Search

Electrodes modified with gold particles, multi-walled carbon nanotubes, an ionic liquid based on 1-butyl-3-methylimidazolium hexafluorophosphate, and a composite derived from these materials have been developed for the voltammetric determination of sulfamethazine, sulfacetamide, and sulfathiazole. Cyclic voltammetry reveals that modifying the surface of a glassy carbon electrode with gold particles, a composite of carbon nanotubes, and an ionic liquid increases its effective surface area. Electrochemical impedance data indicate that the rate of electron transfer on the modified electrodes surpasses that on the unmodified ones. The composite electrode containing gold particles, carbon nanotubes, and the ionic liquid, exhibited the best performance, was utilized for the amperometric determination of sulfonamides in a batch-injection analysis system. Optimal parameters for the determination of sulfonamides in the batch-injection setup were found. The relationship between the analytical signal and the concentration of the compounds on the logarithmic coordinates is linear, ranging from 1 × 10–8 to 5 × 10–3 M for sulfamethazine and sulfacetamide, and from 1 × 10–7 to 5 × 10–3 M for sulfathiazole. The proposed method for determining sulfonamides has been tested in ananalysis of pharmaceutical preparations. [ABSTRACT FROM AUTHOR]

A method was developed to fabricate a glassy carbon electrode with electrodeposited palladium particles and a molecularly imprinted polymer derived from nicotinamide. This approach enables the determination of dopamine in the presence of structurally related compounds. The incorporation of a polymer featuring specific recognition sites tailored to the template molecule significantly enhanced the sensitivity and selectivity of dopamine detection. The immobilization of palladium particles on the electrode surface further improved the selectivity of voltammetric dopamine determination, even in the presence of adrenaline and noradrenaline, which exhibited a 200 mV difference in oxidation peak potentials. The analytical signal showed a linear bilogarithmic dependence on dopamine concentration within the range 5.0 × 10–9 to 5.0 × 10–3 M. This method was successfully applied to an analysis of urine samples, demonstrating its practical utility in real-world applications. [ABSTRACT FROM AUTHOR]

In this paper, we describe the use of a screen-printed graphite electrode modified with a two-dimensional leaf-like zeolitic imidazolate framework-L (Zn), ZIF-L (Zn) for the deter¬mination of sulphite. We started by using linear sweep voltammetry to investigate the redox properties of the modified electrode at different scan rates (10 to 400 mV s-1). Next, we evaluated sulphite oxidation in the modified electrode. Using differential pulse voltammetry (DPV), the linear dynamic range of 0.04-900.0 µM and the limit of detection (3s/m) of 0.01 μM were obtained. DPV was also used to quantify sulphite in various real samples using the standard addition method.

Background and purpose: Dopamine has an impact on the cardiovascular, endocrine, renal, and central neurological systems. Electrochemical techniques are becoming more and more popular among researchers as a way to assess dopamine and uric acid levels. Experimental approach: Using electrochemical techniques, a new Universitet i Oslo MOF (UiO-66)-graphene oxide nanocomposite-modified carbon paste electrode was created to investigate the electrooxidation of uric acid and dopamine as well as their combinations. At the redesigned electrode, uric acid and dopamine were detected concurrently in a very sensitive way using differential pulse voltammetry (DPV). Key results: Dopamine DPV peak currents increase in a linear fashion at doses between 0.05 and 600.0 µM. Conclusion: Uric acid and dopamine levels in urine and dopamine injection samples may be determined with the help of the proposed sensor, which is reasonably priced and performs well.

Modified electrodes based on gold particles, mixed-valence ruthenium oxides, and a binary system combining these components were developed for the voltammetric determination of ceftriaxone, cefotaxime, and cefoperazone. The electrode with the binary system of gold particles and mixed-valence ruthenium oxides, which exhibited the best performance, was used for the detection of cephalosporins in flow-injection analysis. Optimal conditions for the detection of cephalosporins in a flow-injection system were selected. The dependence of the analytical signal on the concentration of the compounds under consideration is linear on logarithmic coordinates over the range from 5 × 10–7 to 5 × 10–3 M. The proposed procedure was tested in the determination of cephalosporins in pharmaceuticals. [ABSTRACT FROM AUTHOR]

It is found that mixed-valence iridium oxides electrodeposited on the surface of a glassy carbon electrode exhibit catalytic activity in the oxidation of caffeine. In this case, a more pronounced catalytic effect is obtained on an electrode modified with a composite based on a film of a perfluorinated sulfopolymer (Nafion) and mixed-valence iridium oxides. A selective voltammetric method for the determination of caffeine is developed. A linear logarithmic dependence of current on the caffeine concentration is observed in the range from 1 × 10–8 to 5 × 10–3 M. The developed method was used to determine caffeine in energy drinks. [ABSTRACT FROM AUTHOR]

A voltammetric sensor based on a glassy carbon electrode with a layer-by-layer combination of carboxylated multi-walled carbon nanotubes and electropolymerized pyrogallol red has been developed for the determination of eugenol in essential oils. Conditions for obtaining a poly(pyrogallol red) film in potentiodynamic mode in a neutral medium were optimized to provide the best voltammetric response of eugenol. The electrode was characterized using scanning electron microscopy and a set of electrochemical methods. A significant improvement in the voltammetric characteristics of eugenol on the polymer-modified electrode was shown. The electrooxidation parameters of eugenol were calculated, and it was shown that the reaction proceeded with the formation of o-quinone. Under conditions of differential pulse voltammetry in a Britton–Robinson buffer with pH 2.0, the analytical range of eugenol was 0.75−100 μM with a detection limit of 0.73 μM. High selectivity for the determination of eugenol in the presence of inorganic ions and typical phenolic and terpene components of essential oils has been shown. This approach was successfully tested with eugenol-containing essential oils and compared with an independent method. [ABSTRACT FROM AUTHOR]

Simple and rapid determination of Sudan I, a synthetic azo dye banned in the food industry over health concerns, is needed to ensure foodstuff safety and quality. In this study, a voltammetric approach based on Sudan I oxidation at the glassy carbon electrode (GCE) modified with manganese dioxide nanorods (MnO2 NRs) dispersed in hexadecyl pyridinium bromide was developed. The effectiveness of MnO2 NRs as a modifier was confirmed by a 7.9- and 9.2-fold increase in the electroactive surface area and the electron transfer rate, respectively, as compared to GCE. The irreversible electrooxidation of Sudan I was found to be accompanied by proton transfer and controlled by both diffusion and surface processes. Differential pulse voltammetry in phosphate buffer pH 6.5 was used for analytical purposes. The linear response of the electrode to Sudan I was shown in the ranges of 0.050–2.5 and 2.5–25 μM, with a detection limit of 13.5 nM. The developed approach was tested on dried and smoked paprika and Atlantic salmon. The obtained recovery values of 99–101% suggest that there is no matrix effect and that the method can be applied in practice.

