Mycotoxins: Simultaneous Detection of Zearalenone and Citrinin by Voltammetry on Edge Plane Pyrolytic Graphite Electrode

Mycotoxins are highly toxic compounds often found in the food. It is of paramount importance to have analytical technique for point‐of‐care on‐spot detection for authorised personnel to immediately take the action required. Electrochemistry offers the portability for miniaturized sensor of mycotoxins. Here we show that edge‐plane pyrolytic electrode offers excellent selectivity and sensitivity towards simultaneous detection of zearalenone and citrinin. This will have a great impact for point‐of‐care mycotoxin detection.     

Electrochemical Reduction Behavior and Polarographic Determination of Methoxy Triazine Herbicides in Environmental Samples

The electrochemical reduction behavior of 1,3,5-triazine herbicides, Atraton (AN), Prometon (PN), Secbumeton (SN), and Terbumeton (TN) at mercury electrodes was studied in aqueous Britton Robinson buffer (BR) solutions by using different voltammetric techniques. The nature of the electrode process was examined. Number of electrons involved in the reduction process of all the four compounds was evaluated and a reduction mechanism was proposed. The electrolysis products were separated and identified by IR spectra. For analytical purposes, BR buffer of pH 4.0 was chosen as working medium for all the four analytes. The detection limits were found to be 1.5 × 10^?8 mol l^?1, 2 × 10^?8 mol l^?1, 2.8 × 10^?8 mol l^?1, and 1 × 10^?8 mol l^?1 for AN, PN, SN, and TN, respectively. A differential pulse voltammetric method was developed for the determination of these compounds in agricultural formulations, water, and soil samples. The interference from the ions and other herbicides were also evaluated.     

Differential Pulse Voltammetric Determination of L-Cysteine After Cyclic Voltammetry in Presence of Catechol with Glassy Carbon Electrode

An electrochemical method of determination of cysteine has been developed in the solution containing catechol as the indicator. Nucleophilic addition of the thiol species to the electrogenerated o-quinone results in the formation of o-quinone-cysteine adducts that easily accumulate use at the surface of the electrode in the acidic solution. Therefore, the use of cyclic voltammetry leads to the amplification of the o-quinone-cysteine adduct's reductive current. As cyclic voltammetry was performed prior to differential pulse voltammetry, the peak of o-quinone-cysteine could be separated preferentially from o-quinone in the differential pulse voltammogram and the selectivity of the method has been assessed with no interference from ascorbic acid, glycine, L-tyrosine, or L-lysine. The magnitude of o-quinone-cysteine peak is proportional to the concentration of cysteine, and thus it can be exploited to determine cysteine within the injection. The results were consistent with those obtained by means of HPLC analysis.     

Poly(Methyl Red) Modified Glassy Carbon Electrodes: Electrosynthesis,Characterization, and Sensor Behavior

Poly(methyl red), PMR, was electropolymerized on glassy carbon electrodes by potential cycling in 50 mM phosphate buffer solution at pH 7.0 and 8.0 and Britton Robinson buffer solution in the pH range 7.0‐11.0. The electrochemical behavior of PMR modified electrodes was investigated by cyclic voltammetry in Britton Robinson buffer solution at different pHs from 5.0 to 10.0 and found that the best PMR film formation was obtained at pH 9.0. Uric acid was quantitatively determined at PMR modified electrodes by cyclic voltammetry and differential pulse voltammetry in Britton Robinson buffer at pH 5.0. Both methods presented a linear dependence between the anodic peak current and the concentration of uric acid in the range of 0.4 to 60 μM and 0.08 to 100 μM with the limits of detection of 0.038 and 0.009 μM for cyclic voltammetry and differential pulse voltammetry, respectively. Poly(methyl red) as redox mediator allowed the determination of uric acid without any interferences from the substances in serum samples.     

Role of carbonyl sites in the electrochemical response of 2,6-diaminopurin-8-ol

Modified graphite electrodes were prepared with materials containing carbonyl functional groups, including polypyrrole containing poly(methyl vinyl ketone). The effect of the modification on the electrochemical response of 2,6-diaminopurin-8-ol, a small, electrochemically fast biological molecule with primary amine groups which absorbs on active graphite, was evaluated. The results show that the chemical interactions between 2,6-diaminopurin-8-ol and the surface carbonyl functional groups do not by themselves contribute to the reactivity of the probe molecule.     

