Synthesis of cobaltocenium salts for use as redox labels and their incorporation into Nafion films

A cobaltocenium label was covalently attached to two antidepressants, nortriptyline and desipramine, via an amide linkage, and also to the hydrazine derivative of the biologically important compound biotin (vitamin H), again via an amide linkage. Analytically pure samples of these new cobaltocenium salts could be obtained by chromatography on silica gel followed by elution with aqueous acetone solutions containing sodium chloride (NaCl). These positively charged cobaltocenium ions preconcentrate in a polyanionic Nafion film coated on a glassy carbon surface, albeit at different concentration levels. One factor which seems to influence the amount of cobaltocenium ion that enters the film is polarity since the cobaltocenium ion containing the rather polar biotin preconcentrates at the lowest level in the relatively hydrophobic Nafion. Square-wave voltammograms of Nafion films containing these cobaltocenium cations exhibit a one-electron, reversible, reduction wave at approximately ?1.1 V (vs Ag/AgCl) with peak currents that are sufficiently large to permit detection of 10^?8 M quantities of these substances in the bulk solution.     

Solid-state electrochemiluminescence sensor based on the Nafion/poly(sodium 4-styrene sulfonate) composite film

An effective electrochemiluminescence (ECL) sensor based on Nafion/poly(sodium 4-styrene sulfonate) (PSS) composite film-modified ITO electrode was developed. The Nafion/PSS/Ru composite film was characterized by atomic force microscopy, UV-vis absorbance spectroscopy and electrochemical experiments. The Nafion/PSS composite film could effectively immobilize tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) via ion-exchange and electrostatic interaction. The ECL behavior of Ru(bpy)₃²⁺ immobilized in Nafion/PSS composite film was investigated using tripropylamine (TPA) as an analyte. The detection limit (S/N = 3) for TPA at the Nafion/PSS/Ru composite-modified electrode was estimated to be 3.0 nM, which is 3 orders of magnitude lower than that obtained at the Nafion/Ru modified electrode. The Nafion/PSS/Ru composite film-modified indium tin oxide (ITO) electrode also exhibited good ECL stability. In addition, this kind of immobilization approach was simple, effective, and timesaving.     

Probing Second Harmonic Components of pH‐Sensitive Redox Processes in a Mesoporous TiO2‐Nafion Film Electrode with Fourier‐Transformed Large‐Amplitude Sinusoidally Modulated Voltammetry

Electrochemical processes in mesoporous TiO₂‐Nafion thin films deposited on indium tin oxide (ITO) electrodes are inherently complex and affected by capacitance, Ohmic iR‐drop, RC‐time constant phenomena, and by potential and pH‐dependent conductivity. In this study, large‐amplitude sinusoidally modulated voltammetry (LASMV) is employed to provide access to almost purely Faradaic‐based current data from second harmonic components, as well as capacitance and potential domain information from the fundamental harmonic for mesoporous TiO₂‐Nafion film electrodes. The LASMV response has been investigated with and without an immobilized one‐electron redox system, ferrocenylmethyltrimethylammonium⁺. Results clearly demonstrate that the electron transfer associated with the immobilized ferrocene derivative follows two independent pathways i) electron hopping within the Nafion network and ii) conduction through the TiO₂ backbone. The pH effect on the voltammetric response for the TiO₂ reduction pathway (ii) can be clearly identified in the 2^nd harmonic LASMV response with the diffusion controlled ferrocene response (i) acting as a pH independent reference. Application of second harmonic data derived from LASMV measurement, because of the minimal contribution from capacitance currents, may lead to reference‐free pH sensing with systems like that found for ferrocene derivatives.     

聚氨基黑10B/Nafion修饰电极上多巴胺的检测

用电化学聚合法制备了聚氨基黑10B/Nafion修饰电极,利用循环伏安法研究了多巴胺在此修饰电极上的电化学行为.在磷酸盐缓冲溶液(pH 6.0)中,多巴胺在修饰电极上呈现可逆的氧化还原峰.其峰电位都随pH值的增加而负移.多巴胺氧化还原峰电流与其浓度在0.2～30 μmol/L范围内呈良好的线性关系;检出限为1.0×10~7 mol/L.实验结果表明:本修饰电极具有良好的重现性、稳定性和较强的抗干扰能力.将此修饰电极用于多巴胺注射液和小牛血清中多巴胺的检测,结果令人满意.     

Pervaporation of water from aqueous sulfuric acid at elevated temperatures using Nafion membranes

The concentration of sulfuric acid by pervaporation has been studied using Nafion-112^® and Nafion-117^® membranes, which have been characterized in terms of flux, permeability, and separation factor at 100 and 120 °C. Feed acid concentrations investigated ranged from 40 to over 80 wt%. In general, water fluxes ranged from 100 to 8000 g/m² h, depending on feed acid concentration and separation factors as high as 10⁴ were observed. Membrane stability was probed using dynamic mechanical analysis that revealed an increase in the temperature at which the α transition is observed, which corresponds to the glass transition (T_g) of the hydrophilic domain, upon use, suggesting embrittlement of the polymer structure. Further studies showed that the embrittlement was due to an interaction with the acid and was not induced by the operating temperature.     

