Enhanced electrocatalytic oxidation of hydroxylamine on Pt/polypyrrole composite modified glassy carbon electrode

A sensitive hydroxylamine sensor is developed by electrodeposition of Pt nanoparticles on pre-synthesized polypyrrole nanoparticles modified glassy carbon electrode. The modified electrode presents distinctly electrocatalytic activity toward hydroxylamine oxidation. The kinetic parameters such as the overall numbers of electrons involved in hydroxylamine oxidation, the electron transfer coefficient, standard heterogeneous rate constant, and diffusion coefficient are evaluated. The current response increases linearly with increasing hydroxylamine concentrations and exhibits two wide linear ranges of 5.0?×?10^?7–1.1?×?10^?3 and 1.1?×?10^?3–18.8?×?10^?3 M with a detection limit of 0.08 μM (s/n?=?3). The proposed electrode presents excellent operational and storage ability for determining hydroxylamine. Moreover, the sensor shows good sensitivity, selectivity, and reproducibility properties.     

Voltammetric sensor for simultaneous determination of ascorbic acid,acetaminophen, and tryptophan in pharmaceutical products

A novel carbon paste electrode modified with carbon nanotubes and 5-amino-2′-ethyl -biphenyl-2-ol was fabricated. The electrochemical study of the modified electrode, as well as its efficiency for electrocatalytic oxidation of ascorbic acid (AA), is described. The electrode was employed to study the electrocatalytic oxidation of AA, using cyclic voltammetry, chronoamperometry, and square-wave voltammetry (SWV) as diagnostic techniques. It has been found that the oxidation of AA at the surface of modified electrode occurs at a potential of about 250 mV less positive than that of an unmodified carbon paste electrode. SWV exhibits a linear dynamic range from 2.0?×?10^?7 to 5.0?×?10^?4 M and a detection limit of 1.0?×?10^?7 M for AA. In addition, this modified electrode was used for simultaneous determination of AA, acetaminophen (AC), and tryptophan (TRP). Finally, the modified electrode was used for determination of AA, AC, and TRP in pharmaceutical products.     

Benzoylferrocene-modified carbon nanotubes paste electrode as a voltammetric sensor for determination of hydrochlorothiazide in pharmaceutical and biological samples

The electrooxidation of hydrochlorothiazide (HCT) at the surface of a benzoylferrocene modified multi-walled carbon nanotube paste electrode was studied using electrochemical approaches. Under the optimized conditions (pH 7.0), the square wave voltammetric peak current of HCT increased linearly with HCT concentration in the ranges of 6.0?×?10^?7 to 3.0?×?10^?4 M. The detection limit was 9.0?×?10^?8 M HCT. The diffusion coefficient (D?=?1.75?×?10^?5 cm²/s) and electron transfer coefficient (α?=?0.45) for HCT oxidation were also determined. The proposed sensor was successfully applied for the determination of HCT in human urine and tablet samples.     

Highly sensitive electrochemical detection of dopamine and uric acid on a novel carbon nanotube-modified ionic liquid-nanozeolite paste electrode

A novel biosensor has been constructed by incorporating modified nanosized natural zeolite and 3-hydroxypropanaminium acetate (HPAA) as a novel room temperature ionic liquid, supported on multiwalled carbon nanotube (MWCNTs) and employed for the simultaneous determination of dopamine (DA) and uric acid (UA). A detailed investigation by transmission electron microscopy and electrochemistry is performed in order to elucidate the preparation process and properties of the composites. The voltammetric studies using the modified carbon paste electrode show two well-resolved anodic peaks for DA and UA with a potential difference of 160 mV, revealing the possibility of the simultaneous electrochemical detection of these compounds. The modified carbon paste electrode shows good conductivity, stability, and extraction effect due to the synergic action of HPAA, MWCNTs, and iron ion-doped natrolite zeolite. Under optimized conditions, the peak currents are linear from 8.12?×?10^?7 to 3.01?×?10^?4?mol?L^?1 and from 9.31?×?10^?7 to 3.36?×?10^?4?mol?L^?1 with detection limits of 1.16?×?10^?7 and 1.33?×?10^?7?mol?L^?1 for DA and UA using the differential pulse voltammetric method, respectively. Finally, the modified carbon paste electrode proved to have good sensitivity and stability and is successfully applied for the simultaneous determination of DA and UA in human blood serum and urine samples.     