Sunset Yellow FCF (SY FCF) is one of the widely used synthetic azo dyes in the food industry whose content has to be controlled for safety reasons. Electrochemical sensors are a promising tool for this type of task. A voltammetric sensor based on a combination of tin and cerium dioxide nanoparticles (SnO2–CeO2 NPs) with surfactants has been developed for SY FCF determination. The synergetic effect of both types of NPs has been confirmed. Surfactants of various natures (sodium lauryl sulfate (SLS), Brij® 35, and hexadecylpyridinium bromide (HDPB)) have been tested as dispersive media. The best effects, i.e., the highest oxidation currents of SY FCF, have been observed in the case of HDPB. The sensor demonstrates a 4.5-fold-higher electroactive surface area and a 38-fold-higher electron transfer rate compared to the bare glassy carbon electrode (GCE). The electrooxidation of SY FCF is an irreversible, two-electron, diffusion-driven process involving proton transfer. In differential pulse mode in Britton–Robinson buffer (BRB) pH 2.0, the sensor gives a linear response to SY FCF from 0.010 to 1.0 μM and from 1.0 to 100 μM with an 8.0 nM detection limit. The absence of an interferent effect from other typical food components and colorants has been shown. The sensor has been tested on soft drinks and validated with the standard chromatographic method. [ABSTRACT FROM AUTHOR]

The control of the precise concentration of steroid hormones and their synthetic analogs in biomedical objects is a relevant analytical task. A method for selective and highly sensitive simultaneous amperometric determination of adrenaline, melatonin, and cortisol with the use of a two-detector flow-injection system is developed. Screen-printed carbon electrodes (SPE) with one or two working electrodes modified with a gold–palladium binary system that exhibits catalytic activity upon electrooxidation of the organic compounds under consideration are used as detectors. The high sensitivity of determination is attributed to the catalytic properties of the metal modifier: the transition from the metal to the binary system leads to an increase in the catalytic oxidation current of hormones. The selectivity of determination of adrenaline in the presence of melatonin and cortisol is provided by the difference in the oxidation potentials of the hormones on the proposed electrode. For selective determination of melatonin and cortisol, the surface of the modified working electrode is coated with a Nafion film. The difference of potentials of the peaks of oxidation of adrenaline, melatonin, and cortisol on such an electrode is 300 mV. The proposed method is tested in the analysis of urine samples. The flow-injection scheme is supplemented with a dialyzer and a chromatographic minicolumn to eliminate the interfering effect of electrophilic compounds. The linear bilogarithmic dependence of the analytical signal on the concentration of adrenaline, melatonin, and cortisol is observed in the ranges of 5.0 × 10–10–5.0 × 10–3, 5.0 × 10–11–5.0 × 10–3, and 5.0 × 10–12–5.0 × 10–3 mol/L, respectively. Amperometric determination of the hormones in the flow-injection system leads to an increase in the productivity of the analysis and a decrease in the consumption of the sample and makes it possible to automate the process. [ABSTRACT FROM AUTHOR]

The electrochemical study of 2‐Sulfanylidene‐1,3‐thiazolidin‐4‐one (rhodanine, R) was performed on a glassy carbon working electrode by using three methods: differential pulse voltammetry (DPV), cyclic voltammetry (CV), and linear sweep voltammetry (LSV) at rotating disk electrode voltammetry (RDE). The CV, DPV, and LSV at RDE curves for R were recorded at different concentrations in 0.1 M TBAP/CH3CN. Polymeric films were formed by successive cycling at different potentials and by controlled potential electrolysis. The film formation was proved by recording the CV curves of the chemically modified electrodes (CMEs) in transfer solutions containing ferrocene in 0.1 M TBAP/CH3CN. The obtained CMEs were used for the detection of heavy metal ions. Synthetic samples of heavy metal ions (Cd (II), Pb (II), Cu (II), Hg (II)) of concentrations between 10−7 and 10−5 M were analyzed using CMEs prepared in different conditions. The most intense signal was obtained for Pb(II) ion (estimated detection limit = 10−7 M), which shows that these CMEs can be used for Pb(II) ion detection. The ability of R to form complexes with Pb(II) ion was also tested by UV‐Vis spectrometry. The obtained results showed the formation of Pb(II)R2 as the most stable complex. [ABSTRACT FROM AUTHOR]

Sulfur-containing antioxidants are an important part of the antioxidant defense systems in living organisms under the frame of a thiol–disulfide equilibrium. Among them, l-cysteine, l-homocysteine, l-methionine, glutathione, and α-lipoic acid are the most typical representatives. Their actions in living systems are briefly discussed. Being electroactive, sulfur-containing antioxidants are interesting analytes to be determined using various types of electrochemical sensors. Attention is paid to the chemically modified electrodes with various nanostructured coverages. The analytical capabilities of electrochemical sensors for sulfur-containing antioxidant quantification are summarized and discussed. The data are summarized and presented on the basis of the electrode surface modifier applied, i.e., carbon nanomaterials, metal and metal oxide nanoparticles (NPs) and nanostructures, organic mediators, polymeric coverage, and mixed modifiers. The combination of various types of nanomaterials provides a wider linear dynamic range, lower limits of detection, and higher selectivity in comparison to bare electrodes and sensors based on the one type of surface modifier. The perspective of the combination of chromatography with electrochemical detection providing the possibility for simultaneous determination of sulfur-containing antioxidants in a complex matrix has also been discussed. [ABSTRACT FROM AUTHOR]

