Electrocatalytic Properties of a Novel Poly‐1‐Naphthylamine‐Modified Electrode Using Ascorbic Acid as Molecule Probe

A glassy carbon electrode was modified with an electropolymerized film of 1‐naphthylamine in aqueous solution. The electrocatalytic properties of this modified electrode (ME) were investigated using ascorbic acid (AA) as probe molecule. The electrochemical behavior of AA in buffer solution was examined by voltammetry and amperometry. The results showed that the ME exhibited good electrocatalytic activity towards the oxidation of AA, as a consequence, it can be used as amperometric sensor of this analyte in a flow injection system with good sensitivity. Calibration curves were linear over the concentration range 0.05–1.50 mM with a phosphate buffer solution pH 3 as the carrier, the detection limit was 1 ppm (S/N=3). The methods were applied to the determination of AA in beverages and pharmaceutical products. A good correlation with a reference method was attained.     

聚苯胺修饰电极上抗坏血酸与多巴胺氧化峰的分离

本文介绍一种分离抗坏血酸(AA)和多巴胺(DA)氧化峰的新方法。聚苯胺(PA)对AA和DA有不同的催化性,因而在PA修饰电极上,AA和DA在不同的电位被氧化,从而解决了二者氧化峰不能分离的问题。实验表明,在PA膜电极上,AA和DA氧化峰可分开约140mV。     

Determination of Uric Acid in the Presence of Ascorbic Acid Using Poly(3,4‐ethylenedioxythiophene)‐Modified Electrodes

A poly(3,4‐ethylenedioxythiophene) (PEDOT) modified glassy carbon electrode (GCE) was used to determine uric acid in the presence of ascorbic acid at physiological pH facilitating a peak potential separation of ascorbic acid and uric acid oxidation (ca. 365 mV), which is the largest value reported so far in the literature. Also, an analytical protocol involving differential pulse voltammetry has been developed using a microchip electrode for the determination of uric acid in the concentration range of 1 to 20 μM in presence of excess of ascorbic acid.     

聚苯胺对抗坏血酸的电催化氧化及磁效应

磁场对生物体系及其中物理现象和化学反应的影响历来是人们关注的焦点[1]．磁场能影响分子、细胞、组织、器官乃至整个生物体系的新陈代谢功能．磁场对化学反应的影响通常是通过对自由基（对）施加作用而体现的，磁场改变了未成对电子的自旋方式，从而改变了反应的墙，进而改变化学反应的速率[2]．此外，磁场对电化学体系的影响也有报导[3]，外加磁场激发溶液流动，产生磁流体动力学效应（MHD）[4]，增大传质速度，影响电化学进程．本文研究聚苯胺（PAN）修饰电极上抗坏血酸（AA）的电催化氧化，并讨论了膜厚、溶液pH值、AA浓度（CAA…     

A Selective Catalytic Oxidation of Ascorbic Acid at the Aminopyrimidyl Functionalized‐Conductive Polymer Electrode

A simple detection method of ascorbic acid (AA) through selective catalytic oxidation has been developed using a novel conducting polymer poly‐3′‐(2‐aminopyrimidyl)‐2,2′:5′,2“‐terthiophene (pAPTT). The pAPTT electrode showed an excellent selectivity in facilitating the electron transfer of AA and blocked the interferences of cationic species due to the positively charged pAPTT film. This method proved to be effective in the determination of AA in the presence of various biological interfering species. The dynamic range of AA detection was from 10 to 200 µM and the detection limit was 1.4±0.06 µM.     

Preparation of Au Nanoparticles Decorated Polyaniline Nanotube and Its Catalytic Oxidation to Ascorbic Acid

With sulfonated electrospun polystyrene fiber as a template, uniform polyaniline(PANI) nanotubes were fabricated via polymerization of aniline followed by template removal. Au nanoparticles(Au_nano) were decorated on the PANI nanotube successfully via auto-reduction of HAuCl₄ on the PANI nanotube. The morphology of the nanotubes was characterized by means of scanning electron microscopy(SEM) and transmittance electron microscopy(TEM). By varying precursor concentration and incubation time, Au_nano-PANI with different size of Au_nano was obtained conveniently. Glassy carbon electrode modified with the Au_nano decorated PANI nanotubes (Au_nano-PANI/GCE) was prepared and used seccessfully for the catalytic oxidation of ascorbic acid(AA). The results of differential pulse voltammetry indicate that there is a good linear relationship between the peak currents and the concentrations of AA in the range of 5-3000 μmol/L, with the limit of detection of 1 μmol/L(S/N>3). There is no mutual interference between AA and dopamine. The electrode has been successfully applied in the detection of AA in vitamin C tablet sample.     