Electrochemical and catalytic investigations of epinephrine,acetaminophen and folic acid at the surface of titanium dioxide nanoparticle-modified carbon paste electrode

In the present paper, the use of a carbon paste electrode modified with 1-(4-(1, 3-dithiolan-2-yl)-6, 7-dihydroxy-2-methyl-6, 7-dihydrobenzofuran-3-yl)ethanone (DDE) and TiO₂ nanoparticles prepared by a simple and rapid method was described. The modified electrode showed excellent properties for electrocatalytic oxidization of epinephrine (EP), acetaminophen (AC) and folic acid (FA). The apparent charge transfer rate constant, k _s?=?1.14 s^?1, and transfer coefficient, α?=?0.54, for electron transfer between the modifier and carbon paste electrode were calculated. It has been found that under optimum condition (pH?=?7.0) in cyclic voltammetry, the oxidation of EP occurs at a potential about 280 mV less positive than that of an unmodified carbon paste electrode. The values of transfer coefficients (α?=?0.46), catalytic rate constant (k?=?1.2?×?10⁴ M^?1 s^?1) and diffusion coefficient (D?=?2.70?×?10^?5 cm² s^?1) were calculated for EP. Differential pulse voltammetry (DPV) exhibited two linear dynamic ranges of 0.5 to 50.0 μM and 50.0 to 1,000 μM for EP. This modified electrode is quite effective not only for the detection of EP, AC and FA but also for the simultaneous determination of these species in a mixture. The limit of detection for EP, AC and FA is 0.10, 1.80 and 2.36 μM, respectively.     

Voltammetric determination of uric acid in the presence of ascorbic acid and dopamine using chitosan/ionic liquid composite electrode

A chitosan/ionic liquid composite electrode was prepared and used to determine uric acid (UA) in the presence of a large excess of ascorbic acid (AA) and dopamine (DA) by linear sweep voltammetry (LSV). The modified electrode shows large peak separations between DA, AA, and UA. Due to the existence of chitosan and ionic liquid in the composite, the modified electrode exhibits strong electrochemical catalytic activity toward the oxidation of UA. Under optimal conditions, the peak current is linearly dependent on the UA concentration in the range of 5?×?10^?7–2?×?10^?4 M in the presence of 5?×?10^?4 M AA and 5?×?10^?5 M DA with a correlation coefficient of 0.9978, and the detection limit is 5?×?10^?8 M at a signal-to-noise ratio of 3. With good sensitivity and stability, the constructed sensor was applied in the determination of UA in human serum samples and satisfactory results were obtained.     

Electrochemical methods for determination of thymine in medical pipefish samples based on HPMαFP/Ppy/GCE-modified electrode

A sensitive electrochemical method was developed for the voltammetric determination of thymine at a composite film-modified electrode 1-phenyl-3-methyl-4-(2-furoyl)-5-pyrazolone (HPMαFP)/polypyrrole (Ppy)/glassy carbon electrode (GCE). The electrochemical parameters of thymine were investigated by cyclic voltammetry and differential pulse voltammetry. In pH?=?7.4, one sensitive oxidation peak of thymine with E _pa?=?0.968 V was observed on the HPMαFP/PPy-modified electrode. The difference of peak potential (?E _pa) was 188 mV lower than that for bare GCE. Compared to the bare GCE and Ppy/GCE, the HPMαFP/Ppy/GCE-modified electrode showed an excellent electrocatalytic effect on the oxidation of thymine and displayed a shift of the oxidation potential in the negative direction with significant increase in the peak current. Under the optimum condition, the concentration calibration range and detection limit are 2?×?10^?6–1?×?10^?4 and 4.85?×?10^?7?M for thymine. This developed method had been applied to the direct determination of thymine in medical pipefish samples with satisfactory results.     

