Voltammetric determination of captopril using a novel ferrocene-based polyamide as a mediator and multi-wall carbon nanotubes as a sensor

A modified carbon paste electrode was prepared by incorporating multi-wall carbon nanotubes with a ferrocene-based polyamide (FDADO-IPC). A mixture of fine graphite powder with 10 wt % of multi-wall carbon nanotubes was applied to the preparation of the carbon paste (by dispersing in paraffin) that was finally modified with a ferrocene polyamide complex. The electrocatalytic oxidation of captopril (CAP) was investigated on the surface of the FDADO-IPC multi-wall carbon nanotubes modified carbon paste electrode (FDADO-IPC-MCNTPE) using cyclic voltammetry (CV), differential pulse voltammetry (DPV), chronoamperometry (CHA) and chronocoloumetry (CHC). Using the modified electrode, the kinetics of CAP electrooxidation was considerably enhanced by lowering the anodic overpotential through a catalytic fashion. A linear dynamic range of 0.2–200 μM for CAP was obtained in buffered solutions at pH 7.0. The detection limit was 0.08 μM. Differential pulse voltammetry as a simple, rapid, sensitive, and selective method was developed for the determination of CAP in tablet and human urine without any treatment.     

Nanostructure-based electrochemical sensor for determination of glutathione in hemolysed erythrocytes and urine

A sensitive and selective electrochemical method was developed for the determination of glutathione (GSH) in hemolysed erythrocyte using vinylferocene modified carbon nanotubes paste electrode (VFMCNTPE). The results indicate that the electrode is efficient in terms of its electrocatalytic activity for the oxidation of GSH, leading to a reduced overpotential by more than 470 mV. Also, the values of catalytic rate constant (k), and diffusion coefficient (D) for GSH were calculated. The electrocatalytic oxidation peak current of GSH showed two linear dynamic ranges with a detection limit of 0.09 μM GSH. The linear calibration ranges were obtained between 0.2–4.0 and 4.0–250.0 μM GSH using square wave voltammetry (SWV) method. The proposed method was also examined as a selective, simple and precise electrochemical sensor for the determination of GSH in real samples such as urine and hemolysed erythrocyte.     

Glassy carbon electrode modified with hemin and new melamine compounds for H<Subscript>2</Subscript>O<Subscript>2</Subscript> amperometric detection

In an attempt to increase the stability and efficiency of hemin-modified electrodes, the present work reports the preparation of a new modified glassy carbon electrode obtained by immobilization of hemin (Hm) on the electrode surface together with a new N-substituted melamine (2,4,6-triamino-1,3,5-triazine) based G-2 dendrimer comprising p-aminophenol as peripheral unit (Den) or with one of its analogues, a melamine G-0 dimer (Dim). Basic structural features, able to determine intimate relationships between Hm and Dim (or Den) at room temperature in solid state, were evidenced with the use of vibrational analysis carried out by FT-IR. This method revealed contacts between Hm and Dim or Den respectively as H-bond interactions, proton-interchange, and π-π stacking interactions. The new modified electrodes were characterized by cyclic voltammetry and electrochemical impedance spectroscopy and tested for amperometric detection of H₂O₂. In this purpose, GC/Hm-Dim electrode exhibited better catalytic properties than GC/Hm-Den electrode, but lower stability.     

Preparation of Pt/MWCNTs Catalyst by Taguchi Method for Electrooxidation of Nitrite

Abstract—The Pt nanoparticles-functionalized multiwall carbon nanotubes (f-MWCNTs) modified glassy carbon electrodes were used to study the electrooxidation of nitrite. Pt nanoparticles were electrodeposited on the f-MWCNTs modified glassy carbon (GC) electrode by applying a constant potential to the electrode for a specific time. By applying optimized conditions (using Minitab software), Pt/MWCNTs/GC electrode was prepared by immobilizing 40 μL of f-MWCNTs on the GC electrode and applying a potential of–0.20 V vs. Ag/AgCl for 120 s. The electrooxidation of nitrite was studied on the prepared electrode in 0.1 M KCl solution. The amperometric response of the prepared electrode linearly changes with the concentration of nitrite from 4.0 μM to 2.4 mM. The detection limit of the electrode was found to be 1.5 μM (S/N = 3) with a sensitivity of 28.7 μA/mM.     