Major depressive disorder is a widespread condition with antidepressants as the main pharmacological treatment. However, some patients experience concerning adverse reactions or have an inadequate response to treatment. Analytical chromatographic techniques, among other techniques, are valuable tools for investigating medication complications, including those associated with antidepressants. Nevertheless, there is a growing need to address the limitations associated with these techniques. In recent years, electrochemical (bio)sensors have garnered significant attention due to their lower cost, portability, and precision. Electrochemical (bio)sensors can be used for various applications related to depression, such as monitoring the levels of antidepressants in biological and in environmental samples. They can provide accurate and rapid results, which could facilitate personalized treatment and improve patient outcomes. This state-of-the-art literature review aims to explore the latest advancements in the electrochemical detection of antidepressants. The review focuses on two types of electrochemical sensors: Chemically modified sensors and enzyme-based biosensors. The referred papers are carefully categorized according to their respective sensor type. The review examines the differences between the two sensing methods, highlights their unique features and limitations, and provides an in-depth analysis of each sensor. [ABSTRACT FROM AUTHOR]

The electrochemical polymerization of suitable monomers is a powerful way to create voltammetric sensors with improved responses to a target analyte. Nonconductive polymers based on phenolic acids were successfully combined with carbon nanomaterials to obtain sufficient conductivity and high surface area of the electrode. Glassy carbon electrodes (GCE) modified with multi-walled carbon nanotubes (MWCNTs) and electropolymerized ferulic acid (FA) were developed for the sensitive quantification of hesperidin. The optimized conditions of FA electropolymerization in basic medium (15 cycles from −0.2 to 1.0 V at 100 mV s−1 in 250 µmol L−1 monomer solution in 0.1 mol L−1 NaOH) were found using the voltammetric response of hesperidin. The polymer-modified electrode exhibited a high electroactive surface area (1.14 ± 0.05 cm2 vs. 0.75 ± 0.03 and 0.089 ± 0.003 cm2 for MWCNTs/GCE and bare GCE, respectively) and decreased in the charge transfer resistance (21.4 ± 0.9 kΩ vs. 72 ± 3 kΩ for bare GCE). Under optimized conditions, hesperidin linear dynamic ranges of 0.025–1.0 and 1.0–10 µmol L−1 with a detection limit of 7.0 nmol L−1 were achieved, which were the best ones among those reported to date. The developed electrode was tested on orange juice and compared with chromatography. [ABSTRACT FROM AUTHOR]

The review covers the specific features of the structure of flavanones and a critical review of methods for their determination in various samples. The data are summarizes according to the methods of analysis: chromatographic, electrophoretic, spectral, and electrochemical. Analytical possibilities of each group of methods and their advantages and disadvantages are discussed. Special attention is paid to the use of chemically modified electrodes based on carbon nanomaterials, 3D nanoporous metal structures, composites of metal oxides and sulfide nanoparticles or dyes with carbon nanomaterials, and also combinations of modifiers of various types in flavanone voltammetry. [ABSTRACT FROM AUTHOR]

Medicinal plants are an important source of bioactive compounds with a wide spectrum of practically useful properties. Various types of antioxidants synthesized in plants are the reasons for their application in medicine, phytotherapy, and aromatherapy. Therefore, reliable, simple, cost-effective, eco-friendly, and rapid methods for the evaluation of antioxidant properties of medicinal plants and products on their basis are required. Electrochemical methods based on electron transfer reactions are promising tools to solve this problem. Total antioxidant parameters and individual antioxidant quantification can be achieved using suitable electrochemical techniques. The analytical capabilities of constant-current coulometry, potentiometry, various types of voltammetry, and chrono methods in the evaluation of total antioxidant parameters of medicinal plants and plant-derived products are presented. The advantages and limitations of methods in comparison to each other and traditional spectroscopic methods are discussed. The possibility to use electrochemical detection of the antioxidants via reactions with oxidants or radicals (N- and O-centered) in solution, with stable radicals immobilized on the electrode surface, via oxidation of antioxidants on a suitable electrode, allows the study of various mechanisms of antioxidant actions occurring in living systems. Attention is also paid to the individual or simultaneous electrochemical determination of antioxidants in medicinal plants using chemically modified electrodes. [ABSTRACT FROM AUTHOR]

The catalytic activity of particles of gold, cobalt, and a gold–cobalt binary system electrodeposited on the surface of planar carbon electrodes was found in the oxidation of glucose in a neutral medium. The amperometric response of a screen-printed electrode modified with a gold–cobalt binary system was used as an analytical signal in the determination of glucose in a sequential injection system. The linear logarithmic dependence of current on the glucose concentration was observed in the range from 5 × 10–8 to 5 × 10–2 M. The use of a screen-printed electrode modified with a gold–cobalt binary system as an amperometric detector in a sequential injection system makes it possible to selectively determine glucose in saliva in the concentration range used for medical diagnosis. [ABSTRACT FROM AUTHOR]

Featured Application: Direct voltammetric determination of brilliant blue FCF and tartrazine in soft and isotonic sports drinks. Synthetic colorants, in particular tartrazine and brilliant blue FCF, are widely used in food chemistry and technology although they can give negative health effects of various severities. Therefore, sensitive, selective, simple, and reliable methods for the quantification of these dyes are required. A glassy carbon electrode (GCE) modified with manganese dioxide nanorods (MnO2 NR) dispersed in cetylpyridinium bromide gives a sensitive response to tartrazine and brilliant blue FCF in mixtures. Electrode modification provides a 7.9-fold increase in the electroactive surface area and a 72-fold decrease in electron transfer resistance. Simultaneous voltammetric quantification of colorants was performed in phosphate buffer pH 7.0 in differential pulse mode. The linear dynamic ranges of 0.10–2.5 and 2.5–15 µM of tartrazine and 0.25–2.5 and 2.5–15 µM of brilliant blue FCF were obtained with the limits of detection of 43 and 41 nM, respectively. The advantage of the sensor developed is the high selectivity of response in the presence of typical interferences (inorganic ions, saccharides, ascorbic and sorbic acids) and other food colorants (riboflavin, indigo carmine, and sunset yellow). The practical applicability of the approach is shown in soft and isotonic sports drinks and is validated by comparison to chromatography. [ABSTRACT FROM AUTHOR]

