Voltammetric Determination of Folic Acid with a Multi-Walled Carbon Nanotube-Modified Gold Electrode

The voltammetric behavior of folic acid (FA) at a multi-walled carbon nanotube (MWNT) modified gold electrode has been investigated by cyclic voltammetry, chronoamperometry and chronocoulometry. The modified electrode exhibits a good promoting effect on the electrochemical reaction of FA. FA can generate a well-defined anodic peak at around 0.83 V (vs. SCE) in 0.1 M H₃PO₄–NaH₂PO₄ buffer solution of pH 2.5. The peak results from a 2-electron transfer of FA, and the standard potential of FA is estimated to be 0.79 V (vs. SCE). The parameters affecting the response of FA, such as solution pH, accumulation time, accumulation potential, and amount of MWNTs are optimized for the determination of FA. Under the optimum conditions, the peak current changes linearly with FA concentration in the range from 2.0 × 10⁻⁸ M to 1.0 × 10⁻⁶ M. This method has been applied to the determination of FA in drug tablets, and the recovery is 93.9–96.9%. In addition, the influence of some coexistent species is examined. When a Nafion layer is introduced on the gold electrode before deposition of MWNTs, the resulting composite electrode can give better response to FA. At the same time, the interference by some foreign species is suppressed to some extent.     

Electrochemical Determination of 4-Nitrophenol Using a Single-Wall Carbon Nanotube Film-Coated Glassy Carbon Electrode

A single-wall carbon nanotubes (SWNT) film coated glassy carbon electrode (GCE) was fabricated for the direct determination of 4-nitrophenol (4-NP). The electrochemical behaviors of 4-NP at the SWNT-film coated GCE were examined. In 0.1M phosphate buffer with a pH of 5.0, 4-NP yields a very sensitive and well-defined reduction peak at the SWNT-modified GCE. It is found that the SWNT film exhibits obvious electrocatalytic activity towards the reduction of 4-NP since it not only increases the reduction peak current but also lowers the reduction overpotential. Based on this, an electrochemical method was proposed for the direct determination of 4-NP. The reduction peak current varies linearly with the concentration of 4-NP ranging from 1×10^–8 to 5×10^–6M, and the detection limit is 2.5×10^–9M after 3min of open-circuit accumulation. The relative standard deviation at 2×10^–7M 4-NP was about 6% (n=10), suggesting excellent reproducibility. This new method was successfully employed to determine 4-NP in several lake water samples.     

Electrochemical Study and Selective Determination of Dopamine at a Multi-Wall Carbon Nanotube-Nafion Film Coated Glassy Carbon Electrode

A homogeneous and stable suspension of multi-wall carbon nanotubes (MWNT) was achieved by dispersing MWNT into 0.1% Nafion ethanol solution. A uniform MWNT-Nafion cast film was obtained over a glassy carbon electrode (GCE) via solvent evaporation. The electrochemical behavior of dopamine (DA) was examined, and a reversible two-electron redox reaction was observed. In comparison with the bare GCE and the Nafion-modified GCE, the MWNT-Nafion modified GCE shows obvious electrocatalytic activity towards DA. Moreover, the MWNT-Nafion film coated electrode exhibits excellent selectivity towards DA even in the presence of high concentrations of ascorbic acid (AA) and uric acid (UA). The oxidation peak current was proportional to the concentration of DA over the range of 1×10^–8 to 1×10^–5molL^–1, and a detection limit of 2.5×10^–9molL^–1 was obtained after 2min. of open-circuit accumulation. The dispersion and morphology of MWNT-Nafion film were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Fourier transfer (FT) IR spectra.     

