Irreversible Oxidation Peak Research Articles

A commercially viable electrochemical sensor for the immunosuppressant drug mycophenolate mofetil utilizing pencil graphite electrode

An electrochemical sensor facilitating the electro oxidation of the immunosuppressant, mycophenolate mofetil (MMF) on pencil graphite electrode (PGE) has been developed. The electrochemical characteristics of the electrode was evaluated by virtue of cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The PGE was characterized by XRD analysis and FE-SEM before and after the electrooxidation of MMF at the electrode. CV of MMF exhibited two irreversible oxidation peaks at about 0.66 V and 0.84 V. In the DPV studies, two linear ranges were observed towards the determination of MMF concentration from 20 nM – 300nM and 300 - 1000 nMin 0.1M phosphate buffer with pH 6. The limit of detection of the sensor was estimated to be 1.80nM. The proposed sensor exhibited acceptable selectivity for quantifying the MMF in pharmaceutical dosage forms and urine samples.

Synthesis of Polyaniline/Graphene Nanocomposites and Electrochemical Sensing Performance for Formaldehyde

Background: Formaldehyde has been recognized as the important liquid environmental pollutant which can cause health risk. Great effort has been devoted to detecting formaldehyde in liquid environment. It is of important significance to develop a sensitive method for measuring formaldehyde from the environmental and health viewpoints. Methods: Polyaniline/graphene nanocomposites have been prepared by a simple in-situ polymerization process using graphene and aniline as the raw materials. The nanocomposites were characterized by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) and high-resolution TEM (HRTEM). The polyaniline/graphene nanocomposites were applied to modify the glassy carbon electrode for the detection of formaldehyde by cyclic voltammetry (CV) method. Results: The polyaniline/graphene nanocomposites consist of hexagonal graphite phase. The polyaniline particles are dispersed and attached to the surface of the graphene nanosheet-shaped morphology. The thickness of the graphene nanosheets is less than 50 nm. The electrocatalytic performance of the polyaniline/graphene nanocomposites modified glassy carbon electrode towards formaldehyde was obtained. The potential of the irreversible oxidation peak is located at +0.19 V. The polyaniline/graphene nanocomposites modified glassy carbon electrode shows a wide linear range of 0.0001-2 mM and low detection limit of 0.085 μM. Conclusion: The nanocomposites modified glassy carbon electrode possesses good reproducibility and stability. The polyaniline/graphene nanocomposites show great application potential for the electrochemical sensors to detect formaldehyde in liquid environments.

A pencil graphite electrode modified with poly nicotinamide as a framework for the electrochemical detection of propranolol hydrochloride

Herein, a novel polymer film modified pencil graphite electrode as an electrochemical sensor for the propranolol hydrochloride (PROP) is reported. A poly nicotinamide modified pencil graphite (Poly-NA-PGE) electrode was used for the electrochemical detection of propranolol hydrochloride using differential pulse voltammetry. The modified electrode was characterized by Scanning Electron Microscopy. Furthermore, the experimental parameters like pH of the supporting electrolyte, concentration of the nicotinamide and polymerisation cycles were optimized. The cyclic voltammetry of propranolol hydrochloride showcased an irreversible oxidation peak at 0.9361V. The sensor showed a linear range from 1μM - 20μM with a correlation co-efficient of 0.99825. The repeatability of the electrode was excellent with an RSD of 3.5%. The sensor was utilized effectually for the determination of propranolol from the commercially available pharmaceutical tablet.

New and sensitive sensor for voltammetry determination of Methamphetamine in biological samples

An electrochemical sensor was developed for determining ethamphetamine (MA) using glassy carbon electrode (GCE) modified with amine functionalized multi-walled carbon nanotube (MWCNT-NH2) and gold nanoparticles (Au-NPs) linked to nanomagnetic core shells (Fe3O4@SiO2-Si-(CH2)3-SH). Cyclic voltammetry (CV) shows that at GCE Methamphetamine has a very weak irreversible oxidation peak at about 0.80 V, but after modification of the GCE the anodic peak current increased significantly. The mechanism involve the equal number of electrons and protons. The oxidation peak mechanism was controlled via diffusion. Square-wave voltammetry (SWV) has been used as a very sensitive method for measuring MA under optimal conditions. The developed sensor, has an acceptable analytical performance in terms of linearity from 5.0 × 10− 8 to 5.0 × 10− 5 mol L− 1 (R2 = 0.999) with the detection limit 16 nM. Standard addition method was used for determination of MA in human urine.

