Voltammetric determination of sinomenine in biological fluid using a glassy carbon electrode modified by a composite film of polycysteic acid and carbon nanotubes

Polycysteic acid based electrochemical oxidation of L-cysteine (CySH) and carbon nanotubes (CNTs) formed a composite thin film material at a glassy carbon electrode (GCE) that was used a novel modifier for electroanalytical determination of sinomenine which is used for rheumatoid arthritis treatment. The determination of sinomenine at the composite modified electrode was studied by differential pulse voltammetry (DPV). The peak current obtained at + 0.632 V (vs SCE) from DPV was linearly dependent on the sinomenine concentration in the range of 1.0 x 10(-7) to 6.0 x 10(-5) M in a B-R buffer solution (0.04 M, pH 1.81) with a correlation coefficient of 0.998. The detection limit (S/N = 3) was 5.0 x 10(-8) M. The electrochemical reaction mechanism of sinomenine was also discussed. This new method was then applied to the high-throughput determination of sinomenine in human serum samples with satisfactory results. This polycysteic acid/CNTs composite film may be considered to be a promising, low-cost, durable, and biocompatible material for the modification of sensors in applications to pharmaceutical and biomedical analysis.     

Voltammetric oxidation and determination of cinnarizine at glassy carbon electrode modified with multi-walled carbon nanotubes

We discovered a novel method to prepare a protein-based hydrogel, that is, a “Three-Dimensional Nanostructured Protein Hydrogel (3D NPH)”, which is composed of protein–polymer hybrid nanoparticles. In this study, we propose a novel protein microarray whose 3D NPH spots were prepared by dispensing a small volume of the solution of protein–polymer mixture on a substrate. The dispensed solution had a short time for cross-linking before its drying-up and the resulting 3D NPH had loosely cross-linked, thin spongy structure. Therefore, the reaction ratio between ligands and analytes was drastically improved in this system compared with the large volume system for Surface Plasmon Resonance (SPR) protein microarray.     

Voltammetric determination of antibacterial drug gemifloxacin in solubilized systems at multi-walled carbon nanotubes modified glassy carbon electrode

A sensitive electroanalytical method for determination of gemifloxacin in pharmaceutical formulation has been investigated on the basis of the enhanced electrochemical response at multi-walled carbon nanotubes modified glassy carbon electrode in the presence of CTAB. Solubilized system of different surfactants including SDS, Tween-20 and CTAB were taken for the study of electrochemical behaviour of gemifloxacin at modified electrode. The reduction peak current increases in the presence of CTAB while other surfactants show opposite effect. The modified electrode exhibits catalytic activity, high sensitivity, stability and is applicable over wide range of concentration for the determination of gemifloxacin. The mechanism of electrochemical reduction of gemifloxacin has been proposed on the basis of CV, SWV, DPV and coulometeric techniques. The proposed squarewave voltammetric method shows linearity over the concentration range 2.47-15.5 μg/mL. The achieved limits of detection (LOD) and quantification (LOQ) are 0.90 ng/mL and 3.0 ng/mL respectively.     

Voltammetric determination of disinfectants at multiwalled carbon nanotube modified glassy carbon electrode

The voltammetric method for simultaneous determination of some disinfectants at glassy carbon electrode modified with multiwalled carbon nanotubes is presented. The examined compounds are: 2-phenylphenol, 4-chloro-3-methylphenol, triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol and 2-mercaptobenzothiazole. The measurements has been performed using cyclic voltammetry and differential pulse voltammetry in Britton-Robinson buffers as supporting electrolytes. The modification of electrode surface with multiwalled carbon nanotubes enhances the peak current. It is possible to measure mixtures of two compounds (2-phenylphenol and 2-mercaptobenzothiazole, 4-chloro-3-methylphenol and 2-mercaptobenzothiazole, triclosan and 2-mercaptobenzothiazole) in the solution of pH 9.9, which provides the best separation of oxidation peaks.     