多壁碳纳米管修饰玻碳电极测定乙炔雌二醇

多壁碳纳米管修饰玻碳电极测定乙炔雌二醇;多壁碳纳米管;乙炔雌二醇;化学修饰电极;电化学测定     

多壁碳纳米管修饰玻碳电极测定多巴酚丁胺的研究

研究了多巴酚丁胺在多壁碳纳米管修饰电极上的电化学行为,建立了一种直接测定多巴酚丁胺的电化学方法。在0.3mol·L-1H2SO4底液中,氧化峰电位为0.57V(vs.Ag/AgCl),峰电流与多巴酚丁胺的浓度在5.0×10-8～1.0×10-5mol·L-1范围内呈良好的线性关系。该法的检出限为3.0×10-8mol·L-1。平均回收率为99.15%。1.0×10-5mol·L-1多巴酚丁胺平行测定8次的标准偏差为4.8%。用拟定的方法测定了多巴酚丁胺注射液中多巴酚丁胺的含量,结果满意。     

Electrochemical Determination of Dopamine Using a Carboxyl-functionalized Carbon Nanotube-Modified Carbon Paste Electrode Doped with Polymeric Ferric Sulfate

A novel electrochemical device for the sensitive determination of dopamine was developed based on a carbon paste electrode with polymeric ferric sulfate doped in the carbon paste and a carboxyl-functionalized carbon nanotube thin film on the surface. The modified electrode was characterized by scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. The conditions for the preparation of electrode were optimized. The carbon nanotubes were shown to be stable on the surface of carbon paste electrode. The novel electrochemical device provided excellent activity toward dopamine. Amperometry and differential pulse voltammetry were used for the determination of dopamine in pH 7.0 phosphate buffer with a long linear range from 0.8 to 261?µM and a detection limit of 0.2?µM. The modified electrode showed excellent repeatability, good stability, and satisfactory reproducibility, thus demonstrating potential for practical applications.     

Electrochemical determination of acetaminophen using a glassy carbon electrode coated with a single-wall carbon nanotube-dicetyl phosphate film

Single-wall carbon nanotubes (SWNT) were dispersed into water in the presence of dicetyl phosphate (DCP), and then a SWNT-DCP film-coated glassy carbon electrode (GCE) was constructed. The electrochemical behavior of acetaminophen at bare GCE and SWNT-DCP modified GCE were compared, suggesting that the SWNT-DCP-modified GCE significantly enhances the oxidation peak current of acetaminophen. A sensitive and simple electrochemical method with a good linear relationship in the range of 1.0 × 10⁻⁷–2.0 × 10⁻⁵ mol L⁻¹, was developed for the determination of acetaminophen. The detection limit is 4.0 × 10⁻⁸ mol L⁻¹ for 3-min accumulation. This method was successfully demonstrated with tablets.     

Sensitive Adsorption Stripping Voltammetric Determination of Reserpine by a Glassy Carbon Electrode Modified with Multi-Wall Carbon Nanotubes

Adsorption stripping voltammetry, a very sensitive electroanalytical method, was employed to determine reserpine, a kind of anti-hypertensive drug. In 0.1M phosphate buffer with a pH of 6.0, reserpine was accumulated at a multi-wall carbon nanotubes (MWNT)-modified glassy carbon electrode (GCE) surface under the condition of open-circuit. In the following anodic sweep from 0.20 to 1.00V, reserpine, adsorbed at the MWNT-modified GCE surface, was oxidized and yielded a sensitive oxidation peak at 0.64V. Due to its unique structure and extraordinary properties, MWNT shows a ten times higher accumulation efficiency toward reserpine, compared with a bare GCE. Hence, the amount of reserpine at the MWNT-modified GCE surface increases significantly, and finally the oxidation peak current improves greatly. The experimental conditions, such as supporting electrolyte, pH value, the amount of MWNT-DHP suspension, accumulation time and scan rate, were optimized for the measurement of reserpine, and a sensitive electroanalytical method was proposed for reserpine determination. The oxidation peak current varies linearly with the concentration of reserpine over the range of 2×10^–8 to 1×10^–5M, and the detection limit is 7.5×10^–9M after 4min open-circuit accumulation. The relative standard deviation at 1×10^–6M reserpine was about 4.7% (n=7), indicating excellent reproducibility. This new method was successfully demonstrated with reserpine injections and tablets.     

