Fabrication of novel coated graphite electrodes for the selective nano-level determination of Cd ions in biological and environmental samples

Novel cadmium selective coated graphite electrodes were prepared using three different ionophores N¹, N²-dicyanoethyl-N¹, N²-bis(pyridin-2-ylmethyl)benzene-1, 2-diamine [L₁], N¹, N²-dicyanoethyl-N¹, N²-bis(thiophen-2-ylmethyl) benzene-1, 2-diamine [L₂] and N¹, N²-dicyanoethyl-N¹, N²-bis(furan-2-ylmethyl)benzene-1, 2-diamine [L₃], and their potentiometric characteristics were determined. Membranes having different compositions of poly(vinylchloride) (PVC), the plasticizer o-nitrophenyloctylether (o-NPOE), sodium tetraphenylborate (NaTPB) as an anionic additive and ionophores were coated onto the graphite surface. The potential response measurements showed that the best performance was exhibited by the electrodes with membranes having the composition L₁: o-NPOE:NaTPB:PVC as 4:51:2.5:42.5 (wt.%), L₂: o-NPOE:NaTPB:PVC as 3:52.5:1.5:43 (wt.%) and L₃: o-NPOE:NaTPB:PVC as 7:49:3.5:40.5 (wt.%). These electrodes had the widest working concentration range, Nernstian slope and fast response times of 12 s, 7 s and 17 s for L₁, L₂ and L₃, respectively. The selectivity studies showed that these electrodes have higher selectivity towards Cd²⁺ over a large number of cations and could tolerate up to 20 vol.% non-aqueous impurities. Furthermore, the electrodes generated constant potentials in the pH range 2.0–8.0, with a shelf life of approximately four to six weeks. The high selectivity of these electrodes permits their use in the detection of the Cd²⁺ content in some medicinal plants, soil and industrial wastewater samples. The electrodes could also be used as an indicator electrode in the potentiometric titration of Cd²⁺ with EDTA.     

Influence of ionic and nonionic surfactants on analytical parameters of ion-selective electrodes based on chelating active substances

The effects of the cationic (tetrabutylammonium chloride, TBC), anionic (sodium dodecyl sulfate, SDS) and nonionic (TRITON X-100) surfactants on the potentiometric properties of zinc- and cadmium-selective electrodes (ISEs) were investigated. The studies were carried out with plasticized PVC membranes doped with several new acidic chelating ionophores. The electrode basic analytical parameters, such as measurement range, slope characteristics, detection limit, response time and selectivity coefficients in relation to some inorganic cations in the presence and absence of surfactants, were investigated. As follows from the studies, the presence of surfactants in the sample is responsible first of all for the increase in response time and in detection limit, and a decrease in the characteristic slope as well as reduction of electrode selectivity.     

Corroles as receptors in liquid membrane electrodes and their potentiometric response towards salicylic acid

Here, we report on the application of corroles as analytically active compounds in liquid membrane electrodes (ISE) that are sensitive towards salicylic acid and salicylate.The potentiometric signals generated by corrole-incorporated ISEs strongly depend on the pH of the aqueous sample solution and the membrane composition, such as the presence of lipophilic sites. Corrole incorporating ISEs are characterised by a low detection limit (4.0 × 10⁻⁵ M) and a wide linear range (4.0 × 10⁻⁵ to 5.3 × 10⁻³ M). Also, they are free from interference versus other organic anions.The mechanism of the generation of the potentiometric signals of corrole incorporating ISEs in the presence of salicylate anion, as well salicylic acid, will be discussed.     

Dicyclohexano-18-crown-6 as active material in PVC matrix membrane for the fabrication of cadmium selective potentiometric sensor

PVC based membrane containing dicyclohexano-18-crown-6 (I) as active material along with sodium tetraphenyl borate (NaTPB) as an anion excluder and dibutyl phthalate as solvent mediator in the ratio 20:4:150:150 (w/w) (I-NaTPB-DBP-PVC) exhibits good properties with a Nernstian response of 29.0±1.0 mV per decade of activity and a working concentration range of 2.1×10⁻⁵-1.0×10⁻¹ M. The working pH range of the sensor is 1.9-7.0. It exhibits a fast response time as fast as 17 s and has a lifetime of about 6 months. The proposed sensor has good selectivity for cadmium over alkali, alkaline earth, some transition and heavy metal ions. The sensor works satisfactorily in mixtures having 10% (v/v) non-aqueous content without showing any considerable change in working concentration range or slope. It has been successfully used as an indicator electrode for the potentiometric titration of Cd²⁺ against EDTA as well as for its determination in wastewaters.     