Carbon black-chitosan film-based electrochemical sensor for losartan

A novel electrochemical method for determination of losartan using a glassy carbon electrode modified with carbon black nanoparticles immobilized within a crosslinked chitosan film is proposed. The electrochemical behavior of losartan was investigated using cyclic voltammetry, which presented an irreversible oxidation peak at a potential of + 1.28 V vs. Ag/AgCl (3.0 mol L−1 KCl). The electroactivity of losartan on the modified electrode was significantly improved in terms of peak potential and peak current intensity comparatively to bare working electrode. Using square-wave voltammetry technique under optimized conditions, the modified electrode showed a linear response in the concentration range of 4.97 to 47.6 μmol L−1 with a limit of detection of 0.479 μmol L−1. The developed electrochemical method was successfully applied for the determination of losartan in pharmaceutical formulation samples, with results consistent with those obtained by a comparative UV-Vis spectrophotometric method at 95% confidence level. In addition, losartan quantification was also achieved at synthetic biological fluid samples.

In situ growth of ZIF-67 on ultrathin CoAl layered double hydroxide nanosheets for electrochemical sensing toward naphthol isomers

Zeolitic imidazole frameworks (ZIF) and ultrathin layered double hydroxide nanosheets (LDHNS) have drawn growing attention in the electrocatalysis field. Combining the merits and maximizing the electrocatalytic activity of each building block in the corresponding composite is imperative but challenging. This work thus proposes a simple strategy for the in situ growth of ZIF-67 on ultrathin CoAl-LDHNS (LDHNS@ZIF-67) without an additional Co2+ source. Thanks to the ultrathin nature, CoAl-LDHNS provide more Co reactive sites for the ordered growth of ZIF-67 nanocrystals on this 2D matrix via coordination interactions between Co2+ and 2-methylimidazole. The obtained LDHNS@ZIF-67 provides more convenient pathways to rapid electron transportation between the basal electrode and analytes. Hence, the modified electrode can be applied for the truly simultaneous detection of naphthol isomers by differential pulse voltammetry. α-naphthol and β-naphthol exhibit irreversible oxidation peaks at 0.327 and 0.487 V vs. saturated calomel electrode, respectively, making their simultaneous detection feasible. The voltammetric responses of both isomers are linear in concentrations ranging from 0.3 to 150 μM with limits of detection of 62 and 94 nM, respectively. The sensor exhibits advantages including good reproducibility, stability, selectivity, and practicability for the simultaneous detection of naphthol isomers in real water samples.

Square-Wave Adsorptive Stripping Voltammetric Determination of Hesperidin Using a Boron-Doped Diamond Electrode

In the present study, an electroanalytical method for the determination of hesperidin using adsorptive stripping voltammetry at an unmodified boron-doped diamond (BDD) electrode is presented. In cyclic voltammetry, the compound showed one irreversible and adsorption-controlled oxidation peak, resulting in the formation of a couple with a reduction and re-oxidation wave at less positive potentials. Using square-wave stripping mode, the observed anodic peak current in 0.1 M perchloric acid solution at +0.90 V (vs. Ag/AgCl) (after 30 s accumulations at a fixed potential of +0.4 V) increased linearly from 2.5 to 70 μg/mL (4.09 × 10–6–1.15 × 10–4 M). A detection limit of 0.7 μg/mL (1.2 × 10–6 M) and relative standard deviation of 8.2% for the concentration of 2.5 µg/mL (n = 10) were observed. To evaluate the practical applicability of the BDD electrode, it was used for the quantification of hesperidin in the commercial dietary supplement formulations.