Electrochemical preparation, characterization, and electrocatalytic studies of Nafion–ruthenium oxide modified glassy carbon electrode

Electrochemical synthesis of ruthenium oxide (RuOx) onto Nafion-coated glassy carbon (GC) electrode and naked GC electrode were carried out by using cyclic voltammetry. Electrochemical deposition of RuOx onto Nafion-coated electrode was monitored by in situ electrochemical quartz crystal microbalance (EQCM). Surface characterizations were performed by scanning electron microscope (SEM) and atomic force microscope (AFM). SEM and AFM images revealed that ruthenium oxide particles incorporated onto the Nafion polymer film. In addition, a GC electrode modified with ruthenium oxide–Nafion film (RuOx–Nf–GC) was shown excellent electrocatalytic activity towards dopamine (DA) and ascorbic acid (AA). The anodic peak current increases linearly over the concentration range of 50 μM–1.1 mM for DA with the correlation coefficient of 0.999, and the detection limit was found to be (S/N = 3) 5 μM. Owing to the catalytic effect of the modified film towards DA, the modified electrode resolved the overlapped voltammetric responses of AA and DA into two well-defined voltammetric peaks with peak-to-peak separation about 300 mV. Here, RuOx–Nf–GC electrode employed for determination of DA in the presence of AA. This modified electrode showed good stability and antifouling properties.     

Spatial and temporal mapping of water content across Nafion membranes under wetting and drying conditions

Water transport and water management are fundamental to polymer electrolyte membrane fuel cell operation. Accurate measurements of water content within and across the Nafion layer are required to elucidate water transport behavior and validate existing numerical models.We report here a direct measurement of water content profiles across a Nafion layer under wetting and drying conditions, using a novel magnetic resonance imaging methodology developed for this purpose. This method, multi-echo double half k-space spin echo single point imaging, based on a pure phase encode spin echo, is designed for high resolution 1D depth imaging of thin film samples. The method generates high resolution (<8 μm) depth images with an SNR greater than 20, in an image acquisition time of less than 2 min. The high temporal resolution permits water content measurements in the transient states of wetting and drying, in addition to the steady state.     

Infrared study of hydration and association of functional groups in a perfluorinated Nafion membrane. — Part 2

The state of sulfonic acid groups in a thoroughly dried and slightly hydrated Nafion membrane has been analysed applying infrared spectroscopy. IR spectra in thevOH stretching vibration region were analysed in detail. A computer-curve resolution technique was used to determine band parameters of each OH band. The results of this analysis indicate a rather complex process of association of sulfonic groups in the Nafion membrane. The association of these groups in the Nafion membrane differs in several respects from that in the polystyrenesulfonic acid membrane which results from the differencies in membrane structures, both on molecular and supermolecular level.     

基于单壁碳纳米管/Nafion/铜纳米粒子复合材料的多巴胺传感器的研制

通过电沉积金属铜于单壁碳纳米管( SWNTs)/Nafion 修饰的玻碳电极表面构建了一种经济且制备简单的多巴胺传感器。该纳米材料的形貌和成分用扫描电镜和能谱仪表征。不同扫速和pH条件下,以其修饰玻碳电极构建的电化学体系受吸附控制。多巴胺在该电极表面的反应机理为两电子双质子的过程,电荷转移系数α=0.6,电子转移数n=2.67,异相电子转移速率ks=1.38 s-1。在优化条件下,用微分脉冲伏安法检测多巴胺的线性方程为Ipa(μA)=-0.054c(μmol/L)-3.82(R2=0.9988),线性范围5~100μmol/L,检出限为0.014μmol/L(S/N=3)。此传感器制备简单、成本低、灵敏性高、稳定性好、重现性好,检测人尿液中多巴胺的回收率为96.5%~100.4%,相对标准偏差为1.2%~2.4%。     

碳纤维微电极研究（ⅩⅧ）──亚甲基蓝／Nafion修饰微柱碳纤维电极测定血红蛋白的研究

研究了ＭＢ／Ｎａｆｉｏｎ修饰微柱碳纤维电极的制备方法，用扫描电镜对它的表面形态进行了观察。该电极在缓冲溶液中扫描或放置的稳定性都很好，在弱酸性介质中，对血红蛋白在碳纤维电极上的氧化有催化作用，峰电流的增加与血红蛋白的浓度在５×１０－６～５×１０－５ｍｏｌ／Ｌ范围内有良好的线性关系，对６×１０－６ｍｏｌ／Ｌ的血红蛋白测定６次的变异系数为３．５％，可用于血清中血红蛋白的直接电化学测定，探讨了电催化作用的机理。