Electrochemical Reduction of Pyridinic Herbicides Picloram and Clopyralid on a Mercury Pool Electrode

This paper presents the identification by GC/MS of the products obtained after the total reduction of picloram and clopyralid on a mercury pool electrode. The products found in the strongly acidic media reduction of picloram are 4‐amino‐3,5,6‐trichloro‐2‐pyridinecarboxaldehyde, 4‐amino‐3,5,6‐trichloro‐2‐pyridinecarbinol and 4‐amino‐3,5‐dichloro‐2‐pyridinecarboxylic acid; at pH 3–4 the first compound is substituted by 4‐amino‐3,5‐dichloro‐2‐pyridinecarboxaldehyde. For clopyralid 3,6‐dichloro‐2‐pyridinecarbinol was detected. Under the light of such products the overall reduction processes are discussed showing the partial reductive cleavage of chlorine atoms in both cases.     

Electrochemical Characterization and Determination of Mercury Using Carbon Paste Electrodes Modified with Cyclodextrins

In this work the characterization and determination of mercury in HClO₄ media using carbon paste electrodes modified with α‐ and β‐cyclodextrins (CPE_α‐CD and CPE_β‐CD) at E_d=?0.7 V with a t_d = 20 s and a potential scan v=20 mV s^?1 is studied‥ The statistical results obtained indicate that the modified electrodes displayed a better analytical performance as compared to that obtained with the unmodified CPE. The detection limits for the CPE_α‐CD and for the CPE_β‐CD were 0.05 and 0.09 μM, respectively, while for the CPE it was 0.41 μM. The CPE_β‐CD exhibited greater sensitivity as compared to that of the CPE_α‐CD.     

A Contribution to the Study of the Adsorption of s‐Triazine Herbicides on Glassy Carbon Electrodes by Differential‐Capacity Measurements

Measurements of differential capacity vs. potential have been made for a series of s‐triazine herbicides at different concentrations. In all cases the decrease in capacity was independent of the applied potential, so the adsorption is also independent of the potential. From the measurements it can be established that the adsorption follows Langmuir type isotherms. Adsorption constants were obtained for the different herbicides at 25 °C (simetryn, simazine, terburyn and prometon) as well as those to simetryn at different temperatures, from which the adsorption enthalpy of this herbicide was calculated being its value of 17.5 kJ mol^?1.     

Single‐Wall Carbon Nanotube Paste Electrodes: a Comparison with Carbon Paste,Platinum and Glassy Carbon Electrodes via Cyclic Voltammetric Data

A new carbon electrode material, obtained by mixing single wall carbon nanotubes (SWNTs) with a mineral oil binder is studied. Carbon nanotube pastes show the special properties of carbon nanotubes combined with the various advantages of composite electrodes such as a very low capacitance (background current) and the possibility of an easy preparation, modification and renewal. A better knowledge of the characteristics of electrode reactions at carbon nanotube paste (CNTP) electrodes was obtained studying the electron transfer rates of various redox couples under different pretreatment conditions. A critical comparison with carbon paste (CP), platinum (Pt) and glassy carbon (GC) electrodes was also carried out. Capacitance and resistance values were also calculated for all electrodes investigated. Both untreated and treated CNTP electrodes showed a low resistance while the capacitance was markedly reduced with CNTP electrodes previously treated with concentrated nitric acid. An electrochemical pretreatment on CNTP electrodes was developed which showed an excellent result towards two‐electron quinonic structure species. After this treatment the heterogeneous standard rate constants for p‐methylaminophenol sulfate (MAP) and dopamine resulted to be significantly higher (2.1×10^?2 cm/s and 2.0×10^?2 cm/s, respectively) than those obtained with the other electrodes studied. Reproducibility, stability and storage characteristics of CNTP electrodes were also reported.     

Adsorption of Carbon Monoxide on Palladium Electrode from Alkaline Solutions

Abstract

The adsorption of carbon monoxide from basic solution (0.1 M LiOH) on a palladium electrode was investigated. It was found that adsorption of CO takes place below the potential -0.25 V (vs. SCE). Surface concentration of the adsorption products, their composition and structure depend on the adsorption potential. The CO adsorption products block hydrogen absorption in palladium but in contrary to acidic solutions don't block the hydrogen desorption process.     

