多壁碳纳米管修饰电极测定诺氟沙星

运用循环伏安法、线性扫描伏安法及示差脉冲伏安法等测试技术研究了诺氟沙星在多壁碳纳米管修饰玻碳电极上的电化学行为,建立了一种直接测定诺氟沙星的电化学分析方法.结果表明,与裸玻碳电极相比,多壁碳纳米管修饰电极能显著提高诺氟沙星的氧化峰电流.在优化的实验条件下,氧化峰电流与诺氟沙星浓度在1.0×10-7～1.0×10-6mol/L和1.0×10-6～2.5×10-5 moL/L范围呈现良好的线性关系,检出限为3.0×10-8mol/L对1.0×10-5mol/L诺氟沙星溶液平行测定10次的RSD为4.1%.测定了诺氟沙星胶囊中诺氟沙星的含量,结果满意.     

Voltammetric determination of bisoprolol fumarate in pharmaceutical formulations and urine using single-wall carbon nanotubes modified glassy carbon electrode

The electrochemistry of bisoprolol fumarate (BF) has been investigated by differential pulse voltammetry at a single-wall carbon nanotubes (SWNTs) modified glassy carbon electrode (GCE). The prepared electrode showed an excellent electrocatalytic activity towards the oxidation of BF leading to a marked improvement in sensitivity as compared to bare glassy carbon electrode where electrochemical activity for the analyte cannot be observed. The SWNTs-modified GCE exhibited a sharp anodic peak at a potential of ∼950 mV for the oxidation of BF. Under optimum conditions linear calibration curve was obtained over the BF concentration range 0.01-0.1 mM in 0.5 M phosphate buffer solution (pH 7.2) with a correlation coefficient of 0.9789 and detection limit of 8.27 × 10⁻⁷ M. The modified electrode has been applied for the drug determination in human urine with no prior extraction and in commercial tablets. The proposed method has also been validated.     

Multivariate curve resolution as a tool to minimize the effects of electrodic adsorption in normal pulse voltammetry

Multivariate curve resolution by alternating least squares (MCR-ALS) was applied to normal pulse voltammograms (NPV) of heavy metal complexes that adsorb on the electrode. Adsorption usually causes: (i) a maximum superimposed on NPV waves, (ii) a decrease of the limiting current and (iii) a shift of half-wave potentials. Together, these effects result in excessively high stability constants when electrochemical methods of equilibrium calculation are applied. As an example of this behaviour, the Cd(II)-polymethacrylate (PMA) system was chosen.Despite the non-linearity of electrodic adsorption, MCR-ALS allows the decomposition of currents into three ca. linear contributions: (i) reduction of the free metal ion diffusing from the bulk solution, (ii) reduction of the metal complex also diffusing from the bulk and (iii) reduction of the metal ion accumulated by adsorption onto the electrode surface prior to pulse application. This almost ideal situation is achieved at high pulse times (which ensures that the adsorptive contribution is not much higher than the diffusive ones) and especially when NPV signals are analyzed in derivative form. Under these conditions, reasonable lacks of fit are obtained, as well as stability constants coincident with these determined by reverse pulse voltammetry (RPV), a technique especially unaffected by adsorption.     

Simultaneous determination of levodopa, carbidopa and tryptophan using nanostructured electrochemical sensor based on novel hydroquinone and carbon nanotubes: Application to the analysis of some real samples

In the present paper, the use of a novel carbon paste electrode modified by 2, 2′-[1,2-ethanediylbis (nitriloethylidyne)]-bis-hydroquinone (EBNBH) and carbon nanotubes prepared by a simple and rapid method for the determination of levodopa (LD), carbidopa (CD) and tryptophan (Trp) was described. In the first part of the work, cyclic voltammetry was used to investigate the redox properties of this modified electrode at various scan rates. The apparent charge–transfer rate constant, k_s, and transfer coefficient, α, for electron transfer between EBNBH and carbon nanotube paste electrode were calculated. In the second part of the work, the mediated oxidation of LD at the modified electrode was described. It has been found that under optimum condition (pH 7.0) in cyclic voltammetry, the oxidation of LD occurs at a potential about 460 mV less positive than that of an unmodified carbon paste electrode. The values of electron transfer coefficient (α), catalytic rate constant (k_h′) and diffusion coefficient (D) were calculated for LD, using electrochemical approaches. Differential pulse voltammetry (DPV) exhibited two linear dynamic ranges and a detection limit (3σ) of 0.094 μM for LD. In the third part of the work, simultaneous determination of LD, CD and Trp at the modified electrode was described. Finally, this method was used for the determination of LD in some real samples, using standard addition method.     