Isopropylmethylphenols, namely thymol and carvacrol, are natural phenolic monoterpenoids with a wide spectrum of bioactivity making them applicable in the cosmetic, pharmaceutical, and food industry. The dose-dependent antioxidant properties of isopropylmethylphenols require their quantification in real samples. Glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNTs) and electropolymerized thymolphthalein has been developed for the sensitive quantification of isopropylmethylphenols. Conditions of thymolphthalein electropolymerization (monomer concentration, number of cycles, and electrolysis parameters) providing the best response to thymol have been found. Scanning electron microscopy and electrochemical methods confirm the effectivity of the electrode developed. The linear dynamic ranges of 0.050–25 and 25–100 µM for thymol and 0.10–10 and 10–100 µM for carvacrol with detection limits of 0.037 and 0.063 µM, respectively, have been achieved in differential pulse mode in Britton–Robinson buffer pH 2.0. The selectivity of the isopropylmethylphenols response in the presence of typical interferences (inorganic ions, saccharides, ascorbic acid) and other phenolics (caffeic, chlorogenic, gallic and rosmarinic acids, and quercetin) is a significant advantage over other electrochemical methods. The electrode has been used in the analysis of oregano and thyme spices. Total isopropylmethylphenols contents have been evaluated after a single sonication-assisted extraction with methanol. [ABSTRACT FROM AUTHOR]

The possibility of psilocin electrochemical determination over cobalt (III) oxyhydroxide-modified anode is evaluated from the mathematical point of view. Psilocin is thereby oxidized yielding either micro- or macromolecular product, being both of them important for the economical and green conducting polymer composite for electrocatalysis, electroanalysis and energy conversion. The analysis of the correspondent mathematical model confirms, that, despite of the high probability of the oscillatory behavior, the electrochemical process is efficient from both analytical and synthetical point of view.

Cognac and brandy quality control is an actual topic in food analysis. Aromatic aldehydes, particularly syringaldehyde and vanillin, are one of the markers used for these purposes. Therefore, simple and express methods for their simultaneous determination are required. The voltammetric sensor based on the layer-by-layer combination of multi-walled carbon nanotubes (MWCNTs) and electropolymerized p-aminobenzoic acid (p-ABA) provides full resolution of the syringaldehyde and vanillin oxidation peaks. Optimized conditions of p-ABA electropolymerization (100 µM monomer in Britton–Robinson buffer pH 2.0, twenty cycles in the polarization window of −0.5 to 2.0 V with a potential scan rate of 100 mV·s−1) were found. The poly(p-ABA)-based electrode was characterized by scanning electron microscopy (SEM), cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). Electrooxidation of syringaldehyde and vanillin is an irreversible two-electron diffusion-controlled process. In the differential pulse mode, the sensor allows quantification of aromatic aldehydes in the ranges of 0.075–7.5 and 7.5–100 µM for syringaldehyde and 0.50–7.5 and 7.5–100 µM for vanillin with the detection limits of 0.018 and 0.19 µM, respectively. The sensor was applied to cognac and brandy samples and compared to chromatography. [ABSTRACT FROM AUTHOR]

Previous studies performed on 2-(azulen-1-yldiazenyl)-5-phenyl-1,3,4-thiadiazole (T) showed that T is a ligand with complexing properties towards heavy metals (HMs) in solution and can be attached to electrode surfaces. Films of T were deposited on glassy carbon to obtain chemically modified electrodes (T-CMEs), either through scanning or using controlled potential electrolysis in tetrabutylammonium perchlorate in acetonitrile. They were investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), and spectroelectrochemistry. All methods provided evidence for showing the formation of insulating films, with properties depending on their electropolymerization potential. CV and EIS studies of T-CMEs in tetrabutylammonium perchlorate in acetonitrile as supporting electrolyte, and in the presence of a ferrocene redox probe resulted in a thickness of ~10 µm, an active surface area about 6 times higher than the geometrical one, and conductivity of about 10−6 S/cm. This characterization performed using voltammetric techniques reveals the symmetry of the reversible anodic and cathodic redox CV peaks for the polymer, while spectroelectrochemistry shows the intensification of the charge transport process through polarons, due to the anodic polarization of the film. [ABSTRACT FROM AUTHOR]

Tartrazine and brilliant blue FCF are synthetic dyes used in the food, cosmetic and pharmaceutical industries. The individual and/or simultaneous control of their concentrations is required due to dose-dependent negative health effects. Therefore, the paper presents experimental results related to the development of a sensing platform for the electrochemical detection of tartrazine and brilliant blue FCF based on a glassy carbon electrode (GCE) modified with MnO2 nanorods, using anodic differential pulse voltammetry. Homogeneous and stable suspensions of MnO2 nanorods have been obtained involving cetylpyridinium bromide solution as a cationic surfactant. The MnO2 nanorods-modified electrode showed a 7.9-fold increase in the electroactive surface area and a 72-fold decrease in the electron transfer resistance. The developed sensor allowed the simultaneous quantification of dyes for two linear domains: in the ranges of 0.10–2.5 and 2.5–15 μM for tartrazine and 0.25–2.5 and 2.5–15 μM for brilliant blue FCF with detection limits of 43 and 41 nM, respectively. High selectivity of the sensor response in the presence of typical interference agents (inorganic ions, saccharides, ascorbic and sorbic acids), other food dyes (riboflavin, indigo carmine, and sunset yellow), and vanillin has been achieved. The sensor has been tested by analyzing soft and isotonic sports drinks and the determined concentrations were close to those obtained involving the chromatography technique. [ABSTRACT FROM AUTHOR]