Voltammetry of Osmium End‐Labeled Oligodeoxynucleotides at Carbon,Mercury, and Gold Electrodes

Voltammetric behavior of oligodeoxynucleotide (ODN) 5′‐T₄₀ (GAA)₇–3′ end‐labeled with osmium tetroxide,2,2‐bipyridine [Os(VIII)bipy] was compared with Os(VIII)bipy‐base‐ and with Os(VI)bipy‐sugar‐modified thymine ribosides. Cyclic voltammograms of Os(VIII)bipy‐modified ODN at mercury and carbon electrodes were similar but not identical to those of Os(VIII)bipy‐modified thymine riboside. Treatment of the ODN with Os(VI)bipy did not result in the ODN modification, in agreement with the known specificity of the reagent to the sugar cis‐diols. We show that in addition to mercury and carbon electrodes, the gold electrode can be used to detect Os(VIII)bipy‐labeled ODN. Comparison of voltammetric behavior of end‐labeled ODN using three types of electrodes most frequently used in DNA analysis may help to optimize electrochemical DNA sensors.     

Voltammetry of Metallic Powder Suspensions on Mercury Electrodes

Ultrafine powder samples of Cu, Fe, Ni, Mo and W were examined voltammetrically in aqueous suspensions with hanging mercury drop electrode. According to chemical interaction of the metallic powder particles with the dispersing medium the voltammetric curves either consist of a set of individual current peaks given by particulate reduction of surface oxides on impingements of particles from their suspension upon the electrode, or correspond to electroactivity of dissolved products of chemical reaction between particles and the medium.     

The Reduction of 2,6‐Dimethoxy‐4‐chloro‐1,3,5‐triazine on Mercury Electrodes in Aqueous Solutions in Relation with the Reduction of s‐Triazine Herbicides

This paper presents polarographic and voltammetric studies on the electroreduction of 2,6‐dimethoxy‐4‐chloro‐1,3,5‐triazine on mercury electrodes in aqueous solutions and in the acidity range 2 M H₂SO₄ to pH 7. Above pH 6.5 no signals were obtained. In both DC and DP polarography and voltammetry, one or two partially overlapped reduction waves were observed, depending on the pH of the medium. The overall process corresponded to a four‐electron irreversible reduction. In strongly acidic media (pH<4.5) the protonated reactant was reduced through a two‐electron process to give a dechlorinated molecule that is subsequentely reduced at the potentials of the second wave. It was concluded that the reduction of the chlorinated s‐triazine rings seems to occur through the reductive cleavage of the chlorine irrespective of the nature of the groups bonded to the ring in positions 2, 6.     

Novel Studies about the Electrooxidation of a Deoxynivalenol (DON) Mycotoxin Reduction Product Adsorbed on Glassy Carbon and Carbon Paste Electrodes

A novel and fast square‐wave adsorptive anodic stripping voltammetric procedure on glassy carbon and carbon paste electrodes is described for the indirect trace quantitation of deoxynivalenol (DON) mycotoxin that frequently contaminates soya and foodstuff. The in situ homogeneous reduction of the toxin by product/s of dissolved oxygen electroreduction in pH 8 buffer solution makes the quantitation of DON possible through a simple electroanalytical technique. Moreover, its potential use for the analysis of real samples was demonstrated using a soya flour sample spiked with DON without previous separating procedures. The DON detection limits were 3.6 and about 6 ppb from standard solutions and soya flour matrix, respectively.     

Electroanalytical Application of Carbon Based Electrodes to the Pharmaceuticals

Abstract

Carbon and its derivatives, as the high performance material, occupy a special place in electrochemistry due to its ‐in many ways‐ extreme properties. Recent trends and advances in the electrochemistry of carbon‐based electrodes are reviewed. The varieties of carbon‐based electrodes, their basic physicochemical properties and some characteristics are surveyed. Special attention is paid to the possibilities of carbon‐based electrodes in electroanalytical investigation in pharmaceutical dosage forms and biological samples using modern electrochemical techniques. This review includes a summary of the rules that must be considered for drug analysis from its dosage forms and biological samples using carbon‐based electrodes. The present review is the first comprehensive report on the heterogeneous and homogeneous carbon electrodes, and an addition to many excellent reviews on carbon electrodes in the literature. This review summarizes some of the recent developments and applications of carbon‐based electrodes for drug compounds in their dosage forms and in biological samples in the period from 1996 till 2006. Also some further selected designs (screen‐printed; carbon nanotubes, etc.) and applications have been discussed.     

