Modified glassy carbon electrode with Nafion/MWNTs as a sensitive voltammetric sensor for the determination of paeonol in pharmaceutical and biological samples

A simple, highly sensitive method was reported for directly voltammetric determination of paeonol in drug samples and human biological samples. Nafion/multi-wall carbon nanotubes’ (MWNTs) composite film was coated on the glassy carbon electrode. The adsorptive voltammetric behavior of paeonol on the Nafion/MWNTs-modified electrode was investigated using cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV). The results indicated that the Nafion/MWNTs-modified electrode could remarkably enhance electrocatalytic activity toward the oxidation of paeonol, and showed an excellent resistance capability toward the electrode passivation. A highly sensitive voltammetric sensor was developed for the detection of paeonol in pharmaceutical and biological samples. Under the optimum conditions, the anodic peak current was proportional to paeonol concentration in the range of 6.0 × 10⁻⁷–6.0 × 10⁻⁵ M with a detection limit of 4.0 × 10⁻⁷ M. Some kinetic parameters were determined, and multi-step mechanism for oxidation of paeonol was proposed.     

Pulse anodic stripping voltammetric determination of copper with an amoxicillin–nafion modified glassy carbon electrode

The analysis of Cu²⁺ by pulse anodic stripping voltammetry using a Nafion-modified glassy Carbon electrode incorporated with Amoxicillin is described. A significant increase in the voltammetric response was achieved at the modified electrode compared to a bare glassy carbon electrode. Cu²⁺ was accumulated in HAc–NaAc buffer (pH 3.6) at a potential of −0.7 V (vs. Ag/AgCl) for a certain time and then determined by pulse anodic stripping voltammetry. Parameters and conditions, such as the mass of Nafion, the concentration of Amoxicillin, the pH of medium, the accumulation potential, and the accumulation time were optimized. Under the optimum conditions, the calibration curve was linear in the range 8 × 10⁻¹⁰–2 × 10⁻⁸ M with a correlation coefficient of 0.9998 and relative standard deviation 4.87% (n = 5). The detection limit was 1.3 × 10⁻¹⁰ M. A study of interfering substances was also performed and the analytical utility of the method was demonstrated by applying to various pharmaceutical products.     

Multiwalled carbon nanotube-4-tert-butyl calix[6]arene composite electrochemical sensor for clenbuterol hydrochloride determination by means of differential pulse adsorptive stripping voltammetry

The electrochemical behavior of clenbuterol hydrochloride (CLB) was studied at a multiwalled carbon nanotube-4-tert-butyl calix[6]arene composite chemically modified electrode by means of cyclic voltammetry, electron impedance spectroscopy, and differential pulse adsorptive stripping voltammetry. Surface characterization of the electrode was carried out by means of SEM. The results revealed that 4-tert-butyl calix[6]arene along with multiwalled carbon nanotubes demonstrated a high sensitivity for determination of CLB. Employing differential pulse adsorptive stripping voltammetry allowed a linear response over the concentration range of 1.99?×?10^?8–4.76?×?10^?5?M with a detection limit of 1.38?×?10^?9?M for CLB. The described method has been applied for the estimation of CLB in biological fluids such as urine and serum.     

Polymethylthiophene/Nafion-modified glassy carbon electrode for selective detection of dopamine in the presence of ascorbic acid

The possible use of an electrode modified with electroactive conductive poly(3-methylthiophene) (PMeT)/Nafion as a chemical sensor was investigated for the voltammetric analysis of Dopamine (DA). The electrochemical behavior of dopamine was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. By using a PMeT-modified glassy carbon (GC/PMeT) electrode, DA and Ascorbic Acid (AA) signals could be separated but the AA at high concentrations still caused significant interference by overlapping the DA peak. In comparison to the GC/PMeT electrode, the glassy carbon (GC/Nafion/PMeT) electrode modified with hybrid film Nafion/PMeT was found to permit a superior separation by shifting the oxidation of AA peak toward the less positive potential. The DPV curves for a mixture of DA and AA at an GC/Nafion/PMeT electrode in a 0.1 M H₂SO₄ solution showed peaks of DA and AA, at 0.45 and 0.21 V, respectively, indicating that the difference in the oxidation potential was 240 mV. In the 0.1 M H₂SO₄ solution, the oxidation peak current on the differential pulse voltammograms for the GC/PMeT electrode increased linearly with the concentration of DA in the range 1 × 10⁻⁶ to 1 × 10⁻³ M, and the oxidation peak current on the differential pulse voltammograms for the GC/Nafion/PMeT electrode in the range 5 × 10⁻⁷ to 2 × 10⁻⁴ M. The DA detection sensitivity of the GC/Nafion/PMeT electrode (26.7 μA μM⁻¹ cm⁻²) was 22 times higher than that of the GC/PMeT electrode (1.21 μA μM⁻¹ cm⁻²).     