Electrochemical detection of zinc oxide nanoparticles in water contamination analysis based on surface catalytic reactivity

An electroanalytical method for determining the concentration of ZnO nanoparticles (< 50 nm) in aqueous dispersion has been developed. The nanoparticles are first allowed to coat a screen-printed electrode by air-drying, which provides a significant magnification of the reduction current for KCl electrolyte at negative potentials. Phenol is next added as a chemical probe for electrochemical analysis by cyclic voltammetry. Measurement of the reduction current at an applied potential of − 0.3 V provides adequate sensitivity for the indirect quantification of ZnO nanoparticles down to a low concentration of 0.1 mg/mL. Other nanoparticles such as TiO2 and CeO2 do not produce any similar reduction peak. Furthermore, the irreversible oxidation peak at + 0.6 V and the charge storage capacity are both linearly proportional to ZnO concentrations (below 0.2 mg/mL) and can afford a detection limit of 0.01 mg/mL nanoparticles. Hence, the new method comprising three simultaneous measurements is good for both the identification and quantification of ZnO nanoparticles.

Square-wave Adsorptive Anodic Stripping Voltammetric Determination of Antidiabetic Drug Linagliptin in Pharmaceutical Formulations and Biological Fluids Using a Pencil Graphite Electrode.

A simple, sensitive, low-cost, quick and reliable square-wave anodic stripping voltammetric method is described for the determination of the antidiabetic drug Linagliptin (LNG) in pure form, tablets, and spiked human urine and plasma samples. Using a pencil graphite electrode (PGE), cyclic voltammetry (CV) was applied to study the electrochemical behavior of LNG. In a Teorell-Stenhagen buffer (pH 5.5) containing 0.1 M NaClO4 as a supporting electrolyte, the LNG yields an irreversible well-defined oxidation peak at about 1.2 V vs. Ag/AgCl electrode. The various affecting factors, such as the pH, buffer type, supporting electrolyte, accumulation potential, scan rate and accumulation time, were tested and optimized. Also, square-wave adsorptive anodic stripping voltammetric (SWAdASV) studies show that the peak current various linearly over the LNG concentration range of 0.24 - 5.20 μg mL-1 (R2 = 0.9994). The detection and quantification limits were calculated to be 0.10 and 0.33 μg mL-1, respectively. The proposed procedure exhibits a good precision, selectivity, and stability and was applied successfully to determine the LNG in pharmaceutical formulations (tablets) and biological fluids (spiked human urine and plasma samples).

Ionic liquid-supported magnetite nanoparticles as electrode modifier materials for estrogens sensing

This paper reports the application of a carbon paste electrode modified with magnetite nanoparticles and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate in the electroanalytical determination of 17β-estradiol and estriol. These estrogens are potential endocrine disruptors and thus it is relevant the development of devices for their monitoring. Transmission electron microscopy, scanning electron microscopy and zeta potential techniques were applied to characterization of the modifier materials. In cyclic voltammetry experiments, irreversible oxidation peaks were observed for 17β-estradiol and estriol at +0.320 V and +0.400 V, respectively. The anodic currents obtained were approximately three times greater than those provided by the unmodified electrode due to the presence of magnetic nanoparticles and the ionic liquid, which improved the sensitivity of modified electrode. For the analysis, the parameters of the square-wave voltammetry (scan increment, amplitude and frequency) were optimized by Box-Behnken factorial design for each estrogen. For 17β-estradiol in B-R buffer pH 12.0, the calibration plot was linear from 0.10 to 1.0 μmol L−1, with a detection limit of 50.0 nmol L−1. For estriol in B-R buffer pH 11.0, the linear range was 1.0 to 10.0 μmol L−1, with a detection limit of 300.0 nmol L−1. The modified electrode was applied in the determination of 17β-estradiol and estriol in pharmaceutical formulations and the results were comparable to those obtained using UV/VIS spectrometry. Statistical tests were applied to evaluate the results and it was concluded that there was no significant difference regarding the precision and accuracy of the data provided by the two methods.

