Voltammetric determination of norepinephrine in the presence of acetaminophen using a novel ionic liquid/multiwall carbon nanotubes paste electrode

A novel multiwall carbon nanotubes (MWCNTs) modified carbon ionic liquid electrode (CILE) was fabricated and used to investigate the electrochemical behavior of norepinephrine (NP). MWCNTs/CILE was prepared by mixing hydrophilic ionic liquid, 1-methyl-3-butylimidazolium bromide (MBIDZBr), with graphite powder, MWCNTs, and liquid paraffin. The fabricated MWCNTs/CILE showed great electrocatalytic ability to the oxidation of NE. The electron transfer coefficient, diffusion coefficient, and charge transfer resistant (R_ct) of NE at the modified electrode were calculated. Differential pulse voltammetry of NE at the modified electrode exhibited two linear dynamic ranges with slopes of 0.0841 and 0.0231 μA/μM in the concentration ranges of 0.3 to 30.0 μM and 30.0 to 450.0 μM, respectively. The detection limit (3σ) of 0.09 μM NP was achieved. This modified electrode exhibited a good ability for well separated oxidation peaks of NE and acetaminophen (AC) in a buffer solution, pH 7.0. The proposed sensor was successfully applied for the determination of NE in human urine, pharmaceutical, and serum samples.     

Electrocatalytic determination of dopamine in the presence of uric acid using an indenedione derivative and multiwall carbon nanotubes spiked in carbon paste electrode

In the present study, a modified carbon paste electrode (CPE) containing multi-wall carbon nanotubes and an indenedione derivative(IMWCNT?CPE) was constructed and was successfully used for dopamine(DA) electrocatalytic oxidation and simultaneous determination of DA and uric acid (UA). Cyclic voltammograms of the IMWCNT?CPE show a pair of well-defined and reversible redox. The obtained results indicate that the peak potential of DA oxidation at IMWCNT?CPE shifted by about 65 and 185 mV toward the negative values compared with that at a MWCNT and indenedione modified CPE, respectively. The electron transfer coefficient, α, and the heterogeneous electron transfer rate constant, k′, for the oxidation of DA at IMWCNT?CPE were calculated 0.4 ± 0.01 and (1.13 ± 0.03) × 10^? 3 cm s^? 1, respectively. Furthermore, differential pulse voltammetry (DPV) exhibits two linear dynamic ranges of 1.9–79.4 μM, and 79.4–714.3 μM and a detection limit of 0.52 μM for DA determination. Then IMWCNT?CPE was applied to the simultaneous determination of DA and UA with DPV. Finally, the activity of the modified electrode was also investigated for determination of DA and UA in real samples, such as injection solution of DA and urine, with satisfactory results.     

Amperometric sensor based on a graphene/copper hexacyanoferrate nano-composite for highly sensitive electrocatalytic determination of captopril

In this work, a bi-layer modified glassy carbon electrode (GCE) was prepared by depositing appropriate amounts of multilayered graphene (GR) on the surface of GCE, followed by electrodepositing copper hexacyanoferrate (CuHCF) nano-particles on the graphene layer. The combination of graphene and CuHCF considerably improved the current response of the GCE towards the oxidation of captopril. Studies showed that the best response of the modified electrode could be achieved within neutral pHs. At a fixed potential under hydrodynamic conditions (stirred solutions), the oxidation current is proportional to the captopril concentration and the calibration plots were linear over the concentration ranges of 0.2 to 5.8 μM and 5.8 to 480 μM. The detection limit of the method was 0.09 μM. The modified electrode was used for electrocatalytic determination of captopril in some real samples.     

Application of ionic liquid–TiO2 nanoparticle modified carbon paste electrode for the voltammetric determination of benserazide in biological samples

An ionic liquid–TiO₂ nanoparticle modified carbon paste electrode (IL–TiO₂/CPE) was used as a fast and sensitive tool for the investigation of the electrochemical oxidation of benserazide using voltammetry. This modified electrode has been fabricated using hydrophilic ionic liquid (n-hexyl-3-methylimidazolium hexafluoro phosphate) as a binder. The modified electrode offers a considerable improvement in voltammetric sensitivity toward benserazide, compared to the bare electrode. Using differential pulse voltammetry (DPV), the electrocatalytic oxidation peak current of benserazide shows a linear calibration curve in the range of 1.0–600 μmol L^? 1 benserazide. The limit of detection was equal to 0.4 μmol L^? 1. The relative standard deviation (RSD%) for eight successive assays of 10 μmol L^? 1 benserazide was 1.1%. Finally, the proposed method was successfully applied to the determination of benserazide in real samples such as blood serum and urine.     