Fabrication of carbon nanotube and dysprosium nanowire modified electrodes as a sensor for determination of curcumin

Two sensitive sensors for determination of curcumin (CM) were described. CM can be detected using multiwall carbon nanotube (MWCNT)-modified electrodes and dysprosium nanowire carbon paste electrode using the technique of adsorptive stripping voltammetry (AdSV) in stationary solution and the fast Fourier transform voltammetry at the flowing solution. Both electrodes did show less passivation effect that occurs on the unmodified electrodes and displayed better stability and reproducibility. This electrode enabled selective determination of CM in the presence of interfering species. Under optimized conditions, CM could be detected over a linear range with a detection limit of 5.0 × 10⁻⁹ mol L⁻¹ and 5.0 × 10⁻¹⁰ mol L⁻¹ for the traditional square wave and fast Fourier transform square wave voltammetry (FFTSWV) with RSD between 0.2 and 0.5%. Comparison with other reported methods showed these studies are about 100 times more sensitive than previous ones. Good selectivity and high sensitivity obtained by Square wave voltammetry can open new possibilities of direct CM determination.     

Electrocatalytic oxidation of glutathione at carbon paste electrode modified with 2,7-<Emphasis Type="Italic">bis</Emphasis> (ferrocenyl ethyl) fluoren-9-one: application as a voltammetric sensor

Electrooxidation of glutathione (GSH) was studied at the surface of 2,7-bis (ferrocenyl ethyl) fluoren-9-one modified carbon paste electrode (2,7-BFEFMCPE). Cyclic voltammetry (CV), double potential-step chronoamperometry, and differential pulse voltammetry (DPV) were used to investigate the suitability of this ferrocene derivative as a mediator for the electrocatalytic oxidation of GSH in aqueous solutions with various pH. Results showed that pH 7.00 is the most suitable pH for this purpose. At the optimum pH, the oxidation of GSH at the surface of this modified electrode occurs at a potential of about 0.410 V versus Ag|AgCl|KCl_sat. The kinetic parameters such as electron transfer coefficient, α = 0.61, and rate constant for the chemical reaction between GSH and redox site in 2,7-BFEFMCPE, k _h = 1.73 × 10³ cm³ mol⁻¹ s⁻¹, were also determined using electrochemical approaches. Also, the apparent diffusion coefficient, D _app, for GSH was found to be 5.0 × 10⁻⁵ cm² s⁻¹ in aqueous buffered solution. The electrocatalytic oxidation peak current of GSH showed a linear dependence on the glutathione concentration, and linear calibration curves were obtained in the ranges of 5.2 × 10⁻⁵ M to 4.1 × 10⁻³ M and 9.2 × 10⁻⁷ M to 1.1 × 10⁻⁵ M with cyclic voltammetry and differential pulse voltammetry methods, respectively. The detection limits (3σ) were determined as 1.4 × 10⁻⁵ M and 5.1 × 10⁻⁷ M for the CV and DPV methods, respectively. This method was also examined as a selective, simple, and precise new method for voltammetric determination of GSH in real sample such as hemolysed erythrocyte.     