二茂铁在几种离子液体中的迁移行为

采用循环伏安法研究了二茂铁(Fc)在几种离子液体中的迁移行为. 计算了Fc在各离子液体中的扩散系数和粘度系数,探讨了离子液体粘度与离子液体结构之间的关系. 实验结果表明, 离子液体的粘度随阳离子取代基碳链长度的增加而增加, 随阴离子对称性的增加而增加.     

植物生物分子的电分析化学研究X槟榔碱电化学行为及测定

槟榔碱主要存在于棕榈科植物槟榔的种子内。槟榔是我国目前亟待开发的天然植物资源,广泛分布于海南、广西、云南、福建及台湾等地。槟榔碱味辛、温,具有杀虫、破积、下气、行水的功能。由于槟榔碱对M—胆碱受体的作用,平时嚼食槟榔,可促使唾液分泌增加、增进     

聚邻氨基对酚磺酸修饰电极测定尿酸

尿酸(UA)是核蛋白和核酸的代谢产物,人体内尿酸的水平与肝脏疾患[1]、肾病[2]以及心血管疾病[3]等有着密切的关系.因此,对人体体液中尿酸的定量分析无论在药物控制方面还是在临床诊断方面都具有重要意义.     

Electrochemical Determination of Capsaicin and Silymarin Using a Glassy Carbon Electrode Modified by Gold Nanoparticle Decorated Multiwalled Carbon Nanotubes

The goal of this study was to develop a suitable electroanalytical method for the determination of primary compounds in the extracts of capsaicin and silymarin. For this purpose, a glassy carbon electrode immobilized with multiwalled carbon nanotubes decorated with gold nanoparticles was characterized by high resolution transmission electron microscopy and attenuated total reflectance infrared spectroscopy. The developed electrochemical sensor had a linear dynamic range from 0.15 to 35.0 µM. In addition, the limits of quantification for silymarin and capsaicin with the gold nanoparticle decorated multiwalled carbon nanotubes were 0.1564 and 0.2761 µg L^?1 with relative standard deviations (n = 3) of 1.65% and 2.09% and equivalent mass percentages of 93.33% and 62.02%, respectively. The methodology may be employed for the determination of capsaicin and silymarin in pharmaceutical and food products.     

Determination of Rutin by a Graphene-Modified Glassy Carbon Electrode

A reduced graphene oxide-modified glassy carbon electrode for sensitive detection of rutin is reported. The modified electrode was obtained by one-step electrochemical reduction of graphene oxide on the bare glassy carbon electrode. In the presence of graphene, an enhanced electrochemical response for rutin appeared with a pair of well-defined anodic and cathodic peaks in pH 3.0 phosphate buffer. Under the optimized conditions, the anodic peak currents exhibited a linear relationship with rutin concentration from 0.1 to 2.0 µM with a detection limit of 23.2 nM. The modified electrode was employed to the analysis of tablets (with satisfactory recovery of 19.96 mg/per tablet) and Flos Sophorae. The graphene-modified electrode exhibited high sensitivity, good stability, and selectivity for the determination of rutin.     

Voltammetric determination of salicylic acid in pharmaceuticals formulations of acetylsalicylic acid

The electrochemical oxidation of salicylic acid (SA) has been studied on a glassy carbon electrode using cyclic voltammetry and differential pulse voltammetric (DPV) method. SA gives a single irreversible oxidation wave over the wide pH range studied. The irreversibility of the electrode process was verified by different criteria. The mechanism of oxidation is discussed. Using differential pulse voltammetry, SA yielded a well-defined voltammetric response in Britton-Robinson buffer solution, pH 2.37 at 1.088 V (versus Ag/AgCl). The method was linear over the SA concentration range: 1-60 μg ml⁻¹. The method was successfully applied for the analysis of SA as a hydrolysis product, in solid pharmaceutical formulations containing acetylsalicylic acid (ASA).     

姜黄素的电化学性质及其测定

在0.1 mol/L磷酸盐缓冲液(pH 3.0)中,姜黄素于玻碳电极上存在可逆的单电子转移过程,据此,本文建立了以差示脉冲伏安扫描法检测姜黄素含量的新方法.在+0.8V(vs.SCE)电位下,含姜黄素的电解液(试样)于玻碳电极上经过富集,可得一灵敏的还原峰,峰电位Ep为+0.386V.峰电流Ip与姜黄素浓度(1.0×10-8~2.5×10-7mol/L范围内)成线性关系,最低检出限为4.0×10-9mol/L.本法操作简单、快速、灵敏、准确,可用于药物中姜黄素含量直接测定.     