The first electrochemical sensor for determination of mangiferin based on an ionic liquid–graphene nanosheets paste electrode

A novel carbon paste electrode modified with graphene nanosheets and an ionic liquid (n-hexyl-3-methylimidazolium hexafluoro phosphate) was fabricated and used for the electrochemical study of mangiferin for the first time. This modified electrode offers a considerable improvement in voltammetric sensitivity toward mangiferin, compared to the bare electrode. Square wave voltammetry (SWV) exhibits a linear dynamic range from 5.0?×?10^?8 to 2.0?×?10^?4 M and a detection limit of 20.0 nM for mangiferin. Finally, the proposed method was successfully applied to the determination of mangiferin in real samples such as serum and urine.     

Ultrasonic preparation of tetraoxalyl ethylenediamine melamine resin-coated multiwalled carbon nanotubes for trace Ni(II) sensing

Under an aid of ultrasonic, tetraoxalyl ethylenediamine melamine resin-coated multiwalled carbon nanotubes were prepared for Ni(II) sensing in aqueous solution. The processes involved the fabrication of tetraoxalyl ethylenediamine melamine resin by one pot way, the coating of tetraoxalyl ethylenediamine melamine resin at multiwalled carbon nanotubes (MWCNTs), and the determination of Ni(II). The present materials were carefully examined by Fourier transform infrared spectroscopy, field emission scanning electron microscope, and electrochemistry techniques. A great deal of amorphous microsphere could be observed for tetraoxalyl ethylenediamine melamine resin with an average diameter of 1.2 μm, and MTE could evenly adhere at the surface of MWCNTs by the ultrasonic. Tetraoxalyl ethylenediamine melamine resin-coated multiwalled carbon nanotube-modified paraffin-impregnated graphite electrode was successfully used for the determination of Ni(II) by differential pulse adsorptive anodic stripping voltammetry. The current responses (?0.3 V) were linearly increased depending on the concentration from 1?×?10^?11 to 3?×?10^?10 M (i (μA)?=?11.1?+?7.9 c (1?×?10^?12 M); R?=?0.9901, 3σ?=?7?×?10^?12 M).     

Differential pulse anodic stripping voltammetric determination of Hg2+ at poly(Eriochrome Black T)-modified carbon paste electrode

The electrochemical behavior of Hg²⁺ was investigated in poly(Eriochrome Black T)-modified carbon paste electrode (CPE) using cyclic voltammetry (CV). Poly(Eriochrome Black T) was prepared in an alkaline medium on the surface of the CPE using a solution of Eriochrome Black T with the CV technique. The electrochemical impedance study revealed a better charge transfer kinetics at the modified electrode. The effects of variation of the experimental conditions, such as the concentration of electrolytes, pH, deposition time, and the deposition potential, which maximize current efficiency were studied. The optimum response of Hg²⁺ was observed in 1.0 M KCl solution. The differential pulse anodic stripping voltammetric technique was employed successfully to detect Hg²⁺, which gave a good linear response at low concentration levels of Hg²⁺. The detection limit was found to be 2.2?×?10^?10 M (S/N?=?3), which is comparable with that achieved in multiwall carbon nanotube-modified electrode. The remarkable electroanalytical performance of the modified electrode makes it amenable to employ it successfully as an electrochemical sensor for the determination of hazardous pollutant Hg²⁺ in environmental samples.     

Sensitive and selective electrochemical sensor for magnolol based on the enhancement effect of multiwalled carbon nanotubes

Herein, insoluble multiwalled carbon nanotubes (MWNTs) were dispersed into N,N-dimethylformamide (DMF) via ultrasonication, resulting in a stable and homogeneous MWNTs suspension. After evaporation of DMF, the surface of glassy carbon electrode was successfully coated with MWNTs film, as confirmed from scanning electron microscopy measurements. In pH 7 phosphate buffer, an irreversible oxidation peak was observed for magnolol, and the peak currents greatly increased on MWNTs film surface. The influences of pH value, amount of MWNTs and accumulation conditions were studied. Based on the remarkable enhancement effect of MWNTs, a new electrochemical sensor with high sensitivity was developed for magnolol. The linear range was from 5 μg?L^?1 to 1 mg?L^?1, and the detection limit was 2 μg?L^?1 (7.51?×?10^?9?M) after a 3-min accumulation. This novel sensor was successfully used to detect the content of magnolol in Chinese traditional medicines, and the recovery was over the range from 98.1 to 99.1 %.     

