Electrochemical investigation of hymecromone at a multi-wall carbon nano-tube/cetyl pyridine bromine composite film electrode

A multi-wall carbon nanotube (MWNT)/cetyl pyridine bromine (CPB) composite film modified glassy carbon electrode (GCE) was developed for the electrochemical determination of hymecromone in phosphonate buffer. Electrochemical behaviour of hymecromone at the composite film electrode was investigated with voltammetry. Compared with an irreversible oxidation of hymecromone at the bare GCE, the oxidation peak current was enhanced greatly at the film electrode. Some parameters such as pH, scan rate, accumulation potential and accumulation time were optimized. Under optimal conditions, an oxidation peak at 0.82 V was employed to determine hymecromone electrochemically. A linearity between the oxidation peak current and the hymecromone concentration was obtained in the range of 3.0 × 10⁻⁷ − 2.0 × 10⁻⁵ mol 1⁻¹ with a detection limit of 8.0 × 10⁻⁸ mol 1⁻¹. The proposed procedure was successfully applied to assay hymecromone in pharmaceutical formulation with satisfactory results. The text was submitted by the authors in English.     

The electrochemical properties of dopamine,epinephrine and their simultaneous determination at a poly(L-methionine) modified electrode

A poly(L-methionine) modified electrode, fabricated by electrochemical immobilization of the L-methionine on a glassy carbon electrode, was used for simultaneous determination of dopamine and epinephrine through cyclic voltammetry. The electrochemical properties of dopamine and epinephrine have been investigated. This sensor gave two separated cathodic peaks at −0.282 and 0.112 V for EP and DA, respectively. A linear response was obtained in the range of 5.0 × 10⁻⁷ to 1.0 × 10⁻⁴ mol l⁻¹ for epinephrine, and 1.0 × 10⁻⁶ to 5.0 × 10⁻⁴ mol l⁻¹ for dopamine. The detection limits were 3.6 × 10⁻⁷ mol l⁻¹ and 4.2 × 10⁻⁷ mol l⁻¹ for epinephrine and dopamine, respectively. This method was successfully applied for simultaneous determination of dopamine and epinephrine in human urines. The text was submitted by the authors in English.     

Preconcentration and Voltammetric Determination of the Antihypertensive Doxazosin on a C8 Modified Carbon Paste Electrode

 An electrochemical study of the doxazosin oxidative process at carbon paste electrodes using different voltammetric techniques has been carried out. The process is irreversible and controlled by adsorption, giving rise to an oxidation wave around 1.0 V in citric acid-citrate buffer (pH 3.0). A mechanism based on the oxidation of the amine group is postulated. Two methods based on adsorptive stripping (AdS) of doxazosin at the C₈-modified carbon paste electrode (C₈-MCPE), before its voltammetric determination, are studied, using differential pulse voltammetry (DPV) and square wave voltammetry (SWV) as redissolution techniques. By means of AdS-DPV and C₈-MCPE, doxazosin can be determined over the 1.0 × 10⁻⁹ to 3.0 × 10⁻⁸ mol L⁻¹ range with a variation coefficient of 2.2% (2.0 × 10⁻⁸ mol L⁻¹) and a limit of detection of 7.4 ×10⁻¹⁰ mol L⁻¹. If AdS-SWV is used, a linear range from 1.0 × 10⁻⁹ to 4.0 × 10⁻⁸ mol L⁻¹ is obtained, the variation coefficient being 2.8% (2.0 × 10⁻⁸ mol L⁻¹, and the limit of detection reached 7.7 × 10⁻¹⁰ mol L⁻¹. The AdS-DPV procedure was applied to the determination of doxazosin in urine and formulations. Received March 13, 1999. Revision December 23, 1999.     

Electrochemical behaviors of ofloxacin and its voltammetric determination at carbon nanotubes film modified electrode

A multi-wall carbon nanotubes (MWNTs)-Nafion film-coated glassy carbon electrode (GCE) was fabricated and the electrochemical behavior of ofloxacin on the MWNTs-Nafion film-coated GCE were investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The oxidation peak current of ofloxacin increased significantly on the MWNTs-Nafion film modified GCE compared with that using a bare GCE. This nano-structured film electrode exhibited excellent enhancement effects on the electrochemical oxidation of ofloxacin. A well-defined oxidation peak attributed to ofloxacin was observed at 0.97 V and was applied to the determination of ofloxacin. The oxidation peak current was proportional to ofloxacin concentration in the ranges 1.0 × 10⁻⁸ to 1.0 × 10⁻⁶ mol/L and 1.0 × 10⁻⁶ to 2.0 × 10⁻⁵ mol/L. A detection limit of 8.0 × 10⁻⁹ mol/L was obtained for 400 s accumulation at open circuit (S/N = 3). This method for the detection of ofloxacin in human urine was satisfactory. __________ Translated from Chinese Journal of Applied Chemistry, 2007, 24(5): 540–545 [译自: 应用化学]     

