Square-wave Anodic Voltammetry Research Articles

SENSORS BASED ON TRACK-ETCHED MEMBRANES FOR ELECTROCHEMICAL DETECTION OF CADMIUM IONS

Among electrochemical detection methods, square-wave anodic voltammetry (SW-ASV) is the most popular. However, this method has a number of limitations, for instance, mercury or bismuth electrodes are usually used as a working electrode, which are highly toxic substances. This article is devoted to the study of the use of track-etched membranes based on polyethylene terephthalate as a basis for electrochemical sensors. The modification of the surface of membranes was carried out by the method of photoinitiated graft polymerization of methacrylic acid. Magnetron sputtering with a mask was used to obtain electrodes on both sides of the membrane. The sensor has been tested for sensing toxic cadmium ions in a concentration range of 0.5 to 12.5 mg/L.

Voltammetric determination of lapachol in the presence of lapachones and in ethanolic extract of Tabebuia impetiginosa using an epoxy-graphite composite electrode

Square-wave anodic voltammetry (SWV) was used to determine lapachol using a laboratory-made graphite-epoxy electrode. The electrolytic medium consisted of an aqueous solution containing cationic surfactant CTAB (1.2×10−4molL−1), buffer phosphate (4.0×10−2molL−1; pH6.0) and KNO3 (1.0molL−1). The cationic surfactant improved diffusion and interaction of the analyte with the electrode, producing a reversible process that improved the total current measured by SWV. Lapachol signal was measured at −470mV after pre-concentration at 400mV during 140s, using frequency of 30Hz, pulse amplitude of 40mV with step potential of 20mV. The instrumental limit of detection was 0.029mgL−1 and the dynamic linear range covered two decades. In the presence of β-lapachone (structural isomer) selectivity was achieved by first order derivative of the SWV signal. Lapachol determination in ethanolic extract of heartwood of Tabebuia impetiginosa was accomplished after a simple thin-layer chromatographic separation of the analyte from components of the complex sample. The results agreed (at 95% confidence level) with the ones achieved by using high performance liquid chromatography with absorciometric detection.

Carbon paste electrode modified with ferrimagnetic nanoparticles for voltammetric detection of the hormone estriol

A very simple, novel and environmentally-friendly electrochemical detector for estriol, based on a carbon paste electrode modified with ferrimagnetic nanoparticles, is proposed herein. The ferrimagnetic nanoparticles increase the surface area of the electrode and act as a catalyst for the electrochemical reaction of estriol. Estriol is an estrogen naturally produced by women during pregnancy. Its imbalance may engender disruption of the endocrine system, thereby impairing human growth and reproduction. Estriol is also considered to be an emergent pollutant. The proposed modified carbon paste electrode was used for the determination of estriol by anodic square-wave voltammetry. In 0.1molL−1 B-R buffer (pH6.0), estriol presented a well-defined single oxidation peak at +0.68V, indicating that under these conditions the electrochemical process is irreversible. The overall reaction rate is controlled by an adsorption step. Two protons and two electrons are involved in the estriol oxidation. The calibration curve for estriol showed good linearity in the concentration range of 0.86 to 32.0ppm (R2=0.997). The detection and quantification limits achieved were 0.79 and 2.41ppm, respectively. The proposed modified electrode was successfully applied to the analysis of pharmaceutical and simulated urine samples; the results being comparable to those obtained using the UV–vis technique.

Electroanalytical determination of Azapropazone at Glassy Electrode Using Differential Pulse and Anodic Square-Wave Voltammetry in Pure Formulation and Pharmaceutical Formula

A sensitive electroanalytical method for determination of azapropazone has been investigated on the basis of the enhancement electrochemical response at glassy carbon electrode during oxidation of azapropazone, Cyclic voltammetric undergo one irreversible anodic peak at Ep = 0.48 mV in Britton - Robinson (BR) (pH 4.0). Cyclic voltammetric study indicated that the oxidation process is irreversible and adsorption controlled. The number of exchanged electrons in the electro -oxidation process was obtained. Differential pulse voltammetry (DPV) and square wave voltammetry (SWV) were studied and a linear calibration obtained from: 0.0014– 0.026µg/ml, 0.014–0.134µg/ml using DPV and SWV respectively. The RSD for five measurements were found in the ranges: 0.854% and 0.911% for DPV and SWV, respectively. Precision and accuracy of the developed method was checked by recovery studies. The method was applied to determine azapropazone in pure form, pharmaceutical formulations, and compared with official methods.