Poly(2-amino-4-thiazoleacetic acid)/multiwalled carbon nanotubes modified glassy carbon electrodes for the electrochemical detection of copper(II)

Poly(2-amino-4-thiazoleacetic acid)/multiwalled carbon nanotubes modified glassy carbon electrodes obtained by electropolymerization of 2-amino-4-thiazoleacetic acid, were used for the voltammetric determination of copper ions. The voltammetric response of copper ions at poly(2-amino-4-thiazoleacetic acid)/multiwalled carbon nanotubes modified glassy carbon electrodes was evaluated by differential pulse stripping voltammetry. The peak currents were linearly dependent on the concentrations of the copper ions in the range from 7.0 × 10⁻⁷ M to 5.0 × 10⁻⁵ M, with a coefficiency of 0.9987. The detection limit is 5.0 × 10⁻¹⁰ M calculated for a signal-to-noise ratio of 3 (S/N = 3). And it could be used for the simultaneous determination of copper and cadmium ions. The proposed method was successfully applied to the determination of copper ions in natural water. The concentration of Cu²⁺ was calculated to be 2.0 × 10⁻⁵ M by standard addition method. The recovery rate was 94%.     

Fabrication of the single-wall carbon nanotube compound polymer film electrode and the simultaneous electrochemical behavior of aminophenol isomers

We describe a simple, rapid and selective voltammetry for simultaneous determination of electroactive isomers using nanometer composite electrode. The electrode was constructed by electropolymerization of 4-aminopyridine at single-wall carbon nanotubes modified glassy carbon electrode (SWNTs/POAPE). The configuration and electrochemical properties of SWNTs/POAPE were characterized by scanning electronic micrographs (SEM) and voltammetry. The SWNTs/POAPE showed an excellent electrocatalytic activity to the oxidation of aminophenol isomers and capability of determining three aminophenol isomers simultaneously. The oxidation peak potential difference between m-aminophenol and o-aminophenol was 416 mV, o-aminophenol and p-aminophenol 119 mV, indicating that the o-, m- and p-aminophenol could be identified entirely at the SWNTs/POAPE. The proposed electrode has been applied to the simultaneous voltammetric determination of aminophenol isomers in mixture without previous chemical or physical separations.     

Preparation and characterization of a 1,10-phenanthroline-modified glassy carbon electrode

This paper describes the grafting of 1,10-phenanthroline (P) molecules on the surface of a glassy carbon (GC) electrode. This modification was carried out in both aqueous and non-aqueous media. Britton Robinson (BR) was used in aqueous experiments at different pHs and tetrabutylammonium tetrafluoroborate (TBATFB), 0.1 M in acetonitrile (ACN) was used in non-aqueous experiments. Surface modification experiments were performed in the +1.2–2.7 V potential range with a scan rate of 100 mV/s and 30 cycles. The presence of P at the GC surface was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), contact angle measurement (CAM) and ellipsometry. The ability of the complex to modify surfaces was investigated with differential pulse voltammetry (DPV).     

Simultaneous determination of diclofenac and indomethacin using a sensitive electrochemical sensor based on multiwalled carbon nanotube and ionic liquid nanocomposite

Multiwalled carbon nanotube and ionic liquid-modified carbon ceramic electrode (MWCNT–IL|CCE) was employed for the simultaneous determination of diclofenac and indomethacin (IND). The measurements were carried out by differential pulse voltammetry method in optimal conditions. The prepared electrode showed appropriate voltammetric responses to DCF and IND with 0.225 V difference in the oxidation peak potentials, making fabricated electrode suitable for simultaneous determination of these compounds. The calibration curves were linear over a wide range of concentrations of each species including 0.05–50 μmol L^?1 for DCF and 1–50 μmol L^?1 for IND. Detection limits were found to be 18 and 260 nM for DCF and IND, respectively. The developed method having good stability and sensitivity was successfully applied for DCF and IND in commercial tablet as well as human blood plasma samples.     