石墨烯修饰玻碳电极伏安法测定美洛昔康

通过在玻碳电极表面电化学还原氧化石墨烯的方法制备了石墨烯修饰电极,研究了美洛昔康在该修饰电极上的电化学行为。优化了包括支持电解质及pH、修饰剂用量、富集电位及时间等测定条件,据此建立了一种直接测定美洛昔康的电化学分析方法。在0.1 mol/L Britton-Robinson缓冲液(pH 3.0)中,氧化峰电流与美洛昔康浓度在1.0×10-6～8.0×10-5mol/L范围内呈现良好的线性关系,检出限为3.0×10-7mol/L(S/N=3)。方法可用于片剂和尿样中美洛昔康的测定。     

Voltammetric determination of tinidazole using a glassy carbon electrode modified with single-wall carbon nanotubes.

An electrochemical method based on a single-wall carbon nanotubes (SWNTs) film-coated glassy carbon electrode (GCE) was described for the determination of tinidazole. In a 0.1 M Britton-Robinson buffer with a pH of 10.0, tinidazole yields a very sensitive and well-defined reduction peak at -0.78 V (vs. SCE) on a SWNTs-modified GCE. Compared with that on a bare GCE, the reduction peak of tinidazole increases significantly on the modified GCE. Thus, all of the experimental parameters were optimized and a sensitive voltammetric method is proposed for tinidazole determination. It is found that the reduction peak current is proportional to the concentration of tinidazole over the range from 5 x 10(-8) to 4 x 10(-5) M, and that the detection limit is 1 x 10(-8) M at 3 min open-circuit accumulation. This new analysis method was demonstrated with tinidazole drugs.     

碳纳米管-TiO_2修饰电极伏安法测定维生素K_3

利用碳纳米管、二氧化钛两种纳米材料制成碳纳米管-TiO2复合膜修饰电极,进行了维生素K3电化学行为的研究。维生素K3在碳纳米管-TiO2复合膜修饰电极的电化学响应优于碳纳米管修饰电极,表明前者具有更好的催化作用。通过条件实验的优化,结果表明维生素K3在pH=9.42的氨水-NH4Cl底液中,富集时间为10s,富集电位于-0.60V,扫描速度为0.1V/s时有稳定的灵敏的氧化还原峰。峰电流与维生素K3浓度在3.0×10-6～8.0×10-5mol/L范围内呈良好的线性关系,检出限为5.0×10-7 mol/L。考查了修饰电极的重现性,5次平行测量的RSD为1.78%。该方法用于片剂药品中维生素K3含量的测定,回收率在97.5%～102%之间。     

Simultaneous determination of hydroquinone and catechol at PASA/MWNTs composite film modified glassy carbon electrode

A poly-amidosulfonic acid and multi-wall carbon nanotubes composite (PASA/MWNTs) modified electrode has been constructed by electropolymerization on glassy carbon electrode (GCE). The electrochemical behaviors of hydroquinone (HQ) and catechol (CC) were investigated using cyclic and differential pulse voltammetries (DPVs) at the prepared electrode. Separation of the reductive peak potentials for HQ and CC was about 120 mV in pH 6.0 phosphate buffer solution (PBS), which makes it suitable for simultaneous determination of these compounds. In the presence of 1.0 × 10⁻⁴ mol L⁻¹ isomer, the reductive peak currents of DPV are proportional to the concentration of HQ in the range of 6.0 × 10⁻⁶ to 4.0 × 10⁻⁴ mol L⁻¹, and to that of CC in the range of 6.0 × 10⁻⁶ to 7.0 × 10⁻⁴ mol L⁻¹. When simultaneously changing the concentration of both HQ and CC, the linear concentration range of HQ (or CC) is 6.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹ (or 6.0 × 10⁻⁶ to 1.8 × 10⁻⁴ mol L⁻¹), and the corresponding detection limits are 1.0 × 10⁻⁶ mol L⁻¹. The proposed method has been applied to simultaneous determination of HQ and catechol in water sample, and the results are satisfactory.     

