聚苯胺纳米纤维修饰石墨箔电极的制备及电化学性能

以石墨箔(GF)为工作电极, 采用循环伏安法(CV), 通过电化学聚合, 制备了聚苯胺(PANI)纳米纤维修饰GF电极(Nano-PANI/GF). 利用红外光谱(FTIR)研究了Nano-PANI/GF修饰电极上聚合物的组成, 利用扫描电镜(SEM)观测了Nano-PANI/GF修饰电极的表面形貌. 利用循环伏安法研究了Nano-PANI/GF修饰电极在0.1 mol/L磷酸盐缓冲溶液(pH=6.9)中的电化学活性, 发现Nano-PANI/GF修饰电极在中性溶液中有良好的电化学活性. Nano-PANI/GF修饰电极对抗坏血酸(AA)电化学氧化的催化作用结果表明, 在0.2 V(vs. SCE)电位下, 在浓度范围1.7~2.0×10³ μmol/L内, 抗坏血酸的氧化电流与浓度呈良好线性关系, 线性方程式为y=0.00013x+0.0031. 修饰电极对抗坏血酸的最低检测限为1.7 μmol/L(S/N=3).     

Spectrophotometric determination of ascorbic acid using copper(II)-neocuproine reagent in beverages and pharmaceuticals

The proposed method for ascorbic acid (Vitamin C) (AA) determination is based on the oxidation of AA to dehydroascorbic acid with a Cu(II)-2,9-dimethyl-1,10-phenanthroline (neocuproine (Nc)) reagent in ammonium acetate-containing medium at pH 7, where the absorbance of the formed bis(Nc)-copper(I) chelate is measured at 450 nm. This chelate was formed immediately and the apparent molar absorptivity for AA was found to be 1.60 × 10⁴ dm³ mol⁻¹ cm⁻¹. Beer's law was obeyed between 8.0 × 10⁻⁶ and 8.0 × 10⁻⁵ M concentration range. The relative standard deviation for 90 μg AA was 3%. The Cu(II)-Nc reagent is a milder and therefore more selective oxidant than the conventional Fe(III)-1,10-phenanthroline (phen) reagent used for the same assay. This feature makes the proposed method superior for real samples such as fruit juices containing weak reductants such as citrate, oxalate and tartarate that otherwise produce positive errors in the Fe(III)-phen method when equilibrium is achieved. The developed method was applied to a number of commercial fruit juices, pharmaceutical preparations containing Vitamin C, and red wine. The meta-bisulfite content of wine was removed with an anion exchanger at pH 3 prior to analysis, and a difference extractive–spectrophotometric method of AA assay in wine was developed so as to suppress the interferences caused by wine anthocyanins and polyphenols. The findings of the developed method for fruit juices and pharmaceuticals were also statistically compared with those of HPLC so as to establish it as a reliable novel method.     

钴（Ⅱ）的抗坏血酸螯合物的红外光谱表征

合成了钴(Ⅱ)的抗坏血酸螯合物。用红外光谱、元素分析等对整合物进行了表征,并据此提出了该螯合物的构型。     

Preparation and characterization of PtAu hybrid film modified electrodes and their use in simultaneous determination of dopamine, ascorbic acid and uric acid

A novel biosensor was fabricated by electrochemical deposition of platinum and gold nanoparticles (nanoAu) with l-Cysteine on glassy carbon electrode. It was found that the nanoAu particle size distribution range was (50-80 nm), and the platinum particle size range was (200-300 nm). The hybrid film could be produced on gold and transparent indium tin oxide electrodes for different kind of studies such as electrochemical quartz crystal microbalance (EQCM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) and electrochemical studies. The PtAu hybrid film was applied to the electro catalytic oxidation of dopamine (DA), ascorbic acid (AA) and uric acid (UA) at pH 4.0 using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The modified electrode was quite effective not only to detect DA, AA and UA individually but also in simultaneous determination of these species in a mixture. The overlapping anodic peaks of DA, AA and UA were resolved into three well-defined voltammetric peaks in CV and DPV. The catalytic peak currents obtained from CV and DPV increased linearly with concentration. The relative standard deviation (% R.S.D., n = 10) for AA, DA and UA were less than 2.0% and DA, AA and UA can be determined in the ranges of 0.103-1.65, 0.024-0.384 and 0.021-0.336 mM, respectively. In addition, the modified electrode also shows good sensitivity, and stability. Satisfactory results were achieved for the determination of DA, AA and UA in dopamine injection solution, vitamin C tablets and human urine samples.     