Sensitive electrodes based on complexing azulene polymer films were prepared by electrochemical deposition on glassy carbon electrodes. The characterization of 4-(azulen-1-yl)-2,6-bis((E)-2-(thiophen-2-yl)vinyl)pyridine (M) and its polymerization were performed by voltammetric methods on glassy carbon disk working electrodes in millimolar solutions of acetonitrile in the presence of 0.1 M tetrabutylammonium perchlorate (TBAP). The films containing complexing (thiophen-2-yl)vinyl symmetrically substituted pyridine fragments were deposited either by scanning or by controlled potential electrolysis (CPE). Investigation and morphological characterization of samples by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Atomic Force Microscopy (AFM), Fourier Transform IR Spectroscopy (FTIR), and fluorescence showed particular features of the CMEs obtained at variable potentials and charges and suggested the conservation the complexing units in the films. The characterization methods for chemically modified electrodes (CMEs) were chosen depending on the desired uses of this monomer for heavy metal sensors or optical applications, respectively. [ABSTRACT FROM AUTHOR]

Tannins are a class of natural phenolic antioxidants represented by oligomers and polymers. Tannic acid (gallotannin) (TA) is one of the most typical compounds widely distributed in plants. It has a wide application area in food technology and as a part of traditional herbal medicine in the treatment of various diseases. TA is one of the standards used in medicinal plant quality control for plants rich in tannins. Therefore, the development of sensitive and simple methods for TA quantification is of practical interest. Glassy carbon electrode modified with multi-walled carbon nanotubes (GCE/MWCNTs) has been developed for the determination of TA in medicinal plants. An improvement in TA voltammetric response has been achieved using modified electrode due to the high electroactive surface area and electron transfer rate vs. bare electrode. TA electrooxidation at the GCE/MWCNTs is an irreversible surface-controlled process involving the transfer of two electrons and two protons in the first step. In differential pulse mode using Britton–Robinson buffer pH 2.0 as the supporting electrolyte, a linear dynamic range of 0.10–7.5 μM with a detection limit of 0.038 μM has been obtained. The method has been applied for the analysis of infusions and decoctions of tannin-containing medicinal plants and compared to the spectrophotometric method. A positive correlation has been observed with ferric reducing power reflecting the total content of phenolic compounds in the sample.

Voltammetric sensors based on CeO2, SnO2, CeO2·Fe2O3 nanoparticles (NPs) and MnO2 nanorods (NRs) were developed for the quantification of various organic substances. Surfactant media were applied as dispersive agents for metal oxide nanomaterials, providing a high stability of the dispersions after sonication and a decrease in the NPs’ size, as well as the preconcentration of the target analytes at the sensor surface due to the hydrophobic interactions between the surfactant and the analyte molecules. Natural phenolics (quercetin, rutin, gallic acid, taxifolin, eugenol, vanillin, and hesperidin), propyl gallate, α-lipoic acid, and synthetic food colorants (tartrazine, brilliant blue FCF, and sudan I) were studied as analytes. The effect of the nature and concentration of the surfactant on the target analyte response was evaluated. Cationic surfactants (cetylpyridinium (CPB) or cetyltriphenylphosphonium bromides (CTPPB)) showed the best effect for the majority of the analytes. Wide linear dynamic ranges and low detection limits were obtained and were improved vs. reported to date. The simultaneous quantification of tartrazine and brilliant blue FCF was achieved with a high selectivity. The practical applicability of the sensors was shown on the real samples and was validated by comparison to independent methods.

Sulfur-containing antioxidants are an important part of the antioxidant defense systems in living organisms under the frame of a thiol–disulfide equilibrium. Among them, l-cysteine, l-homocysteine, l-methionine, glutathione, and α-lipoic acid are the most typical representatives. Their actions in living systems are briefly discussed. Being electroactive, sulfur-containing antioxidants are interesting analytes to be determined using various types of electrochemical sensors. Attention is paid to the chemically modified electrodes with various nanostructured coverages. The analytical capabilities of electrochemical sensors for sulfur-containing antioxidant quantification are summarized and discussed. The data are summarized and presented on the basis of the electrode surface modifier applied, i.e., carbon nanomaterials, metal and metal oxide nanoparticles (NPs) and nanostructures, organic mediators, polymeric coverage, and mixed modifiers. The combination of various types of nanomaterials provides a wider linear dynamic range, lower limits of detection, and higher selectivity in comparison to bare electrodes and sensors based on the one type of surface modifier. The perspective of the combination of chromatography with electrochemical detection providing the possibility for simultaneous determination of sulfur-containing antioxidants in a complex matrix has also been discussed.

[Display omitted] • Carbon-coated Fe 3 O 4 derived from MOF have high catalytic activity. • The formation of rGO-Fe@C decreased metal particle aggregation. • The rGO-Fe@C exhibits excellent activity on Hg(II) determination. • The as-fabricated sensor is promising for real water samples analyses. Mercury, a well-known neurotoxicant, mainly occurs as Hg0, Hg2+ or Hg (CH 3) 2 in the environment. Therefore, there is an urgent need to develop new analytical methods to rapidly screen for mercury in natural water. In this work, rGO-MIL-101(Fe) was fabricated using reduced graphene oxide (rGO) and MIL-101 by one spot solvothermal method, and then was pyrolyzed at 500 °C to yield carbon-coated Fe 3 O 4 dispersed on rGO (hereafter rGO-Fe@C). The rGO-Fe@C was characterized by SEM, TEM, TGA, XRD, XPS and Raman spectroscopic methods for its morphological features, particulate size & gradations, element redox states. An electrochemical sensing interface was constructed for Hg2+ determination using rGO-Fe@C modified glassy carbon electrode(rGO-Fe@C/GCE) by square wave anode stripping voltammetry (SWASV). The rGO-Fe@C/GCE exhibits high sensitivity for Hg2+ determination with a sensitivity of 34.47 μA/μM and a limit detection of 4.5 nM. The sensitive mechanism of Hg2+ in the electrochemical interface was investigated by XPS and DFT calculations. The presence of common cations as Cd2+, Cu2+ and Pb2+ in comparable molarities does not interfere with Hg2+ detection. Moreover, the electrode sensor possesses good stability and reproducibility for repetitive analysis of samples. The rGO-Fe@C/GCE sensor can be used in Hg2+ detection with minimal matrix interference by ions ubiquitous in natural water. [ABSTRACT FROM AUTHOR]