A selective sensor for nanolevel detection of lead (II) in hazardous wastes using ionic-liquid/Schiff base/MWCNTs/nanosilica as a highly sensitive composite

An effective potentiometric sensor had been fabricated for the rapid determination of Pb²⁺ based on carbon paste electrode consisting of room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆), multiwalled carbon nanotubes (MWCNTs), nanosilica, synthesized Schiff base, as an ionophore, and graphite powder. The constructed nanocomposite electrode showed better sensitivity, selectivity, response time, response stability, and lifetime in comparison with typical Pb²⁺ carbon paste electrode for the successfully determination of Pb²⁺ ions in water and in waste water samples. The best response for nanocomposite electrode was obtained with electrode composition of 18% ionophore, 20% BMIM-PF₆, 49% graphite powder, 10% MWCNT, and 3% nanosilica. The new electrode exhibited a Nernstian response (29.76?±?0.10 mV decade^?1) toward Pb²⁺ ions in the range of 5?×?10^?9?C1.0?×?10^?1 mol L^?1 with a detection limit of 2.51?×?10^?9 mol L^?1. The potentiometric response of prepared sensor is independent of the pH of test solution in the pH range of 4.5?C8.0. It has quick response with response time of about 6 s. The proposed electrode show fairly good selectivity over some alkali, alkaline earth, transition, and heavy metal ions.     

Electrocatalytic oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-tyrosine at carboxylic acid functionalized multi-walled carbon nanotubes modified carbon paste electrode

The electrocatalytic oxidation of l-tyrosine (Tyr) was investigated on a carboxylic acid functionalised multi-walled carbon nanotubes modified carbon paste electrode using cyclic voltammetry and amperometry. The surface morphology of the electrodes was studied using field emission (FE)-SEM images, and the interface properties of bare and modified electrodes were investigated by electrochemical impedance spectroscopy (EIS). The influence of the amount of modifier loading and the variation of the pH of the solution on the electrochemical parameters have been investigated. Cyclic voltammetry was carried out to study the electrochemical oxidation mechanism of Tyr, which showed an irreversible oxidation process at a potential of 637.0 mV at modified electrode. The anodic peak current linearly increased with the scan rate, suggesting that the oxidation of Tyr at modified electrode is an adsorption-controlled process. A good linear relationship between the oxidation peak current and the Tyr concentration in the range of 0.8–100.0 μM was obtained in a phosphate buffer solution at pH 7.0 with a detection limit of 14.0?±?1.36 nM (S/N?=?3). The practical utility of the sensor was demonstrated by determining Tyr in spiked cow’s milk and human blood serum. The modified electrode showed excellent reproducibility, long-term stability and antifouling effects.     

Electrochemical detection of aqueous nitrite based on poly(aniline-<Emphasis Type="Italic">co</Emphasis>-<Emphasis Type="Italic">o</Emphasis>-aminophenol)-modified glassy carbon electrode

Nitrite is a common contaminant in drinking water and groundwater with high environmental and health risks. Electrochemical sensing method is a selective and easy technique to detect nitrite in water. In this study, we report a research about a poly(aniline-co-o-aminophenol)-modified glassy carbon electrode (PAOA/GCE) for aqueous nitrite detection. With stable redox activity and conductivity in a wide pH range compared with polyaniline, PAOA is suitable to be used as electrode material in a neutral medium. The PAOA/GCE was prepared by cyclic voltammogram method by electrochemical copolymerization of o-aminophenol and aniline. SEM and FT-IR results proved the formation of PAOA, and the electrode exhibited higher responses toward nitrite oxidation compared with polyaniline-modified GCE and bare GCE. We also studied the impact of scan rate, pH, and temperature on nitrite detection. The PAOA/GCE could be used in a wide pH range from 2 to 8 and used to detect nitrite in the linear range from 5.0 × 10^?6 to 2.0 × 10^?3 M with the detection limit of 2 × 10^?6 M. Its excellent reproducibility, stability, and anti-interference ability make it a promising electrode in detecting aqueous nitrite in drinking water and groundwater.     

