An electrochemiluminescent sensor for glucose employing a modified carbon nanotube paste electrode

A carbon nanotube paste (CNTP) electrode and a carbon nanotube paste/glucose oxidase (CNTP/GOx) electrode were prepared, and the electrochemiluminescent (ECL) behavior of luminol in the presence of glucose was investigated in detail at each of these electrodes. Compared to the classical carbon paste (CP) electrode, the CNTP electrode incorporating glucose oxidase greatly enhanced the response of the ECL sensor to glucose due to the electrocatalytic activity of the carbon nanotubes, the specificity of the enzymatic reaction, and the sensitivity of the luminol ECL reaction. Under optimal conditions, the electrode was found to respond linearly to glucose in the concentration range 1.0x10(-6) approximately 2.0x10(-3) mol/L, and the detection limit (defined as the concentration that can be detected at a signal-to-noise ratio of 3) was found to be a glucose concentration of 5.0x10(-7) mol/L. The method used to prepare the CNTP/GOx electrode was very convenient, and the electrode surface could be renewed in the case of fouling by simply polishing or cutting it to expose a new and fully active surface. The relative standard deviations (RSD) were found to be 6.8% and 8.9% for the CNTP electrode and the CNTP/GOx electrode (n=6). The electrode retained 95% of its initial response after two weeks.     

Sensitive voltammetric determination of tryptophan using an acetylene black paste electrode modified with a Schiff's base derivative of chitosan

Chitosan was modified by salicylaldehyde via Schiff's base reaction and the resulting product was modified on the surface of an acetylene black paste electrode (ABPE) by the drop-coating method. In 0.5 mol L(-1) acetate buffer (pH 4.2), a substantial increase in the anodic stripping peak current of tryptophan (Trp) (compared to conventional bare carbon paste electrode (CPE) and bare ABPE) is observed at the Schiff's base chitosan-modified electrode. The parameters influencing voltammetric determination of Trp have been optimized. Under the selected conditions, the linearity between the anodic peak currents and concentrations of Trp demonstrated a wide range of 6.0 × 10(-8) mol L(-1) to 2.0 × 10(-6) mol L(-1), 2.0 × 10(-6) mol L(-1) to 4.0 × 10(-5) mol L(-1) and 4.0 × 10(-5) mol L(-1) to 1.0 × 10(-4) mol L(-1), a low detection limit of 2.0 × 10(-9) mol L(-1) was obtained after a 60 s accumulation. In addition, the developed electrochemical sensor has been successfully applied for the determination of Trp in pharmaceutical and biological samples with satisfactory assay results.     

The electrochemical oxidation of pentachlorophenol and its sensitive determination at chitosan modified carbon paste electrode

We report on a novel electrochemical method to detect trace pentachlorophenol (PCP) by using a chitosan (CS) modified carbon paste electrode (CS/CPE). Compared with that at a bare carbon paste electrode (CPE), the current response was greatly improved at the CS/CPE due to the enhancement effect of CS. Under optimal working conditions, the oxidation peak current of PCP was proportional to its concentration in the range of 1.0 × 10^?7 to 5.0 × 10^?6 and 5.0 × 10^?6 to 1.0 × 10^?4 mol/L, with an extremely low detection limit of 4.0 × 10^?8 mol/L. Our method was successfully used to detect the PCP concentration in vegetable samples.     

Accumulation and trace measurement of chloroquine drug at DNA-modified carbon paste electrode

The voltammetric behaviour of chloroquine was investigated at carbon paste and dsDNA-modified carbon paste electrodes in different buffer systems over a wide pH range using cyclic and differential pulse voltammetry. Chloroquine was oxidized in the pH range 2.0-11.0 yielding one irreversible main oxidation peak. A second peak was also observed only in the pH range 5.0-7.0. The modification of the carbon paste surface with dsDNA allowed a preconcentration process to take place for chloroquine such that higher sensitivity was achieved as compared with the bare surface. The response was characterized with respect to solution pH, ionic strength, accumulation time and potential, chloroquine concentration, and other variables. Stripping voltammetric response showed a linear calibration curve in the range 1.0 × 10⁻⁷ to 1.0 × 10⁻⁵ mol l⁻¹ with a detection limit of 3.0 × 10⁻⁸ mol l⁻¹ at the dsDNA-modified electrode. Application of the modified electrode to serum, without sample pretreatment, resulted in good recovery higher than 95% and the higher standard deviation was 3.0%.     