Acyclovir and valacyclovir are oxidized on a glassy carbon electrode (GCE) with immobilized reduced graphene oxide coated with a polyglycine film. We selected the conditions for forming a polymer film, reducing graphene oxide on the GCE, and recording the maximum catalytic current on the composite surface. A procedure was developed for the selective voltammetric determination of acyclovir and valacyclovir on an electrode with a reduced graphene oxide–polyglycine film composite. A method is proposed for the amperometric detection of guanine-based antiviral drugs with this modified electrode under the conditions of flow-injection analysis. The dependence of the analytical signal on the concentration of acyclovir and valacyclovir is linear up to 5 × 10–6 M in the static mode and up to 1 × 10–7 M in the flow-injection system. The developed voltammetric method for determining acyclovir and valacyclovir was tested in the analysis of pharmaceutical preparations. [ABSTRACT FROM AUTHOR]

We created glassy carbon electrodes (GCEs) modified with CeO2 nanoparticles and various surfactants and determined the voltammetric characteristics of tartrazine oxidation on them. The electrode modified with the cationic surfactant cetyltriphenylphosphonium bromide (CTPPB) ensures a 72.5-fold increase in the oxidation currents of tartrazine compared to a GCE. The oxidation of tartrazine on the CeO2-CTPPB/GCE proceeds irreversibly, involves one electron, and is controlled by surface processes. A procedure was developed for the voltammetric determination of tartrazine on a CeO2-CTPPB/GCE. The analytical range is 1.00–250 µM of tartrazine with a limit of detection of 0.4 µM. The procedure was applied to quantify tartrazine in the Tarkhun beverage. [ABSTRACT FROM AUTHOR]

The electrochemical sensors for carmoisine detection were explored and applied in the field of food safety because of the striking merits of fast detection speed, high sensitivity and easy operation. Herein, we de­veloped a high-performance electrochemical carmoisine sensor based on g-C3N4 and ionic liquids (ILs), prepared by a one-pot hydrothermal synthesis method. Most importantly, the sensing per­formances of electrochemical carmoisine sensors based on g-C3N4 (graphitic carbon nitride)/IL (1-butyl-3-methylimidazolium hexafluorophosphate) are better than the bare carbon paste electrode (CPE) sensors. The detection limit of this sensor (g-C3N4/ILs/CPE) de­ter­mined via differential pulse voltammetry was 0.1 µM over a wide linear range of 0.4–125.0 µM.

Featured Application: Developing new sensing materials. Electrochemical and spectral studies of benzylidenerhodanine (BR) were performed in order to develop new sensors for heavy metals (HMs) based on chemically modified electrodes (CMEs). CMEs were obtained by cycling and by controlled potential electrolysis at different potentials and charges. Film formation was demonstrated by recording the CV curves of CMEs in transfer solutions containing ferrocene in 0.1 M TBAP/CH3CN. BR-CMEs were used for the analysis of HMs. Samples of Cd(II), Pb(II), Cu(II), and Hg(II), each possessing concentrations between 10−7 and 10−5 M, were analyzed by using CMEs prepared in different conditions. The most intense signal was obtained for the Pb(II) ion. These BR-CMEs can be used for the analysis of Pb(II) in monitored waters. An electrochemical study was performed at different concentrations of BR in 0.1 M TBAP/CH3CN on a glassy carbon electrode by differential pulse voltammetry, cyclic voltammetry, and rotating disk electrode voltammetry. The complexation ratio in the homogeneous solution has been established by the Mollard method in acetonitrile solutions. [ABSTRACT FROM AUTHOR]

The electrochemical polymerization of suitable monomers is a powerful way to create voltammetric sensors with improved responses to a target analyte. Nonconductive polymers based on phenolic acids were successfully combined with carbon nanomaterials to obtain sufficient conductivity and high surface area of the electrode. Glassy carbon electrodes (GCE) modified with multi-walled carbon nanotubes (MWCNTs) and electropolymerized ferulic acid (FA) were developed for the sensitive quantification of hesperidin. The optimized conditions of FA electropolymerization in basic medium (15 cycles from −0.2 to 1.0 V at 100 mV s−1 in 250 µmol L−1 monomer solution in 0.1 mol L−1 NaOH) were found using the voltammetric response of hesperidin. The polymer-modified electrode exhibited a high electroactive surface area (1.14 ± 0.05 cm2 vs. 0.75 ± 0.03 and 0.089 ± 0.003 cm2 for MWCNTs/GCE and bare GCE, respectively) and decreased in the charge transfer resistance (21.4 ± 0.9 kΩ vs. 72 ± 3 kΩ for bare GCE). Under optimized conditions, hesperidin linear dynamic ranges of 0.025–1.0 and 1.0–10 µmol L−1 with a detection limit of 7.0 nmol L−1 were achieved, which were the best ones among those reported to date. The developed electrode was tested on orange juice and compared with chromatography.

Isopropylmethylphenols, namely thymol and carvacrol, are natural phenolic monoterpenoids with a wide spectrum of bioactivity making them applicable in the cosmetic, pharmaceutical, and food industry. The dose-dependent antioxidant properties of isopropylmethylphenols require their quantification in real samples. Glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNTs) and electropolymerized thymolphthalein has been developed for the sensitive quantification of isopropylmethylphenols. Conditions of thymolphthalein electropolymerization (monomer concentration, number of cycles, and electrolysis parameters) providing the best response to thymol have been found. Scanning electron microscopy and electrochemical methods confirm the effectivity of the electrode developed. The linear dynamic ranges of 0.050–25 and 25–100 µM for thymol and 0.10–10 and 10–100 µM for carvacrol with detection limits of 0.037 and 0.063 µM, respectively, have been achieved in differential pulse mode in Britton–Robinson buffer pH 2.0. The selectivity of the isopropylmethylphenols response in the presence of typical interferences (inorganic ions, saccharides, ascorbic acid) and other phenolics (caffeic, chlorogenic, gallic and rosmarinic acids, and quercetin) is a significant advantage over other electrochemical methods. The electrode has been used in the analysis of oregano and thyme spices. Total isopropylmethylphenols contents have been evaluated after a single sonication-assisted extraction with methanol.