A green,simple, catalyst-free,and efficient method for electro-organic synthesis of new benzofuran derivatives

In this work, the electrochemical oxidation of catechols 1a and 1b was studied in the presence of pyrazolidine-3,5-dione (3a), as a nucleophile, in a mixture of ethanol and a phosphate buffer solution (0.1 M, pH 7), as a green medium, using the cyclic voltammetry and controlled-potential coulometry techniques. The results obtained indicated that the oxidized forms of these catechols (2a and 2b) participated in the Michael addition reactions with pyrazolidine-3,5-dione (3a), and converted, via an ECEC mechanism, to their corresponding benzofurans (7a and 7b). In this work, some new benzofuran derivatives were synthesized with good yields and high purities using a facile, one-pot, and environmentally friendly electrochemical method in the absence of any chemical catalyst, toxic solvent, and hard conditions.     

Electrochemical synthesis of a graphene sheet and gold nanoparticle-based nanocomposite, and its application to amperometric sensing of dopamine

We describe a simple, green and controllable approach for electrochemical synthesis of a nanocomposite made up from electrochemically reduced graphene oxide (ERGO) and gold nanoparticles. This material possesses the specific features of both gold nanoparticles and graphene. Its morphology was characterized by scanning electron microscopy which reveals a homogeneous distribution of gold nanoparticles on the graphene sheets. Cyclic voltammetry was used to evaluate the electrochemical properties of this nanocomposite towards dopamine by modification of it on surface of glassy carbon electrode (GCE). Compared to the bare GCE, the electrode modified with gold nanoparticles, and the electrode modified with ERGO, the one modified with the nanocomposite displays better electrocatalytic activity. Its oxidation peak current is linearly proportional to the concentration of dopamine (DA) in the range from 0.1 to 10?μM, with a detection limit of 0.04?μM (at S/N?=?3). The modified electrode also displays good storage stability, reproducibility, and selectivity.

Electrocatalytic performance of cobalt microparticles film-modified platinum disk electrode for amperometric detection of ascorbic acid

Deposited cobalt microparticales (Co-MPs) film onto the platinum disk electrode has been successfully used as a new amperometric sensor for the determination of ascorbic acid (AA). AA is detected by surface catalyzed oxidation involving cobalt(III) oxyhydroxides in alkaline solution. The Co-MPs/Pt electrode exhibits a high electrocatalytic activity toward the AA oxidation. The diffusion coefficient of AA (6.09 × 10⁵ cm²/s) and the catalytic rate constant (k _cat = 6.27 × 10³ M^–1s^–1) have been determined using electrochemical approaches. The amperometric response of the modified electrode is linear against the AA concentration in the range (0.01?0.48 mM). The sensor displays the best activity with a high response signal, a good sensitivity of 74.3 μA/mM, a low detection limit of 2.5 μM (signal/noise = 3) and a fast response time (<3 s). Moreover, the reproducibility, selectivity and applicability of this biosensor are satisfactorily evaluated.     

One-pot electrochemical synthesis of highly symmetric and conjugated coumarin derivative

A facile and one pot electrochemical synthesis of disubstituted hydroquinone generated from the electrochemical oxidation of 4-1-(4-(4-hydroxyphenyl)piperazin-1-yl)ethanone (1) in the presence of 4-hydroxy-6,7-dimethylcoumarin (3) has been reported. The results revealed that p-quinone imine derived from oxidation of (1) participate in Michael addition reactions with 3 and followed by a hydrolysis reaction attain to the highly symmetric and conjugated coumarin derivative. We derived a new product in good yield based on controlled potential electrochemical oxidation at carbon electrode in a divided cell.     