Poly(pyridine‐3‐boronic acid)/Multiwalled Carbon Nanotubes Modified Glassy Carbon Electrodes for Simultaneous Determination of Ascorbic Acid, 3,4‐Dihydroxyphenylacetic Acid and Uric Acid

Poly(pyridine‐3‐boronic acid) (PPBA)/multiwalled carbon nanotubes (MWCNTs) composite modified glassy carbon electrode (GCE) was used for the simultaneous determination of ascorbic acid (AA), 3,4‐dihydroxyphenylacetic acid (DOPAC) and uric acid (UA). The anodic peaks for AA, DOPAC and UA at the PPBA/MWCNTs/GCE were well resolved in phosphate buffer solution (pH 7.4). The electrooxidation of AA, DOPAC and UA in the mixture solution was investigated. The peak currents increase with their concentrations increasing. The detection limits (S/N=3) of AA, DOPAC and UA are 5 µM, 3 µM and 0.6 µM, respectively.     

Simultaneous Determination of Ascorbic Acid,Dopamine and Uric Acid Based on Gold Nanoparticles‐PTCA‐Cys Composites Modified Electrodes

In this study, a nanocomposite of 3, 4, 9, 10‐perylenetetracarboxylic acid and L‐cysteine (PTCA‐Cys) with satisfactory water‐solubility and film‐forming ability was prepared and worked as substrate for modifying the glassy carbon electrode. Then, gold nanoparticles (AuNPs) were immobilized to achieve a PTCA‐Cys‐AuNPs modified electrode which provided more reaction positions on the sensor. Scanning electron microscopy, transmission electron microscopy, cyclic voltammetry and different pulse voltammetry were employed to characterize the assembly process of the sensor. The constructed sensor displayed desirable sensitivity, selectivity and stability towards the simultaneous detection of ascorbic acid (AA), dopamine (DA) and uric acid (UA). Under the optimal experimental conditions, the oxidation peaks of AA, DA and UA appeared at 64, 240 and 376 mV, respectively. The corresponding linear response ranges were 3.2–435, 0.04–100 and 0.80–297 μM, and the detection limits were 1.1, 0.010 and 0.27 μM (S/N=3), respectively.     

Selective Detection of Ascorbic Acid Using Octacyanomolybdate‐Doped‐Glutaraldehyde‐Cross‐Linked Poly‐L‐Lysine Film Modified Glassy Carbon Electrode

The present work describes oxidation of ascorbic acid (AA) at octacyanomolybdate‐doped‐glutaraldehyde‐cross‐linked poly‐L ‐lysine (PLL‐GA‐Mo(CN) film modified glassy carbon electrode in 0.1 M H₂SO₄. The modified electrode has been successfully prepared by means of electrostatically trapping Mo(CN) mediator in the cationic film of glutaraldehyde‐cross‐linked poly‐L ‐lysine. The dependence of peak current of modified electrode in pure supporting indicates that the charge transfer in the film was a mixed process at low scan rates (5 to 200 mV s^?1), and kinetically restrained at higher scan rates (200 to 1000 mV s^?1). Cyclic voltammetry and rotating disk electrode (RDE) techniques are used to investigate the electrocatalytic oxidation of ascorbic acid and compared with its oxidation at bare and undoped PLL‐GA film coated electrodes. The rate constant of catalytic reaction k obtained from RDE analysis was found to be 9.5×10⁵ cm³ mol^?1 s^?1. The analytical determination of ascorbic acid has been carried out using RDE technique over the physiological interest of ascorbic acid concentrations with a sensitivity of 75 μA mM^?1. Amperometric estimation of AA in stirred solution shows a sensitivity of 15 μA mM^?1 over the linear concentration range between 50 and 1200 μM. Interestingly, PLL‐GA‐Mo(CN) modified electrode facilitated the oxidation of ascorbic acid but not responded to other electroactive biomolecules such as dopamine, uric acid, NADH, glucose. This unique feature of PLL‐GA‐Mo(CN) modified electrode allowed for the development of a highly selective method for the determination of ascorbic acid in the presence of interferents.     