T This research applied a nanostructured electrochemical sensor with a screen-printed electrode (SPE) for examining the dopamine (DA) electrocatalytic oxidation when uric acid (UA) was present. Cu(salophen) nanostructured modified SPE Cu(salophen)/SPE was employed to investigate the electrochemical behavior of DA. At optimal pH (pH 7.0), oxidation of DA at the modified electrode takes place at a potential around 100 mV less positive than at the unmodified SPE. Chronoamperometry was used to determine the diffusion coefficient of DA (D = 1.96×10-5 cm2 s-1). Differential pulse voltammetry (DPV) showed linear response in the range between 0.2-450.0 μM for DA. The limit of detection (LOD) of DA was computed to be 0.05 μM. Moreover, Cu(salophen)/SPE was employed for determining DA in the presence of UA using DPV. The DPV results showed that at the modified electrode, two well-separated oxidation peaks of DA and UA could be obtained at potentials of 180 and 325 mV, respectively. This separation forms the basis for the co-detection of these two materials on the surface of Cu(salophen)/SPE. This sensor was then employed to determine DA and UA in real specimens.

Synthetic colorants, in particular tartrazine and brilliant blue FCF, are widely used in food chemistry and technology although they can give negative health effects of various severities. Therefore, sensitive, selective, simple, and reliable methods for the quantification of these dyes are required. A glassy carbon electrode (GCE) modified with manganese dioxide nanorods (MnO2 NR) dispersed in cetylpyridinium bromide gives a sensitive response to tartrazine and brilliant blue FCF in mixtures. Electrode modification provides a 7.9-fold increase in the electroactive surface area and a 72-fold decrease in electron transfer resistance. Simultaneous voltammetric quantification of colorants was performed in phosphate buffer pH 7.0 in differential pulse mode. The linear dynamic ranges of 0.10–2.5 and 2.5–15 µM of tartrazine and 0.25–2.5 and 2.5–15 µM of brilliant blue FCF were obtained with the limits of detection of 43 and 41 nM, respectively. The advantage of the sensor developed is the high selectivity of response in the presence of typical interferences (inorganic ions, saccharides, ascorbic and sorbic acids) and other food colorants (riboflavin, indigo carmine, and sunset yellow). The practical applicability of the approach is shown in soft and isotonic sports drinks and is validated by comparison to chromatography.

Gold deposit immobilized on the surface of glassy carbon electrodes (GCE) and included in the polymer film of polyvinylpyrrolidone (Au-PVPr) shows electrocatalytic properties toward tetracycline oxidation. The catalytic effect observed at the GCE modified by gold deposit is expressed in a multiple increase of the current of antibiotic oxidation and in a decrease of the potential on 250 mV in comparison with the GCE. A two-fold increase in the oxidation current of tetracycline has been recorded on the GCE coated by the PVPr film with gold deposit (Au-PVPr-GCE) in comparison with its oxidation at the Au-GCE. The working conditions for the immobilization of the Au-PVPr composite on the GCE have been found. A method for voltammetric determination of tetracycline on the Au-PVPr-GCE has been proposed. Linear dependence of the current at this electrode on the tetracycline concentration has been observed in the range from 1?10–7 to 1?10–3 mol?L–1. The developed voltammetric method has been tested in determination of the tetracycline content in milk.

The working conditions of naringin electropolymerization on the glassy carbon electrode modified with multi-walled carbon nanotubes (MWNT/GCE) under the conditions of potentiodynamic electrolysis have been found. The effect of monomer concentration, polarization window, potential scan rate, and number of cycles on the electrochemical properties of the polynaringin-modified electrode has been evaluated using hexacyanoferrate(II) ions as a redox standard. The best results have been observed for the polymeric coverage obtained from 0.20 mM naringin by tenfold potential cycling in the range of 0.2–0.8 V at a scan rate of 75 mV/s in the Britton-Robinson buffer solution, pH 8.0. The surface of the glassy carbon and modified electrodes has been characterized by scanning electron microscopy, cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The high porosity of the polynaringin layer leads to an increase of the electrode effective surface area in comparison to GCE (8.2 ? 0.3 and 12.6 ? 0.6 mm2 for GCE and polynaringin/MWNT/GCE, respectively). The electrochemical impedance spectroscopy data indicate an increase of the electron transfer rate on the polynaringin-modified electrode in comparison to GCE and MWNT/GCE (6.0 ? 0.5 kΩ vs. 181 ? 5 and 6.8 ? 0.3 kΩ, respectively).

There is an urgent need to develop a highly sensitive detection system for detecting trace amount of food contaminants. The environmental analysis of Sudan I, a carcinogenic azo-dye, has attracted wide attention due to their increasing levels and high toxicities. Several methods have been developed to detect the presence of this compound. For example, analytical methods based on chromatography and spectroscopy has attracted significant attentions for the determination of Sudan I. However, these methods require complex separation processes, expensive equipment, toxic chemicals, long analysis times, and expert staff. Electroanalytical methods can be considered as promising alternative techniques due to their advantages such as simplicity, low cost, high sensitivity, and fast analysis speed. Electroanalytical methods have been also investigated for the determination of Sudan I. Chemically modified electrodes have been widely used to counter the problems of poor sensitivity and selectivity faced at bare electrodes. We have reviewed the materials that have been extensively used to fabricate modified electrode surfaces for detection of Sudan I. The characteristics of the materials that improve the electrocatalytic activity of the modified surfaces are discussed. [ABSTRACT FROM AUTHOR]