Electrochemical Determination of 10-Hydroxycamptothecin Using a Multi-Wall Carbon Nanotube-Modified Electrode

We report a sensitive and convenient voltammetric method for the direct determination of 10-hydroxycamptothecin (HCPT). At a multi-wall carbon nanotube (MWNT)-modified electrode, HCPT yields a very sensitive and well-shaped oxidation peak, which can be used as analytical signal for HCPT determination. Compared with the poor electrochemical signal at the unmodified GCE, the electrochemical response of HCPT at the MWNT-modified GCE was greatly improved, as confirmed by the significant peak current enhancement. This result indicates that the MWNT-modified GCE has great potential in the sensitive determination of HCPT. Based on this, a very sensitive and simple electrochemical method was proposed for HCPT determination after all the experimental parameters were optimized. The newly-proposed method possesses very low detection limit (2 × 10⁻⁹ mol L⁻¹) and wider linear range (from 1 × 10⁻⁸ to 4 × 10⁻⁶ mol L⁻¹). Rapid and simple sample analysis is another advantage. Finally, this method was successfully demonstrated using HCPT drugs.     

Electrochemical study of brucine on an electrode modified with magnetic carbon-coated nickel nanoparticles

A novel type of glassy carbon electrode modified with magnetic carbon-coated nickel nanoparticles (C-Ni/GCE) was fabricated and the electrochemical properties of brucine were studied using it. The carbon-coated nickel nanoparticles showed excellent electrocatalytic activity for the redox of brucine and an enhanced electron transfer rate. The electrochemical behavior of brucine on the C-Ni/GCE was explored by cyclic voltammetry (CV), and a redox mechanism for brucine was proposed. A series of electrochemical parameters were calculated for brucine by CV and controlled-potential electrolysis. The C-Ni/GCE showed good sensitivity, selectivity and stability, and was applied to determine the concentration of brucine. The differential pulse voltammetry (DPV) response of the C-Ni/GCE showed that the catalytic current was linear with the concentration of brucine in the range of 4.7 × 10⁻⁸ to 2.4 × 10⁻⁴ mol l⁻¹, with a correlation coefficient of 0.998. The detection limit was 1.4 × 10⁻⁸ mol l⁻¹.     

Preconcentration and Voltammetric Study of Nicergoline at a Carbon Paste Electrode

 The electrochemical oxidation of nicergoline is investigated using cyclic and differential pulse voltammetry at a carbon paste electrode. For the determination of nicergoline an adsorptive stripping procedure is proposed. The response is characterized with respect to pH, ionic strength, preconcentration time, accumulation potential, nicergoline concentration, reproducibility and other variables. By differential pulse voltammetry at a carbon paste electrode and pH 8.0, a linear calibration in the range 5×10⁻⁸ M to 1×10⁻⁷ M and a detection limit of 1×10⁻⁸ M are obtained. The preconcentration medium-exchange approach was used for a selective determination of nicergoline in urine. For dilute urine samples a detection limit of 5×10⁻⁸ M is obtained after 3 min of accumulation and medium-exchange. The procedure also is applied for the determination of nicergoline in dosage form. Received August 24, 1998. Revision April 8, 1999.     

Sensitive determination of 4-nitrophenol based on multi-walled carbon nano-tube/ionic liquid/chitosan composite film modified electrode

A composite film modified glassy carbon electrode (GCE) fabricated with spinning coating of multiwalled carbon nano-tube (MWNT) /1-butyl-3-methylimidazolium tetrafluoroborate/chitosan sol was developed for the electrochemical determination of 4-nitrophenol (4-NP). An obvious reduction peak located at about −0.688 V was observed with voltammetric measurements in the potential range from 0.200 V to −1.00 V. Compared with the bare GCE, the reduction peak potential shifted positively and the peak current increased significantly. All experimental parameters for the determination of 4-NP were optimized. It was found that the reduction peak current was proportional to 4-NP concentration in the range from 3.00 × 10⁻⁷ to 2.00 × 10⁻⁵ mol l⁻¹ with the detect limitation of 1.00 × 10⁻⁷ mol l⁻¹ (S/N = 3) after accumulation for 90 s. The proposed method was successfully applied for the determination of trace amounts of 4-NP in lake water.     