Kinetics and mechanism of the electrochemical reduction of [1,2-bis(tert-butylperoxy)ethyl]benzene under conditions of the in situ recovery of a platinum surface

The behavior of [1,2-bis(tert-butylperoxy)ethyl]benzene (I) on Pt electrode is studied by means of cyclic voltammetry (CVA). A comparison of the electrochemical properties of I and the properties of previously studied bridge-type 1,2,4,5-tetraoxane ((1,4)-1,4-dimethyl-7-(4-methylbenzyl)-2,3,5,6-tetraoxabicyclo[2.2.1]heptane) (II) shows that the biperoxide studied in this work is reduced on a Pt electrode at lower cathodic potentials and is resistant to electrooxidation.     

Mechanism of the anodic dissolution of gold in solutions of 6-alkyl-1,5-diazabicyclo[3.1.0]hexanes

The electrochemical corrosion of gold in solutions of 6,6-dimethyl-1,5-diazabicyclo[3.1.0]hexane (I) and 6-methyl-1,5-diazabicyclo[3.1.0]hexane (II) on a gold electrode is studied via cyclic voltammetry. It is shown that the galvanostatic electrolysis of weakly basic aqueous solutions of I and II on gold anodes results in the corrosion of Au electrodes, probably with the formation of organic complexes of gold that are reduced to form a gold mirror on the inner surface of an electrochemical cell during electrolysis. A mechanism is proposed for the investigated processes.     

Detection of salicylic acid by electrocatalytic oxidation at a nickel-modified glassy carbon electrode

An electrochemical biosensor for the accurate determination of salicylic acid (SA) is prepared by potentiostatic deposition of nickel on the glassy carbon electrode (GCE). The electrochemical performance of the Ni/GCE film and the parameters affecting its activity are investigated by cyclic voltammetry, amperometry and electrochemical impedance spectroscopy (EIS). The electrooxidation of SA is significantly enhanced on Ni/GCE, compared to GCE. Indeed, the modified electrode has a fast response (less than 3 s) and excellent linear behavior over a wide SA concentration range (2 μM-0.55 mM) with a detection limit (LD) of 0.5 μM (signal/noise = 3) under the optimal conditions. Moreover, the stability and the reproducibility of the biosensor are satisfactorily evaluated.     

Amperometric enzyme electrodes for the determination of volatile alcohols in the headspace above fruit and vegetable juices

The surface of a glassy carbon electrode (GCE) was modified by electropolymerization of acridine red followed by drop-coating of graphene. The morphology was characterized by scanning electron microscopy. Uric acid (UA) is effectively accumulated on the surface of the modified electrode and generates a sensitive anodic peak in solutions of pH 6.5. Differential pulse voltammetry was used to evaluate the electrochemical response of the modified GCE to UA. Compared to the bare GCE, the GCE modified with acridine red, and to the graphene modified electrode, the new GCE displays high electrochemical activity in giving an oxidation peak current that is proportional to the concentration of UA in the range from 0.8 to 150?μM, with a detection limit of 0.3?μM (at an S/N of 3). The modified electrode displays excellent selectivity, sensitivity, and a wide linear range. It has been applied to the determination of UA in real samples with satisfactory results.

Voltammetric determination of paracetamol at NiO nanoparticles-modified carbon paste electrode in bulk and tablet dosage forms

Nickel oxide (NiO) nanoparticles were synthesized by a rapid method and well characterized. The nanoparticles were then used with graphite powder to prepare modified carbon paste electrode (CPE/NiO) for electrocatalytic oxidation of paracetamol (AC). The CPE/NiO showed higher electrocatalytic activity than nickel rod electrode in electrocatalytic oxidation of AC in alkaline media. The assay of AC, mechanism and kinetics of the electrooxidation process were investigated by cyclic voltammetry and chronoamperometry. The catalytic rate constant and the charge transfer coefficient of AC electrooxidation by the active nickel species and the diffusion coefficient of AC were also reported. The linear dependence of the peak current on the concentration of the AC was observed in the range 2–14 mM. This procedure was successfully applied to the determination of AC in tablets. The results showed sufficient precision, accuracy and achieved a mean recovery of 97.2% (RSD = 6.7%).     

