electron transfer become slower (namely, irreversible, Eirr) or e− transfer reaction is coupled with homogeneous chemical reactions such as a prior reaction (CEr) or a follower-up reaction (ECr). From measured values of such symmetry ratios above, one can gain insight to the nature of the electrochemical systems enabling us to determine various kinetic parameters associated with a system. A diagnostic criteria for assigning an electrode mechanism is devised based on the values of asymmetry parameters measured, which are unity for a simple reversible electron transfer process.

Antimony Tin Oxide—Prussian Blue Screen-Printed Electrodes for Electrochemical Sensing of Potassium Ions

In this work, the characterization and the electro-analytical applications of antimony tin oxide (ATO)–Prussian blue (PB) screen printed electrodes (SPE) are presented. The ATO conducting particles have been used recently in the development of screen-printed electrodes due to their excellent spectroelectrochemical properties. PB is a transition metal hexacyanoferrate with high electrocatalytic properties towards various biologically active compounds like hydrogen peroxide, besides its outstanding electrochromic properties. A combination of ATO and PB ingredients into a screen-printing paste provided a versatile and cost-effective way in the development of novel electrode materials for electrochemical sensing. The ATO-PB electrode material displayed good electrochemical properties demonstrated by means of cyclic voltammetry and electrochemical impedance measurements. In addition, the PB provided a high selectivity towards potassium ions in solution due to its zeolitic structures and excellent redox behavior. The cyclic voltammetric responses recorded at the ATO-PB-SPE device in the presence of potassium ions revealed a linear dependence of the cathodic peak current and cathodic peak potential of the Prussian blue/Everitt’s salt redox system on the potassium concentrations ranging from 0.1 to 10 mM. This finding could be exploited in the development of an electrochemical sensor for electro-inactive chemical species. The potential application of the ATO-PB electrode in the electrochemical sensing of electro-active species like caffeic acid was also studied. An increase of the anodic peak current of the PB/ES redox wave in the presence of caffeic acid was observed. These results point out to the potential analytical applications of the ATO-PB electrode in the sensing of both electro-active and electro-inactive species.

Voltammetric Generation and Kinetic Stability of Nitro Anion Radical from Nitrofurazone in Ionic Liquids

The nitrofurazone (NF) electrochemical reduction has been studied by cyclic voltammetry (CV) and square wave voltammetry (SWV) in non-aqueous medium using three different ionic liquids (IL): BMImTf2N, BMImBF4 and BMMImTf2N, having a carbon fiber microelectrode as working electrode. In all of them, two reversible cathodic peaks were recorded for NF. Under higher frequency values, only one reversible cathodic peak was registered. The systems reversibility could also be observed by CV, since a reversible redox couple was registered for this reduction. The systems reversibility with product and reagent adsorptions on the electrode surface was confirmed and the electrons number involved in this reduction indicated the nitro-anion radical formation followed by its respective dianion. For the first reduction, the EC mechanism (an electrochemical step followed by a chemical one) was considered for the systems in aprotic medium, in which there was a probable second-order chemical reaction after the charge transfer process, being the kinetic constants calculated following the Olmstead and Nicholson model.

Electrodeposition of aluminum-doped thin silicon films from the KF-KCl-KI-K2SiF6-AlF3 melt

Cyclic voltammetry, chronoamperometry, scanning electron microscopy, atomic force microscopy, and Raman spectroscopy were used to study the regularities of silicon and aluminum co-deposition on glassy carbon from KF-KCl (2:1) - 75 mol% KI - 0.15 mol% K2SiF6 - (up to 0.15 mol%) AlF3 melts at 998 K. Cyclic voltammograms demonstrated the presence of only one cathodic peak (or nucleation loop at a low reverse potential) and the corresponding anodic peak. The cathodic peak shifted in the cathodic direction with a decrease in the concentration of aluminum ions in the melt or an increase in the scan rate. The Scharifker - Hills model was used to analyze potentiostatic current density transients and estimate the values of the apparent diffusion coefficient and the number density of nuclei. The morphology and elemental analysis of the samples obtained during potentiostatic and galvanostatic deposition for 30-60 s were studied. Continuous thin silicon films doped with aluminum were obtained under galvanostatic conditions.

Electrochemical determination of the levels of lead and cadmium in soil samples from Niger and Ogun States, Nigeria: remediation potential with chitosan phosphate and implications for human health and disease

Lead and cadmium poisoning is common in some parts of Nigeria as a result of artisanal mining of gold. The poisoning has led to the deaths of hundreds of women and children below the age of five years. In this study, the concentrations of lead and cadmium in eight soil samples collected from selected artisanal gold mining locations in Niger State and battery dismantling site in Ogun State were electrochemically determined. Linear sweep stripping voltammetry technique was used with glassy carbon as working electrode, Ag/AgCl as reference and platinum as auxiliary electrode. The cathodic peak current for the reduction of lead was observed at − 490 mV while that of cadmium was observed at − 675 mV. The concentrations of lead in the soil samples ranged between 19 and 417 mg/kg while that of cadmium was in the range 20–182 mg/kg. The ability of chitosan phosphate to adsorb lead and cadmium in the polluted soil samples was investigated as a step towards carrying out remediation of the polluted environment. Chitosan phosphate was derived from chitosan which was prepared by the deacetylation of chitin obtained from crab. The chitosan phosphate was found to remove the lead and cadmium from all the soil samples studied.