Homogeneous electrocatalytic oxidation of <Emphasis Type="SmallCaps">d</Emphasis>-penicillamine with ferrocyanide at a carbon paste electrode: application to voltammetric determination

The electrooxidation of d-penicillamine (d-PA) was studied in the presence of ferrocyanide as a homogeneous mediator at the surface of a carbon paste electrode in aqueous media using cyclic voltammetry (CV) and chronoamperometry. Under optimum pH in CV the oxidation of d-PA occurs at a potential about 380 mV less positive than that in the absence of ferrocyanide. The catalytic oxidation peak current was dependent on the d-PA concentration and a linear calibration curve was obtained in the ranges 4.0 × 10⁻⁵–2.0 × 10⁻³ M and 8.0 × 10⁻⁶–1.8 × 10⁻⁴ M of d-PA with CV and differential pulse voltammetry (DPV) methods, respectively. The detection limits (3σ) were determined as 1.9 × 10⁻⁵ and 3.2 × 10⁻⁶ M by CV and DPV methods. This method was also used for the determination of d-PA in pharmaceutical preparations by the standard addition method.     

Simultaneous determination of dopamine and uric acid on nafion/sodium dodecylbenzenesulfonate composite film modified glassy carbon electrode

A novel electrochemical sensor has been constructed by using a glassy carbon electrode (GCE) coated with nafion/sodium dodecylbenzenesulfonate (SDBS). Differential pulse voltammetry (DPV) was used to study the electrochemical behaviors of dopamine (DA) and uric acid (UA). An optimum of 5 mM SDBS together with 0.05 wt% of nafion was used to improve the resolution and the determination sensitivity successfully. In 0.1 M phosphate buffer solution (pH 6.5), the modified electrode exhibited high electrocatalytical activity toward the oxidation of DA and UA with obvious reduction of overpotential. Compared with bare GCE, the modified electrode resolved the voltammetric response of DA and UA into two well-defined voltammetric peaks by DPV, which can be used for simultaneous determination of these species in mixture. The peak currents obtained from DPV were linearly related to the concentrations of DA and UA in the ranges of 4.0 × 10⁻⁷–8.0 × 10⁻⁵ M and 4.0 × 10⁻⁶–8.0 × 10⁻⁴ M, respectively. The detection limit of DA and UA (signal-to-noise ration was 3) were 5.0 × 10⁻⁸ and 4.0 × 10⁻⁷ M, respectively.     

Square-wave adsorptive stripping voltammetric determination of candesartan cilexetil in pharmaceutical formulations

A sensitive, simple and rapid square-wave adsorptive stripping voltammetric method was developed and validated for the determination of candesartan cilexetil in pharmaceutical formulations. The proposed method was based on electrochemical reduction of candesartan cilexetil at a hanging mercury drop electrode in phosphate buffer at pH 5.0. A well-defined reduction peak was observed at −1340 mV with 30 s of accumulation time and −1100 mV of accumulation potential. Under these optimized conditions, the square-wave adsorptive stripping voltammetric peak current showed a linear correlation on drug concentration over the range of 0.25–1.34 μg mL⁻¹ with a correlation coefficient of 0.9986 for the proposed method. The detection and quantitation limits for this method were 1 × 10⁻² and 2.5 × 10⁻¹ μg mL⁻¹, respectively. The results obtained for intra-day and inter-day precision (as RSD%) were between 1.10 and 3.90%. This method was applied successfully for the determination of candesartan cilexetil in its tablet dosage forms with mean recoveries of 101.13 ± 0.78% with RSD of 2.06% for 8 mg tablet and 99.84 ± 0.89% with RSD of 2.36% for 16 mg tablet. The results obtained from the developed square-wave adsorptive stripping voltammetric method were compared with those obtained by the analytical method reported in the literature.     

