A new voltammetric sensor for the determination of sulfite in water and wastewater using modified-multiwall carbon nanotubes paste electrode

The electrochemical response of a modified-carbon nanotubes paste electrode with p-aminophenol was investigated as an electrochemical sensor for sulfite determination. The electrochemical behaviour of sulfite was studied at the surface of the modified electrode in aqueous media using cyclic voltammetry and square wave voltammetry. It has been found that under the optimum condition (pH 7.0) in cyclic voltammetry, the oxidation of sulfite occurs at a potential about 680?mV less positive than that of an unmodified-carbon nanotubes paste electrode. Under the optimized conditions, the electrocatalytic peak current showed linear relationship with sulfite concentration in the range of 2.0?×?10^?7–2.8?×?10^?4?mol?L^?1 with a detection limit of 9.0?×?10^?8?mol?L^?1 sulfite. The relative standard deviations for ten successive assays of 1.0 and 50.0?µmol?L^?1 sulfite were 2.5% and 2.1%, respectively. Finally, the modified electrode was examined as a selective, simple and precise new electrochemical sensor for the determination of sulfite in water and wastewater samples.     

All-solid-state Cr(III)-selective potentiometric sensor based on Cr(III)-imprinted polymer nanomaterial/MWCNTs/carbon nanocomposite electrode

A novel potentiometric sensor, based on carbon paste electrode (CPE), modified with ion-imprinted polymer (IIP) and multi-walled carbon nanotubes (MWCNTs), is introduced for detection of chromium (III). The IIP nanomaterial was synthesised and characterised by using scanning electron microscopy and Fourier Transform Infrared. The modification of the CPE with the IIP (as a ionophore) resulted in an all-solid-state Cr(III)-selective sensor. However, the presence of appropriate amount of MWCNTs in the electrode composition was found to be necessary to observe Nernstian response. The optimised electrode composition was 76.7% graphite, 14.3% binder, 5% IIP, and 4% CNT. The proposed sensor exhibited Nernstian slope of 20.2 ± 0.2 mV decade^?1 in the working concentration range of 1.0 × 10^?6?1.0 × 10^?1 mol L^?1 (52 µg L^?1–5.2 g L^?1), with a detection limit of 5.9 × 10^?7 mol L^?1 (30.68 µg L^?1) and a fast response time of less than 40 s. It displayed a stable potential response in the pH range of 2–5. It exhibited also high selectivity over some interfering ions. The proposed sensor was successfully applied for the determination of Cr(III) in real samples (sea, river water and soil).     

Electrochemical Detection of Nitrite in Meat and Water Samples Using a Mesoporous Carbon Ceramic SiO2/C Electrode Modified with In Situ Generated Manganese(II) Phthalocyanine

Mesoporous carbon ceramic SiO₂/50 wt % C (S_BET=170 m² g^?1), where C is graphite, were prepared by the sol‐gel method. The materials were characterized using N₂ sorption isotherms, scanning electron microscopy, and conductivity measurements. The matrix was used as support for the in situ immobilization of Mn(II) phthalocyanine (MnPc) on their surface. XPS was used to determine the Mn/Si atomic ratios of the MnPc‐modified materials. Pressed disk electrodes were prepared with the MnPc‐modified matrix, and tested as an electrochemical sensor for nitrite oxidation. The linear response range, sensitivity, detection limit and quantification limit were 0.79–15.74 µmol L^?1, 17.31 µA L µmol^?1, 0.02 µmol L^?1 and 0.79 µmol L^?1, respectively, obtained using cyclic voltammetry. The repeatability of the proposed sensor, evaluated in terms of relative standard deviation was 1.7 % for 10 measurements of a solution of 12.63 µmol L^?1 nitrite. The sensor employed to determine nitrite in sausage meat, river and lake water samples showed to be a promising tool for this purpose.     

Determination of Hydrogen Peroxide Using a Novel Sensor Based on Fe3O4 Magnetic Nanoparticles

Fe₃O₄ magnetic nanoparticles were synthesized by chemical co-precipitation with sodium citrate as a surfactant and were used with chitosan to construct a novel hydrogen peroxide sensor. The electrochemical behavior of hydrogen peroxide at the sensor was investigated by cyclic voltammetry. The composite film electrocatalyzed the reduction of hydrogen peroxide, and the peak current increased linearly with concentration from 1.00 × 10^?5 to 1.00 × 10^?3 mol · L^?1 (R = 0.9974) with a detection limit of 1.53 × 10^?6 mol · L^?1. This novel nonenzyme sensor provided good sensitivity, stability, and precision with potential applications.     