Synthesis and Redox Behavior of Novel 9,10‐Diphenylphenanthrenes

The synthesis and electrochemical investigations of 9,10‐diphenylphenanthrene 2a and its derivatives 2b – 2e are reported. The cyclic voltammetry of derivatives 2a – 2c and 2e in different solvent/Bu₄NPF₆ electrolyte systems reveals that the redox properties are dependent on solvent, temperature, and sweep rate. The oxidation of 9,10‐diphenylphenanthrene 2a occurred as an irreversible process, while two fully reversible oxidation waves were observed for dimethoxy derivative 2c . The room‐temperature oxidation of brominated compound 2b is reversible, whereas AcO‐substituted phenanthrene 2e displayed a reversible oxidation peak only at low temperature. Furthermore, the electronic nature of the substituent affects the oxidation potentials. In the CH₂Cl₂‐based electrolyte system, the first oxidation potentials increase in the order 2c < 2e < 2b .     

微分脉冲阴极溶出伏安法测定阿米卡星

硫酸阿米卡星(Am ikacin sulfate)是一种氨基糖苷酸类抗生素,化学名为O-3氨基-3-脱氧-а-D-蒲吡喃糖基-(1-6)-O-[6-氨基-6-脱氧-а-D-蒲吡喃糖基-(1-4)]-N-(4-氨基-2-羟基-1-氧丁基)-2-脱氧?D-链霉胺硫酸盐。目前报道的测定方法主要有高效液相法[1]、镍毛细管电泳法[2]。本文研究了阿米卡星在玻碳电极上的电化学行为。微分脉冲溶出伏安法是一种灵敏度很高的痕量分析方法,本文利用该方法对阿米卡星进行了测定,发现阿米卡星在pH=2的盐酸底液中,产生一灵敏的还原峰,可用于定量测定。平行测定了7次,RSD为2·05%,该方法可用于注射液及血清中…     

Amperometric determination of paracetomol by a surface modified cobalt hexacyanoferrate graphite wax composite electrode

A stable electro active thin film of cobalt hexacyanoferrate (CoHCF) was deposited on the surface of an amine adsorbed graphite wax composite electrode using a simple method. Cyclic voltammetric experiments showed two pairs of well defined peaks for this CoHCF modified electrode which exhibited excellent electrocatalytic property for the oxidation of paracetomol at a reduced overpotential of 100 mV and over a concentration range of 3.33 × 10⁻⁶ to 1.0 × 10⁻³ M with a slope of 0.208 μA/μM with good sensitivity. The influence of the supporting electrolyte on peak current and peak potential were also obtained in addition with effects of common interference (e.g., ascorbic acid) on the response of the modified electrode. Various parameters that influence the electrochemical behavior of the modified electrode were optimized by varying scan rates and pH. Electrochemical impedance spectroscopy studies suggested that the electrode reaction of the CoHCF film is mainly controlled by transport of counter ion. The immobilized CoHCF maintained its redox activity showing a surface controlled electrode reaction with the electron transfer rate constant (K_s) of 0.94 s⁻¹ and charge transfer coefficient of 0.42. Hydrodynamic and chronoamperometric studies were done to explore the utility of the modified electrode in dynamic systems. The results of the differential pulse voltammetry (DPV) using the modified electrode was applied for the determination of paracetomol in commercially available tablets. The results obtained reveal that the electrode under study could be used as an effective sensor for online monitoring of paracetomol.     

Electrochemical behaviour of triclosan at a screen-printed carbon electrode and its voltammetric determination in toothpaste and mouthrinse products

Cyclic voltammetry was used to investigate the electrochemical behaviour of triclosan (2,2,4′-trichloro-2′-hydroxydiphenyl ether) at a screen-printed carbon electrode (SPCE). It was found that a single anodic peak occurred over the pH range 6.0–12.0; this peak was considered to result from an irreversible oxidation reaction at the phenolic moiety. A plot of E_p versus pH was constructed and from the break point a pK_a value of 7.9 was obtained, thus agreeing with the literature value. Detailed voltammetric studies were performed at pH 10, where the analyte exists as an anion. It was demonstrated that, at an initial potential of 0 V, the anion underwent electrosorption prior to electrochemical oxidation. The oxidation reaction appeared to involve a one-electron transfer, as deduced from a calculated n_a value of 0.5; the same value was obtained at pH 7.0. In contrast to triclosan, triclosan monophosphate was found to be electrochemically inactive when subjected to voltammetry under the stated conditions.