A modified sensitive carbon paste electrode for 5-fluorouracil based using a composite of praseodymium erbium tungstate

This paper describes the modification of a modified carbon paste electrode (CPE) using nanoparticles of praseodymium erbium tungstate (Pr:Er). The modified electrode was used for the sensitive voltammetric detection of an anticancer drug (5-fluorouracil (5-FU)) using. The modified-CPE was evaluated using cyclic voltammetry (CV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) and the resulting data showed the irreversible 5-fluorouracil oxidation peak around 1.0 V vs. Ag/AgCl. Some key parameters such as pH, the amount of the modifier, potential amplitude, step potential and frequency were studied and optimized. The square wave voltammetry (SWV) analytical calibration curve was linear in the range of 0.01–50 μM, with a detection limit of 0.98 nM analyses. The electron transfer coefficient (α) was also determined to be 0.76. The analyte concentration was also determined in pharmaceutical formulations and recovery percentages were found to be in the range of 96–102%. The sensor had good reproducibility and repeatability with acceptable RSD values of 3.6%, and 1.02% and a rather long-term stability of around one month. The as-synthesized nanoparticles were also characterized using FESEM, TEM, FTIR and XRD techniques.

Electrochemical quantification of pyridoxine (VB6) in human blood from other water-soluble vitamins

For the first time reporting a pencil graphite electrode modified with gold nanoparticles and non-conducting polymeric film of o-aminophenol for the selective determination of pyridoxine (VB6) from other water-soluble vitamins in human blood. The fabricated electrode was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, and attenuated total reflection infrared spectroscopy. Voltammetric response of VB6 on the fabricated electrode was investigated out using cyclic and differential pulse voltammetric techniques. Under optimized conditions, an irreversible oxidation peak at + 0.632 V was observed which corresponds to the oxidation of VB6. The oxidation peak current and the pyridoxine concentration were found to be linear in the range from 5 to 200 μM with a detection limit of 0.30 μM. The sensitivity of the proposed electrode was calculated to be 3.373 μA/μM/cm2 with excelled reproducibility and stability. The electrode is suitable for the routine analysis of VB6 in human blood samples as it highly selective from other water-soluble vitamins.

Piroxicam voltammetric determination by ultra low cost pencil graphite electrode

Piroxicam (PRX) was determined in pharmaceutical capsules with differential pulse voltammetry (DPV) in a three electrode system consisting of a pencil graphite electrode (PGE) as working electrode, a Pt wire and a reference electrode of Ag/AgCl/KCl 3 M. An irreversible oxidation peak was observed in Epa c.a. 0.6 V, which correlates to the oxidation of PRX. The coefficient of linear correlation obtained was 0.9946, with limit of detection of 2.1 µM and limit of quantification of 4.7 µM. PGE assays showed good analytical performance compared to high performance liquid chromatography and spectrophotometry, showing the potential to be further developed and employed in quick and simple analyses.

A new voltammetric platform for reliable determination of the sport performance-enhancing stimulant synephrine in dietary supplements using a boron-doped diamond electrode.

For the first time, we propose a new modification-free voltammetric platform for simple, fast and reliable quantification of the sport performance-enhancing stimulant synephrine (SYN) based on the usage of a commercial screen-printed boron-doped diamond (BDD) electrochemical sensor. Applying cyclic voltammetry, SYN exhibited one well-shaped, irreversible and diffusion-driven oxidation peak at a peak potential of +1.45 V (vs. the silver pseudoreference electrode) in the presence of 2 M HClO4. Under the selected experimental conditions, the following analytical parameters for determination of SYN were obtained: linear concentration ranges from 19.6 up to 1000 μM and from 9.9 up to 1000 μM for differential pulse (DPV) and square-wave voltammetry (SWV), respectively, detection limits at micromolar concentration levels and intra-day repeatability with a relative standard deviation below 4% for both pulse techniques. The interference study revealed fair selectivity when considering the target dietary supplements. The feasibility of the developed voltammetric platform was verified in the analysis of commercially available dietary supplements and reasonable recovery values were achieved by DPV and SWV, respectively. In addition, the method can be performed directly without higher consumption of chemicals, waste generation, complex sample extraction and higher instrumentation cost. The advanced BDD electrochemical sensor has appeared to be a suitable competitor for efficient applications in food quality control analysis.