<Emphasis Type="Italic">Meso</Emphasis>-Tetra-(3,5-Dibromo-4-Hydroxydroxyphenyl) Porphyrin Copper (II) Self-Assembled Modified Gold Electrode Through <Emphasis Type="SmallCaps">l</Emphasis>-Cysteine: The Preparation,Electrochemical Behavior and its Application

In this study, a sensor for the sensitive determination of ascorbic acid (AA) has been fabricated based on meso-tetra-(3,5-dibromo-4-hydroxydroxyphenyl) porphyrin copper (II) (T(DBHP)P-Cu) modified Au electrode through l-cysteine (l-cys). Firstly, l-cys modified Au electrode was prepared through self-assembled technology. Then T(DBHP)P-Cu was adsorbed on l-cys/Au through covalent binding. The fabrication process and electrochemical behavior of T(DBHP)P-Cu/l-cys/Au were studied by cyclic voltammetry and differential pulse voltammetry. The results showed that AA exhibited good electrochemical activity at T(DBHP)P-Cu/l-cys/Au. The oxidation peak current increased linearly with AA concentration in the range of 1.00 × 10⁻³–1.02 × 10⁻⁵ mol L⁻¹ with a detection limit of 5.41 × 10⁻⁷ mol L⁻¹. Additionally, the modified electrode could be applied to the detect AA in practical samples.     

Voltammetric studies of a novel bicopper complex modified glassy carbon electrode for the simultaneous determination of dopamine and ascorbic acid

A novel modified glassy carbon electrode (GCE) with a binuclear copper complex was fabricated using a cyclic voltammetric method in phosphate buffer solution. This modified electrode shows very efficient electrocatalytic activity for anodic oxidation of both dopamine (DA) and ascorbic acid (AA) via substantial decrease in anodic overpotentials for both compounds. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) using this modified electrode show two well-resolved anodic waves for the oxidation of DA and AA in mixed solution, which makes it possible for simultaneous determination of both compounds. Linear analytical curves were obtained in the ranges 2.0–120.0 μM and 5.0–160.0 μM for DA and AA concentrations by using DPV methods, respectively. The detection limits were 1.4 × 10⁻⁶ M of DA and 2.8 × 10⁻⁶ M of AA. This electrode was used for AA and DA determinations in medicine and foodstuff samples with satisfactory results.     

Carbon nanotube-modified glassy carbon electrode for anodic stripping voltammetric detection of Uranyle

A multi-wall carbon nanotube (MWNT) modified glassy carbon electrode (GCE) is described for the measurement of trace levels of uranium by anodic stripping voltammetry. In a pH 4.4 NaAc-Hac buffer containing 0.010 mol L⁻¹ Mg(NO₃)₂, UO₂ ²⁺ was adsorbed onto the surface of a MWNT film coated glassy carbon electrode and then reduced at −0.40 V vs. Ag/AgCl. During the positive potential sweep the reduced uranium was oxidized and a well-defined stripping peak appeared at +0.20 V vs. Ag/AgCl. Low concentrations of Mg²⁺ significantly enhanced the stripping peak currents since they induced UO₂ ²⁺ to adsorb at the electrode surface. The response was linear up to 1.2 × 10⁻⁷ mol L⁻¹ and the relative standard deviation at 2.0 × 10⁻⁸ mol L⁻¹ uranium was 5.2%. Potential interferences were examined. The attractive behavior of the new “mercury-free” uranium sensor holds promise for on-site environmental and industrial monitoring of uranium.     

Selective electrochemical behavior of highly conductive boron-doped diamond electrodes for fluvastatin sodium oxidation

Boron-doped diamond electrodes have received much attention for electrochemical determination due to their attractive electrochemical properties over other electrodes. The electrooxidation of fluvastatin sodium at boron-doped diamond electrode was investigated using cyclic, differential pulse and square wave voltammetry. The possible mechanism of oxidation was discussed with model compounds that have indole oxidation. The dependence of the peak current and potentials on pH, concentration, scan rate, and the nature of the buffer were investigated. The oxidation of fluvastatin was irreversible and exhibited a diffusion-controlled fashion. The slope of the log i_p–log v linear plot was 0.44 indicating the diffusion control for pH 10.00 Britton–Robinson buffer solution. The linear response was obtained in the ranges of 1 × 10^− 6 M–6 × 10^− 4 M in pH 10.00 BR buffer solution. The detection limit of the standard solution is estimated to be 1.37 × 10^− 7 M for DPV, 1.44 × 10^− 7 M for SWV. The repeatability of the methods was found as 0.66 and 0.15 RSD % for peak currents for differential pulse and square wave voltammetry, respectively. The practical analytical value of the method is demonstrated by quantitative determination of fluvastatin in pharmaceutical formulation and human serum, without the need for separation or complex sample preparation, since there was no interference from the excipients and endogenous substances. Selectivity, reproducibility and accuracy of the developed methods were demonstrated by recovery studies.     