Simultaneous voltammetric determination of tramadol and acetaminophen using carbon nanoparticles modified glassy carbon electrode

A sensitive and selective electrochemical sensor was fabricated via the drop-casting of carbon nanoparticles (CNPs) suspension onto a glassy carbon electrode (GCE). The application of this sensor was investigated in simultaneous determination of acetaminophen (ACE) and tramadol (TRA) drugs in pharmaceutical dosage form and ACE determination in human plasma. In order to study the electrochemical behaviors of the drugs, cyclic and differential pulse voltammetric studies of ACE and TRA were carried out at the surfaces of the modified GCE (MGCE) and the bare GCE. The dependence of peak currents and potentials on pH, concentration and the potential scan rate were investigated for these compounds at the surface of MGCE. Atomic force microscopy (AFM) was used for the characterization of the film modifier and its morphology on the surface of GCE. The results of the electrochemical investigations showed that CNPs, via a thin layer model based on the diffusion within a porous layer, enhanced the electroactive surface area and caused a remarkable increase in the peak currents. The thin layer of the modifier showed a catalytic effect and accelerated the rate of the electron transfer process. Application of the MGCE resulted in a sensitivity enhancement and a considerable decrease in the anodic overpotential, leading to negative shifts in peak potentials. An optimum electrochemical response was obtained for the sensor in the buffered solution of pH 7.0 and using 2 μL CNPs suspension cast on the surface of GCE. Using differential pulse voltammetry, the prepared sensor showed good sensitivity and selectivity for the determination of ACE and TRA in wide linear ranges of 0.1-100 and 10-1000 μM, respectively. The resulted detection limits for ACE and TRA was 0.05 and 1 μM, respectively. The CNPs modified GCE was successfully applied for ACE and TRA determinations in pharmaceutical dosage forms and also for the determination of ACE in human plasma.     

A selective determination of levodopa in the presence of ascorbic acid and uric acid using a glassy carbon electrode modified with reduced graphene oxide

A selective determination of levodopa (LD) in the presence of ascorbic acid (AA) and uric acid (UA) has been investigated at a glassy carbon electrode modified with reduced graphene oxide (rGO). The graphene oxide was synthesized chemically by Hummers method and characterized by energy-filtered transmission electron microscopy (EF-TEM). The reduced graphene oxide modified glassy carbon electrode (rGO/GCE) showed excellent electrochemical performance in the simultaneous electrochemical detection of LD, AA, and UA due to the unique properties of graphene, such as large surface area, facile electronic transport and high electrocatalytic activity. The redox characteristics of rGO/GCE were investigated with cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Well-resolved oxidation peak potentials, corresponding to the oxidation of AA, LD, and UA, were observed from their mixture solution at 0.098, 0.285, and 0.423 V, respectively. The rGO/GCE showed that LD can be detected without the interference of AA and UA. Under the optimized conditions, the oxidation peak current of LD is linear with the concentration of LD from 2.0 to 100 μM with the detection limit of 1.13 μM (S/N = 3). The present electrode system was also successfully applied to direct determination of LD in commercially available tablets and urine samples.     

Electrocatalytic and simultaneous determination of isoproterenol, uric acid and folic acid at molybdenum (VI) complex-carbon nanotube paste electrode

This paper describes the development, electrochemical characterization and utilization of a novel modified molybdenum (VI) complex-carbon nanotube paste electrode for the electrocatalytic determination of isoproterenol (IP). The electrochemical profile of the proposed modified electrode was analyzed by cyclic voltammetry (CV) that showed a shift of the oxidation peak potential of IP at 175 mV to less positive value, compared with an unmodified carbon paste electrode. Differential pulse voltammetry (DPV) in 0.1 M phosphate buffer solution (PBS) at pH 7.0 was performed to determine IP in the range from 0.7 to 600.0 μM, with a detection limit of 35.0 nM. Then the modified electrode was used to determine IP in an excess of uric acid (UA) and folic acid (FA) by DPV. Finally, this method was used for the determination of IP in some real samples.     