Determination of tramadol in pharmaceutical forms and urine samples using a boron-doped diamond electrode

The present work describes the electroanalytical investigation and a novel voltammetric method for the cheap, fast and simple quantification of tramadol (TRH) using a boron-doped diamond electrode. TRH displayed one well-defined, irreversible and adsorption-controlled oxidation peak at about 1.58 V (vs. Ag/AgCl) in Britton?Robinson buffer (BR, 0.1 mol L-1, pH 3.0) using the cyclic voltammetry technique. The voltammetric responses of the oxidation peaks are dependent on pH and their sensitivity was significantly enhanced in the presence of surfactant media (sodium dodecyl sulphate, SDS). Under the optimized experiment conditions, employing the square-wave stripping mode, it was found that there was an excellent correlation between oxidation peak current and the TRH concentration in the range 0.25 to 50.0 ?g mL-1 (8.34?10-7?1.67?10-4 mol L-1), with a detection limit of 0.072 ?g mL-1 (2.40?10-7 mol L-1) in 0.1 mol L-1 BR buffer (pH 3.0) solution comprising 8?10-4 mol L-1 SDS at 1.52 V (after 30 s accumulation at open-circuit conditions). The developed approach could be used for the quantification of TRH in pharmaceutical formulations and spiked human urine samples with acceptable recoveries.

Fullerene/MWCNT/Nafion Modified Glassy Carbon Electrode for the Electrochemical Determination of Caffeine

Herein, a convenient method based on a fullerene/multiwalled carbon nanotube/Nafion modified glassy carbon electrode (fullerene/MWCNT/Naf/GCE) for the electrochemical determination of caffeine (CAF) is reported. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to study ionic exchange properties and conductivity the proposed electrode using [Fe(CN)6]3-/4- redox couple. Caffeine gave an irreversible oxidation peak around +1.33 V (vs. Ag/AgCl reference electrode) in HClO4 (pH 1). The linear dependence of the peak current with the square root of the scan rate showed that the electron transfer process is controlled by diffusion. After optimization of key analytical parameters involved in differential pulse voltammetry (DPV), the oxidation peak current varied linearly with CAF concentration in the range of 10 to 1000 μM. A detection limit of 7.289 × 10-8 M (S/N = 3) was found. Kinetic and chronocoulometric studies were also performed to characterize the diffusion of CAF. The developed electrode exhibited good stability and was easily regenerated. The influence of some potential interfering compounds such as dopamine, uric acid, glucose and sulfite ions on the anodic peak current of CAF was also examined. The proposed method was successfully employed in the determination of CAF in some commercial drugs.

Simple and rapid voltammetric determination of cephalosporin drug cefixime on boron-doped diamond electrode

A boron-doped diamond electrode was used for the first time in sensitive and selective analysis of cefixime, a third-generation cephalosporin drug, using the square-wave voltammetry technique. The effect of the pretreatment procedure on the current response at the electrode was investigated. The best signals were obtained by polishing the electrode with a polishing pad after applying anodic and cathodic electrochemical pretreatment to the electrode. Cefixime gave a well-defined, irreversible and diffusion-controlled oxidation peak in 0.1 mol dm−3 H2SO4 support electrolyte at + 1.25 V (vs. Ag/AgCl 3 mol dm−3 NaCl). Under the best instrumental conditions and with the pretreatment procedure, a calibration curve was obtained with linearity between 2.2 × 10−6 mol dm−3 and 1.3 × 10−4 mol dm−3 at 5.9 × 10−7 mol dm−3 detection limit. The effect of possible interference substances on the current response for cefixime was investigated and the method was found to have sufficient selectivity. The developed method was successfully applied for the analysis of cefixime from pharmaceutical formulations. The method can be an alternative to the other analytical approaches due to its speed, simplicity, low cost, wide calibration range, and repeatable responses.