Voltammetric determination of nicotinic acid by glassy-carbon electrode modified with multiwall carbon nanotubes

A glassy-carbon electrode modified with a thin film of multiwall carbon nanotubes is used for the determination of nicotinic acid (NA). At the electrode, the latter yields a well-defined and very sensitive oxidation peak at 0.21 V (SCE). Investigation of the electrochemical behavior of NA shows that the electrode significantly enhances the NA oxidation peak current, compared with the non-modified electrode. Based on this, a very sensitive and simple electrochemical method is proposed for the NA determination after the optimization of all experimental parameters. The oxidation peak current is proportional to the NA concentration over the range 2×10⁻⁷ to 4×10⁻⁵ M, and the detection limit is 8×10⁻⁸ M after a 4-min accumulation. The relative standard deviation of 5.4% for the successive determination of 1×10⁻⁶ MNA (n=10) indicates excellent reproducibility. The analysis method is successfully demonstrated using tablet samples. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 2, pp. 190–195. The text was submitted by the author in English.     

Nafion-graphene composite film modified glassy carbon electrode for voltammetric determination of p-aminophenol

A Nafion-graphene (Nafion-GR) nanocomposite film modified glassy carbon electrode was fabricated by a simple drop-casting method, and used in the electrochemical detection of p-aminophenol (4-AP). Owing to the large surface area, good conductivity of GR and good affinity of Nafion, the sensor exhibited excellent electrocatalytic activity for the oxidation of 4-AP. The electrochemical behaviors of 4-AP on Nafion/GR film modified glassy carbon electrodes were investigated by cyclic voltammetry and differential pulse voltammetry. A calibration curve is constructed in the same matrix, urine, as the unknown samples to be analyzed. The Nafion-GR film modified electrode was linearly dependent on the 4-AP concentration and the linear analytical curve was obtained in the ranges of 0.5–200 μM with differential pulse voltammetry (DPV) and the detection limit was 0.051 μM. The Nafion-graphene nanocomposite modified electrode exhibited good reusability than pure graphene modified GCE. This procedure can be used for the determination of p-aminophenol in the presence of its degradation products and paracetamol. Finally, the proposed method was successfully used to determine p-aminophenol in local tap water samples in urine samples and pharmaceutical preparations.     

石墨烯修饰玻碳电极伏安法测定酪氨酸

制备了石墨烯修饰玻碳电极,研究了酪氨酸在修饰电极上的电化学行为.优化了包括支持电解质、溶液pH、修饰剂用量、富集电位及时间等测定条件.在0.1 mol·L-1pH 7.0的磷酸盐缓冲溶液中,峰电流与酪氨酸的浓度在3×10-6～1.2×10-4mol·L-1的范围内呈良好的线性关系,检出限为2 × 10-7 mol·L-...     

Voltammetric determination of nitrendipine on composite film modified electrode

This paper was focused on the use of electrochemical methods based on a novel composite film modified electrode for the pharmaceutical analysis. This modified electrode was fabricated by integration of room-temperature ionic liquids (1-butyl-3-methylimidazolium hexafluophosphate) and multi-walled carbon nanotubes with polymeric matrix (chitosan). This sensor showed good stability and high accumulation efficiency. Electrochemical behavior of nitrendipine at this electrode was investigated in detail. A sensitive cathodic peak was observed at −0.76 V on the modified electrode. Under the optimized conditions, the peak current was linear to nitrendipine concentration in the range of 4.0 × 10⁻⁷ ∼ 5.0 × 10⁻⁵ M, and the detection limit was estimated to be 1.0 × 10⁻⁷ M after an accumulation for 150 s on open circuit. In addition, the proposed method was applied to the determination of nitrendipine in real samples, and the recovery was from 97.6 to 102.5%.     

Voltammetric determination of bisphenol A in food package by a glassy carbon electrode modified with carboxylated multi-walled carbon nanotubes

A highly sensitive and mercury-free method for determination of bisphenol A (BPA) was established using a glassy carbon electrode that was modified with carboxylated multi-walled carbon nanotubes. A sensitive oxidation peak is found at 550?mV in linear sweep voltammograms at pH?7. Based on this finding, trace levels of bisphenol A can be determined over a concentration range that is linear from 10?nM to 10⁴?nM, the correlation coefficient being 0.9983, and the detection limit (S/N?=?3) being 5.0?nM. The method was successfully applied to the determination of BPA in food package.