聚苯基荧光酮修饰玻碳电极吸附溶出伏安法测定痕量汞

研究利用聚苯基荧光酮修饰玻碳电极测定痕量汞的溶出伏安法,在0.1 mol.L-1氨水-NH4Cl缓冲溶液中(pH 9.5),开路搅拌,Hg(Ⅱ)富集于修饰电极表面,通过介质交换至0.1mol.L-1盐酸溶液中,于-0.40 V还原后阳极化线性扫描,在0 V左右处获得一灵敏汞的溶出峰。其氧化峰电流与Hg(Ⅱ)浓度在9.0×10-8~8.0×10-7mol.L-1范围内呈线性关系,开路富集5 min,检出限达2.0×10-8mol.L-1。应用此方法于尿液中汞的测定,所得平均RSD值小于4.02%,回收率试验结果在98.4%~103.2%间。     

Development of Disposable Carbon Nanofibers Electrodes Supported on Filters

The purpose of this work is to develop simple and reproducible ways to fabricate carbon nanofibers (CNFs) electrodes. Disposable CNFs electrodes were fabricated after filtering CNFs through polytetrafluoroethylene filters (PTFE), using directly as electrodes these filters with the CNFs film. The electrochemical behaviour of CNFs/PTFE electrodes were tested with ferrocenemethanol and tris(2,2′‐bypyridyl)dichlororuthenium(II) (Ru(bipy)₃²⁺). As a proof of concept of the analytical usefulness of the CNFs/PFTE electrodes, the study of vitamin B₁₂ was carried out. Multivariate calibrate has been successfully used to determine vitamin B₁₂ in a complex medium with vitamins B₁ and B₆ as interferents.     

Stripping Voltammetry of Mercury(II) with a Chemically Modified Carbon Paste Electrode Containing Silica Gel Functionalized with 2,5‐Dimercapto‐1,3,4‐thiadiazole

The accumulation voltammetry of mercury(II) was investigated at a carbon paste electrode chemically modified with silica gel functionalized with 2,5‐dimercapto‐1,3,4‐thiadiazole (DTTPSG‐CPE). The repetitive cyclic voltammogram of mercury(II) solution in the potential range ?0.2 to +0.8 V (vs. Ag/AgCl), (0.02 mol L^?1 KNO₃ ; v=20 mV s^?1) show two peaks one at about 0.0 V and other at 0.31 V. However, the cathodic wave peak, around 0.0 V, is irregular and changes its form in each cycle. This peak at about 0.0 V is the reduction current for mercury(II) accumulated in the DTTPSG‐CPE. The anodic wave peak at 0.31 V is well‐defined and does not change during the cycles. The resultant material was characterized by cyclic and differential pulse anodic stripping voltammetry performed with the electrode in differents supporting electrolytes. The mercury response was evaluated with respect to pH, electrode composition, preconcentration time, mercury concentration, “cleaning” solution, possible interferences and other variables. The precision for six determinations (n=6) of 0.05 and 0.20 mg L^?1 Hg(II) was 2.8 and 2.2% (relative standard deviation), respectively. The method was satisfactory and used to determine the concentration of mercury(II) in natural waters contaminated by this metal.     

基于碳纳米管的化学修饰电极及电化学生物传感器的研究进展

综述了碳纳米管的结构、合成、纯化、功能化、分散及基于碳纳米管的化学修饰电极和电化学生物传感器的研究进展。     

Quantitative Studies of Metal Ion Adsorption on a Chemically Modified Carbon Surface: Adsorption of Cd(II) and Hg(II) on Glutathione Modified Carbon

The adsorption behavior of model toxic metal cations namely Cd(II) and Hg(II) on carbon surfaces chemically modified by glutathione was investigated as a function of the concentration of Cd²⁺ and Hg²⁺ ions, time and the amount of modified carbon used. Square wave and linear sweep anodic stripping voltammetry was used to monitor the uptake of Cd(II) and Hg(II) ions respectively. Kinetic and adsorption isotherm studies reveal that both Cd(II) and Hg(II) ions undergo similar large adsorption with the modified glutathione carbon material (Glu‐carbon).     

Electrode Kinetics and Sensitivity of Nanostructured Electrodes from Different Carbon Fiber Precursor Materials

Correlation of properties of common carbon fiber precursor materials, polyacrylonitrile (PAN) and pitch, with kinetics and sensitivity of microdisk electrodes, PAN T650, PAN HCB and Pitch P25, nanostructured by an electrochemical etching method was tested. Sensitivity of PAN electrodes is higher but kinetics are slower than at pitch electrodes due to more defects in PAN. Because of more surface oxides at PAN T650 adsorption of dopamine is greater than at PAN HCB electrodes but for uric acid adsorption is greater at PAN HCB. Uric acid sensitivity is related to high conductivity of PAN fibers, with an inverse relationship observed for dopamine.     