Glassy carbon electrode modified with a bilayer of multi-walled carbon nanotube and polypyrrole doped with new coccine: Application to the sensitive electrochemical determination of Sumatriptan

A promising electrochemical sensor was developed based on a layer by layer process by electro-polymerization of pyrrole in the presence of new coccine (NC) as dopant anion on the surface of the multi-walled carbon nanotubes (MWCNTs) pre-coated glassy carbon electrode (GCE). The modified electrode was used as a new and sensitive electrochemical sensor for voltammetric determination of sumatriptan (SUM). The electrochemical behavior of SUM was investigated on the surface of the modified electrode using linear sweep voltammetry (LSV). The results showed a remarkable increase (∼12 times) in the anodic peak current of SUM in comparison to the bare GCE. The effect of experimental variables such as, drop size of the casted MWCNTs suspension, pH of the supporting electrolyte, accumulation conditions and the number of cycles in the electro-polymerization process on the electrode response was investigated. Under the optimum conditions, the modified electrode showed a wide linear dynamic range of 0.02–10.0 μmol L⁻¹ with a detection limit of 6 nmol L⁻¹ for the voltammetric determination of SUM. The prepared electrode showed high sensitivity, stability and good reproducibility in response to SUM. This sensor was successfully applied for the accurate determination of trace amounts of SUM in pharmaceutical and clinical preparations.     

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.     

预处理玻碳电极线性扫描伏安法测定槲皮素的研究

运用循环伏安法、线性扫描伏安法等测试技术研究了槲皮素在预处理玻碳电极上的电化学行为,建立了一种直接测定槲皮素的电化学分析方法。结果表明,与裸玻碳电极相比,预处理玻碳电极能显著提高槲皮素的氧化峰电流。在优化的实验条件下,氧化峰电流与槲皮素浓度在1.0×10-7～2.0×10-5mol/L范围内呈良好的线性关系,最低检测限为6.2×10-8mol/L。该方法简便、快捷、准确、灵敏度高。本法用于芦丁水解产物槲皮素的测定,效果良好。     

A new modified multiwalled carbon nanotube paste electrode for quantification of tin in fruit juice and bottled water samples

In this paper, a new modified multiwalled carbon nanotube electrode is reported for anodic stripping voltammetry quantification of tin. The electrode is based on the use of N-Nitrozo-N-Phenylhydroxylamine (cupferron) and multiwalled carbon nanotube. The influence of supporting electrolytes, deposition time, and applied potential on the sensitivity of electrode were investigated. The detection limit was 0.12 ng/ml and the RSD at a concentration level of 50 ng/ml, was 1.5%. The electrode has been applied for the determination of tin in fruit juice and bottled water with the satisfactory results.     

Simultaneous determination of acetaminophen and dopamine using SWCNT modified carbon–ceramic electrode by differential pulse voltammetry

A highly sensitive method was investigated for the simultaneous determination of acetaminophen (AC) and dopamine (DA) using single wall carbon nanotubes modified carbon–ceramic electrode (SWCNT/CCE). The SWCNT/CCE displayed excellent electrochemical catalytic activities towards the oxidation of AC and DA. Under optimized experimental conditions in differential pulse voltammetry technique, AC and DA gave linear response over the ranges 0.2–100.0 μM (R² = 0.996) and 0.4–150.0 μM (R² = 0.999), respectively. The detection limits (S/N = 3) were found to be 0.12 μM for AC and 0.22 μM for DA. The present method was applied to the determination of AC and DA in some commercial pharmaceutical samples.     

Photoisomerization of electroactive polyimide/multiwalled carbon nanotube composites on the effect of electrochemical sensing for ascorbic acid