The electrochemical oxidation of triclosan at a SPCE was exploited for its determination (0.3%) in commercial toothpaste and mouthrinse products using differential pulse voltammetry. The recovery and precision data indicated that this approach may have application in routine quality control analysis.     

Hemin Modified Carbon Fat Electrode for Analyzing Antimalarial Endoperoxide Artemisinin in Artemisia annua

A hemin bulk modified carbon electrode with Adeps neutralis (solid fat) as binder was developed for the determination of antimalarial endoperoxide artemisinin in plant matrix. The hemin modified electrode showed significant catalytic activity for the electrochemical reduction of artemisinin at about ?380 mV vs. Ag/AgCl in phosphate buffer solution of pH 7 by using cyclic and differential pulse voltammetry. Under optimized conditions strict linearity between artemisinin concentration and height of the cathodic catalytic current peak was observed in 4.8×10^?6–7.8×10^?5 M concentration range (R=0.9991) when using differential pulse voltammetry. The detection limit was calculated as 1.4×10^?6 M of artemisinin. The developed electroanalytical device is suitable for the determination of artemisinin in Artemisia annua extracts.     

A novel sensor based on electropolymerization of β-cyclodextrin and l-arginine on carbon paste electrode for determination of fluoroquinolones

An electrochemical sensor for fluoroquinolones (FQs) based on polymerization of β-cyclodextrin (β-CD) and l-arginine (l-arg) modified carbon paste electrode (CPE) (P-β-CD-l-arg/CPE) was built for the first time. Synergistic effect of l-arg and β-CD was used to construct this sensor for quantification of these important antibiotics. Scanning electron microscope (SEM) image shows that polymer of β-CD and l-arg has been successfully modified on electrode. Electrochemical impedance spectroscopy (EIS) and cyclic voltammograms (CV) further indicate that polymer of β-CD and l-arg efficiently decreased the charge transfer resistance value of electrode and improved the electron transfer kinetic between analyte and electrode. Under the optimized conditions, this modified electrode was utilized to determine the concentrations of ciprofloxacin, ofloxacin, norfloxacin and gatifloxacin. The differential pulse voltammogram (DPV) exhibits the oxidation peak currents were linearly proportional to their concentration in the range of 0.05–100 μM for ciprofloxacin, 0.1–100 μM for ofloxacin, 0.1–40 μM for norfloxacin and 0.06–100 μM for gatifloxacin, respectively. This method was also successfully used to detect the concentrations of each drug in pharmaceutical formulations and human serum samples. In addition, this proposed fluoroquinolones sensor exhibited good reproducibility, long-term stability and fast current response.     

铂/多壁碳纳米管修饰玻碳电极用于微分脉冲伏安法测定左旋多巴

采用微波辅助加热多元醇技术制备了载铂多壁碳纳米管复合材料,并将该复合材料分散在N,N′-二甲基甲酰胺溶液中得到悬浮液,取14μL悬浮液滴涂在玻碳电极表面,制备铂/多壁碳纳米管修饰电极(Pt/MWCNT′s/GCE)。循环伏安法研究了在0.05mol·L~(-1)硫酸支持电解质中,在0.30～0.70V(vs.SCE)电位范围内,左旋多巴在修饰电极上的电化学行为,结果表明:左旋多巴在Pt/MWCNT′s/GCE上于电位0.548V处可见明显的氧化峰,且氧化峰电流显著高于在MWCNT′s/GCE和裸玻碳电极上的氧化峰电流。提出了用微分脉冲伏安法测定左旋多巴的方法。左旋多巴的浓度在8.0×10~(-6)～2.0×10~(-1)mol·L~(-1)范围内与其氧化峰电流呈线性关系,检出限(3S/N)为1.9×10~(-6)mol·L~(-1),平均回收率为102.8%。     

在抗坏血酸存在下用L-赖氨酸修饰玻碳电极测定多巴胺

采用电化学氧化法制备了L-广赖氮酸单分子层修饰玻碳电极,研究了多巴胺（DA）和抗坏血酸（AA）在该电极上的电化学行为。结果表明,L-广赖氨酸单分子层修饰玻碳电极不仅能改善多巴胺和抗坏血酸的电化学行为,而且能将多巴胺和抗坏血酸二者在裸电极上的完全重叠的单氧化峰分开成为两个完全独立的氧化峰,循环伏安（CV）图上峰间距为507mV,差分脉冲伏安（DPV）图上峰间距为460mV,由此可实现在AA的共存下对样品中的DA进行选择性测定。