Electrochemical study of atenolol at a carbon paste electrode modified with mordenite type zeolite

The electrochemical behavior of atenolol (ATN) at the surface of a carbon paste electrode modified with mordenite zeolite (MOR-MCPE) is described. The prepared electrode shows a good electrocatalytic activity toward the oxidation of atenolol, which is leading to considerable improvement of sensitivity (anodic current). Whereas at the surface of unmodified electrode an electrochemical activity for atenolol cannot be observed, a sharp anodic wave is obtained using the prepared modified electrode. The mechanism of oxidation of ATN at the surface of the MOR-MCPE containing various percents of mordenite is thoroughly investigated by cyclic and differential pulse voltammetry. Acetate, hydrogen phosphate and ammonium buffers were tested as the supporting electrolyte to find the optimal pH value. The optimal pH value was 5.0 for acetate buffer. A linear voltammetric response for ATN was obtained in the concentration range of 0.4 to 80 µM with a slope of 0.676 µA/µM. The LOD and LOQ of the electrode were 0.1 µM (26.6 µg/L) and 0.35 μM (93.1 µg/L), respectively. The results obtained for ATN in pharmaceutical formulations (tablets) was in agreement with compared reference method. In conclusion, this study has illustrated that the proposed electrode modified with mordenite is suitable for selective measurements of ATN.     

MWCNTs/Cu(OH)2 nanoparticles/IL nanocomposite modified glassy carbon electrode as a voltammetric sensor for determination of the non-steroidal anti-inflammatory drug diclofenac

This paper describes the development and utilization of a new nanocomposite consisting of Cu(OH)₂ nanoparticles, hydrophobic ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIMPF₆) and multiwalled carbon nanotubes for glassy carbon electrode modification. The nanocomposite was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDX). The modified electrode was used for electrochemical characterization of diclofenac. Using differential pulse voltammetry, the prepared sensor showed good sensitivity and selectivity with low overpotential for the determination of diclofenac in the range from 0.18 to 119 μM, with a detection limit of 0.04 μM. Electrochemical studies suggested that the MWCNTs/Cu(OH)₂ nanoparticles/IL nanocomposite modified electrode provided a synergistic augmentation on the voltammetric behavior of electrochemical oxidation of diclofenac, which was indicated by the improvement of anodic peak current.     

Novel nanostructure-based electrochemical sensor for simultaneous determination of dopamine and acetaminophen

A carbon-paste electrode modified with a novel molybdenum (VI) complex and carbon nanotubes have been applied to the electrocatalytic oxidation of dopamine (DA) which reduced the overpotential by about 125 mV with obviously increase the current response. Due to its strong electrocatalytic activity towards DA, the modified carbon-paste electrode can resolve the overlapped voltammetric waves of DA and acetaminophen (AC) into two well-defined voltammetric peaks with peak-to-peak separation in potentials of about 230 mV. This property allows to selective determination of DA in the presence of AC. The transfer coefficient (a) for the electrocatalytic oxidation of DA and diffusion coefficient of this substance under the experimental conditions were also investigated. In phosphate buffer solution of pH 7.0, the oxidation current increased linearly with two concentration intervals of DA, one is 0.1 to 40.0 μM and, the other is 40.0 to 800.0 μM. The detection limit (3σ) obtained by DPV was 76.0 nM. The proposed method was successfully applied to the determination of DA, and AC in some commercial pharmaceutical samples.     

Electrochemical oxidation of adenosine-5′-triphosphate on a chitosan–graphene composite modified carbon ionic liquid electrode and its determination

In this paper a new electrochemical method was proposed for the determination of adenosine-5′-triphosphate (ATP) based on a chitosan (CTS) and graphene (GR) composite film modified carbon ionic liquid electrode (CTS–GR/CILE). CILE was fabricated by using ionic liquid 1-butyl-3-methylimidazolium dihydrogen phosphate ([BMIM]H₂PO₄) as the binder, which was further modified by GR and CTS composite. The modified electrode exhibited an excellent electrocatalytic activity toward the oxidation of ATP with the increase of the oxidation peak current and the decrease of the oxidation peak potential. The electrochemical parameters of ATP on CTS–GR/CILE were calculated with the electron transfer coefficient (α) as 0.329, the electron transfer number (n) as 2.15, the apparent heterogeneous electron transfer rate constant (ks) as 3.705 × 10^? 5 s^? 1 and the surface coverage (Γ_T) as 9.33 × 10^? 10 mol cm^? 2. Under the optimal conditions the oxidation peak current was proportional to ATP concentration in the range from 1.0 × 10^? 6 to 1.0 × 10^? 3 M with the detection limit of 0.311 μM (S/N = 3). The proposed electrode showed excellent reproducibility, stability, anti-interference ability and further successfully applied to the ATP injection sample detection.     