Electrochemical determination of ascorbic acid at the surface of a graphite electrode modified with multi-walled carbon nanotubes/tetradecyltrimethylammonium bromide

A multi-walled carbon nanotubes (MWCNTs)–tetradecyltrimethylammonium bromide (TTAB) film-coated graphite electrode (GE) was fabricated, and the electrochemical oxidation of ascorbic acid (AA) was studied in Britton–Robinson (B–R) buffer (pH 7.0) using cyclic, square wave, and differential pulse voltammetry (CV, SWV, and DPV). An electroanalytical study of AA and acetaminophen (ACOP) and of several mixtures of these compounds in different ratios was made. A sensitive linear voltammetric response for AA was obtained for the concentration range of 5 × 10⁻⁷ to 1.7 × 10⁻⁴ mol L⁻¹, with a correlation coefficient of 0.992, and the detection limit for AA was found to be 1.1 × 10⁻⁷ mol L⁻¹ using DPV. The relative standard deviation (RSD) was 2.7%, suggesting that the film electrode has excellent day-to-day reproducibility. The proposed voltammetric approach was also applied to the determination of the AA concentration in commercial tablets.     

Selective determination of uric acid in the presence of ascorbic acid at poly(<Emphasis Type="Italic">p</Emphasis>-aminobenzene sulfonic acid)-modified glassy carbon electrode

The electrocatalytic behavior of uric acid has been investigated with a glassy carbon electrode modified with p-aminobenzene sulfonic acid through electrochemical polymerization. This resulting electrode shows an excellent electrocatalytic response to uric acid and ascorbic acid, with a peak-to-peak separation of 0.267 V in a 0.1 mol L⁻¹ phosphate buffer solution (PBS) at pH 7.0. These results indicate that the proposed electrode can eliminate the serious interference of ascorbic acid, which coexists with uric acid in body fluids. Differential pulse voltammetry (DPV) was used for detecting uric acid with selectivity and sensitivity. The anodic peak current of uric acid was proportional to its concentration in the range of 1.2 × 10⁻⁷–8.0 × 10⁻⁴ mol L⁻¹, with a detection limit of 4.0 × 10⁻⁸ mol L⁻¹. The proposed method has been applied with satisfactory results to the determination of uric acid in human urine without any pretreatment.     

Voltammetric behavior and the determination of quercetin at a flowerlike Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles modified glassy carbon electrode

Flowerlike Co₃O₄ nanoparticles were used as a modifier on the glassy carbon electrode to fabricate a quercetin (Qu) sensor. The morphology and crystallinity of the prepared Co₃O₄ material were investigated by scanning electron microscopy and X-ray diffraction. Electrochemical behavior of Qu at the sensor was studied by cyclic voltammetry and semi-derivative voltammetry. Results suggested that the modified electrode exhibited a strong electrocatalytic activity toward the redox of Qu. The electron transfer coefficient (α), the number of electron transfer (n), and the diffusion coefficient (D) of Qu at the sensor were calculated. Under the optimum conditions, the catalytic peak currents of Qu were linearly dependent on the concentrations of Qu in the range from 5.0 × 10⁻⁷ to 3.3 × 10⁻⁴ M, with a detection limit of 1.0 × 10⁻⁷ M. This proposed method was successfully applied to determine the quercetin concentration in Ginkgo leaf tablet and human urine samples.     

Development of a new biosensor for mediatorless voltammetric determination of hydrogen peroxide and its application in milk samples

A new biosensor for the voltammetric detection of hydrogen peroxide was developed based on immobilization of catalase on a clinoptilolite modified carbon paste electrode using bovine serum albumin and glutaraldehyde. The biosensor response was evaluated according to electrode composition, reaction time, solution pH and temperature. The voltammetric signals were linearly in proportion to H₂O₂ concentration in the range 5.0 × 10⁻⁶–1.0 × 10⁻³ M with a correlation coefficient of 0.9975. The detection limit is 8.0 × 10⁻⁷ M and the relative standard deviation for 4.0 × 10⁻⁴ M hydrogen peroxide was 1.83% (n = 6). The biosensor exhibited high sensitivity, and it was determined that it could be used for more than 2 months. In addition, the biosensor was successfully applied for the determination of hydrogen peroxide in milk samples.     