Sensitive immunoassay for the β-agonist ractopamine based on glassy carbon electrode modified with gold nanoparticles and multi-walled carbon nanotubes in a film of poly-arginine

We are presenting an electrochemical immunosensor for the determination of the β-agonist and food additive ractopamine. A glassy carbon electrode (GCE) was modified with gold nanoparticles and a film of a composite made from poly(arginine) and multi-walled carbon nanotubes. Antibody against ractopamine was immobilized on the surface of the modified GCE which then was blocked with bovine serum albumin. The assembly of the immunosensor was followed by electrochemical impedance spectroscopy. Results demonstrated that the semicircle diameter increases, indicating that the film formed on the surface hinders electron transfer due to formation of the antibody-antigen complex on the modified electrode. Under optimal conditions, the peak current obtained by differential pulse voltammetry decreases linearly with increasing ractopamine concentrations in the 0.1 nmol?L^?1 to 1 μmol?L^?1 concentration range. The lower detection limit is 0.1 nmol?L^?1. The sensor displays good stability and reproducibility. The method was applied to the analysis of spiked swine feed samples and gave satisfactory results. Figure

Immunoassay for ractopamine based on glassy carbon electrode modified with gold nanoparticles and a film of a composite made from poly (arginine) and multi-walled carbon nanotubes was proposed. Under optimal conditions, the peak currents obtained by differential pulse voltammetry decreases linearly with increasing ractopamine concentrations in the 0.1 nmol?L^?1 to 1 μmol?L^?1 concentration range. The detection limit is 0.1 nmol?L^?1.     

Voltammetric Determination of 4‐Nitrophenol and 5‐Nitrobenzimidazole Using Different Types of Silver Solid Amalgam Electrodes – A Comparative Study

The voltammetric behavior of two genotoxic nitro compounds (4‐nitrophenol and 5‐nitrobenzimidazole) has been investigated using direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at a polished silver solid amalgam electrode (p‐AgSAE), a mercury meniscus modified silver solid amalgam electrode (m‐AgSAE), and a mercury film modified silver solid amalgam electrode (MF‐AgSAE). The optimum conditions have been evaluated for their determination in Britton‐Robinson buffer solutions. The limit of quantification (L_Q) for 5‐nitrobenzimidazole at p‐AgSAE was 0.77 µmol L^?1 (DCV) and 0.47 µmol L^?1 (DPV), at m‐AgSAE it was 0.32 µmol L^?1 (DCV) and 0.16 µmol L^?1 (DPV), and at MF‐AgSAE it was 0.97 µmol L^?1 (DCV) and 0.70 µmol L^?1 (DPV). For 4‐nitrophenol at p‐AgSAE, L_Q was 0.37 µmol L^?1 (DCV) and 0.32 µmol L^?1 (DPV), at m‐AgSAE it was 0.14 µmol L^?1 (DCV) and 0.1 µmol L^?1 (DPV), and at MF‐AgSAE, it was 0.87 µmol L^?1 (DCV) and 0.37 µmol L^?1 (DPV). Thorough comparative studies have shown that m‐AgSAE is the best sensor for voltammetric determination of the two model genotoxic compounds because it gives the lowest L_Q, is easier to prepare, and its surface can be easily renewed both chemically (by new amalgamation) and/or electrochemically (by imposition of cleaning pulses). The practical applicability of the newly developed methods was verified on model samples of drinking water.     

Effects of covalent versus non-covalent interactions on the electrocatalytic behavior of tetracarboxyphenoxyphthalocyanine in the presence of multi-walled carbon nanotubes

Tetracarboxyphenoxy phthalocyanine was covalently linked to multi-walled carbon nanotubes and the conjugate was used for modification of glassy carbon electrodes for the detection of hydrogen peroxide. The electrocatalytic behavior was examined by cyclic voltammetry, square wave voltammetry, and rotating disk electrode. The results show that covalent linking is attractive in terms of high detecting currents, low overpotential, and high catalytic rate constants. Very low detection limits were observed with CoTCPhPc-DAMN-MWCNT(linked)-GCE at 0.33 nM. The resulting catalytic rate constant was 1.1 × 10³ M^?1s^?1.     

Analytical Potentialities of Carbon Nanotube/Silicone Rubber Composite Electrodes: Determination of Propranolol

A new composite electrode based on multiwall carbon nanotubes (MWCNT) and silicone‐rubber (SR) was developed and applied to the determination of propranolol in pharmaceutical formulations. The effect of using MWCNT/graphite mixtures in different proportions was also investigated. Cyclic voltammetry and electrochemical impedance spectroscopy were used for electrochemical characterization of different electrode compositions. Propranolol was determined using MWCNT/SR 70 % (m/m) electrodes with linear dynamic ranges up to 7.0 µmol L^?1 by differential pulse and up to 5.4 µmol L^?1 by square wave voltammetry, with LODs of 0.12 and 0.078 µmol L^?1, respectively. Analysis of commercial samples agreed with that obtained by the official spectrophotometric method. The electrode is mechanically robust and presented reproducible results and a long useful life.     