Electrooxidation of trifloxystrobin at the boron-doped diamond electrode: electrochemical mechanism, quantitative determination and degradation studies

ABSTRACTThe boron-doped diamond (BDD) presents attractive electrochemical sensing characteristics that are useful in analytical applications based on voltammetry and amperometry. It has a wide potential window in aqueous solutions enabling the quantification of the fungicide trifloxystrobin, measured at +1744 mV (versus Ag/AgCl), by square-wave anodic voltammetry in a Britton–Robinson (BR) buffer (0.04 mol L−1; pH 4.00)/acetonitrile 70/30% v/v. The activation of the electrode was made using galvanostatic chronopotentiometry and cyclic voltammetry (CV). The linear analyte addition curve, Ip (µA) = (1.0 × 10–1 ± 4.8 × 10–6) C (mol L−1) + (8.8 × 10–2 ± 1.1 × 10–3); R2 = 0.997, was obtained using amplitude of 40 mV, frequency of 30 Hz, step potential of 20 mV. The instrumental limit of detection (LOD) was 1.4 × 10–7 mol L−1 (0.058 mg L−1) and the dynamic linear range covered three decades (up to 1 × 10–5 mol L−1 or 4.1 mg L−1). The samples were analysed with recoveries about 80% in orange juice samples and from 92.4% to 104.0% in water samples. A study to evaluate potential interferences was made in the presence of other fungicides. Diagnostic studies indicated that oxidation of trifloxystrobin in aqueous medium at the surface of the BDD is irreversible, involving two steps, each one with two electrons. The UV degradation of trifloxystrobin was evaluated using the proposed electrochemical method and the kinetics of degradation established with half-life of 1.07 min.

Assessment of metabolic activity of human cells in solution and in polymer matrix with the use of metabolite-sensitive sensors

We developed metabolite-sensitive electrochemical sensors on the basis of electrodes modified with a thick film of carbon nanotubes. Modified electrodes provide efficient pre-adsorption of cellular metabolites and their sensitive detection using anodic square-wave voltammetry. On the electrode surface both adhered and non-adhered human cells produce three oxidation peaks at the potentials of +0.82, +1.05, and +1.17V attributed to three groups of cellular metabolites: amino acid-derived antioxidants including glutathione, guanine nucleotides, and also adenine nucleotides including ATP. The electrochemical response was well correlated with cell viability, intracellular ATP level and induction of apoptosis, as determined by independent assays. Developed sensors allow for robust and cost-effective assessment of ATP in cells in contrast to enzyme-based electrodes and conventional bioluminescent assay. Results can be used for rapid analysis of human cells for the purpose of medical diagnostics, transplantology, and toxicological screening. Additionally, we combined modified electrodes with human cells entrapped in agarose matrix. The resulting biosensor allowed for electrochemical monitoring of metabolic activity and death of cells within polymeric matrix that is of interest for tissue engineering applications.

A highly sensitive method for determination of β-blocker drugs using a Nafion-coated glassy carbon electrode

The electrochemical response of bisoprolol fumarate (BF) and propranolol hydrochloride (PR) is significantly enhanced by immobilization of a Nafion film on the surface of the glassy carbon electrode. The positively charged drug molecules were accumulated in 0.1 mol L −1 sulfuric acid solution at a potential of +0.6 V for 120 s, and then determined by square-wave anodic voltammetry. The enhancement mechanism and effect factors such as pH value, mass of Nafion, accumulation potential and pre-concentration time, were explored. The peak current is proportional to the concentration in the range from 5 × 10 −8 to 5 × 10 −7 mol L −1 for BF and from 8 × 10 −8 to 6 × 10 −7 mol L −1 for PR, with the sensitivities of 1.49 × 10 8 and 2.47 × 10 7 μA mol −1 L, respectively. The modified electrode was used to determine both β-blockers in commercial tablets. The quantification of BF in urine samples with no prior extraction was carried out after selective accumulation at the electrode surface under stirring. Together with low cost and ease preparation, the modified electrode is a promising sensor in electroanalysis, not only for the detection of BF and PR, but also for other β-blocker drugs.