Polyaniline‐Based Sensor Material for Potentiometric Determination of Ascorbic Acid

Polyaniline (PANI)‐based sensor material for determination of ascorbic acid was synthesized by oxidative chemical polymerization of aniline on a screen‐printed carbon‐paste electrode. The influence of PANI chemical structure formed under various polymerization conditions on the sensor response was investigated. The presence of aniline dimer derivatives in PANI structure was found to induce significant improvement of the limit of detection and the linear dynamic range without a change in sensitivity. The sensor prepared by aniline polymerization in pH 7 buffer leading to the product containing mainly the aniline dimer‐based units showed the best detection limit of 0.1 µM. It was shown that the PANI‐based sensor could be used for ascorbic acid analysis in the presence of citrate and lactate as interfering ions. A quantitative determination of ascorbic acid concentration in beverages and vitamins was performed.     

Electro-Catalytic Oxidation of Ascorbic Acid at a Cobalt-Salen Polymer Modified Electrode and Analytical Applications

ABSTRACT

The preparation and electrochemical characteristics of electrodes modified by cobalt complexes of N, N' - bis(salicylidene)-ethane -1, 2- diamine (salen) are described. A cobalt-salen polymer film modified electrode has strong electro-catalytic effects for the oxidation of ascorbic acid. The anodic peak potential of ascorbic acid shifted negatively for 400 m V. The catalytic reaction rate constant determined by rotating disk experiments is 7.08×10⁵ mol s^?1 cm^3. The catalytic mechanism and the effect of film thickness are discussed. A sensitive voltammetric response for ascorbic acid was obtained covering a linear range from 1.0×10^?6 to 1.0×10^?3 mol-L^?1 The modified electrode showed good stability and reproducibility. The electrode was used to the determination of ascorbic acid in fruit juices and showed promising results compared with conventional methods. The electro-catalytic effect of several metal-salen complexes and a similar Schiff base derivative for ascorbic acid was compared.     

Direct In Situ Determination of Ascorbic Acid in Fruits by Screen‐Printed Carbon Electrodes Modified with Nylon‐6 Nanofibers

A simple sensing unit based on a disposable screen printed carbon electrode coated by an electrospun nylon‐6 nanofibrous membrane was developed for in situ selective determination of ascorbic acid (AA) in different types of fruits. The membrane, prepared by electrospinning, represents a selective barrier to possible interferents, such as phenolic compounds, allowing an improved selectivity towards AA. No sample preparation and/or dilution is necessary since the new device is applied directly “pricking” the fruit with the electrode. A good correlation was obtained between the amperometric in situ method and a reference chromatographic methodology (HPLC‐UV) when applied to various fruit samples.     

多巴胺和抗坏血酸在CPB现场修饰碳糊电极上的电化学及电化学动力学性质

用现场修饰方法制备了溴化十六烷基吡啶(CPB)修饰碳糊电极(CPB/CPE)。运用循环伏安法(cyclic voltammetry,CV)、电位阶跃计时电流法(chronoamperometry,CA)及电位阶跃计时库仑法(chronocoulometry,CC)法研究了多巴胺(DA)和抗坏血酸(AA)在裸碳糊(CPE)和CPB/CPE上的电化学行为,测得了动力学参数如电荷转移系数α,扩散系数D,反应级数和电极反应速率常数kf。研究结果表明CPB/CPE可用于AA和DA共存体系中DA的电化学选择性测定。     

A New Redox Reaction of Ascorbic Acid at Platinum Electrodes

A pair of new redox peaks of ascorbic acid at a platinum electrode was found and studied in detailed by spectroelectrochemistry and electrochemistry technologies. This is a quasi‐reversible redox reaction with a one‐electron transfer process. The intermediate of tertiary carbon free radical exists in this process. The appearance reaction rate constant and the diffusion coefficient were investigated. A possible reaction mechanism has been proposed.     