A simple electroanalytical methodology for the simultaneous determination of dopamine,serotonin and ascorbic acid using an unmodified edge plane pyrolytic graphite electrode

A simple method using an unmodified edge plane pyrolytic graphite electrode (EPPGE) is reported for the simultaneous determination of dopamine (DA), serotonin (ST) and ascorbic acid (AA). The performance of this electrode is superior to other unmodified carbon-based electrodes and also to many modified electrodes in terms of detection limit, sensitivity and peak separation for determination of DA, ST and AA. Using this method, detection limits of 90 nM, 60 nM and 200 nM were obtained for DA, ST and AA respectively. No electrode fouling is observed during a set of experiments and good sensitivity is obtained for the simultaneous determination of DA, ST and AA. The peaks for the three species are well resolved from each other and the electrode is successfully utilised for their determination in standard and real samples.      

铁氰化钾-Fe（Ⅲ）分光光度法测定抗坏血酸的含量

基于抗坏血酸定量还原Fe（Ⅲ）为Fe（Ⅱ）,Fe（Ⅱ）与铁氰化钾生成普鲁士蓝的反应建立了测定抗坏血酸的分光光度法。方法可用于药品、水果中抗坏血酸含量的测定。     

A novel automated electrochemical ascorbic acid assay in the 24-well microtiter plate format

Automatic ascorbic acid (AA) voltammetry was established in 24-well microtiter plates. The assay used a movable assembly of a pencil rod working, an Ag/AgCl reference and a Pt counter electrode with differential pulse voltammetry (DPV) for concentration-dependent current generation. A computer was in command of electrode (z) and microtiter plate (x, y) positioning and timed potentiostat operation. Synchronization of these actions supported sequential approach of all wells and subsequent execution of electrode treatment procedures or AA voltammetry at defined intervals in a measuring cycle. DPV in well solutions offered a linear current/concentration range between 0.1 and 8.0 mM, a sensitivity of about 1 μA mM⁻¹ AA, and a detection limit of 50 μM. When used with a calibration curve or standard addition, automated voltammetry of samples with added known amounts of AA demonstrated good recovery rates. Also, the assay achieved the accurate determination of the AA content of vitamin C tablets, a fruit juice and an herbal tea extract. Robotic AA voltammetry has the advantage of conveniently handling multiple samples in a single measuring run without the continuous attention of laboratory personnel. It is a good option when the goal is cost-effective AA screening of sample libraries and has potential for applications in health care and the food processing, cosmetic and pharmaceutical industries.     

Facile Synthesis of Gold Nanoparticle-loaded Carbon Nanofiber Composites and Their Electrocatalytic Activity Towards Dopamine, Ascorbic Acid and Uric Acid

A facile approach for the synthesis of gold nanoparticle-loaded carbon nanofiber(Au/CNF) composites was developed. When applied to electrochemistry, these composites showed attractive performances such as high conductivity and facile electron transfer kinetics. Under physiological conditions, the Au/CNF composite modified electrode exhibits highly electrocatalytic activity for the oxidation of dopamine, ascorbic acid and uric acid. Owing to the good selectivity for the simultaneous detection of these three ...     

Dielectric relaxation study of ascorbic acid solutions in pure dimethylsulfoxide (or diethylsulfoxide) and in dimethylsulfoxide (or diethylsulfoxide)/water mixtures

The complex dielectric spectra of ascorbic acid solutions in pure dimethylsulfoxide (or diethylsulfoxide) and in dimethylsulfoxide (or diethylsulfoxide)/water mixtures have been measured at frequencies between 100 MHz and 20 GHz at 298.15 K.Two kinds of dielectric relaxation processes were observed in each solution. The low frequency relaxation (Debye term) is assigned to solute. The high frequency relaxation (Cole-Davidson term) is ascribed to practically unaffected solvent.From the results obtained it follows that relaxation time and relaxation strength in DESO containing solutions (i.e. binary AA/DESO and ternary AA/DESO/water systems) are greater than those in DMSO containing solutions.     

Vitamin C Functionalized Poly(Methyl Methacrylate) for Free Radical Scavenging

Abstract

In the present work, a strategy was developed to use mild and highly selective enzymatic methods to covalently couple the primary hydroxyl group of vitamin C with methyl methacrylate monomer, followed by a second enzymatic reaction catalyzed by horseradish peroxidase to polymerize the vinyl monomer yielding a vitamin C functionalized poly(methyl methacrylate) (PMMA). Vitamin C, L‐ascorbyl methylmethacrylate and PMMA, when used at concentrations up to 133 µM, fully scavenged 2,2‐diphenyl‐1‐picryl hydrazyl free radicals (0.2 mM). Thus, the formation of vinyl polymers with active pendent antioxidant compounds, in this case vitamin C, retained an ability to scavenge radicals while in polymeric form. The functionalized antioxidant on a PMMA backbone has implications for consumer‐related applications like foods, pharmaceuticals, and personal care products.