Kinetic characterization of Prussian Blue-modified graphite electrodes for amperometric detection of hydrogen peroxide

Prussian Blue-modified graphite electrodes (G/PB) with electrocatalytic activity toward H₂O₂ reduction were obtained by PB potentiostatic electrodeposition from a mixture containing 2.5 mm FeCl₃ + 2.5 mm K₃[Fe(CN)₆] + 0.1 m KCl + 0.1 m HCl. From cyclic voltammetric measurements, performed in KCl aqueous solutions of different concentrations (5 × 10⁻²–1 m), the rate constant for the heterogeneous electron transfer (k _s) was estimated by using the Laviron treatment. The highest k_s value (10.7 s⁻¹) was found for 1 m KCl solution. The differences between the electrochemical parameters of the voltammetric response, as well as the shift of the formal potential, observed in the presence of Cl⁻ and NO₃⁻ compared to those observed in the presence of SO₄²⁻ ions, points to the involvement of anions in the redox reactions of PB. The G/PB electrodes showed a good electrochemical stability proved by a low deactivation rate constant (0.8 × 10⁻¹² mol cm² s⁻¹). The electrocatalytic efficiency, estimated as the ratio , was found to be 3.6 (at an applied potential of 0 mV vs. SCE; Γ = 5 × 10⁻⁸ mol cm⁻²) for a H₂O₂ concentration of 5 mm, thus indicating G/PB electrodes as possible H₂O₂ sensors.     

A novel potentiometric sensor for promethazine based on a molecularly imprinted polymer (MIP): The role of MIP structure on the sensor performance

A novel potentiometric sensor based on a molecularly imprinted polymer (MIP) for determination of promethazine (PMZ) was prepared. Promethazine MIP particles were prepared and dispersed in 2-nitrophenyloctyl ether and then embedded in a polyvinyl chloride matrix. The effect of the monomers type on the sensor performance was investigated, and an important role for this parameter was shown. It was shown that the membrane electrode with a MIP prepared by vinylbenzene and divinylbenzene had a better performance in comparison to membrane electrodes containing MIPs prepared with methacrylic acid-ethylene glycol dimethacrylate or vinylbenzene-ethylene glycol dimethacrylate. After optimization, the membrane electrode constructed with a MIP of vinylbenzene-divinylbenzene exhibited a Nernstian response (31.2 ± 1.0 mV decade⁻¹) over a wide concentration range, from 5.0 × 10⁻⁷ to 1.0 × 10⁻¹ M, with a low detection limit of 1.0 × 10⁻⁷ M and a response time of ∼50 s. The method has the requisite accuracy, sensitivity and precision to assay PMZ in syrup samples and biological fluids.     

Glassy carbon electrodes coated with poly(allylamine hydrochloride), PAH: Characterization studies and application to ion-exchange voltammetry of trace lead(II) at combined PAH/mercury film electrodes

Glassy carbon electrodes coated with adsorbed single layers of the cationic polyelectrolyte poly(allylamine hydrochloride), PAH, were produced by solvent evaporation for subsequent development of PAH modified thin mercury film electrodes (PAH/TMFE). The present work describes the preparation, incorporation features towards lead(II) species, as well as the morphological characterization of PAH coatings of different molar loadings, prepared from polyelectrolyte solutions of different composition. The present PAH films revealed interesting morphologic features, related to the process of solvent evaporation and to the specific structural properties of the PAH polyelectrolyte in the assembling medium.The novel PAH-thin mercury film electrodes, developed for the determination of trace lead(II) as its anionic forms in chloride medium, were found to be stable, sensitive and reproducible. Concentrations in the ppb concentration region could be easily assessed using 20 s accumulation time (detection limit 1.2 ppb, i.e. 6 nM, 3σ) with low relative standard deviations (<2.5%). The sensitivity of the SWASV determination of lead(II) increased 20% compared to the uncoated TMFE. The linearity range reached at least two orders of magnitude. Additionally, the PAH-coated mercury film electrodes presented an improved resistance to fouling by common surfactants.     

An experimental study on the placement of reference electrodes in alkaline polymer electrolyte membrane fuel cells

The ability to accurately measure separate in situ anode and cathode overpotentials and impedance responses is still a source of debate when investigating fuel cells of planar configuration containing <100 μm thickness solid electrolytes and when using the common three-electrode arrangement. The results obtained in this study indicate that the overpotentials and impedances of the anode and cathode can be successfully measured when using two spatially separated reference electrodes and when the cathode and anode of alkaline membrane electrode assemblies (for alkaline polymer electrolyte membrane fuel cells) are precisely and optimally misaligned. The frequency dependent response between the two reference electrodes is attributed to the membrane response and the “crosstalk” between anode and cathode.     