Electrochemical Determination of Tannins Using Multiwall Carbon Nanotubes Modified Glassy Carbon Electrode

A novel chemically modified electrode is prepared on the basis of the attachment of multiwall carbon nanotubes (MWNTs) to the surface of a glassy carbon electrode (GCE) in the presence of a hydrophobic surfactant. The electrochemical behavior of tannins at the MWNTs-modified GCE is investigated. Tannins yield a well-defined oxidation at about 0.30 V (SCE) at the MWNTs-modified GCE. MWNT-film shows remarkable enhancement effect on the oxidation peak current of tannins. The experimental parameters are optimized, and a direct electrochemical method to detect tannins is proposed. The oxidation peak current is proportional to the concentration of tannins over the range from 4 × 10^–7 to 2 × 10^–4 M, and the detection limit is 1 × 10^–7 mol/l after 5 min of accumulation. The relative standard deviation of 6% for determination of 2 × 10^–6 mol/l tannins indicates excellent reproducibility. The analysis method is demonstrated by using tea and Chinese gall samples.     

维生素b12在多壁碳纳米管修饰玻碳电极上的电化学行为及其分析测定

维生素b12;多壁碳纳米管;循环伏安法;修饰电极     

Electrocatalysis of Tryptophan at Multi-Walled Carbon Nanotube Modified Electrode

Acid-treated multi-walled carbon nanotubes (MWNTs) were immobilized on the surface of a glassy carbon electrode to form an MWNT-modified electrode. The electrocatalytic response of the modified electrode towards tryptophan (Trp) was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results demonstrated that the modified electrode exhibited a high degree of catalytic activity towards the oxidation of Trp. An oxidation peak was obtained in Trp solution at the MWNT-modified electrode. Compared with a bare electrode, the peak current had obviously increased, and the peak potential had shifted in a negative direction. However, under the same conditions, no response was observed for other amino acids. The oxidation peak currents were proportional linearly to the concentration of Trp, a property which could be utilized to detect Trp. The determination conditions, such as the concentration, the composition and the pH values of the supporting electrolyte, accumulation time, as well as scan rate etc. were optimized. Under the chosen conditions, the DPV peak current is linear to the concentration of Trp in the range of 2.5×10^–7 to 1.0×10^–4molL^–1, and the detection limit is 2.7×10^–8molL^–1. Moreover, the detection is free of interference from other amino acids. The modified electrode has been successfully applied to determine the concentration of Trp in composite amino acid injections, and it displays excellent repeatability and higher sensitivity.     

琥乙红霉素在碳糊电极上的电化学测定方法

以碳糊电极为工作电极,采用循环伏安（CV）法和示差脉冲伏安（DPV）法研究了琥乙红霉素（EEs）在电极上的电化学行为,建立了一种测定EEs的电化学新方法。 研究结果表明,在0.1 mol/L磷酸盐（pH=8.0）的缓冲液中,EEs在0.83和0.97 V(vs.SCE）处出现2个氧化峰。 用计时安培法(I-t)对EEs进行定量分析,峰电流Ip与琥乙红霉素的浓度分别在2.0×10-7~2.8×10-6 mol/L和2.8×10-6~3.1×10-5 mol/L范围内呈良好的线性关系检出限（S/N=3）为1.0×10-7 mol/L。 采用标准加入法测得回收率为950%～988%,RSD为3.4%(n=3)。 该方法具有较高的选择性和灵敏度,可用于药剂中EEs含量的测定,结果令人满意。     