Screen-Printed Electrodes Modified by Bismuth Film for the Determination of Released Lead in Moroccan Ceramics

Screen-printing technology is a particularly attractive technique for the mass production of cheap and disposable sensors, and the use of screen-printed electrodes (SPEs) in conjunction with portable, electrochemical instrumention greatly facilitates the feasibility of on-site testing. In this work, a simple, electrochemical method using screen-printed probes has been applied to test for the presence of released lead (Pb) in the glazes of different ceramic tajines collected randomly from a local market square in Morocco. Square-wave anodic voltammetry (SWAV) was employed with SPEs that had been modified with a bismuth film and 5 µl of 0.5% nafion (SPEBi-Na). This probe displayed excellent linear behavior over the examined concentration range, from 5 to 80 µg/L Pb2+ in 100 mM acetate buffer, pH 5, with a detection limit of 4 ppb for lead and (r2 = 0.9972). The good reproducibility obtained with this system led us to apply it to determine lead in this typical Moroccan cookware under conditions relevant to its use. The results showed that when tajines containing 3% acetic acid were heated for 30 min, the amounts of leached lead ranged from 16.8 to 26.4 ppm. When the tajines contains lemon instead of 3% acetic acid and was heated for 30 min, then amounts of lead released exceeded 37 ppm. These values are greater than the allowed maximum concentrations in the United States and Canada.

Functionalised resin-modified carbon paste sensor for the voltammetric determination of Pb(II) within a wide concentration range

A carbon paste electrode bulk-modified with a functionalised macroporous resin is described as a voltammetric sensor for Pb(II) ions. The commercially available product, QuadraPure™TU, admixed into the paste at a ratio of 30% (v/v), contains thiourea residues that act as a highly effective functional group for chelating Pb(II). By combining with square-wave anodic voltammetry and “open-circuit” accumulation, the stripping peak of lead in 0.1 M acetate buffer could be calibrated over a wide concentration range of 0.005–5 mg l −1 Pb, with possible extension up to 25 mg l −1, when the signal of interest was not seriously affected by the presence of other common metals. Applicability of the sensor in practical analysis has been tested on selected water samples or a certified reference material and the respective results agreed well to those obtained by ICP-MS and to the content declared.

Selective and sensitive hydroxypropyl-beta-cyclodextrin based sensor for simple monitoring of (+)-catechin in some commercial drinks and biological fluids

(+)-Catechin (CAT) was considered as a polyphenolic compound abundantly contained in plants. It exerts protective effect against cancer, inflammatory and cardiovascular diseases. These protective effects are mainly attributed to its antioxidative activity by scavenging free radicals. Therefore, the need of simple, selective and sensitive monitoring of (+)-catechin in commercial drinks and biological fluids is crucial. A new selective and sensitive voltammetric quantification of (+)-catechin was investigated at low cost hydroxypropyl-beta-cyclodextrin modified carbon paste sensor in acidic solutions. The constructed sensor was treated in simple and fast manner to increase its stability for catechin determination. The effect of solution and instrumental parameters was investigated by using osteryoung square-wave anodic voltammetry (OSWAV) at pH 2.20 and differential pulse cathodic voltammetry (DPCV) at pH 4.40 in 0.10 M Britton-Robinson buffer. Acidic solutions were chosen to increase the stability of (+)-catechin, reduce its adsorption on the sensor surface and increase the selectivity of proposed method. Cyclic voltammetry (CV) was used to elucidate the electrochemical mechanism of catechin at the modified electrochemical sensor. A linear range up to 7.20 and 4.20 μg mL −1 of catechin was achieved in anodic and cathodic voltammetry, respectively. The method gave reproducible and reliable results with 1.50 (g mL −1 catechin (S.D. 0.062). Limit of detection of 0.12 and 0.30 ng mL −1 and limit of quantification (LOQ) of 1.10 and 2.80 ng mL −1 were easily achieved using anodic and cathodic voltammetry, respectively. Selectivity of the proposed procedure was estimated by testing recovery and adding the most interfering metal ions and/or organic compounds. The proposed method was applied successfully to selective determination of catechin in some commercial drinks like tea, cocoa and coffee with acceptable recovery range (98–102%). The extraction of catechin was rather simple, making it suitable for studies with a large number of commercial samples. Furthermore, the application to urine samples without pretreatment was achieved and statistically confirmed at 95% confidence level. It was easy to analyze catechin in urine down to 0.55 ng mL −1.