Electrochemical Characterization of Horse Spleen Ferritin Covalently Immobilized on Self‐Assembled Monolayer Modified Gold Electrodes

Horse spleen ferritin was covalently attached to SAM‐modified gold electrodes using cross‐linking agents. Reduction of ferritin occurs at negative potentials and is electrochemically irreversible. The voltammetry reveals the presence of a new electrochemical couple that has been determined to be a dissolved iron species released upon the reduction of ferritin. Covalently attached ferritin retains its ability to release iron as evidenced by the absence of the dissolved couple peaks when ferritin is reduced in the presence of nitrilotriacetate. As the SAM chain length increases, the reduction potential becomes more negative, suggesting a tunneling mechanism is involved in the electron transfer.     

铜氮杂配合物修饰金电极对抗坏血酸的分析测定

本实验制备了一种新型的氮杂铜配合物修饰金电极,该电极可用于抗坏血酸的测定。采用循环伏安法和扫描电化学显微镜技术对电极进行了表征。该修饰电极可催化氧化抗坏血酸,相对于裸电极抗坏血酸在修饰电极上氧化电位移动了250mV,并且氧化电流在抗坏血酸的浓度为5.0×10−7 to 4.0×10−5 mol/L时呈线性关系,检测限为4.8×10-8 mol/L。用此方法测定抗坏血酸与文献报道的测定结果一致,这表明该电极可用作抗坏血酸测定的电化学传感器。     

肾上腺素在脱氧核糖核酸修饰金电极上的电化学行为及铅离子的影响

用干燥／吸附法制备了脱氧核糖核酸(DNA)修饰金电极(DNA／Au)，采用循环伏安法、计时库仑法、微分脉冲伏安法、交流阻抗以及紫外光谱法研究了肾上腺素(EP)在该电极上的伏安行为及Pb^2 产生的影响。结果表明：在5mmol/L pH7．7Tris底液中，EP在DNA／Au上产生一不可逆的氧化峰(Ep＝0．16V)。该峰较EP在裸金电极上的峰(Ep＝0．11V)电位为正，灵敏度高。在有Pb^2 存在时，峰电位负移，峰高增大。微分脉冲峰高与EP浓度在0．5-75μmol/L范围内呈线性关系。氧化峰为扩散控制为主并兼有弱的吸附性。本文还探讨了其电极反应的机理，认为在无Pb^2 的情况下，EP与DNA的结合是EP嵌入DNA中为主并兼有一定程度的静电吸附。有Pb^2 存在的情况下EP是以EP-Pb^2 嵌入DNA的双螺旋结构中和通过静电吸附在DNA骨架上的Pb^2 为桥梁与DNA结合。     

Electrochemical Studies of Ochratoxin A Mycotoxin at Gold Electrodes Modified with Cysteamine Self‐Assembled Monolayers. Its Ultrasensitive Quantification in Red Wine Samples

The quantification of ochratoxin A is studied at cysteamine self‐assembled monolayer modified gold electrodes in red wine samples by square wave voltammetry. Detection and quantification limits of 0.004 µg L^?1 and 0.012 µg L^?1, respectively, were determined. The recovery percentages were in the range from 146 % to 94.0 % at spiking levels ranging from 0.02 to 5 µg L^?1. The variation coefficients for within‐laboratory repeatability varied from 31.4 to 11.5 % for spiked level from 0.02 to 2.0 µg L^?1. The developed electrochemical method is efficient, reproducible, and ultrasensitive for the quantification of OTA in red wine samples.     

Electrochemical Determination of Cu(II) Ions by 4‐Formylphenylboronic Acid Modified Gold Electrode

A self‐assembled monolayer (SAM) modified by 4‐formylphenylboronic acid was formed on the gold electrode, which was applied for the determination of trace concentrations of Cu(II). The formation of advanced SAM on the gold electrode was evidenced by electrochemical impedance spectroscopy, atomic force microscopy and contact angle measurements. Electrochemical determination of Cu(II) ions was performed by square wave voltammetry. Some mutual interferences caused by Cd(II), Co(II), Fe(II), Ni(II) and Pb(II) ions were investigated and it was demonstrated how the negative effects of these interfering ions could be eliminated by adjustment of proper parameters of square wave voltammetry.     

Investigation of Electrochemical Behavior of Some Dithiophosphonates in Acetonitrile on the Platinum and Gold Electrodes

Some dithiophosphonate derivatives were synthesized and the electrochemical reduction mechanism was investigated by cyclic voltammetry (CV), square wave voltammetry (SWV) and chronoamperometry (CA) in 0.1 M tetrabutylammoniumtetrafluoroborate (TBATFB) in acetonitrile at platinum (Pt) and gold (Au) electrodes. Dithiophosphonates showed a cyclic voltammetric reduction peak at about ?1.1 V at Pt and ?1.3 V at Au electrode (vs. Ag/Ag⁺) in this media. It was also shown that dithiophosphonates can be determined quantitatively in acetonitrile using a calibration graph. The number of electrons transferred were calculated as 2 using ferrocene as a reference compound at the UME electrode. Mechanism of dithiophosphonates was also examined on Pt and Au electrodes and electrochemical reduction of dithiophosphonates seems to follow an EC mechanism with an irreversible electron transfer step. The reaction product in the bulk electrolysis experiment was isolated and identified using proton‐coupled P‐31 NMR, ¹³C‐NMR and IR spectroscopy. The adsorption tests for dithiophosphonates were revealed that no strong or weak adsorption phenomena exist on both Pt and Au electrodes. Simulation curves were acquired by DigiSim 3.03 version to investigate the reduction mechanism and to estimate the kinetic parameters for electrochemical and chemical steps.     

Electrochemical Determination of Ascorbic Acid in Room Temperature Ionic Liquid BPPF6 Modified Carbon Paste Electrode

A room temperature ionic liquid N‐butylpyridinium hexafluorophosphate (BPPF₆) was used as a binder to make an ionic liquid modified carbon paste electrode (IL‐CPE), which showed good characteristics such as simple preparation procedure, fast electrochemical response and good conductivity. The electrochemical oxidation of ascorbic acid (AA) on the new IL‐CPE was carefully studied. The oxidation peak potential of AA on the IL‐CPE appeared at 109 mV (vs. SCE), which was about 338 mV decrease of the overpotential compared to that obtained on the traditional carbon paste electrode (CPE) and the oxidation peak current was increased for about four times. The electrochemical parameters of AA on the IL‐CPE were calculated with the charge transfer coefficient (α) and the electrode reaction rate constant (k_s) as 0.87 and 0.800 s^?1, respectively. Based on the relationship of the oxidation peak current and the concentration of AA a sensitive analytical method was established with cyclic voltammetry. The linear range for AA determination was in the range from 1.0×10^?5 to 3.0×10^?3 mol/L with the linear regression equation as I_p (μA)=?2.52–0.064C (μmol/L) (n=13, γ=0.9942) and the detection limit was calculated as 8.0×10^?6 mol/L (3σ). The proposed method was free of the interferences of coexisting substances such as dopamine (DA) and amino acids etc., and successfully applied to the vitamin C tablets determination.