Selective determination of catecholamine in the presence of ascorbic acid or uric acid on the membrane of silver nanoparticles/poly l-phenylalanine

The silver ions and l-phenylalanine were co-deposited and formed a hybrid membrane on the surface of glassy carbon electrode by cyclic voltammetry. The membrane had good properties for catalyzing the redox of catecholamine neurotransmitters, including epinephrine (EP), norepinephrine (NE), and dopamine (DA). The electrochemical behaviors of these neurotransmitters were studied on this modified electrode. and therefore, an assay for each of them is set up and the detection limits for EP, NE, and DA are 7.2?×?10^?9, 6.4?×?10^?9, and 8.5?×?10^?9 mol L^?1, respectively. The proposed method can effectively eliminate the interference of the ascorbic acid and uric acid. The conditions which influenced the analyses were optimized. Using this method to determine the content of EP, NE, and DA in injections, the results were satisfactory.     

Voltammetric behaviors of an emerging pollutant benzotriazole on multiwall carbon nanotubes (MWNTs)—Nafion modified electrode in various pH mediums

The electrochemical behaviors of an emerging pollutant, benzotriazole (BTA), at multiwall carbon nanotubes and Nafion modified glassy carbon electrode (MWNTs-Nafion/GCE) were investigated systematically. The electrochemical reduction of BTA was significantly improved by MWNTs-Nafion compared to bare GCE, ascribed to the excellent adsorption capacity and electrocatalytic activity of MWNTs. BTA presented well-defined reduction peaks only at pH <3.0, suggesting the involvement of lots of protons in the reduction process. Peak potential shifted negatively and peak current decreased significantly with pH increase. BTA showed various UV–Vis absorption spectra in acidic and alkaline mediums. Cathodic peak current increased linearly with square root of sweep rate as well as with the concentration of BTA from 3.0?×?10^?6 to 1.6?×?10^?4 mol L^?1. This suggests a diffusion-controlled and irreversible electrode process. Diffusion coefficient of BTA on MWNTs-Nafion/GCE was obtained as 2.67?×?10^?2 cm² s^?1 with four orders of magnitude larger than that on GCE. MWNTs-Nafion/GCE showed a good selectivity between BTA and O₂ but poor selectivity between BTA and tolyltriazole.     

A calix[4]arene derivative-doped perchlorate-selective membrane electrodes with/without multi-walled carbon nanotubes

In this study, poly (vinyl chloride)(PVC) membrane electrodes with/without multi-walled carbon nanotubes (MWCNTs) based on a calix[4]arene derivative for perchlorate ion were described. The influence of membrane composition, pH, conditioning solution on the potentiometric response of the electrodes was investigated. Perchlorate-selective PVC membrane electrode exhibited a slope of 47.8 ± 0.6 mV/pClO₄ in the range of 1.0 × 10^?7–1.0 × 10^?1 mol L^?1at pH 4.0 while the coated Pt electrodes with MWCNT-OH, MWCNT-COOH and MWCNT displayed slopes of 46.1 ± 0.7 mV/pClO₄ (5.0 × 10^?6–1.0 × 10^?1 mol L^?1), 50.4 ± 1.9 mV/pClO₄ (1.0 × 10^?6–1.0 × 10^?1 mol L^?1) and 44.4 ± 0.3 mV/pClO₄ (1.0 × 10^?5–1.0 × 10^?1 mol L^?1), respectively. Other response characteristics of these electrodes such as response time, lifetime and detection limit were identified, and the selectivity coefficients towards various anions were calculated by separate solution method. Moreover, the perchlorate-selective electrodes described here were successfully used as an indicator electrode for the determination of perchlorate in real samples such as tap water, river water and human urine by direct calibration method.     