Extraction Procedure and Cyclic Voltammetry Assay for Detection of Monosodium Glutamate from Different Processed Food Sources

In this paper, the possibility of direct electrochemical detection of monosodium glutamate (MSG) from food products by the means of cyclic voltammetry is studied. There are four types of processed food included in this study: bologna sausage, frankfurter hot dogs, hot dogs with cheese, and vegetable soup concentrate cubes. The article describes the procedure of MSG extraction from these products. The MSG (as L-glutamic acid) content was precisely determined using an enzymatic spectrophotometry kit provided by Megazyme. Cyclic voltammetry (CV) experiments were performed using three types of screen printed electrodes having carbon, gold or platinum as working electrode. The results show signal appearance for MSG, so qualitative possibility of MSG presence identification; in the case of DRP-110 carbon electrode, the linear correlation between cathodic peak current and MSG concentration suggests the possibility of optimization and use of CV for MSG determination for food industry.

Indirect Determination of Amikacin by Gold Nanoparticles as Redox Probe

: Amikacin is an aminoglycoside antibiotic used for many gram-negative bacterial infections like infections in the urinary tract, infections in brain, lungs and abdomen. Electrochemical determination of amikacin is a challenge in electroanalysis because it shows no voltammetric peak at the surface of bare electrodes. In this approach, a very simple and easy method for indirect voltammetric determination of amikacin presented in real samples. Gold nanoparticles were electrodeposited at the surface of glassy carbon electrode in constant potential. The effect of several parameters such as time and potential of deposition, pH and scan rates on signal were studied. The cathodic peak current of Au3+ decreased with increasing amikacin concentration. Quantitative analysis of amikacin was performed using differential pulse voltammetry by following cathodic peak current of gold ions. Two dynamic linear ranges of 1.0 × 10−8–1.0 × 10-7 M and 5.0 × 10−7–1.0 × 10-3 M were obtained and limit of detection was estimated 3.0× 10−9 M. The method was successfully determined amikacin in pharmaceutical preparation and human serum. The effect of several interference in determination of amikacin was also studied.

Electrochemical, Spectroscopic, and Computational Investigations on Redox Reactions of Selenium Species on Galena Surfaces

Despite previous studies investigating selenium (Se) redox reactions in the presence of semiconducting minerals, Se redox reactions mediated by galena (PbS) are poorly understood. In this study, the redox chemistry of Se on galena is investigated over a range of environmentally relevant Eh and pH conditions (+0.3 to −0.6 V vs. standard hydrogen electrode, SHE; pH 4.6) using a combination of electrochemical, spectroscopic, and computational approaches. Cyclic voltammetry (CV) measurements reveal one anodic/cathodic peak pair at a midpoint potential of +30 mV (vs. SHE) that represents reduction and oxidation between HSeO3− and H2Se/HSe−. Two peak pairs with midpoint potentials of −400 and −520 mV represent the redox transformation from Se(0) to HSe− and H2Se species, respectively. The changes in Gibbs free energies of adsorption of Se species on galena surfaces as a function of Se oxidation state were modeled using quantum-mechanical calculations and the resulting electrochemical peak shifts are (−0.17 eV for HSeO3−/H2Se, −0.07 eV for HSeO3−/HSe−, 0.15 eV for Se(0)/HSe−, and −0.15 eV for Se(0)/H2Se). These shifts explain deviation between Nernstian equilibrium redox potentials and observed midpoint potentials. X-ray photoelectron spectroscopy (XPS) analysis reveals the formation of Se(0) potentials below −100 mV and Se(0) and Se(−II) species at potentials below −400 mV.

Electrochemical Sensor Based on Poly(Azure B)-DNA Composite for Doxorubicin Determination

A new voltammetric DNA sensor has been developed for doxorubicin determination on the platform of a glassy carbon electrode (GCE) covered with electropolymerized Azure B film and physically adsorbed native DNA. The redox properties of polymeric Azure B were monitored at various pH and scan rates. DNA application decreased the peak currents related to polymeric and monomeric forms of the dye, whereas incubation in doxorubicin solution partially restored the peaks in accordance with the drug and DNA concentration. The relative shift of the cathodic peak current caused by doxorubicin depended on the nominal DNA concentration and its application mode. In optimal conditions, the DNA sensor makes it possible to determine between 0.1 μM to 0.1 nM doxorubicin (limit of detection 7 × 10−11 M). The DNA sensor was tested on commercial doxorubicin formulations and on artificial samples the mimicked electrolyte content of human serum.

Experimental and Theoretical Study on the Interaction of P-Aminophenol Hydrochloride with H2O

UV-Vis absorption spectra, cyclic voltammetry and 1H nuclear magnetic resonance (1H NMR) spectra were applied to explore the hydrogen bond interactions of p-aminophenol hydrochloride (PAH) with H2O. The results indicated the hydrogen bonds were formed in PAH–H2O system. The anodic/cathodic peak potentials and UV-Vis absorption bands of PAH in H2O could be affected due to the interactions. The results of density functional theory, atoms in molecules theory and natural bond orbital analyses further confirmed the existence of hydrogen bonds between the phenolic hydroxyl, –NH3+ protons and Cl− of PAH and H2O. Furthermore, the π-π stacking was suggested between PAH benzene rings from the 1H NMR spectra at higher concentrations.