多壁碳纳米管-Nafion膜修饰铂电极的电化学性质

使用多壁碳纳米管(MWCNTs)和Nafion溶液制备了多壁碳纳米管-Nafion膜修饰的铂电极。运用扫描电子显微镜(SEM)对多壁碳纳米管、Nafion膜、多壁碳纳米管-DMF膜和多壁碳纳米管-Nafion膜进行了形貌表征。通过电化学系统研究了铁氰化钾在多壁碳纳米管-Nafion膜修饰电极、多壁碳纳米管-DMF修饰电极以及未修饰铂电极的表面电化学行为。结果显示,多壁碳纳米管-Nafion膜修饰的电极对铁氰化钾有显著的电化学增强作用,于0.185 V处形成了一个尖锐的还原特征峰,比未修饰的铂电极还原峰增强近8.7倍;在0.231 V处形成了一个较强的氧化特征峰,比未修饰的铂电极氧化峰增强近2.7倍。由于多壁碳纳米管的比表面积大,利用其与Nafion修饰的电极能增强电子传输效率,使测定的峰电流增大,从而提高灵敏度,有助于检测低浓度物质。进一步研究发现,铁氰化钾在未修饰的铂电极表面反应为可逆反应,而在MWCNTsNafion膜修饰后的电极表面反应为不可逆反应。     

Electrocatalytic Properties and Voltammetric Determination of Melatonin at a Nanostructured Film Electrode

A multi-wall carbon nanotube (MWNT) film coated glassy carbon electrode (GCE) was fabricated, and the electrochemical behavior of melatonin on the MWNT film coated GCE was investigated. The oxidation peak current of melatonin increases significantly and the oxidation peak position shifts positively at the MWNT film modified GCE compared to that at a bare GCE. This indicates that MWNTs feature highly effective catalysis to the electrochemical oxidation of melatonin. A simple and sensitive electroanalytical method was developed for the determination of melatonin. The oxidation peak current is proportional to the concentration of melatonin from 8×10^–8 to 1×10^–5molL^–1. The detection limit is about 2×10^–8molL^–1 for 3min accumulation. The proposed method was demonstrated to work satisfactorily with commercial capsules.     

聚L-白氨酸-碳纳米管修饰电极同时检测对苯二酚和邻苯二酚

用Nafion将单壁碳纳米管(SWCNT)固定到玻碳电极(GCE)上,再利用电化学聚合方法将L-白氨酸(L-LEU)聚合到SWCNT/GCE上,制备得到poly L-LEU/SWCNT/GCE修饰电极。采用循环伏安法(CV)、差分脉冲伏安法(DPV)和电化学交流阻抗法(EIS)研究了对苯二酚(HQ)、邻苯二酚(CC)共存时,二者在修饰电极上的电化学行为。结果表明:此修饰电极对HQ和CC有很好的电催化和分离作用。二者在修饰电极上的氧化还原峰电流与GCE相比显著增强,HQ和CC的氧化峰电位差和还原峰电位差分别为124 mV和131 mV。HQ和CC的检测线性范围分别为2.0×10-7~1.0×10-4、5.0×10-7~1.0×10-4mol/L。检出限分别为8.0×10-8、1.0×10-7mol/L。制备的修饰电极重现性、稳定性良好。在模拟废水中采用该修饰电极对HQ和CC进行检测,结果满意。     

Electrocatalytic Reduction of Nitrite Using a Carbon Nanotube Electrode in the Presence of Cupric Ions

A simple, inexpensive method for determining nitrite is presented. With a carbon nanotube modified glass carbon electrode (GC), the overpotential for reduction of nitrite decreased, and direct reduction could be achieved in acid solution. Sensitivity, however, was not very high. When cupric ions were added to the solution, the reduction peak current increased significantly, and in particular the presence of multiple nitrate did not interfere. Experimental conditions were optimized, and preliminary studies were performed on the electrochemical mechanism of nitrite reduction in the presence of cupric ions on the carbon nanotube modified electrode. Under optimized conditions, the peak current of reduction achieved with the differential pulse voltammetric method was proportional to the concentration of nitrite in the ranges of 2.0×10^–6–1.0×thinsp;10^–5molL^–1 and 2.0×10^–5–1.0×10^–3molL^–1. The detection limit reached 5.0×10^–7molL^–1, and most of the inorganic ions did not interfere. The determination of nitrite in samples of rain water and river water was satisfactory.     

