碳糊电极测定甲硝唑的研究

报道了用碳糊电极测定甲硝唑的方法。在ｐＨ３．２的ＬｉＣｌ－ＨＣｌ电解溶液中，用二次导数阴极溶出伏安法测定甲硝唑。在碳糊电极上开路富集甲硝唑６０ｓ，然后记录其在－０．５８Ｖ的二次导数阴极溶出峰。溶出峰电流ｉｐ与甲硝唑浓度在３．０×１０－７～３．０×１０－６ｍｏｌ／Ｌ和３．０×１０－６～１．０×１０－４ｍｏｌ／Ｌ范围内呈良好的线性关系，相关系数分别为０．９９８６和０．９９９７，检出限为１．７×１０－７ｍｏｌ／Ｌ，相对标准偏差为６．０％（ｎ＝１０）。本方法直接用于甲硝唑片剂的测定，并用多种方法对甲硝唑在碳糊电极表面的反应机理进行了探讨。     

Zeptomole Detection of Streptavidin Using Carbon Paste Electrode and Square‐Wave Voltammetry

We compared the suitability of avidin and streptavidin for avidin‐biotin technology in view of the sensitivity of the analysis using square‐wave voltammetry. We found out during our preliminary experiments that streptavidin gave approximately 100 times higher electrochemical response in comparison with avidin at the same experimental conditions and concentration. Thus, we used two approaches for streptavidin determination – analysis directly in electrochemical cell and analysis by adsorptive transfer technique (AdTS). Ten minutes long accumulation on carbon paste electrode surface was ascertained as optimal in both cases. Limits of detection were 0.3 aM (electrochemical cell) and 30 aM (AdTS).     

Electrochemical performances of C/Fe nanocomposite and its use for mediator-free glucose biosensor preparation

C/Fe nanocomposite (CFN) was synthesized by a procedure similar to an exfoliation/adsorption process to intercalate Fe³⁺ into graphite oxide (GO) layers and would be reduced in a H₂ atmosphere. The results of X-ray diffractometry (XRD) and transimission electron microscopy (TEM) show that the form of CFN is carbon nanotube-Fe nanoparticle composite with α-Fe distributed on the nanotube wall. Paste electrode has been constructed using CFN mixed with paraffin. The electrochemical characteristics of such carbon-Fe nanocomposite paste electrode (CFNPE) has been compared with that of carbon paste electrode (CPE) and evaluated with respect to the electrochemistry of potassium ferricyanide, ascorbic acid and cysteine by cyclic voltammetry. CFNPE can accelerate the electron-transfer to improve the electrochemical reaction reversibility. To fabricate the third-generation glucose biosensor, glucose oxidase (GOD) was immobilized on CFNPE surface with Nafion covered after a pretreatment. Oxygen, ascorbic acid and uric acid have no interference with the glucose detection. The biosensor displays a remarkable sensitivity and stability and the results used in the determination of glucose in the human serum samples are satisfactory.     

高效毛细管电泳－安培检测法测定牙膏中丙三醇和山梨醇

用高效毛细管电泳－安培检测装置，以２００μｍ铜圆盘电极为工作电极，在碱性介质中，建立了分离测定丙三醇和山梨醇的最佳实验条件。结果表明：平均理论塔板数为２．４×１０５／ｍ，丙三醇和山梨醇的浓度检测限分别为３００μｇ／Ｌ和２００μｇ／Ｌ，线性范围接近３个数量级。在５．００～５０．０ｍｇ／Ｌ内，丙三醇和山梨醇的相关系数分别为０．９９９７和０．９９９５。样品测定结果与用高效液相色谱法测定的结果基本一致，回收率在９２％～１０４％之间     

New Strategy for Dehydrogenase Amperometric Biosensors Using Surfactant to Enhance the Sensitivity of Diaphorase/Ferrocene Modified Carbon Paste Electrodes for Electrocatalytic Oxidation of NADH

A carbon paste electrode (CPE) modified with diaphorase (DAP) and ferrocene (FcH) has been developed for determination of NADH at low working potential. The sensitivity and operational stability, towards the detection of the reduced form of the nicotinamide adenine dinucleotide (NADH) in flow injection analysis (FIA), were greatly improved (5 times) upon adding Tween 20 into the electrode matrix. The magnitude of the amperometric signal was dependent on DAP, FcH and surfactant loading, into the modified carbon paste electrode. A rapid and repeatable response was observed to the variation of NADH concentration in the vicinity of the electrode surface. Such advantages of the DAP/FcH/Tween 20 modified carbon paste were successfully used in the construction of L ‐lactate dehydrogenase modified electrodes. The use of this new approach can be generalized to other dehydrogenases and represents a decisive step for a versatile preparation method of amperometric biosensors.     