碳纳米管阵列电极的构建及电化学研究

本文提出一种改进的氧化铝模板法制备碳纳米管阵列电极:首先结合气相化学沉积和磁控溅射在氧化铝模板中制得碳纳米管阵列电极,然后用HF溶液将沉积了碳纳米管的氧化铝模板阻挡层除去,控制溶出时间即可得到不同溶出长度的碳纳米管阵列电极.循环伏安测试表明,锂离子在该阵列电极中的嵌入脱出反应主要发生在碳纳米管的端口处.此外,还应用固定频率交流阻抗法,研究了不同溶出时间的碳纳米管阵列电极的电容性质.     

介孔碳CMK-3对苯酚的吸附动力学和热力学研究

研究了介孔碳CMK-3对苯酚的吸附性能, 与传统商用活性碳(CAC)进行了比较, 结果表明, CMK-3比CAC的吸附量大、吸附速率快、达到平衡时间短, 是一种较好的吸附剂. 同时探讨了介孔碳CMK-3对苯酚的吸附热力学和动力学特征. CMK-3对苯酚的吸附行为可用Langmuir和Freundlich等温式进行描述, 相关性都较好, 但更符合Freundlich经验公式. 分别采用模拟一阶反应和二阶反应模型考察了吸附动力学, 并计算了这些动力学模型的速率常数. 模拟二级反应模型和实验数据之间有较好的相关性. 分别计算了热力学参数ΔG0, ΔS0和ΔH0, 结果表明, CMK-3对苯酚的吸附过程是吸热和自发的.     

Carbon Nanodots as Electrocatalysts towards the Oxygen Reduction Reaction

Electrocatalysts perform a key role in increasing efficiency of the oxygen reduction reaction (ORR) and as a result, efforts have been made by the scientific community to develop novel and cheap materials that have the capability to exhibit low ORR overpotentials and allow the reaction to occur via a 4 electron pathway, thereby mimicking as close as possible to traditionally utilised platinum. In that context, two different types of carbon nanodots (CNDs) with amide (CND‐CONH₂) and carboxylic (CND‐COOH) surface groups, have herein been fabricated and shown to exhibit excellent electrocatalytic activity towards the ORR in acid and basic media (0.1 M H₂SO₄ and 0.1 M KOH). CND surface modified carbon screen‐printed electrodes allow for a facile electrode modification and enabling the study of the CNDs electrocatalytic activity towards the ORR. CND‐COOH modified SPEs are found to exhibit improved ORR peak current and reduced overpotential by 21.9 % and 26.3 %, respectively compared to bare/unmodified SPEs. Additionally, 424 μg cm⁻² CND‐COOH modified SPEs in oxygenated 0.1 M KOH are found to facilitate the ORR via a near optimal 4 (3.8) electron ORR pathway. The CNDs also exhibited excellent long‐term stability and tolerance with no degradation being observed in the achievable current with the ORR current returning to the baseline level within 100 seconds of exposure to a 1.5 M solution of methanol. In summary, the CND‐COOH could be utilised as a cathodic electrode for PEMFCs offering greater stability than a commercial Pt electrode.     

中分子毒素在碳纳米管上的吸附

研究了两种不同形态的碳纳米管(随机生长多壁碳纳米管(MWCNTs)及定向生长多壁碳纳米管(ACNTs))对典型中分子毒素的吸附性能. 并与两种现有商用血液灌流吸附材料(活性炭(AC)及大孔吸附树脂(MR))进行了对比. 结果显示, 碳纳米管(CNTs)具有优异的中分子吸附能力, 其中MWCNTs对典型中分子毒素的吸附量可达47.18 mg·g-1, 为活性炭的10.8倍, 为大孔吸附树脂的5.5倍. 此外, 碳纳米管的吸附非常迅速, 中分子毒素在MWCNTs及ACNTs达到吸附平衡的时间仅为10 min和15 min, 而活性炭及大孔吸附树脂则分别需要60 min及120 min. 碳纳米管优异的吸附性能得益于其独特的微观结构所形成的发达的中孔. 因此, 碳纳米管可望成为高效的吸附材料, 应用于血液灌流中.