Determination of rutin using a CeO2 nanoparticle-modified electrode

CeO₂ nanoparticles approximately 12 nm in size were synthesized and subsequently characterized by XRD, TEM and UV-vis spectroscopy. Then, a gold electrode modified with CeO₂ nanoparticles was constructed and characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The modified electrode demonstrated strong catalytic effects with high stability towards electrochemical oxidation of rutin. The anodic peak currents (measured by differential pulse voltammetry) increased linearly with the concentration of rutin in the range of 5.0 × 10⁻⁷–5.0 × 10⁻⁴ mol · L⁻¹. The detection limit (S/N = 3) was 2.0 × 10⁻⁷ mol · L⁻¹. The relative standard deviation (RSD) of 8 successive scans was 3.7% for 5.0 × 10⁻⁶ mol · L⁻¹ rutin. The method showed excellent sensitivity and stability, and the determination of rutin in tablets was satisfactory.     

Study and Application of Electrochemical Behavior of Calcium-ARS on a Mercury Film Electrode

A sensitive complex absorptive wave of Ca-ARS was obtained by using differential pulse voltammetry when a mercury film glass carbon electrode was immersed in 0.1 mol L⁻¹ KOH and 4.5×10⁻⁴ mol L⁻¹ ARS solution. The peak potential obtained was −1.17 V (vs Ag-AgCl). The peak current was proportional to the concentration of calcium in the range of 5.0×10⁻⁸−4.2×10⁻⁵ mol L⁻¹. The detection limit was 2.0×10⁻⁸ mol L⁻¹. This method was applied successfully to determining traces of calcium in blood serum. The electrochemical behavior of the system was also studied by cyclic voltammetry, and the experiment results showed that the electrode process was an irreversible absorptive with two electrons participating. Translated from Journal of Beijing Normal University (Natural Science Edition), 2005, 41(2) (in Chinese)     

Application of a Single-Wall Carbon Nano-Tube Film Electrode to the Determination of Trace Amounts of Folic Acid

Single-wall carbon nano-tubes were used to modify the surface of a glassy carbon electrode (GC) and applied in the determination of folic acid with voltammetry. The experiments demonstrated that the presence of a carbon nano-tube film on the electrode greatly increased the reduction peak current of folic acid. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were used in a comparative investigation of the electrochemical reduction of folic acid with the film electrode. Effects of pH on the peak current and the peak potential were studied in the pH range of 4.0–8.0 with Britton-Robinson buffer solution. The reduction peak current was found to be linearly related to folic acid concentration over the range of 1 × 10⁻⁸ to 1 × 10⁻⁴ mol L⁻¹ with a detection limit of 1 × 10⁻⁹ mol L⁻¹ after 5 min accumulation. The film electrode provides an efficient way for eliminating interferences from some inorganic and organic species in the solution. The high sensitivity, selectivity and stability of the film electrode demonstrate its practical application from a simple and rapid determination of folic acid in tablets.     

Electrochemical deposition of silicate–cetyltrimethylammonium bromide nanocomposite film on glassy carbon electrode for sensing of methyl parathion

A novel electrochemical sensor for methyl parathion based on silicate– cetyltrimethylammonium bromide nanocomposite film has been fabricated by electro-assisted deposition onto glassy carbon electrode in one-step via an electrochemical modulation of pH at the electrode/solution interface to promote controlled gelification of tetraethylorthosilicate sol, and was characterized with scanning electron microscopy, X-ray diffraction, and electrochemical impedance spectroscopy. The electrochemical sensing of methyl parathion on the film-modified electrode was investigated applying cyclic voltammetry and square wave voltammetry. Compared to the unmodified electrode, the shapes of the redox peaks were improved and the peak currents significantly increased. Experimental parameters such as deposition time, pH value, and accumulation conditions have been optimized. A linear relationship between the peak current and methyl parathion concentration was obtained in the range from 1.0 × 10⁻⁷ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 1.04 × 10 ⁻⁸ mol L⁻¹ (S/N = 3) after accumulation at 0 V for 120 s. The film electrode shows great promise for determination of methyl parathion in real samples.      