Comparative study for voltammetric investigation and trace determination of pramipexole at bare and carbon nanotube-modified glassy carbon electrodes

A sensitive, simple, and reproducible method was developed in this study for the determination of pramipexole, and in doing that, a glassy carbon electrode modified with –COOH-functionalized multi-walled carbon nanotube was utilized. The modified electrode was compared with a bare glassy carbon electrode in order to prove the sensitivity of the developed sensor. Cyclic, differential pulse, and adsorptive stripping differential pulse voltammetric techniques were used to investigate the oxidation behavior and stripping techniques were used for the determination of pramipexole. Based on optimum experimental conditions, calibration and partial validation studies were realized for bare and modified electrodes. As a result, the values of limit of detection and quantification were determined as be 2.38 × 10⁻¹⁰ and 7.93 × 10⁻¹⁰ M for bare and 1.06 × 10⁻¹⁰ and 3.52 × 10⁻¹⁰ M for modified glassy carbon electrodes, respectively. The applicability of the bare and modified electrodes was demonstrated for the determination of pramipexole in pharmaceutical dosage forms. The selectivity of the developed method was considered in the presence of Ca²⁺, Na⁺, K⁺, and glucose, ascorbic acid, uric acid, and dopamine. Interfering agents except uric acid did not affect pramipexole determination considerably.

     

Nitrogen-doped multi-walled carbon nanotubes for paracetamol sensing

A novel sensor consisting of nitrogen-doped multi-walled carbon nanotubes was fabricated by means of chemical vapor deposition technique with decomposition of acetonitrile onto oxidized silicon wafer using ferrocene as catalyst. The electrochemical response of carbon nanotubes-based sensor towards oxidation of paracetamol to N-acetyl-p-quinone imine was investigated in phosphate buffer solution (pH 7.0) by means of standard electrochemical techniques. A quasi-reversible response for oxidation of paracetamol was identified on carbon nanotubes-based sensor with detection limit and sensitivity of 0.485 μM and 0.8406 A M^?1 cm^?2, respectively. It was found that the nitrogen doping in carbon nanotubes enhances the sensor's detection ability. Namely, electrochemical studies performed on film consisting of pristine carbon nanotubes reveal as well quasi-reversible response towards oxidation of paracetamol but nevertheless poorer detection ability and sensitivity (0.950 μM; 0.601 A M^?1 cm^?2). The findings strongly suggest the application of nitrogen-doped carbon nanotubes in biosensing.     

A sensitive amperometric detection of dopamine agonist drug pramipexole at functionalized multi-walled carbon nanotubes (f-MWCNTs) modified electrode

The electrochemical detection of dopaminergic agonist drug pramipexole dihydrochloride monohydrate (PPX) has been investigated by cyclic voltammetric (CV) and amperometric i–t techniques at functionalized multi-walled carbon nanotubes-modified glassy carbon electrode. For the first time, a sensitive and rapid electrochemical method was developed for the determination of PPX. The surface morphological characteristics of the proposed electrode have been studied by using transmission electron microscopy (TEM); further, electrochemical impedance spectroscopy (EIS) and Fourier transform infrared spectroscopy (FTIR) have been employed. PPX shows an irreversible anodic peak, which may be ascribed to the oxidation of the –NH groups of PPX. The proposed method was showing good sensitivity of 0.993 μA μM^?1 cm^?2 with a linear range of 5 to 340 μM by amperometric i–t and CV technique shows a linear range of 12.5 to 313 μM with a sensitivity of 1.92 μA μM^?1 cm^?2. The recovery of PPX from blood serum samples was found 100.6 and 98.9 %, respectively. Furthermore, the proposed method has been demonstrated for the determination of PPX in commercially available pharmaceutical samples and good agreement of results obtained.