A Simple Approach to Simultaneous Electroanalytical Quantification of Acetaminophen and Tramadol Using a Boron‐doped Diamond Electrode in the Existence of Sodium Dodecyl Sulfate

AbstractThe present work describes the individual, selective and simultaneous quantification of acetaminophen (ACP) and tramadol hydrochloride (TRA) using a modification‐free boron‐doped diamond (BDD) electrode. Cyclic voltammetric measurements revealed that the profile of the binary mixtures of ACP and TRA were manifested by two irreversible oxidation peaks at about +1.04 V (for ACP) and +1.61 V (for TRA) in Britton‐Robinson (BR) buffer pH 3.0. TRA oxidation peak was significantly improved in the presence of anionic surfactant, sodium dodecyl sulfate (SDS), while ACP signal did not change. By employing square‐wave stripping mode in BR buffer pH 3.0 containing 8×10−4 mol L−1 SDS after 30 s accumulation under open‐circuit voltage, the BDD electrode could be used for quantification of ACP and TRA simultaneously in the ranges 1.0–70 μg mL−1 (6.6×10−6–4.6×10−4 mol L−1) and 1.0–70 μg mL−1 (3.3×10−6–2.3×10−4 mol L−1), with detection limits of 0.11 μg mL−1 (7.3×10−7 mol L−1) and 0.13 μg mL−1 (4.3×10−7 mol L−1), respectively. The practical applicability of the proposed approach was tested for the individual and simultaneous quantification of ACP and/or TRA in the pharmaceutical dosage forms.

Synthesis, crystal structures, electrochemical properties, and complexation of ferrocene-based compounds: 1,2-bis(dimethyldithiocarbamate)ferrocene and 1,2-bis(benzothiazol-2-ylthio)ferrocene

Ferrocene-based metalloligands have various applications in material sciences due to their stability in air and redox active properties. Two ferrocene-based compounds, 1,2-bis(dimethyldithiocarbamate)ferrocene (1) and 1,2-bis(benzothiazol-2-ylthio)ferrocene (2), were synthesized from 1,1′-dibromoferrocene and the corresponding disulfides via two steps. The reaction of 1 with PdCl2(PhCN)2 formed a 1:1 metal:ligand complex, [PdCl2(1)]. Compounds 1, 2, and [PdCl2(1)] were structurally characterized by single-crystal X-ray diffraction, and their redox potentials were measured by cyclic voltammetry. Two pseudopolymorphs, ethanol-solvated 1(C2H5OH)0.33 and non-solvated 1, were obtained by recrystallization from ethanol. The Xray structure of [PdCl2(1)] showed that the Pd(II) center was chelated by 1 with two thioketone sulfur atoms; 1 showed two irreversible oxidationpeaks at 0.17 and 0.41 V (vs. Fe(Cp)2/Fe(Cp)2+), corresponding to oxidation of the two substituents and ferrocene, respectively. Conversely, 2 showed a quasi-reversible redox potential at E1/2 = 0.40 V, attributable to the ferrocene moiety. [PdCl2(1)] showed two irreversible oxidation peaks at 0.48 and 0.64 V and a reduction peak at 0.52 V (vs. Fe(Cp)2/Fe(Cp)2+).

Electrochemical Sensor for the Determination of Alizarin Red-S at Non-ionic Surfactant Modified Carbon Nanotube Paste Electrode

The Cyclic Voltammetric (CV) behavior of Alizarin Red-S (ARS), which is an Anthraquinone dye was examined by utilizing TX-100 modified carbon nanotube paste electrode (TX-100MCNTPE). The surfactant utilized is TX-100, and it has been found that it has good electrocatalytic activity towards ARS. Distinctive parameters like pH, scan rate, detection limit have been studied in the potential range of 0.4 V to 1.0 V by using 0.2 M phosphate buffer solution (PBS) as supporting electrolyte. From these studies, it was clear that ARS shows well characterized irreversible oxidation peak in the solution of pH 6.5 at a scan rate of 0.1 V/s. Scan rate studies reveal that the entire process is adsorption controlled. Oxidation peak current rises linearly with the increase in the concentration of ARS. Two linear range is observed in the array of 2 × 10-6 to 10 × 10-6 M and 15 × 10-6 to 35 × 10-6 M. First linear range with a limit of detection (LOD) and limit of quantification (LOQ) of 1×10-6 and 3×10-6 M respectively was considered. The fabricated sensor can be productively employed for the simultaneous determination of ARS and Tartrazine (TZ).