Carbon paste electrode modified with copper(II) phosphate immobilized in a polyester resin for voltammetric determination of <Emphasis Type="SmallCaps"> l </Emphasis>-ascorbic acid in pharmaceutical formulations

A carbon paste electrode modified with copper(II) phosphate immobilized in a polyester resin (CuP-Poly) is proposed for voltammetric determination of L-ascorbic acid in pharmaceutical formulations. The modified electrode allows the detection of L-ascorbic acid at lower anodic potentials than observed at unmodified electrodes. Several parameters that can influence the voltammetric response of the proposed electrode such as carbon paste composition, pH, scan rate, and possible interference were investigated. The peak current was proportional to the concentration of ascorbic acid in the range 2.0 x 10(-5) to 3.2 x 10(-3) mol L(-1) with a detection limit of 1.0 x 10(-5) mol L(-1). The stability and repeatability of the electrode for the determination of L-ascorbic acid are also discussed. Amperometric response was also recorded for electrocatalytic oxidation of the L-ascorbic acid. Concentrations of the vitamin C in pharmaceutical formulations (tablets) measured using the modified electrode and a titrimetric method are in agreement at the 95% confidence level and within an acceptable range of error.     

Spectroscopic and voltammetric studies of Pefloxacin bound to calf thymus double-stranded DNA

Spectral and electrochemical studies have been carried out on the interaction of pefloxacin with calf thymus double-stranded dsDNA. The voltammetric behavior of pefloxacin was investigated at glassy carbon, carbon paste and dsDNA-modified carbon paste electrodes using cyclic voltammetry. Pefloxacin was oxidized, yielding one irreversible oxidation peak. The modification of the carbon paste surface with dsDNA allowed an accumulation process to take place for pefloxacin such that higher sensitivity was achieved compared with the bare surface. The response was characterized with respect to ionic strength, accumulation time, pefloxacin concentration, and other variables. The stripping differential pulse voltammetric response showed a linear calibration curve in the range 1.0×10^–7–1.0×10^–5 mol l^–1 with a detection limit of 5.0×10^–8 mol l^–1 at the dsDNA modified electrode. The method was applied to the direct determination of pefloxacin in diluted urine samples.     

Simultaneous determination of sugars and ascorbic acid by capillary zone electrophoresis with amperometric detection at a carbon paste electrode modified with polyethylene glycol and Cu(2)O

In this paper, a kind of novel carbon paste electrode modified with double modifiers-polyethylene glycol (PEG) and Cu(2)O (PEG/Cu(2)O CPME) in capillary zone electrophoresis with amperometric detection (CZE-AD) was applied to simultaneously determine three sugars: glucose, sucrose, fructose and ascorbic acid (AA). The catalytic electrochemical properties of PEG/Cu(2)O CPME could enhance sensitivity obviously compared with carbon paste electrode modified with only PEG or Cu(2)O at a relatively lower detection potential (+0.3 V versus SCE). Especially, the electrochemical detection response of AA increased obviously to the same level of saccharides by adding PEG into the Cu(2)O carbon paste modified electrode. The four analytes could be perfectly separated within 22 min, the linear ranges were from 1.0 x 10 (-6) to 5.0 x 10(-5) mol L(-1) and the detection limits were at 10(-7) mol L(-1) magnitude (S/N=3). The present working electrode was successfully employed to analyse beverage samples with recoveries in the range 93-107% and RSDs less than 4%. Above results demonstrated that capillary zone electrophoresis coupled with the PEG/Cu(2)O carbon paste modified electrode was of convenient preparation, high sensitivity, good repeatability and could be used in the rapid determination of practical samples.     

The electrochemical oxidation of troxerutin and its sensitive determination in pharmaceutical dosage forms at PVP modified carbon paste electrode

The voltammetric responses of troxerutin were investigated at polyvinylpyrrolidone (cross-linked) (PVP) modified carbon paste electrode (CPE) in 0.1 mol/L KCl by several electrochemical techniques. A well-defined oxidation peak was observed at about 0.97 V. Compared with poor responses of troxerutin at bare electrode that at this modified electrode has been greatly improved. It is PVP that enhances the adsorption of troxerutin to electrode surface based on their hydrophobic property. Under some optimized experimental conditions, a simple and sensitive electroanalytical method was developed for the quantitative analysis of troxerutin. A very low detection limit of 5.0 x 10(-9)mol/L was obtained for 5 min accumulation at open circuit (S/N=3). This proposed method was successfully applied to the detection of troxerutin in pharmaceutical dosage forms and satisfying results had been obtained.     