We present the first investigation of photoisomerization of the azo‐based electroactive polyimide (PI)/amino‐functionalized multiwalled carbon nanotube (MWCNT) composite electrode on the effect of electrochemical sensing for ascorbic acid (AA). First, MWCNTs were grafted with 4‐aminobenzoic acid in a medium of polyphosphoric acid/phosphorous pentoxide to obtain MWCNTs functionalized with 4‐aminobenzoyl groups (AF‐MWCNTs). Subsequently, photoactive and electroactive PI/AF‐MWCNT composites (PEPACCs) were prepared by introducing pendant conjugated oligoaniline (amino‐capped aniline trimer) in the main chain and azobenzene chromophores in the side chain, in the presence of AF‐MWCNTs. Photoactive and electroactive PI (PEPI) and PEPACCs were characterized by ¹H NMR spectra, UV?visible absorption spectra, cyclic voltammetry (CV) and transmission electron microscopy. The CV study shows that the PEPACCs have higher electroactivity than PEPI. The redox and reversible photoisomerization (i.e. cis ? trans) behavior of PEPACCs was analyzed by in situ monitoring through systematic studies of CV and UV?visible spectroscopy. The light of the UV lamp was 365 nm. It should be noted that the sensor constructed from a trans‐PEPACC‐modified carbon‐paste electrode (CPE) demonstrated a higher electrocatalytic activity by 2.75‐fold and 1.12‐fold towards the oxidation of AA compared with those constructed using a PEPI‐ and cis‐PEPACC‐modified CPE, respectively. The detection limit of the trans‐PEPACC‐modified electrode was 1.73‐fold and 1.70‐fold lower than that of PEPI‐ and cis‐PEPACC‐modified CPE. Moreover, the differential pulse voltammetry data showed that the trans‐PEPACC‐modified electrode had high electrochemical sensing ability for the determination of AA, dopamine and uric acid. © 2014 Society of Chemical Industry     

Anodic behavior of sertindole and its voltammetric determination in pharmaceuticals and human serum using glassy carbon and boron-doped diamond electrodes

The electrochemical oxidation of sertindole was investigated using cyclic, linear sweep voltammetry at a glassy carbon and boron-doped diamond electrodes. The aim of this study was to determine sertindole levels in serum and pharmaceutical formulations, by means of electrochemical methods. In cyclic voltammetry, depending on pH values, sertindole showed one or two irreversible oxidation responses. These two responses were found related to the different electroactive part of the molecule. Using second and sharp oxidation peak, two voltammetric methods were described for the determination of sertindole by differential pulse and square wave voltammetry at the glassy carbon and boron-doped diamond electrodes. Under optimized conditions, the current showed a linear dependence with concentration in the range between 1 × 10⁻⁶ and 1 × 10⁻⁴ M in acetate buffer at pH 3.5 and between 4 × 10⁻⁶ and 1 × 10⁻⁴ M in spiked human serum samples for both methods. The repeatability, reproducibility, selectivity, precision and accuracy of all the methods in all media were investigated and calculated. These methods were successfully applied for the analysis of sertindole pharmaceutical dosage forms and human serum samples. No electroactive interferences from the tablet excipients and endogenous substances from biological material were found.     

Gold nanoparticle/carbon nanotube hybrids as an enhanced material for sensitive amperometric determination of tryptophan

In this work, a highly sensitive electrochemical sensor for the determination of tryptophan (Trp) was fabricate by electrodeposition of gold nanoparticles (AuNPs) onto carbon nanotube (CNT) films pre-cast on a glassy carbon electrode (GCE), forming an AuNP-CNT composite-modified GCE (AuNP-CNT/GCE). Scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used for the surface analysis of the electrode. The results indicate that the hybrid nanomaterials induced a substantial decrease in the overpotential of the Trp oxidation reaction and exhibited a remarkable synergistic effect on the electrocatalytic activity toward the oxidation of Trp. In phosphate buffer solution (pH 7.4), the modified electrode showed excellent analytical performance for the amperometric determination of Trp. The peak currents possess a linear relationship with the concentration of Trp in the range of 30 nM to 2.5 μM, and the detection limit is 10 nM (S/N = 3). In addition, the modified electrode was used to determine Trp concentration in pharmaceutical samples with satisfactory results.     

基于PB-CNTs复合体电化学检测多巴胺

采用简单实用的加工普鲁士蓝（PB）-多壁碳纳米管复合材料（MWCNTs）来检测多巴胺（DA）。由于碳纳米管其独特的结构,物理和化学的性质被选定作为PB电沉积的增强兼容平台。因此PB/MWCNTs/GCE修饰电极表现出良好的电化学行为。实验条件通过循环伏安法和微分脉冲伏安法来优化。在优化条件下,发现峰电流与DA的浓度在1.0×10-6～1.0×10-4 mol/L范围内呈良好的线性关系,检出限为4.5×10-7 mol/L（S/N=3）。测定DA时能有效的减少抗坏血酸对它的干扰。