Sensitive Nonenzymatic Electrochemiluminescence Determination of Hydrogen Peroxide in Dental Products using a Polypyrrole/Polyluminol/Titanium Dioxide Nanocomposite

A layer-by-layer assembled of a polypyrrole and polyluminol was synthesized through the electrodeposition of pyrrole and luminol in acidic medium on a graphite electrode. The electrode was then modified by casting titanium dioxide (TiO₂) nanoparticles on its surface for enhancing electrochemiluminescence of luminol. The properties of this electrochemiluminescence sensor were studied by cyclic voltammetry, electrochemical impedance spectroscopy, field emission scanning electron microscopy, and energy dispersive X-ray spectroscopy. The results demonstrated that the modification of this electrochemiluminescence sensor shows sensitive response for the determination of hydrogen peroxide. Figures of merit include broad linearity from 1?pmol L^?1 to 4?µmol L^?1 (R²?=?0.996) with a limit of detection as low as 0.40?pmol L^?1 at a signal-to-noise ratio of three and good reproducibility with relative standard deviation of 4% for the determination of a 400?nmol L^?1 hydrogen peroxide solution (n?=?4), along with favorable long-term stability. The presence of glucose, citric acid, uric acid, dopamine, and ascorbic acid at concentrations as high as 100?nmol L^?1 of H₂O₂ did not produce any electrochemiluminescence signals, which demonstrates the selective nature of this modified electrode. The sensor was also used for the determination of H₂O₂ in mouthwash formulations and dental whitelight gels.     

Synergistic Effect of Graphene and Multiwalled Carbon Nanotubes on a Glassy Carbon Electrode for Simultaneous Determination of Uric Acid and Dopamine in the Presence of Ascorbic Acid

A poly(diallyldimethylammonium chloride)-graphene-multiwalled carbon nanotube modified glassy carbon electrode was fabricated and evaluated by cyclic voltammetry and differential pulse voltammetry. The modified electrode offered high sensitivity, selectivity, excellent long-term stability, and electrocatalytic activity for uric acid and dopamine. This sensor showed wide linear dynamic ranges of 5.0 to 350.0 µmol L^?1 for uric acid and 10.0 to 400.0 µmol L^?1 for dopamine in the presence of 500 µmol L^?1 ascorbic acid. The limits of detection were 0.13 for uric acid and 0.55 µmol L^?1 for dopamine. This functionalized electrode has potential application in bioanalysis and biomedicine.     

Application of a sensitive nanocomposite-based electrochemical sensor for voltammetric determination of dicyclomine hydrochloride in real samples

In the present study a glassy carbon electrode, modified with nanocomposite of gold nanoparticles/multiwalled carbon nanotubes (GNPs/MWCNTs/GCE), was used for determination of dicyclomine hydrochloride (DcCl). The results showed that synergetic effects of GNPs and MWCNTs highly improved electrochemical response and sensitivity of the sensor. The electrochemical oxidation of DcCl was investigated by cyclic voltammetry and differential pulse voltammetry. Also, scanning electron microscopy and energy dispersive x-ray spectroscopy were used to evaluate microstructure of electrochemical sensor. The effect of various experimental parameters including pH and scan rate on the voltammetric response of DcCl were investigated. Under the optimal conditions linear response was observed in range of 1.0–1.2 × 10² µmol L^?1 for DcCl. The lower detection limit was found to be 0.40 µmol L^?1 for DcCl. The investigated method showed good stability, reproducibility and repeatability. The proposed sensor was successfully applied to the determination of DcCl in real samples.     