Voltammetric determination of niclosamide at a glassy carbon electrode

A very sensitive and selective procedure was developed for the determination of niclosamide based on square-wave voltammetry at a glassy carbon electrode. Cyclic voltammetry was used to investigate the electrochemical reduction of niclosamide at a glassy carbon electrode. Niclosamide was first irreversibly reduced from NO2 to NHOH at -0.659 V in aqueous buffer solution of pH 8.5. Reversible and well defined peaks at -0.164 V and -0.195 V (vs. Ag/AgCl) were obtained that are responsible for two electron peaks between NHOH and NO. Following optimisation of the voltammetric parameters, pH and reproducibility, a linear calibration curve over the range 5 x 10(-8)-1 x 10(-6) mol dm(-3) was achieved. The detection limit was found to be 2.05 x 10(-8) mol dm(-3) niclosamide. For eight successive determinations of 5 x 10(-7) mol dm(-3) niclosamide, a relative standard deviation of 2.4% was obtained. This voltammetric method was applied to the direct determination of niclosamide in tablets. The results of the analysis suggest that the proposed method has promise for the routine determination of niclosamide in the products examined.     

聚L-丝氨酸修饰电极伏安法测定对乙酰氨基酚

对乙酰氨基粉(扑热息痛)为芳环对位取代的酰氨类药物,有解热、镇痛作用。临床上广泛用于感冒发烧、关节痛、神经痛及偏头痛、癌性痛及手术后止痛[1]。但过多服用对乙酰氨基酚对人体会造成伤害,对消化系统的影响主要表现为恶心、呕吐、压食、出汗、腹痛等症状;对泌尿系统、血液系统、呼吸系统都有影响,还能使对阿司匹灵过敏患者的支气管痉挛加重,严重时会抑制呼吸中枢。因此建立对乙酰氨基酚的灵敏检测方法是非常必要的。当前用于检测对乙酰氨基酚的方法主要有滴定法[2]、分光光度法[3]、高效液相色谱法[4]、毛细管电泳[5]、荧光法[6]以及电…     

Voltammetric determination of 4-nitrophenol at a sodium montmorillonite-anthraquinone chemically modified glassy carbon electrode

A new method for the determination of 4-nitrophenol(4-NP) by differential pulse voltammetry (DPV) based on adsorptive stripping technique was described. Cyclic voltammetry (CV) and linear scan voltammetry (LSV) were used in a comparative investigation into the electrochemical reduction of 4-NP at a Na-montmorillonite(SWy-2) and anthraquione (AQ) modified glassy carbon electrode. With this chemically modified electrode, 4-NP was first irreversibly reduced from phiNO(2) to phiNHOH at -0.78 V. A couple of well-defined redox peaks at +0.22 V (vs. SCE) were responsible for a two-electron redox peak between phiNHOH and phiNO. Studies on the effect of pH on the peak height and peak potential were carried out over the pH range 2.0-9.0 with the phosphate buffer solution. A pH of 3.4 was chosen as the optimum pH. The other experimental parameters, such as film thickness, accumulation time and potential etc. were optimized. Anodic peak currents were found to be linearly related to concentration of 4-NP over the range 0.3-45 mg l(-1), with a detection limit of 0.02 mg l(-1). The interference of organic and inorganic species on the voltammetric response have been studied. This modified electrode can be used to the determination of 4-NP in water samples.     

Voltammetric behavior and determination of 17 beta-estradiol at multi-wall carbon nanotube-Nafion modified glassy carbon electrode.

For the purpose of low cost and sensitive electrochemical detection of 17 beta-estradiol (E2), a multi-wall carbon nanotube (MWNT)-Nafion modified electrode was fabricated. The MWNT modified electrode shows enhancement for the anodic peak current of E2 compared with the value obtained using a bare electrode. The anodic peak current measured by square wave voltammetry after 5 min open-circuit accumulation was proportional to the concentration of E2 over the range of 2.5 x 10(-7) to 10 10(-6) M, and a detection limit of 1 x 10(-8) M was obtained.     

Electrochemical determination of tartaric acid at nano gold/nano carbon modified glassy carbon electrode

Nano gold/nano carbon coating the surface of glassy carbon electrode is prepared. Electrochemical behavior of tartaric acid at nano gold/graphene modified glassy carbon electrode is investigated. A simple, sensitive, and inexpensive method for determination of tartaric acid in drinks is proposed.