Fabrication of a Multi-wall Carbon Nanotubes Modified Glassy Carbon Electrode and its Catalytic Effect on the Oxidation of Estradiol, Estrone and Estriol

 Multi-wall carbon nanotubes (MWNT) have been dispersed into water with the emulsification of oil of turpentine and emulsifier OP TX-100. An MWNT-modified glassy carbon electrode (GCE) has been achieved through solvent evaporation of MWNT- dispersion. In pH 2.0 phosphate buffer, MWNT- modified GCE has an obvious catalytic effect on the oxidation of estradiol, estrone and estriol. The oxidation peak current of these estrogens at the modified electrode increases significantly in contrast with that at the bare GCE. The experimental conditions which heavily affect the oxidation peak current of estradiol, such as the solution pH, the amount of MWNT, the scan rate, the adsorption potential and adsorption time, were optimized. The peak current is linear to the concentration in the range of 2.5 × 10⁻⁷ to 5 × 10⁻⁵ mol L⁻¹ estradiol. The detection limit is 1 × 10⁻⁸ mol L⁻¹ after 3 min open-circuit adsorption. The relative standard deviation (RSD) of six measurements using an electrode is 3.2% for 1 × 10⁻⁵ mol L⁻¹ estradiol. The effect of interferences of other organic compounds on the determination of estradiol was examined. Author for correspondence: Department of Chemistry, Wuhan University, Wuhan 430072, P.R. China. E-mail: sshu@whu.edu.cn Received June 19, 2002; accepted January 4, 2003 Published online April 11, 2003     

A novel electrochemical method for the determination of trinitrophenol

In pH 5.5, 0.1 mol l⁻¹ HAc-NaAc buffer solution, trinitrophenol has been determined quantitatively with differential pulse voltammetry by detecting its reduction peak currents at the glassy carbon electrode. The detection sensitivity was enhanced significantly by the addition of the surfactant of cetyl pyridinium chloride, and the enhancement mechanism was also studied in detail. The linear calibration range was 8.0 × 10⁻⁷ to 2.0 × 10⁻⁴ mol l⁻¹, and the detection limit was established to be 1.9 × 10⁻⁷ mol l⁻¹. This method has been applied to the determination of trinitrophenol in water sample, and the recovery was from 97.6 to 103.5%.     

Voltammetric determination of 2-chlorophenol using a glassy carbon electrode coated with multi-wall carbon nanotube-dicetyl phosphate film

Multi-wall carbon nanotubes (MWNT) were dispersed into water in the presence of dicetyl phosphate (DCP), and MWNT-DCP composite film coated glassy carbon electrodes (GCE) were constructed. The electrochemical properties of 2-chlorophenol at a bare GCE and MWNT-DCP modified GCE were compared. It was found that MWNT-DCP modified GCEs significantly enhance the oxidation peak current of 2-chlorophenol and lowers its oxidation overpotential, suggesting great potential in the sensitive determination of 2-chlorophenol. Finally, a sensitive and simple voltammetric method was developed for the determination of 2-chlorophenol. The oxidation peak current increases linearly with the concentration in the range of 1.0 × 10⁻⁷–2.0 × 10⁻⁵ mol L⁻¹, and the detection limit is 4.0 × 10⁻⁸ mol L⁻¹ for 2 min accumulation. The method was successfully used to determine 2-chlorophenol in waste water samples.     

Catalytic adsorptive stripping voltammetric determination of copper(II) on a carbon paste electrode

A catalytic adsorptive stripping voltammetric method for the determination of copper(II) on a carbon paste electrode (PCE) in an alizarin red S (ARS)-K₂S₂O₈ system is proposed. In this method, copper(II) is effectively enriched by both the formation and adsorption of a copper(II)-ARS complex on the PCE, and is determined by catalytic stripping voltammetry. The catalytic enhancement of the cathodic stripping current of the Cu(II) in the complex results from a redox cycle consisting of electrochemical reduction of Cu(II) ion in the complex and subsequent chemical oxidation of the Cu(II) reduction product by persulfate, which reduces the contamination of the working electrode from Cu deposition and also improves analytical sensitivity. In Britton-Robinson buffer (pH 4.56±0.1) containing 3.6×10⁻⁵ mol L⁻¹ ARS and 1.6×10⁻³ mol L⁻¹ K₂S₂O₈, with 180 s of accumulation at −0.2 V, the second-order derivative peak current of the catalytic stripping wave was proportional to the copper(II) concentration in the range of 8.0×10⁻¹⁰ to ∼3.0×10⁻⁸ mol L⁻¹. The detection limit was 1.6×10⁻¹⁰ mol L⁻¹. The proposed method was evaluated by analyzing copper in water and soil.     