Electrochemical study of the antineoplastic agent etoposide at carbon paste electrode and its determination in spiked human serum by differential pulse voltammetry

The electrochemical oxidation of the antineoplastic agent etoposide was studied at carbon paste electrode in Britton-Robinson buffer solutions over the pH range 2.0-10.0 using cyclic, linear sweep and differential pulse voltammetry. Oxidation of the drug was effected in a single reversible, diffusion-controlled step within the pH range 2.0-4.0, a second oxidation process was produced above pH 4.0. Using differential pulse voltammetry (DPV), the drug yielded a well-defined voltammetric response in Britton-Robinson buffer, pH 3.0 at 0.500 V (vs. Ag/AgCl) on carbon paste electrode. This process could be used to determine etoposide concentrations in the range 2.5 x 10(-7) to 2.5 x 10(-5) M with a detection limit of 1.0 x 10(-7) M. The method was successfully applied to the determination of the drug in spiked human serum.     

Preparation of aminylferrocene/nanogold modified glassy carbon electrode and its electrocatalysis on dopamine

Aminylferrocene(FcAI)-Nanogold(NG) modified glassy carbon electrode (FcAI/NG/GCE) was prepared by the Au-N bond between Au and FcAI. Electrochemical impedance spectroscopy (EIS) was employed to study the surface of the modified electrode. The electrochemical behavior of dopamine (DA) on the modified electrode was investigated and it was found that the modified electrode had an obvious electrocatalytic effect on DA. Compared with a bare GCE, the modified electrode exhibited an apparent shift of the oxidation peak potential in the negative potential direction and a marked enhancement in the current response for DA. We investigated the determination of DA on the modified electrode by differential pulse voltammetry (DPV). Linear calibration curve was obtained in the range of 7.0 x 10(-7) mol/L to 6x10(-4) mol/L of DA in 0.1 mol/L phosphate buffer solution (pH = 7.0) with a correlation coefficient of 0.9989. The detection limit (S/N = 3) of DA was estimated to be 1.0 x 10(-7) mol/L. Especially, by using the modified electrode, we can separate the oxidation peaks of ascorbic acid (AA) and DA in the PBS and it was satisfactory for the determination of DA with the interference of AA.     

Electroregenerable anion-exchange resin with triiodide carbon paste electrode for the voltammetric determination of adrenaline

An electroregenerable carbon paste electrode modified with triiodide ions immobilized in an anion-exchange resin (Lewatit M500) is proposed for the determination of adrenaline in pharmaceutical products by differential-pulse voltammetry (DPV). Adrenaline was chemically converted into adrenochrome by the I3- ions at the electrode surface. The electrochemical reduction back to adrenaline was obtained at a potential of -0.16 V vs. Ag/AgCl (3 mol l(-1) KCl). A 20% decrease of the initial analytical signal was observed after 350-400 determinations; the carbon paste electrode was 100% electroregenerated at a fixed potential of +0.65 V vs. Ag/AgCl (3 mol l(-1) KCl) in 0.1 mol l(-1) KI solution for 20 min. The differential-pulse voltammograms were obtained by applying a sweep potential between 0.0 and -0.34 V, following the adrenochrome reduction at -0.16 V. Under the optimum conditions established, such as pH 6.0; scan rate 20 mV s(-1) and pulse amplitude 50 mV, the calibration curve was linear from 2.0 x 10(-5) to 3.1 x 10(-4) mol l(-1) adrenaline with a detection limit of 3.9 x 10(-6) mol l(-1). The recovery of adrenaline ranged from 99.8 to 103.1% and the RSD was 2.6% for the solution containing 1.0 x 10(-4) mol l(-1) adrenaline (n = 10). The results obtained for adrenaline in pharmaceutical samples using the proposed carbon paste electrode are in agreement with those obtained using a pharmacopoeial procedure at the 95% confidence level.     

石墨烯/铁氰化钴复合膜修饰玻碳电极同时测定对苯二酚、邻苯二酚和间苯二酚

采用滴涂法和电沉积法制备了石墨烯/铁氰化钴复合膜修饰玻碳电极. 用扫描电镜对该纳米复合膜进行了表征.用循环伏安法研究了对苯二酚(HQ)、邻苯二酚(CT)和间苯二酚(RS)在修饰电极上的电化学行为. 实验结果表明, 相对于裸玻碳电极和石墨烯修饰电极, HQ, CT 和RS 在石墨烯/铁氰化钴修饰电极上的氧化峰电流显著提高. 利用差分脉冲伏安法测定, HQ, CT 和RS 分别在1.0×10^－6～1.5×10^－4 mol/L, 1.0×10^－6～2.0×10^－4 mol/L 和3.5×10^－6～2.5×10^－4 mol/L浓度范围内与氧化峰电流呈良好的线性关系, 相关系数分别为0.991, 0.993 和0.992. 信噪比为3 时, HQ, CT 和RS 检出限分别为2.0×10^－7, 2.1×10^－7 和3.5×10^－7 mol/L. 将该方法用于水样分析, 回收率为95.6%～106.1%.     