多壁碳纳米管修饰玻碳电极伏安法测定香草醛

制备了羧基化多壁碳纳米管修饰玻碳电极(c-MWCNTs/GCE),采用循环伏安法在0.5 mol/L HCl中研究了食品添加剂香草醛的电化学行为。结果显示,该修饰电极对香草醛的电化学氧化具有良好的电催化作用,与裸玻碳电极相比电流响应显著增强。香草醛在该修饰电极上的氧化为不可逆的扩散控制过程。在最佳条件下,采用二阶导数线性扫描伏安法进行测定,香草醛的氧化峰电流与其浓度在0.1～6.0μmol/L和6.0～100μmol/L范围内呈良好的线性关系,检出限(S/N=3)为0.02μmol/L。该修饰电极具有良好的重现性(RSD=4.6%)和稳定性。方法应用于食品中香草醛的测定,回收率为96.3%～104%。     

Electrochemical determination of malachite green using a multi-wall carbon nanotube modified glassy carbon electrode

A multi-wall carbon nanotube (MWNT) film-modified electrode is described for the determination of malachite green (MG). The electrochemical profile of MG was examined using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), suggesting that the MWNT film facilitates the electron transfer of MG in terms of a potential shift and then significantly enhances the oxidation peak current of MG. The experimental parameters, such as supporting electrolyte, thickness of MWNT film, scan rate and accumulation time, were optimized. Consequently, a sensitive and convenient electrochemical method is proposed for the determination of MG. The oxidation peak current is proportional to the concentration of MG over the range from 5.0 × 10⁻⁸ to 8.0 × 10⁻⁶ mol L⁻¹ obeying the following equation: i_p = 0.09 + 1.19 × 10⁷ C (r = 0.995, i_p in μA, C in mol L⁻¹). The detection limit is 6.0 × 10⁻⁹ mol L⁻¹ (signal to noise = 3) after 5 min of accumulation. Moreover, this method possesses good reproducibility (RSD is 5.6%, n = 8) as well as long-term stability. Finally, the new method was employed to determine MG in fish samples. Correspondence: W. Huang, Department of Chemistry, Hubei Institute for Nationalities, Enshi 445000, P.R. China     

介孔碳纳米纤维修饰电极用于黄酮类化合物芦丁的电化学测定

制备了新型的介孔碳纳米纤维修饰热解石墨电极(MCNF/PGE),并将其用于芦丁含量的测定。用循环伏安法、交流阻抗谱法、示差脉冲伏安法研究了该修饰电极膜性能及芦丁在该修饰电极上的电化学行为。结果表明,修饰电极可有效促进探针离子[Fe(CN)6]3-/4-在电极表面的电子传递;芦丁在该修饰电极表面的电化学过程受扩散控制。由于MCNFs大量的石墨边缘缺陷、大比表面积以及介孔结构,与裸电极相比,该修饰电极对芦丁呈现出很高的电催化活性,芦丁阳极峰电流约为裸电极上的18倍。在最佳实验条件下,芦丁的氧化峰电流(Ipa)与其浓度(c)在2.0×10-8～1.2×10-6mol/L范围内呈良好的线性关系,检出限(S/N=3)为5.0×10-9mol/L,线性系数r2=0.999。此外,计算了电荷转移系数(α)、标准速率常数(ks),并推测了芦丁的电化学氧化还原机理。该修饰电极易于制备、可再生,重复性及稳定性良好,可作为一种高灵敏度的电化学传感器应用于芦丁片剂中芦丁的含量测定。     

Direct Electrochemical Oxidation of NADPH at a Low Potential on the Carbon Nanotube Modified Glassy Carbon Electrode

Introduction Because of its novel structural and electronic proper-ties, high chemical stability, and extremely high me-chanical strength and modulus,1 carbon nanotube (CNT), which has become a major subject of many experimen-tal and theoretical investigations, has a wide potential application from structural materials to nanoelectronic components2-12 since its initial discovery by Iijima13 in 1991 and the subsequent report about the synthesis of large quantities of CNT by Ebbesen and cowork…