Electrochemical oxidation of some catechol derivatives in the presence of some betadicetone derivatives: mechanistic and thermodynamic study

Electrochemical oxidations of 4-methylcatechol (1), 4-tert-butylcatechol (5) and catechol (7) in the presence of different nucleophiles have been investigated both experimentally and theoretically. Experimental results have been obtained by means of cyclic voltammetry and controlled-potential coulometry. Also the theoretical results were calculated at DFT (B3LYP) level of theory and 6–311+G (p, d) basis set. The calculated results indicate that oxidation potential of catechols (1, 5, 7) and their substituted species are directly dependent on the ?G _tot, and continuance of reactions during electrolysis is dependent on ?G _tot of produced species on the surface of electrode. The current study indicates that theoretical studies along with empirical research can be useful in displaying electrochemical reaction mechanisms.     

Electrochemical determination of acetaminophen in the presence of propranolol using an electrode modified with a Schiff base from 2-hydroxy-1-naphthaldehyde and ethylenediamine and multi-walled carbon nanotubes

A carbon paste electrode, modified with N,N′-bis-(2-hydroxy-1-naphthalidene)ethylenediamine and multi-walled carbon nanotubes (HNED-MWCNPE), was used for the determination of acetaminophen (ACOP) and propranolol (PP). Cyclic voltammetry (CV), chronocoulometry, chronoamperometry and differential pulse voltammetry (DPV) techniques were employed to study electro-oxidation of ACOP. The results revealed that the modified electrode showed an electrocatalytic activity toward the anodic oxidation of acetaminophen by a marked enhancement in the current response in buffered solution at pH 8.0. Some kinetic parameters such as the electron transfer coefficient (α) were also determined for the ACOP oxidation. The linear concentration range of 1 × 10^?3?1 × 10^?6 M with a detection limit of 4.6 × 10^?8 M (n = 16) for ACOP was obtained using DPV (pH 8.0). The modified electrode shows good sensitivity, selectivity and stability. The prepared electrode was also applied for the determination of ACOP in human blood serum.     

Nonenzymatic sensor for glucose based on a glassy carbon electrode modified with Ni(OH)2 nanoparticles grown on a film of molybdenum sulfide

A glassy carbon electrode (GCE) was modified with nickel(II) hydroxide nanoparticles and a film of molybdenum sulfide. The nanocomposite was prepared by two-step electrodeposition. Scanning electron microscopy reveals that the nanoparticles are uniformly deposited on the film. Cyclic voltammetry and chronoamperometry indicate that this modified GCE displays a remarkable electrocatalytic activity towards nonenzymatic oxidation of glucose. Response is linear in the 10–1,300 μM concentration range (R ² ?=?0.9987), the detection limit is very low (5.8 μM), response is rapid (< 2 s), and selectivity over ascorbic acid, dopamine, uric acid, fructose and galactose is very good.

Synthesis and investigation of spectroelectrochemical properties of peripherally tetra-substituted phthalocyanine bearing 3-(4-{[3-(trifluoromethyl)benzyl]oxy}phenyl)propan-1-ol and its metallo compounds

In this study, the new compounds; 3-(4-{[3-(trifluoromethyl)benzyl]oxy}phenyl)propan-1-ol 3 was prepared by the reaction of 4-(3-hydroxypropyl)phenol 1 with 1-(bromomethyl)-3-(trifluoromethyl)benzene 2 and 4-[3-(4-{[3 (trifluoromethyl)benzyl]oxy}phenyl)propoxy] phthalonitrile 5 was synthesized by the reaction of 4-nitrophthalonitrile 4 with 3-(4-{[3-(trifluoromethyl)benzyl]oxy}phenyl)propan-1-ol 3. Novel peripherally tetra substituted H₂Pc 6, Co(II) 7, Cu(II) 8, Ni(II) 9 and Fe(II) 10 phthalocyanines, which have peripheral positions with 4-[3-(4-{[3 (trifluoromethyl)benzyl]oxy}phenyl)propoxy] groups, were synthesized and all of the new compounds characterized by IR, ¹H NMR, ¹³C NMR, UV–Vis, mass spectroscopies and elemental analysis. The electrochemical and spectroelectrochemical investigation of the phthalocyanines carrying 4-[3-(4-{[3 (trifluoromethyl)benzyl]oxy}phenyl)propoxy] groups were studied using various electrochemical techniques in DMF on a glassy carbon electrode. Cyclic voltammetry and square wave voltammetry studies show that the complexes have either metal based or ligand-based diffusion controlled electron transfer properties. To shed more light on the electron-transfer steps of the complexes and assignments of the redox couples were carried out by spectroelectrochemical measurements. The color changes during spectral changes of redox species were recorded with in situ electrocolorimetric measurements. The electrochemical and in situ UV–Vis spectral change of complexes indicated their applicability in the fields of the electrochemical technologies.     