葡萄糖在亚硝基五氰合铁酸铁修饰碳糊电极上的电化学行为研究

采用亚硝基五氰合铁酸铁(FePCNF)粉末与碳粉质量比为2∶3混合,制备了FePCNF修饰碳糊电极.研究了FePCNF修饰碳糊电极在KNO3溶液中的电化学行为和扫速、pH值及不同支持电解质的影响.该电极可用于催化氧化检测葡萄糖.实验表明:FePCNF修饰碳糊电极在0.5 mol/L KNO3溶液中有一对灵敏的氧化还原峰,峰电流与扫速呈线性关系.氧化峰电流与葡萄糖的浓度在2.0×10-6～2.4×10-5 mol/L之间有良好的线性关系(r=0.9934),检出限为6.3×10-7 mol/L.该电极具有良好的稳定性和重现性,适合于微量葡萄糖的检测.     

Adsorption voltammetry of the scandium-alizarin red S complex onto a carbon paste electrode

For the first time, a new method is described for the determination of scandium based on the cathodic adsorptive stripping of the scandium-alizarin red S complex onto a carbon paste electrode. The second-order derivative linear scan voltammograms of the complex are recorded by use of model JP-303 polarographic analyzer from 0.0 to -1.0 V (versus SCE). Optimum conditions are found to be: an acetic acid (0.36 mol l(-1))-potassium biphthalate (0.064 mol l(-1)) buffer solution (pH 4.0) containing 2.0x10(-5) mol l(-1) alizarin red S, a preconcentration potential of 0.0 V, a preconcentration time of 60 s, a rest time of 10 s and a scan rate of 100 mV s(-1). The results show that the complex can be adsorbed on the surface of a carbon paste electrode, yielding one peak at -0.58 V, corresponding to the reduction of alizarin red S in the complex at the electrode. The detection limit is found to be 6.0x10(-10) mol l(-1) for 3 min of preconcentration time. The linear range is 1.0x10(-9) to 4.0x10(-7) mol l(-1). Application of the procedure to the determination of scandium in the ore samples gave good results.     

Modified carbon paste sensor for cetyltrimethylammonium ion based on its ion-associate with tetrachloropalladate(II).

A comparative study was made between developed chemically modified carbon paste electrodes and PVC membrane electrodes for the cationic surfactant cetyltrimethylammonium bromide (CTAB). The carbon paste electrode modified with cetyltrimethylammonium-tetrachloropalladate(II) (CTA-TClP) provides a more sensitive and stable device than that shown by electrodes with an inner reference solution. The best performance was obtained by an electrode based on the paste containing 3.6 wt% CTA-TCIP, 1.8 wt% ethylhexadecyldimethylammonium bromide, 37.6 wt% graphite and 57 wt% tricresyl phosphate. The sensor exhibited a Nernstian response for CTAB over a wide concentration range of 3.5 x 10(-7) to 1.0 x 10(-3) M with a detection limit of 2.0 x 10(-7) M between pH 2.7 and 8.2 with a fast response time of 相似文献   

Trace Determination of Zirconium（Ⅳ） by Anodic Adsorptive Voltammetry at a Carbon Paste Electrode

A new sensitive adsorptive voltammetric method was described for the determination ofzirconium at a carbon paste electrode (CPE) in the presence of alizarin complexone (ALC).Optimal analytical conditions are: 1.0~ l0“6 or 5.0x l0“7 mol/L ALC, 0.20 mol/L HAC-NaAc (pH4.3), accumulation for 60 s at 0 V (vs. SCE), and linear scanning from 0 V to 1.0 V at 250 mV/s.The peak potential of the complex is at 0.81 V. By using a model JP-303 polarographic analyzer,2.0~ l0l~ mol/L (S/N=3) zirconium can be detected with a 90 s accumulation, when the 2nd-orderderivative linear sweep technique is used, and the linear range is 6.0~ 10l~-2.0~ l0s mol/L (5.0~ l07mol/L ALC) and 2.0~108-2.0~ l07 mol/L (1.0~ 10.6 mol/L ALC), respectively. The developedmethod was applied to the determination of trace zirconium in the ore samples with satisfactoryresults.     