Local anesthetics (LAs) are widely used in anesthesiology, ophthalmology, and otolaryngology as well as for treatment of chronic and oncological pain. However, anesthetics can cause adverse effects up to lethal ones. In this work, we cited reviews on chromatographic and spectroscopic methods of local anesthetics determination published earlier, and the main purpose was to review the possibilities and advantages of voltammetric methods used for the LAs determination. The electrochemical behavior, mechanism of LAs transformation on the various working electrodes and analytical parameters of voltammetric methods used for their determination were reviewed in the work. Vast majority of these methods were developed for the most widely used anesthetics in medicine like benzocaine, lidocaine and procaine. Special attention was paid to possible mechanisms of electrochemical oxidation and in some cases reduction of LAs or their derivatives. Voltammetry is used for the determination of LAs in pharmaceutical formulations and in biological fluids. The analytical characteristics in terms of sensitivity, selectivity, reproducibility also were discussed in the article. [ABSTRACT FROM AUTHOR]

We developed an electrode based on multi-walled carbon nanotubes and electropolymerized Sunset Yellow FCF for the simultaneous voltammetric determination of chlorogenic and ferulic acids. Poly(Sunset Yellow) was obtained potentiostatically under chronoamperometric conditions. Variation of the pH of the supporting electrolyte, monomer concentration, and electrolysis conditions showed that the maximum difference between the oxidation potentials of phenolic acids (190 mV) and high currents were achieved for a coating obtained in an alkaline medium from 50 μM monomer solution at a potential of 1.1 V for 30 s. Poly(Sunset Yellow) consists of spherical particles and their aggregates with a diameter of 26–75 nm, which leads to an increase in the effective surface area of the electrode (44.0 ± 0.6 mm2 compared to 26.1 ± 0.6 mm2 for a glassy carbon electrode modified with carbon nanotubes). The data of electrochemical impedance spectroscopy indicate an increase in the rate of electron transfer on modified electrodes. The data of cyclic voltammetry proved that the electrooxidation of phenolic acids on the polymer-modified electrode is controlled by diffusion and proceeds with the participation of two electrons and two protons with the formation of corresponding o-quinones. The linear dynamic range is 0.10–4.0 µM for chlorogenic acid and 0.5–4.0 µM for ferulic acid with the limits of detection 0.076 and 0.098 µM, respectively. The proposed method was applied to determine these acids in coffee. [ABSTRACT FROM AUTHOR]

We developed a method for the selective and sensitive voltammetric determination of ascorbic and oxalic acids. A screen-printed electrode, modified by gold–palladium bimetallic system and exhibiting catalytic activity in the electrooxidation of the organic acids under consideration, was used as a detector. The difference between the potentials of oxidation peaks of these compounds was 400–500 mV. The proposed method enables an in situ voltammetric determination of ascorbic and oxalic acids in citrus fruits and orange juices without sample preparation. The results of the voltammetric determination are comparable with the data of iodometry and permanganometry, which are the recommended methods for the analysis of fruit juices. [ABSTRACT FROM AUTHOR]

In recent years, practical, inexpensive, and highly specific electroanalytical methods based on modified electrodes have been increasingly developed for forensic science. Simple modification of the carbon paste electrode with Schiff base complexes has become a promising strategy to detect and quantify narcotics. In this context, we aimed to develop voltammetric methods to quantify lysergic acid diethylamide (LSD) by using a carbon paste electrode modified with the complex [UO2(Ac-ophen)]·H2O. The use of an aqueous solution of KCl as supporting electrolyte makes the methodology less polluting, which contrasts with methods that still employ toxic solvents. The developed method for Differential Pulse Voltammetry provides a linear response at various concentrations of LSD and affords analytical curves with standard deviation, detection, and quantification limits around 2.45, 0.625, and 2.08 μmol L-1, respectively. The recovery values of 103 and 108% prove that the developed method is suitable for application in forensic science.

The electrochemical characterization of a new synthesized azulene compound (Z)-5-((5-iso­propyl-3,8-dimethylazulen-1-yl)methylene)-2-thioxoimidazolidin-4-one (L) using cyclic vol­tammetry, differential pulse voltammetry and rotating disk electrode is presented. Chemi­cally modified electrodes were obtained by successive scanning or by controlled potential electrolysis using different electrode potentials or charges. The new modified electrodes were tested in solutions containing different concentrations of the following heavy metals: cadmium, lead, mercury and copper. A good analytical response was obtained for Pb2+.

Electrochemical and spectral studies of benzylidenerhodanine (BR) were performed in order to develop new sensors for heavy metals (HMs) based on chemically modified electrodes (CMEs). CMEs were obtained by cycling and by controlled potential electrolysis at different potentials and charges. Film formation was demonstrated by recording the CV curves of CMEs in transfer solutions containing ferrocene in 0.1 M TBAP/CH3CN. BR-CMEs were used for the analysis of HMs. Samples of Cd(II), Pb(II), Cu(II), and Hg(II), each possessing concentrations between 10−7 and 10−5 M, were analyzed by using CMEs prepared in different conditions. The most intense signal was obtained for the Pb(II) ion. These BR-CMEs can be used for the analysis of Pb(II) in monitored waters. An electrochemical study was performed at different concentrations of BR in 0.1 M TBAP/CH3CN on a glassy carbon electrode by differential pulse voltammetry, cyclic voltammetry, and rotating disk electrode voltammetry. The complexation ratio in the homogeneous solution has been established by the Mollard method in acetonitrile solutions.

2,2-di(4-tert-octylphenyl)-1-picrylhydrazyl (DTOPPH?) immobilized on the electrode surface has been proposed as a reagent for the evaluation of antioxidant activity (AOA). The electroreduction parameters of DTOPPH? immobilized on glassy carbon electrode (GCE) modified with carbon nanotubes, cerium and tin dioxide nanoparticles dispersed in surfactants have been studied. The best characteristics (system reversibility and maximal reduction currents) have been obtained on the electrode modified with cerium dioxide nanoparticles and cetylpyridium bromide (CPB). The reduction currents of the immobilized DTOPPH? are decreased in the presence of the phenolic antioxidants allowing application of the electrode created for their AOA evaluation. Five minutes have been shown to be enough for the reaction of antioxidants with the immobilized DTOPPH?. AOA evaluation has been performed under conditions of differential pulse voltammetry. ЕC50 parameter for tannin, quercetin, catechin and ferulic acid has been found and compared with that one based on the reaction with 2,2-diphenyl-1-picrylhydrazyl under the same conditions. The approach developed has been applied for the evaluation of AOA in juices and nectars.