Selective voltammetric determination of norepinephrine in the presence of acetaminophen and tryptophan on the surface of a modified carbon nanotube paste electrode

A new electrochemical sensor for the determination of norepinephrine (NE), acetaminophen (AC) and tryptophan (TRP) is described. The sensor is based on carbon paste electrode (CPE) modified with 5-mino-3′,4′-dimethyl-biphenyl-2-ol (5ADB) and takes the advantages of carbon nanotubes (CNTs), which makes the modified electrode highly sensitive for the electrochemical detection of these compounds. Under the optimum pH of 7.0, the oxidation of NE occurs at a potential about 170 mV less positive than that of the unmodified CPE. Also, square wave voltammetry (SWV) was used for the simultaneous determination of NE, AC and TRP at the modified electrode.     

Electrosynthesis of pinecone-shaped Pt–Pb nanostructures based on the application in glucose detection

The pinecone-shaped Pt–Pb nanostructures were synthesized by electrochemical deposition. The morphology and composition of the pinecone-shaped Pt–Pb nanostructures were characterized by scanning electron microscopy, energy dispersive X-ray detector, transmission electron microscopy and X-ray photoelectron spectroscopy. Cyclic voltammetry and differential pulse voltammetry were used to evaluate the electrocatalytic performance of the pinecone-shaped Pt–Pb nanostructures electrode toward glucose oxidation in neutral media. As a result, the pinecone-shaped Pt–Pb nanostructures electrode exhibited strong current responses to glucose at a negative potential of ? 0.1 V, where the interference from the oxidation of ascorbic acid was effectively avoided. The sensitivity of the sensor was 10.71 μA mM^?1 cm^?2 with a linearity up to 12 mM and a detection limit of 8.4 μM. In addition, the as-prepared nonenzyme glucose sensor exhibited acceptable stability and reproducibility for determination of glucose. The simple preparation method and good analytical performance can potentially pave the way for effective and highly sensitive non-enzyme glucose sensors.     

Development of a modified electrode with amine-functionalized TiO2/multi-walled carbon nanotubes nanocomposite for electrochemical sensing of the atypical neuroleptic drug olanzapine

In this work, using of amine-functionalized TiO₂/multi-walled carbon nanotubes (NH₂-TiO₂-MWCNTs) nanocomposite for modification of glassy carbon electrode (GCE) was investigated. The nanocomposite was characterized by Fourier transformed infrared spectroscopy, transmission electron microscopy and scanning electron microscopy. The efficiency of modified electrode for electrocatalytic the oxidation of olanzapine was studied by cyclic voltammetry, square wave voltammetry and chronoamperometry. The electrochemical measurements were carried out in phosphate-buffered solution (PBS, pH 5.0). The NH₂-TiO₂-MWCNTs/GCE provided high surface area and more sensitive performance. The charge transfer coefficient (α) and the apparent charge transfer rate constant (k_s) were calculated to be equal to 0.42 and 0.173 s^? 1, respectively. The square wave voltammetry exhibited two linear dynamic ranges and a detection limit of 0.09 μM of olanzapine. In addition, the modified electrode was employed for the determination of olanzapine in pharmaceutical and human blood serum samples in order to illustrate the applicability of proposed method.     

Electrochemical sensor for selective determination of N-acetylcysteine in the presence of folic acid using a modified carbon nanotube paste electrode

In the present paper, a novel benzoylferrocene (BF) modified carbon nanotube paste electrode (BFCNPE) was prepared. The modified electrode was further used for the successful determination of N-acetylcysteine (NAC), and it showed an excellent electrocatalytic oxidation activity toward NAC with a lower overvoltage, pronounced current response, and good sensitivity. Under the optimized experimental conditions, the proposed electrochemical NAC sensor exhibited a linear calibration plot that ranged from 3.0 × 10^? 7 to 7.0 × 10^? 4 M with a detection limit of 9.0 × 10^? 8 M. Also, Square wave voltammetry (SWV) was used for simultaneous determination of NAC and folic acid (FA) at the modified electrode. Finally, the proposed method was applied to the determination of NAC in NAC tablets.     