Electrochemical sensor for detection of imipramine antidepressant at low potential based on oxidized carbon nanotubes,ferrocenecarboxylic acid,and cyclodextrin: application in psychotropic drugs and urine samples

Imipramine (IMP), a tricyclic antidepressant drug, is commonly prescribed for treatment of psychiatric patients suffering from different forms of depression. The appropriate amount of drug intake is crucial to ensure the optimum therapeutic effects minimizing severe collateral effects and toxicity. Therefore, the monitoring of imipramine is essential for its clinical applications. Herein, we report an electrochemical sensor based on a composite of ferrocenecarboxylic acid (FCA), β-cyclodextrin (CD), and oxidized multi-walled carbon nanotubes (f-CNT) modified glassy carbon electrode for detection of IMP at low potential. The electrochemical behavior of the proposed sensor was characterized by scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry. The results show that imipramine determination using the proposed sensor occurs around 0 V vs Ag/AgCl in phosphate buffer pH 7.0. The calibration curves were obtained by cyclic voltammetry and differential pulse voltammetry, with linear ranges of 10 to 350 μmol L^?1 and 0.1 to 10 μmol L^?1, respectively. A detection limit of 0.03 μmol L^?1 was obtained for the detection of IMP. The sensor was applied for IMP determination in psychotropic drugs and urine samples and the results show a recovery percentage between 99 and 101% for the analyte.     

Self-assembled sensor based on boron-doped diamond and its application in voltammetric analysis of picloram

A self-assembled sensor based on a boron-doped diamond was investigated as a sensitive tool for voltammetric analysis of a member of a pyridine herbicide family - picloram. A cyclic voltammetry and a differential pulse voltammetry were applied for investigation of the voltammetric behaviour and quantification of this herbicide. Picloram yielded one well-developed irreversible oxidation signal at a very positive potential about +1.5 V vs. Ag/AgCl/3 mol L^?1 KCl electrode in an acidic medium and 1 mol L^?1 H₂SO₄ was chosen as a suitable supporting electrolyte. Operating parameters of differential pulse voltammetry were optimized and the proposed voltammetric method provided a high repeatability (a relative standard deviation of 20 repeated measurements at a concentration level of picloram of 50 µmol L^?1 equaled to 2.58%), a linear concentration range from 2.5 to 90.9 µmol L^?1 and a low limit of detection (LD = 1.64 µmol L^?1). Practical usefulness of the ‘environmentally-green’ electrochemical sensor was verified by an analysis of spiked water samples with satisfactory recoveries.     

Trace Level Determination of Hydrogen Peroxide at a Carbon Ceramic Electrode Modified with Copper Oxide Nanostructures

An electrochemical sensor was developed for determination of hydrogen peroxide based on nanocopper oxides modified carbon sol‐gel or carbon ceramic electrode (CCE). The modified electrode was prepared by electrodeposition of metallic copper on the CCE surface and derivatized in situ to copper oxides nanostructures and characterized by scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The modified electrode responded linearly to the hydrogen peroxide (H₂O₂) concentration over the range 0.78–193.98 µmol L^?1 with a detection limit of 71 nmol L^?1 (S/N=3) and the sensitivity of 0.697 A mol^?1 L cm^?2. This electrode was used as selective amperometric sensor for determination of H₂O₂ contents in hair coloring creams.     

Square-Wave Anodic Stripping Voltammetry (SWASV) for the Determination of Ecotoxic Metals,Using a Bismuth-Film Electrode

This article reviews the use of square wave anodic stripping voltammetry for the simultaneous determination of ecotoxic metals (Pb, Cd, Cu, and Zn) on a bismuth-film (BiFE) electrode. The BiFE was prepared in situ on a glassy-carbon electrode (GCE) from the 0.1 mol L^?1 acetate buffer solution (pH 4.5) containing 200 µg L^?1 of bismuth (III). The addition of hydrogen peroxide to the electroanalytical cell proved beneficial for the interference-free determination of Cu (II) together with zinc, lead, and cadmium, using the BiFE. The experimental variables were investigated and optimized with the view to apply this type of voltammetric sensor to real samples containing traces of these metals. The performance characteristics, such as reproducibility, decision limit (CC_a), detection capability (CC_β), sensitivity, and accuracy indicated that the method holds promise for trace Cu²⁺, Pb²⁺, Cd²⁺, and Zn²⁺ levels by employment of Hg-free GCE with SWASV. CCa, and CCβ were calculated according to the Commission Decision of 12 August 2002 (2002/657/EC). Linearity was observed in the range 20–280 µg L^?1 for zinc, 10–100 µg L^?1 for lead, 10–80 µg L^?1 for copper, and 5–50 µg L^?1 for cadmium. Using the optimized conditions, the stripping performance of the BiFE was characterized by low limits of detection (LOD). Finally, the method was successfully applied in real as well as in certified reference water samples.     