聚对氨基苯磺酸/石墨烯修饰玻碳电极伏安法测定痕量汞

制备了对氨基苯磺酸/石墨烯复合膜修饰电极,研究了汞在修饰电极上的电化学行为。 在0.1 mol/L、pH=4.0的磷酸盐缓冲液中,以此修饰电极为工作电极,在-1.2 V搅拌富集5 min,用差分脉冲伏安法测定0.31 V处的溶出峰电流。 结果表明,该电极显著提高了汞离子的电化学响应信号。 在优化条件下,峰电流与Hg2+的浓度在1.0×10-6~5.0×10-4 mol/L范围内呈良好的线性关系,相关系数为0.995。 方法的检出限为5.0×10-7 mol/L。 将该法用于水样中痕量汞的测定,回收率为92.2%~105.2%。     

Electrochemical determination of dopamine using a poly(2-picolinic acid) modified glassy carbon electrode

A poly(2-picolinic acid) chemically modified electrode (CME) for the determination of dopamine (DA) by cyclic voltammetry is described. Compared with a bare glassy carbon electrode, the CME exhibits a 200 mV shift of the oxidation potential of DA in the cathodic direction and a marked enhancement of the current response. In pH 7.0 buffer solution, a linear calibration graph is obtained over the range from 2.5 x 10(-7) to 1.0 x 10(-5) mol dm-3 with a correlation coefficient of 0.998. The detection limit is 3.0 x 10(-8) mol dm-3. The modified electrode eliminated efficiently the interference from ascorbic acid (AA) when present in a 150-fold concentration ratio. It also showed excellent stability and reproducibility.     

Amperometric determination of glutathione and cysteine on a Pd-IrO(2) modified electrode with high performance liquid chromatography in rat brain microdialysate

A Pd/IrO(2) co-electrodeposited glassy carbon electrode was prepared and the electrochemical behavior of glutathione (GSH) at this chemically modified electrode (CME) has been studied by cyclic voltammetry (CV). The results indicated that the modified electrode efficiently exhibited electrocatalytic oxidation for GSH with relatively high sensitivity, stability, and long-life. Coupled with high-performance liquid chromatography (HPLC), the Pd/IrO(2) modified electrode was utilized for the electrochemical detection (ECD) of the thiocompounds, glutathione and cysteine (Cys). The peak currents were linear with the substance concentrations in the range of 1.0 x 10(-5) mol L(-1) to 8.0 x 10(-4) mol L(-1) for GSH and 4.0 x 10(-6) mol L(-1) to 2.0 x 10(-4) mol L(-1) for Cys. The detection limits were 2.0 x 10(-6) mol L(-1) for GSH and 5.0 x 10(-7) mol L(-1) for Cys with S/N of 3. The method has been successfully applied to assess the contents of GSH and Cys in rat brain microdialysates.     

Differential pulse anodic stripping voltammetric determination of traces of copper with a tobramycin-Nafion modified electrode.

A Nafion-modified glassy carbon electrode incorporated with tobramycin for the voltammetric stripping determination of Cu2+ has been explored. The electrode was fabricated by tobramycin containing Nafion on the glassy carbon electrode surface. The modified electrode exhibited a significantly increased sensitivity and selectivity for Cu2+ compared with a bare glassy carbon electrode and the Nafion modified electrode. Cu2+ was accumulated in HAc-NaAc buffer (pH 4.6) at a potential of -0.6 V (vs. SCE) for 300 s and then determined by differential pulse anodic stripping voltammetry. The effects of various parameters, such as the mass of Nafion, the concentration of tobramycin, the pH of the medium, the accumulation potential, the accumulation time and the scan rate, were investigated. Under the optimum conditions, a linear calibration graph was obtained in the concentration range of 1.0 x 10(-9) to 5.0 x 10(-7) mol l(-1) with a correlation coefficient of 0.9971. The relative standard deviations for eight successive determinations were 4.3 and 2.9% for 1.0 x 10(-8) and 2.0 x 10(-7) mol l(-1) Cu2+, respectively. The detection limit (three times signal to noise) was 5.0 x 10(-10) mol l(-1). A study of interfering substances was also performed, and the method was applied to the direct determination of copper in water samples, and also in analytical reagent-grade salts with satisfactory results.