Multi-walled carbon nanotubes modified glass carbon electrode and its electrocatalytic activity towards oxidation of paracetamol

Multi-walled carbon nanotubes (MWNTs) modified glassy carbon electrode (GCE) was simply and conveniently fabricated. The electrochemical properties of paracetamol (PCT) at the prepared modified electrode were investigated by cyclic voltammetry (CV). Based on this, an ultrasensitive and rapid electrochemical method was developed for the determination of PCT. The result indicated that the oxidation of PCT was greatly improved at the MWNTs-modified GC (MWNTs/GC) electrode as compared with the bare GC electrode, with relatively high sensitivity, stability and life time. Good linear relationship between the oxidation peak current and the PCT concentration in the range of 1 × 10⁻⁷ to 1 × 10⁻³ M (r = 0.996) was obtained in phosphate buffer solution (PBS) with pH 6.5, the detection limit was 2 × 10⁻⁸ M (S/N = 3) by use of modified electrode. The proposed method was successfully applied to the PCT determination in tablets.     

Voltammetric determination of pentachlorophenol with a silica gel-modified carbon paste electrode

Summary The anodic voltammetric behaviour of pentachlorophenol at a silica gel-modified carbon paste electrode in aqueous solution is reported. Adsorption of the fungicide onto the electrode under open-circuit conditions is followed by application of either differential or square wave voltammetry. The results obtained by differential pulse voltammetry at pH 2.9, with a modifier concentration of 10% and accumulation times of 120 and 300 s, allowed the development of a method to determine pentachlorophenol in the ranges of 1.0×10⁻⁶–1.0×10⁻⁵ and 1.0×10⁻⁷–1.0×10⁻⁶ mol l⁻¹. The relative standard deviation is 2.6% for a concentration of 2.0×10⁻⁷ mol l⁻¹, with a detection limit of 1.8×10⁻⁸ mol l⁻¹ (5 ppb). The effect of other chlorophenols was studied. The results obtained by square wave voltammetry showed a behaviour typical of an irreversible electron transfer. Amplitude, step height and frequency were optimised, taking into account the resolution of the voltammetric response. No improvement in sensitivity was obtained with respect to DPV. Good results were obtained by applying the proposed differential-pulse voltammetric method to the determination of pentachlorophenol in a commercial fungicide.     

Chiral Recognition of Penicillamine Enantiomers Based on DNA‐MWNT Complex Modified Electrode

Double‐stranded DNA and multiwalled carbon nanotube (MWNT) complex modified glassy carbon electrodes (DNA‐MWNT‐GCE) were employed to discriminate penicillamine (PA) enantiomers. Cyclic voltammetry, electrochemical impedance spectroscopy, atomic force microscopy and ultraviolet‐visible spectroscopy were used to characterize the enantioselective phenomenon. The results indicated that the binding effect between L ‐PA and DNA‐MWNTs was stronger than that of D ‐PA and DNA‐MWNTs. In addition, the influencing factors of the modified electrodes were systematically investigated. The modified electrodes exhibited a linear response towards PA enantiomers from 1.0×10^?1 to 1.0×10^?8 mol L^?1 and detection limits of 3.1×10^?9 and 3.3×10^?8 mol L^?1 for L ‐PA and D ‐PA, respectively.     

Simultaneous determination of oxalate, thiosulfate, and thiocyanate in urine by ion-exclusion chromatography with electrochemical detection

Summary A sensitive ion-exclusion chromatographic method has been developed for determination of oxalate, thiosulfate, and thiocyanate. The method is based on separation of these anions on a polymethacrylate-based, weakly acidic cation-exchange resin (TSKgel OApak-A) and detection by means of a glassy carbon (GC) electrode electrochemically modified with polyvinylpyridine (PVP), palladium, and iridium oxide (PVP/Pd/IrO₂). The electrochemical behavior of oxalate, thiosulfate, and thiocyanate at this chemically modified electrode (CME) have been investigated by cyclic voltammetry. The results indicated that electrocatalytic oxidation of these anions by the electrode was efficient and that the sensitivity, stability, and lifetime of the electrode were relatively high. Combined with ion-exclusion chromatography the PVP/Pd/IrO₂ electrode was used as the working electrode for amperometric detection of these anions. All linear ranges were over two orders of magnitude and detection limits, defined asS/N=3, were 9.0×10⁻⁷ mol L⁻¹ for oxalate, 6.7×10⁻⁷ mol L⁻¹ for thiosulfate, and 5.6×10⁻⁷ mol L⁻¹ for thiocyanate. Correlation coefficients were all>0.998. Coupled with microdialysis sampling the method has been successfully applied to the determination of oxalate, thiosulfate, and thiocyanate in urine.