Preparation,electrochemical behavior and electrocatalytic activity of chlorogenic acid multi-wall carbon nanotubes as a hydroxylamine sensor

Electrochemical characteristics of an electrodeposited chlorogenic acid film on multi-wall carbon nanotubes glassy carbon electrode (CGA–MWCNT–GCE) and its role as a sensor for electrocatalytic oxidation of hydroxylamine are described. Cyclic voltammograms of the CGA–MWCNT–GCE indicate a pair of well-defined and nearly reversible redox couple with the surface confined characteristics at a wide pH range of 2.0–12.0. The charge transfer coefficient, α, and the charge transfer rate constant, k_s, of CGA adsorbed on MWCNT were calculated 0.48 and 44 ± 2 s^?1 respectively. The CGA–MWCNT–GCE shows a dramatic increase in the peak current and/or a decrease in the overvoltage of hydroxylamine electrooxidation in comparison with that seen at a CGA modified GCE, MWCNT modified GCE and activated GCE. The kinetic parameters of electron transfer coefficient, α, the heterogeneous electron transfer rate constant, k′, and exchange current, i₀, for oxidation of hydroxylamine at the modified electrode surface were determined using cyclic voltammetry. Four linear calibration ranges and high repeatability with relative standard deviation of 4.6%, for a series of four successive measurements in 17.7 μM hydroxylamine, are obtained at the CGA–MWCNT–GCE using an amperometric method. Finally, the modified electrode was successfully used for determination of spiked hydroxylamine in two water samples.     

Electrocatalytic oxidation and differential pulse voltammetric determination of sulfamethoxazole using carbon nanotube paste electrode

The use of a carbon-nanotube paste electrode provides an effective means for the determination of sulfamethoxazole. A decrease of ca. 110 mV in the overpotential for the oxidation of sulfamethoxazole compared to a traditional carbon paste electrode is reported along with greatly enhanced signal-to-noise characteristics. The oxidation process was found to be dependent on the pH of the supporting electrolyte. Under the optimized conditions the calibration plots are linear in the concentration range of 0.35–30 μg mL^? 1 with slope of 0.0955 μA/μg mL^? 1, LOD 0.1 μg mL^? 1 and LOQ 0.33 μg mL^? 1. Application of the method for the determination of the drug in the form tablet or suspension, without any interference, from the excipients, resulted in acceptable deviation from the stated concentrations.     

Simultaneous electrochemical determination of dopamine and tryptophan using a TiO2-graphene/poly(4-aminobenzenesulfonic acid) composite film based platform

TiO₂-graphene/4-aminobenzenesulfonic acid composite film modified glassy carbon electrode (TiO₂-GR/4-ABSA/GCE) was first employed for the simultaneous determination of dopamine (DA) and tryptophan (Trp). TiO₂-GR/4-ABSA/GCE displayed excellent electrochemical catalytic activities toward the redox of DA and Trp. The cathodic peaks potentials of DA and Trp decreased significantly and their cathodic current peaks increased dramatically at TiO₂-GR/4-ABSA/GCE. Differential pulse voltammograms (DPV) was used for the simultaneous determination of DA and Trp in their dualistic mixture. The peak separation between DA and Trp was large up to 177 mV. The calibration curves for simultaneous determination of DA and Trp were obtained in the range of 1–400 μM. The detection limits (S/N = 3) were 0.1 μM and 0.3 μM for DA and Trp, respectively. The present method was applied to the determination of DA and Trp in human serum samples.     

Application of graphene-ionic liquid-chitosan composite-modified carbon molecular wire electrode for the sensitive determination of adenosine-5′-monophosphate

In this paper, a graphene (GR) ionic liquid (IL) 1-octyl-3-methylimidazolium hexafluorophosphate and chitosan composite-modified carbon molecular wire electrode (CMWE) was fabricated by a drop-casting method and further applied to the sensitive electrochemical detection of adenosine-5′-monophosphate (AMP). CMWE was prepared with diphenylacetylene (DPA) as the modifier and the binder. The properties of modified electrode were examined by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Electrochemical behaviors of AMP was carefully investigated with enhanced responses appeared, which was due to the presence of GR-IL composite on the electrode surface with excellent electrocatalytic ability. A well-defined oxidation peak of AMP appeared at 1.314 V and the electrochemical parameters were calculated by electrochemical methods. Under the selected conditions, the oxidation peak current of AMP was proportional to its concentration in the range from 0.01 μM to 80.0 μM with the detection limit as 3.42 nM (3σ) by differential pulse voltammetry. The proposed method exhibited good selectivity and was applied to the detection of vidarabine monophosphate injection samples with satisfactory results.     