Electrocatalytic Determination of Ampicillin Using Carbon-Paste Electrode Modified with Ferrocendicarboxylic Acid

Abstract

A carbon-paste electrode spiked with ferrocenedicarboxylic acid (FDCMCPE) was constructed by incorporation of ferrocenedicarboxylic acid in a graphite powder–paraffin oil matrix. It has been shown by direct current cyclic voltammetry and double-step chronoamperometry that this electrode can catalyze the oxidation of ampicillin (AMPC) in aqueous buffered solution. It has been found that under the optimum condition (pH 10.0) in cyclic voltammetry, the oxidation of AMPC occurred at a potential of about 480 mV on the surface of the modified carbon-paste electrode. The kinetic parameters such as electron-transfer coefficient, α, and rate constant for the chemical reaction between AMPC and redox sites in FDCMCPE were also determined using electrochemical approaches. Under the optimized conditions, the electrocatalytic oxidation peak current of AMPC showed two linear dynamic ranges with a detection limit of 0.67 µmol L^?1 AMPC. The linear calibration was in the range of 2.34–30 µmol L^?1 and 40–700 µmol L^?1 AMPC using the differential pulse voltammetric method. Finally, this method was also examined as a selective, simple, and precise electrochemical sensor for the determination of AMPC in real samples such as drugs and urine.     

Antibiotic Detection in Urine Using Electrochemical Sensors Based on Vertically Aligned Carbon Nanotubes

A sensitive way to determine levofloxacin using a sensor based on vertical aligned carbon nanotubes is described. The morphology and the electrochemical performance of the electrodes were characterised by atomic force microscopy, cyclic voltammetry and square wave voltammetry. A scan‐rate study and electrochemical impedance spectroscopy showed that the levofloxacin oxidation product is adsorbed on the electrode surface. Differential pulse voltammetry in phosphate‐buffer solution allowed the development of a method to determine levofloxacin levels in the range of 1.0–10.0 µmol L^?1, with a detection limit of 75.2 nmol L^?1. The proposed sensor was successfully applied in the determination of levofloxacin in urine, and the obtained results were in full agreement with those from the HPLC procedure.     

Electrochemical Determination of Dopamine with Ruthenium(III)-Modified Glassy Carbon and Screen-Printed Electrodes

Here is reported for the first time the application of sodium bis[N-2-oxyphenyl-5-bromosalicylideneiminato-ONO]ruthenate(III) as a mediator with multiwalled carbon nanotubes and Nafion at glassy carbon and screen-printed electrodes for the determination of dopamine in the presence of ascorbic acid. Electrochemical studies were performed using cyclic voltammetry, differential pulse voltammetry, and flow injection amperometry. In flow injection mode, the flow rate was 0.4?mL?min^?1, the injection volume 250?µL, and the operation potential 0.05?V vs. Ag/AgCl. In 0.1M pH 7.5 phosphate buffer, the sensor provided a linear dynamic range up to 50?mg?L^?1 dopamine with a detection limit of 0.11?±?0.04?mg?L^?1. The sensor was used for the determination of dopamine in ampoules of dopamine hydrochloride by cyclic voltammetry, differential pulse voltammetry, and flow injection amperometry.     

Synthesis of Functionalized MWCNTs Decorated with Copper Nanoparticles and Its Application as a Sensitive Sensor for Amperometric Detection of H2O2

Functionalized‐multiwall carbon nanotubes decorated with redox active copper nanoparticles have been fabricated for sensitive enzyme‐less H₂O₂ detection. The new nanocomposite was characterized by Transmission electron microscopy, energy dispersive X‐ray analysis and cyclic voltammetry. The response of the modified electrode to H₂O₂ was examined using amperometry at ?0.45 V vs. Ag/AgCl in a buffer solution at pH 10.0. The developed sensor displayed linear concentration ranges of 0.5–10.0 and 10.0–10000.0 µmol L^?1 with a detection limit of 0.3 µmol L^?1. The proposed sensor displayed good selectivity for H₂O₂ detection in the presence of common interferences such as ascorbic acid.     

Sensitive electrochemical detection of picloram utilising a multi-walled carbon nanotube/Cr-based metal-organic framework composite-modified glassy carbon electrode

This study describes the utilisation of a glassy carbon electrode modified with a composite of multi-walled carbon nanotube and Cr-based metal-organic framework (MIL-101, Cr-BDC, BDC = 1,4-benzenedicarboxylate) for the sensitive, simple and fast voltammetric determination of picloram in environmental samples. Under optimum conditions, additions of picloram using square wave voltammetry showed linear ranges of picloram concentrations from 24.15 to 3018 µg?L^?1 (0.1–12.5 μM) and from 3018 to 9658 µg?L^?1 (12.5–40 μM) with a detection limit of 14.49 µg?L^?1 (0.06 µM). The method was successfully applied to the determination of picloram in tap and river water samples spiked with picloram without any purification step by the standard addition method. The good recovery values obtained ranging from 97.5% to 105.0% revealed the reliability and accuracy of the method.