Electrochemical oxidation of cisatracurium on carbon paste electrode and its analytical applications

The electrochemical oxidation of cisatracurium was investigated by cyclic voltammetry and differential pulse voltammetry at a carbon paste electrode and the experimental parameters have been optimized in order to obtain the optimum analytical signal. A differential pulse voltammetric method with carbon paste electrode is described for the determination of cisatracurium with detection limit of 0.38 μg/ml and quantitation limit of 1.26 μg/ml. The proposed method was applied to determine the content of cisatracurium in human urine and human serum, obtaining accurate and precise results.     

pHh-dependent permselectivity of the fibrinogen-modified carbon paste electrode

The modification of carbon paste matrices with fibrinogen is reported. The effect of the pH of the solution on the CV peak currents of positively or negatively charged redox analytes was examined at the fibrinogen-modified carbon paste electrode. In the presence of the coating, pH-dependent selectivity in electrochemical detection of charged species was demonstrated depending on the sign of the supported charge. Above the isoelectric pH attributed to the immobilized protein (5.5), the current response of anionic redox probes [Fe(CN)/Fe(CN)] was impeded while the response was almost totally restored below this pH. Opposite trends were observed with the Ru(NH₃)/Ru(NH₃) cationic redox analytes.     

Copper determination in ethanol fuel by differential pulse anodic stripping voltammetry at a solid paraffin-based carbon paste electrode modified with 2-aminothiazole organofunctionalized silica

Solid paraffin-based carbon paste electrodes modified with 2-aminothiazole organofunctionalized silica have been applied to the anodic stripping determination of copper ions in ethanol fuel samples without any sample treatment. The proposed method comprised four steps: (1) copper ions preconcentration at open circuit potential directly in the ethanol fuel sample; (2) exchange of the solution and immediate cathodic reduction of the absorbate at controlled potential; (3) differential pulse anodic stripping voltammetry; (4) electrochemical surface regeneration by applying a positive potential in acid media. Factors affecting the preconcentration, reduction and stripping steps were investigated and the optimum conditions were employed to develop the analytical procedure. Using a preconcentration time of 20 min and reduction time of 120 s at −0.3 V versus Ag/AgCl_sat a linear range from 7.5 × 10⁻⁸ to 2.5 × 10⁻⁶ mol L⁻¹ with detection limit of 3.1 × 10⁻⁸ mol L⁻¹ was obtained. Interference studies have shown a decrease in the interference effect according to the sequence: Ni > Zn > Cd > Pb > Fe. However, the interference effects of these ions have not forbidden the application of the proposed method. Recovery values between 98.8 and 102.3% were obtained for synthetic samples spiked with known amounts of Cu²⁺ and interfering metallic ions. The developed electrode was successfully applied to the determination of Cu²⁺ in commercial ethanol fuel samples. The results were compared to those obtained by flame atomic absorption spectroscopy by using the F-test and t-test. Neither F-value nor t-value have exceeded the critical values at 95% confidence level, confirming that there are no significant differences between the results obtained by both methods.     

Sensitive Adsorptive Stripping Voltammetric Methodologies for the Determination of Melatonin in Biological Fluids

The reversible redox process that melatonin presented on carbon paste electrodes was the basis of a sensitive methodology for the determination of this hormone. From all the processes presented by this hormone, this was never used before as the basis of voltammetric measurements for melatonin determination. Therefore, parameters that affected the cyclic voltammetric signal were studied. A limit of detection as low as 9×10^?11 M was obtained when optimized alternating current voltammetry was employed. The reproducibility was excellent due to an adequate pretreatment of the solid electrode (RSD=2.7%, n=10). A comparison with methodologies that employ different electrochemical techniques from the point of view of their analytical characteristics was made. This methodology has proved to be suitable for the determination of melatonin in biological fluids.