Highly selective and sensitive voltammetric sensor based on modified multiwall carbon nanotube paste electrode for simultaneous determination of ascorbic acid,acetaminophen and tryptophan

A carbon-paste electrode modified with multiwall carbon nanotubes (MWCNTs) was used for the sensitive and selective voltammetric determination of ascorbic acid (AA) in the presence of 3,4-dihydroxycinnamic acid (3,4-DHCA) as mediator. The mediated oxidation of AA at the modified electrode was investigated by cyclic voltammetry (CV), chronoamperommetry and electrochemical impedance spectroscopy (EIS). Also, the values of catalytic rate constant (k), and diffusion coefficient (D) for AA were calculated. Using square wave voltammetry (SWV), a highly selective and simultaneous determination of AA, acetaminophen (AC) and tryptophan (Trp) has been explored at the modified electrode. The modified electrode displayed strong function for resolving the overlapping voltammetric responses of AA, AC and Trp into three well-defined voltammetric peaks. In the mixture containing AA, AC and Trp, the three compounds can well separate from each other with potential differences of 200, 330 and 530 mV between AA and AC, AC and Trp and AA and Trp, respectively, which was large enough to determine AA, AC and Trp individually and simultaneously.     

Preparation and characterization of copper nanoparticles/zinc oxide composite modified electrode and its application to glucose sensing

We report a new method for selective detection of d(+)-glucose using a copper nanoparticles (Cu-NPs) attached zinc oxide (ZnO) film coated electrode. The ZnO and Cu-NPs were electrochemically deposited onto indium tin oxide (ITO) coated glass electrode and glassy carbon electrode (GCE) by layer-by-layer. In result, Cu-NPs/ZnO composite film topography was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. SEM and AFM confirmed the presence of nanometer sized Cu-NPs/ZnO composite particles on the electrode surface. In addition, X-ray diffraction pattern revealed that Cu-NPs and ZnO films were attached onto the electrode surface. Indeed, the Cu-NPs/ZnO composite modified electrode showed excellent electrocatalytic activity for glucose oxidation in alkaline (0.1 M NaOH) solution. Further, we utilized the Cu-NPs/ZnO composite modified electrode as an electrochemical sensor for detection of glucose. This glucose sensor showed a linear relationship in the range from 1 × 10^? 6 M to 1.53 × 10^? 3 M and the detection limit (S/N = 3) was found to be 2 × 10^? 7 M. The Cu-NPs/ZnO composite as a non-enzymatic glucose sensor presents a number of attractive features such as high sensitivity, stability, reproducibility, selectivity and fast response. The applicability of the proposed method to the determination of glucose in human urine samples was demonstrated with satisfactory results.     

Simultaneous determination of phenylhydrazine and hydrazine by a nanostructured electrochemical sensor

In the present paper, the use of a nanostructured electrochemical sensor was described for simultaneous determination of phenylhydrazine (PhH) and hydrazine (HZ). This electrochemical sensor was prepared by a simple and rapid method by modification of carbon paste electrode with a derivative of hydroquinone and TiO₂ nanoparticles. The modified electrode showed an excellent character for electrocatalytic oxidation of PhH. Using differential pulse voltammetry, a highly selective and simultaneous determination of PhH and HZ has been explored at the modified electrode. Differential pulse voltammetry peak currents of PhH and HZ increased linearly with their concentration at the ranges of 2.0 × 10^? 6 to 1.0 × 10^? 3 M and 7.5 × 10^? 5–1.0 × 10^? 3 M, respectively and the detection limits for PhH and HZ were 7.5 × 10^? 7 M and 9.0 × 10^? 6 M, respectively.     

Voltammetric sensor based on carbon paste electrode modified with molecular imprinted polymer for determination of sulfadiazine in milk and human serum

A new sensitive voltammetric sensor for determination of sulfadiazine is described. The developed sensor is based on carbon paste electrode modified with sulfadiazine imprinted polymer (MIP) as a recognition element. For comparison, a non-imprinted polymer (NIP) modified carbon paste electrode was prepared. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods were performed to study the binding event and electrochemical behavior of sulfadiazine at the modified carbon paste electrodes. The determination of sulfadiazine after its extraction onto the electrode surface was carried out by DPV at 0.92 V vs. Ag/AgCl owing to oxidation of sulfadiazine. Under the optimized operational conditions, the peak current obtained at the MIP modified carbon paste electrode was proportional to the sulfadiazine concentration within the range of 2.0 × 10^? 7–1.0 × 10^? 4 mol L^? 1 with a detection limit and sensitivity of 1.4 × 10^? 7 mol L^? 1 and 4.2 × 10⁵ μA L mol^? 1, respectively. The reproducibility of the developed sensor in terms of relative standard deviation was 2.6%. The sensor was successfully applied for determination of sulfadiazine in spiked cow milk and human serum samples with recovery values in the range of 96.7–100.9%.