Nickel hexacyanoferrate nanoparticles/nano silver coated multiwalled carbon nanotubes nanocomposite for the detection of hydrogen peroxide

A new nanocomposite was developed by combination of nickel hexacyanoferrate nanoparticles (NiNP) and nano silver coated multiwalled carbon nanotubes (nano Ag-MWNTs). The NiNP/nano Ag-MWNTs nanocomposite was charactered by scanning electron microscopy (SEM). The NiNP/nano Ag-MWNTs nanocomposite modified glassy carbon (GC) electrode was used to investigate the electrochemical reduction of hydrogen peroxide. The results showed that NiNP and nano Ag-MWNTs provided the synergistic effect toward this process. The obtained NiNP/nano Ag-MWNTs/GC electrode showed a wide linear response range of 1 × 10^?6 to 1 × 10^?4 and 5 × 10^?4 to 0.01 M hydrogen peroxide with correlation coefficients of 0.998 and 0.997, fast response time (2 s), and good selectivity toward the electrocatalytic reduction of hydrogen peroxide. The detection limit (S/N = 3) of hydrogen peroxide was 5 × 10^?7 M.     

Sputtering deposition of Pt nanoparticles on vertically aligned multiwalled carbon nanotubes for sensing L-cysteine

A highly sensitive electrochemical sensor for determination of L-cysteine (CySH) is presented. It is based on vertically aligned multiwalled carbon nanotubes modified with Pt nanoparticles by magnetron sputtering deposition. The morphology of the nanocomposite was characterized by scanning electron microscopy, transmission electron microscopy and energy-dispersive. The electrochemistry of CySH was investigated by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The mechanism for the electrochemical reaction of CySH at the modified electrode at different pH values is discussed. The electrode exhibits a higher electrocatalytic activity towards the oxidation of CySH than comparable other electrodes. It displays a linear dependence (R ²?=?0.9980) on the concentration of CySH in the range between 1 and 500 μM and at an applied potential of +0.45 V, a remarkably low detection limit of 0.5 μM (S/N?=?3), and an outstandingly high sensitivity of 1.42?×?10³ μA?mM^?1?cm^?2, which is the highest value ever reported. The electrode also is highly inert towards other amino acids, creatinine and urea. The sensor was applied to the determination of CySH in urine with satisfactory recovery, thus demonstrating its potential for practical applications.

Carbon nanotube-ionic liquid nanocomposite modified carbon-ceramic electrode for determination of dopamine in real samples

Room temperature 1-butyl-3-methylimidazolium tetraflouroborate ([BMIM][BF₄]) ionic liquid was employed for dispersion of multi walled carbon nanotubes (MWCNTs) and the formation of nanocomposite on the surface of a carbon-ceramic electrode. The surface of the modified electrode was characterized using scanning electron microscopy and electrochemical impedance spectroscopy. The modified electrode exhibited excellent electrochemical activity to oxidation of dopamine (DA); whereas electro oxidation of ascorbic acid (AA) was not seen and electro oxidation of uric acid (UA) appeared at a more positive potential than DA. The multi walled carbon nanotube-ionic liquid nanocomposite modified carbon-ceramic electrode was used for the selective determination of DA in the presence of high levels of AA and UA using differential pulse voltammetry. The calibration curve for DA was linear in the range of 3.00 to 130 µM with the detection limit (S/N=3) of 0.87 µM. The present electrode was successfully applied to the determination of DA in some commercial pharmaceutical samples and human blood serum.