碳糊电极阴极吸附伏安法测定橙皮甙

在0.4mol/L的NH4Cl-NH3(pH9.0)缓冲液中,使用JP-303极谱分析仪,橙皮甙在碳糊电极(CPE)上有一灵敏的吸附伏安还原峰,峰电位为-1.2V(vs.SCE).该还原峰的二阶导数峰电流与橙皮甙的浓度在2.0×10-8～1.0×10-6mol/L(富集90s)范围内成良好的线性关系,相关系数为0.9963,检出限为1.0×10-8mol/L(S/N=3,富集110s).探讨了橙皮甙在碳糊电极上的伏安性质和电极反应机理,并且成功应用于中草药桔皮中橙皮甙含量的测定.     

改进型聚丙烯酸系高效减水剂的合成

根据分子结构设计原理,合成了一种改进型聚丙烯酸系高效减水剂(PC-C),对影响减水剂性能的几个关键因素进行了探讨,并用红外光谱表征了其分子结构。通过正交实验获得了最佳的合成参数:乙烯基磺酸钠(SVS):丙烯酸(AA):丙烯酸聚乙二醇单酯(PEA)=1.5:5:3,过硫酸铵(APS)用量为单体总质量的3%;同时研究了减水剂侧链和掺量对分散性能的影响。结果表明:采用甲氧基聚乙二醇(MPEG)作为接枝侧链合成减水剂的分散能力优于采用聚乙二醇(PEG)合成的减水剂;PC-C低掺量即可发挥高分散性能,分散保持性能随掺量的增加而得以提高。     

Flow injection analysis of ranitidine based on derivatization reaction producing 2-Methylfuran cation as a sensitive and selective amperometric detector

A new electrochemical sensor in a flow injection system is developed for the determination of ranitidine in pharmaceutical formulations. The method is based on the deamination reaction of ranitidine in an acidic environment in the presence of nitrite ions producing the electroactive species 2-methylfuran and releasing nitrosamine [1]. A wide linear range of ranitidine from 4.4 to 6000 mg L⁻¹, with correlation coefficient R² = 0.996 and the detection limit 1.3 mg L⁻¹ was obtained. The method has been applied in tablet analysis and ampoules; the results are within the confidence limits with 95 % reliability compared to the reference method with HPLC.     

Electroanalytical Study of Fungicide Bixafen on Paste Electrode Based on the Thermally Reduced Graphene Oxide Synthesized in Air Conditions and its Determination in River Water Samples

An electrochemical study of the fungicide bixafen using a paste electrode based on thermally reduced graphene oxide (TRGOPE) synthesized in air is presented for the first time. Cyclic voltammetry and square-wave voltammetry (SWV) were conducted to characterize the mechanism of the underlying electrode process of bixafen. Optimization of the procedure for the quantitative determination of bixafen was carried out by SWV. Excellent electroanalytical performance in terms of a limit of detection of 31.5 nmol L⁻¹ was achieved. The TRGOPE was effectively employed to analyze bixafen in spiked river and tap water samples. The selectivity towards bixafen determination was also assessed.     

Voltammetric Determination of Marbofloxacin at Carbon Paste Sensor Integrated with Copper Oxide Nanoparticles

The present work introduced copper oxide nanoparticles as an efficient electrode modifier for sensitive adsorptive differential pulse voltammetric assaying of marbofloxacin (MRB) in pharmaceutical formulations and surface water samples. In the presence of sodium dodecyl sulphate (SDS) at pH 4.0, the marbofloxacin molecule was irreversibly oxidized at the electrode surface showing an anodic oxidation peak at 0.954 V. The electrode reaction mechanism was assumed as adsorption-reaction controlled accompanied by the transferring of two electrons and proton exchange in agreement with the molecular orbital calculations performed on MRB molecule suggesting the oxidation of the amino group in the piperazinyl ring. At the optimized measuring conditions, the recorded peak heights were linearly correlated with the MRB concentration within the range from 6.67 to 360 ng mL⁻¹, and the estimated LOD value was 2.2 ng mL⁻¹. The integrated sensor showed a prolonged operational lifetime with good reproducibility of measurements. Based on the selectivity and sensitivity of the proposed method, MRB was successfully assayed in pharmaceutical formulations and surface water samples with mean average recoveries agreeable with the official method.     

A Simple Method for Melatonin Determination in the Presence of High Levels of Tryptophan using an Unmodified Carbon Paste Electrode and Square Wave Anodic Stripping Voltammetry

Electrochemical determination of melatonin in the presence of tryptophan is a challenge because of the coincidence of voltammetric signals of these compounds when executing a voltammetric technique. The new method for selective determination of melatonin based on the square wave anodic stripping voltammetry determination of an electroactive product of melatonin was suggested here. This product is produced by previously applied positive pre-potential to a carbon paste electrode, immersed in the test solution. By this means, the electrochemical signal of melatonin was separated effectively from that of tryptophan, making it possible to determine melatonin in the presence of a high concentration of tryptophan. The effect of important parameters on electrode performance was studied and optimized. The optimum response was obtained at pH=2 and utilizing the pre-potential magnitude of +0.8 V, applied for 10 s. A linear relationship was found between peak current intensity and melatonin concentrations over the range of 5.00×10⁻⁷ to 8.00×10⁻⁵ mol L⁻¹. A detection limit of 8.30×10⁻⁸ mol L⁻¹ was calculated for the method (S/N=3). The selectivity of the method was considerably high, because of the independence of melatonin signal to the presence of higher amounts of some potentially interfering agents such as ascorbic acid, tryptophane glucose, etc. As an analytical application, the proposed sensor was used for the determination of melatonin in pharmaceutical and food samples.     

Electrochemical Determination of Tartrazine in Foods by Voltammetry with a Screen-printed Carbon/Chitosan-MnO2 Microcomposite Electrode

This paper presents a new application for a screen-printed carbon electrode (SPCE) modified with chitosan (Cs) and manganese oxide (II). This new electrode (Cs-Mn_OX/SPCE) was applied in the detection of tartrazine (TZ) by linear scan voltammetry (LSV). The anodic peak current for TZ increased by nearly 500 % compared with Cs/SPCE and unmodified SPCE. The surface of the electrode was characterized by cyclic voltammetry. The detection limit was 0.06 μmol/L. The relative standard deviations (RSDs) were between 1.0 and 6.0 % (n=15). The accuracy of the new method was evaluated with real samples spiked with known quantities of TZ.