Silicomolybdate‐Doped PEDOT Modified Electrode: Electrocatalytic Reduction of Bromate and Oxidation of Ascorbic Acid

Electrically conducting poly(3,4‐ethylenedioxythiophene) (PEDOT) film doped with silicomolybdate (SiMo₁₂O₄₀^4? or SiMo₁₂) was synthesized by electrochemical polymerization. The synthesized film is capable of fast charge propagation during redox reactions in strong acid medium 0.2 M H₂SO₄ solution. The modified electrode was used towards reduction of bromate and successfully employed as an amperometric sensor for bromate and also above modified electrode was investigated for ascorbic acid oxidation.     

Catalytic Oxidation of Ascorbic Acid at a Polyhistidine Modified Electrode and Its Application to the Voltammetric Resolution of Ascorbic Acid and Dopamine

Abstract

A new polymer (polyhistidine) modified electrode has been fabricated and was applied to the catalytic oxidation of ascorbic acid (AA), reducing the overpotential by 400 mV. The catalytic rate constant of the modified electrode for the oxidation of AA was determined using a rotating electrode. The catalytic current was linearly dependent on the ascorbic acid concentration between 5×10^?5 and 2×10^?3 M. The catalytic effect on the AA resulted in the separation of the overlapping voltammograms of AA and dopamine (DA) in a mixture. This allowed the determination of AA in the presence of DA. The electrode was rather stable even after several months; a reproducible response of AA was obtained.     

四氰基醌二甲烷修饰碳糊电极电催化氧化测定抗坏血酸

本用四氰基醌二甲烷作价体，制成ＴＣＮＱ－碳糊电极，研究了该电极的性能。电极对水溶液中的抗坏血酸在较宽的ｐＨ和浓度范围内均有良好的电催化氧化作用，电极的稳定性良好，在ＡＨ２浓度５．０×１０＾－５－５．０×１０－２ｍｏｌ／Ｌ范围内，催化峰电流与ＡＨ２浓度呈线性关系，响应时间小于３０ｓ．     

基于溶胶-凝胶普鲁士蓝膜修饰玻碳电极电催化氧化测定水果中抗坏血酸

制备了一种溶胶-凝胶普鲁士蓝膜修饰玻碳电极,研究了抗坏血酸在该电极上的电催化氧化作用,建立了测定抗坏血酸的方法。在磷酸缓冲溶液(pH 5.0)中,在2.5×10-5-3.2×10-3mol.L-1范围内,抗坏血酸的浓度与氧化峰电流呈线性关系,相关系数为0.999 5,检出限为7×10-6mol.L-1。该修饰电极具有制备简单、灵敏度高、响应速度快、稳定性和重现性好等特点。方法已用于水果中抗坏血酸的测定,所得结果与药典法测得结果一致。     

铁氰化镍修饰电极对抗坏血酸电催化氧化的研究

抗坏血酸(AH_2)在玻碳和铂电极上的过电位较大,其电极反应不可逆.有关AH_2在碳及其它修饰电极上的电催化氧化已有一些报道,如减压热处理、Al_2O_3微粒研磨、普鲁士蓝修饰膜和聚乙烯二茂铁修饰膜等.本文研究了铁氰化镍修饰膜电极催化AH_2氧化的电化学行为.发现其阳极峰电流与AH_2浓度呈线性关系,可测定1×10~(-7)mol/L的AH_2,其灵敏度比聚乙烯二茂铁修饰电极提高一个数量级.用于蔬菜、水果中AH_2的测定,结果满意.     

Investigation of Protein Binding With All Solid‐State Ion‐Selective Electrodes

A potentiometric sensor for studying charge based adsorption of proteins was created using a single‐piece polyaniline‐PVC ion‐selective electrode (ISE). Three different ISEs, two for Na⁺ and one for Cl^? ion determination, were studied. The Na⁺‐ISEs consisted of a neutral calixarene‐based ionophore and one with a charged carrier dinonylnapthalenesulfonic acid (DNNSA) whereas for the Cl^? ISE, an anion exchanger tridodecylmethylammonium chloride (TDDMA⁺Cl^?), was used. The Na⁺ ISE with DNNSA as the charged carrier was successfully able to discriminate the binding of two different proteins (bovine serum albumin and lysozyme) based on their intrinsic charge.