Development of an adsorptive catalytic stripping voltammetric method for the determination of an endocrine disruptor pesticide chlorpyrifos and its application to the wine samples

A very sensitive voltammetric method for the determination of an endocrine disruptor Chlorpyrifos (CP) insecticide at ng mL⁻¹ level was described. The pesticide was accumulated at a hanging mercury drop electrode (HMDE) and a well-resolved reduction peak was observed at −1.2 V (vs. Ag/AgCl) in pH: 2.0 media containing 5% aqueous ethanol solution. A systematic investigation of the solution parameters and operational parameters which affect the stripping response were carried out with differential pulse voltammetry. With an accumulation potential of −0.5 V and an accumulation time of 60 s, the detection and quantification limits were found to be 0.14 and 0.45 ng mL⁻¹, respectively. The remarkable sensitivity of the method was attributed to a catalytic process as concluded from cyclic voltammetry. The degree of interference from diverse ions and some other pesticides on the differential pulse stripping signal for CP was evaluated. The method developed was adapted for wine samples. The matrix effect of red wine was eliminated by means of liquid–liquid extraction (LLE) followed by solid-phase extraction (SPE) with satisfactory recovery values. This method offers a very sensitive and inexpensive way for determining CP residues in red wines.     

Simultaneous determination of trace aluminum (III), copper (II) and cadmium (II) in water samples by square-wave adsorptive cathodic stripping voltammetry in the presence of oxine

A validated adsorptive cathodic stripping voltammetry method is described for simultaneous determination of Al(III), Cu(II) and Cd(II) in water samples. In acetate buffer (pH 5) containing 10 μM oxine, these metal ions were determined as oxine complexes following adsorptive accumulation onto the HMDE at −0.05 V versus Ag/AgCl/KCl_s. The best signal to noise ratio was obtained using a square wave of scan increment 10 mV, frequency 120 Hz, and pulse-amplitude 25 mV. Limits of detection as low as 0.020 μg L⁻¹ Al(III), 0.012 μg L⁻¹ Cu(II) and 0.028 μg L⁻¹ Cd(II) were achieved. Interference due to various cations (K(I), Na(I), Mg(II), Ca(II), Mn(II), Fe(III), Bi(III), Sb(III), Se(IV), Pb(II), Zn(II), Ni(II), Co(II)), anions (Cl⁻, NO³⁻, SO₄ ²⁻, PO₄ ³⁻) and ascorbic acid was minimal as the measured signals change by 4% at the maximum. The stripping voltammetry method was successfully applied for simultaneous determination of Al(III), Cu(II) and Cd(II) in tap and natural bottled water samples.     

Electrochemical investigations of an anticancer drug in the presence of sodium dodecyl sulfate as an enhancing agent at carbon paste electrode

In the present work, the electrochemical behavior of an anticancer drug, gemcitabine hydrochloride (GMB) was studied in the presence of a surface active agent (surfactant) at carbon paste electrode (CPE). GMB showed an oxidation peak at 1.101 V. The presence of sodium dodecyl sulfate (SDS) in the electrolyte was found to enhance the oxidation signal of GMB at CPE. The oxidation peak current of GMB in the presence of SDS was observed to be the function of accumulation time, scan rate, pH of the medium, and concentration of GMB. Accumulation time greatly influenced the peak current but did not exhibit significant influence on the peak potential. Based on this, a novel, sensitive, and convenient differential pulse voltammetric method was developed for the determination of GMB in the concentration range of 5.0 × 10⁻⁸–3.0 × 10⁻⁴ M with a limit of detection value of 8.2 × 10⁻⁹ M. The proposed procedure was successfully applied for the determination of GMB in pharmaceutical formulations and spiked biological samples.