Effect of composition on the performance of cermet electrodes. Experimental and theoretical approach

This work aims to analyse the behaviour of cermet electrodes as a function of their composition, i.e. the ratio between ionic and electronic conducting particles. This is an important parameter to be considered to obtain maximum performance from this type of electrode, which is currently under study for application in oxygen sensors and solid oxide fuel cells. Experimental results of overall electrode resistance, including both ohmic and activation polarisation effects, have been obtained through electrochemical impedance spectroscopy measurements of Pt/YSZ electrodes in air. The results compare favourably with the theoretical predictions for several compositions above the percolation threshold of the electronic conductor. For this reason, the model is a useful tool for the design of optimised cermet electrodes; in particular, the experimental data show that maximum performance is attained for compositions very close to the percolation threshold of the electronic conductor, and this is in very good agreement with the modelling results.     

离子膜电解槽的极网修复方式及再运行性能探讨

西安西化氯碱化工有限责任公司的离子膜电解槽的极网共有6种方式:①阳极新网阴极新网、②阳极新网阴极未动、③阳极重涂阴极未动、④阳极重涂阴极重涂、⑤阳极新网阴极膜极距、⑥阳极重涂阴极膜极距。通过对比,找出电解槽不同修复方式的优缺点。     

均相阳离子交换膜的应用与开发研究

本文介绍了均相阳离子的应用与开发情况,并采用聚氯乙烯浸吸单体法制备均相阳离子交换膜,阐述了反应机理与药品选择方案,从而提出制备一种新型的均相阳离子交换膜的方案.     

Highly thiocyanate-selective membrane electrodes based on the N,N′-bis-(benzaldehyde)-glycine copper(II) complex as a neutral carrier

Some novel PVC membrane electrodes based on N,N′-bis-(benzaldehyde)-glycine metallic complexes of Cu(II), Ni(II), Zn(II) and Co(II) as neutral carriers are described. The results showed that the electrode based on the N,N′-bis-(benzaldehyde)-glycine copper(II) complex [Cu(II)-BBAG] had a near-Nernstian response to the thiocyanate ion ranging from 1.0×10⁻¹ to 9.0×10⁻⁷ M in a phosphate buffer solution of pH 4.0 with a detection limit of 7.0×10⁻⁷ M and a slope of −57.6 mV/decade at 25°C. The electrode displays an anti-Hofmeister selectivity sequence in the following order: SCN⁻>ClO⁻₄>Sal⁻>I⁻>Br⁻>NO⁻₂>NO⁻₃>SO²⁻₃>SO²⁻₄>Cl⁻>H₂PO The response mechanism is discussed in view of both AC impedance and UV spectroscopy techniques. The [Cu(II)-BBAG]-based electrode was successfully applied to the determination of the thiocyanate ion in wastewater and human saliva.     

PVC membrane and coated graphite potentiometric sensors based on 1-phenyl-3-pyridin-2-yl-thiourea for selective determination of iron(III)

The construction and performance characteristics of PVC membrane (PME) and coated graphite (CGE) Fe³⁺ ion selective electrodes based on 1-phenyl-3-pyridin-2-yl-thiourea (PPT) are described. The electrodes exhibit a Nernstian slope of 20.2 ± 0.8 (CGE) and 19.9 ± 0.4 (PME) mV decade⁻¹ of activity in Fe³⁺ ion over a wide concentration range from 3.0 × 10⁻⁷ to 1.0 × 10⁻² M for CGE and 6.9 × 10⁻⁷ to 1.0 × 10⁻² M Fe³⁺ for PME. The lower detection limits by CGE and PME are 2.0 × 10⁻⁷ and 3.9 × 10⁻⁷ M, respectively, in the pH range of 1.8-5.6 for PME and 1.8-5.8 for CGE with a fast response time (<10 s). The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the PME. The PME showed the working temperature range of 22-55 °C with isothermal temperature coefficient of 1.33 × 10⁻³ V/°C and it was also used in non-aqueous solvents. The electrodes were successfully applied to determine iron(III) in water samples.     

聚氯乙烯离心母液的双膜法处理及回用

使用双膜法（超滤膜＋反渗透膜）处理PVC离心母液,使之达到聚合工艺用水水质和纯水水质标准。该母液重新回用于氯乙烯的聚合工艺,聚合后的树脂达到国家标准。处理过程中产生的浓缩液,通过再处理达到初次冲釜水的水质标准或经后处理可直接排放。     

D-氨基葡萄糖盐酸盐的虾壳合成及其含量的紫外分光光度法测定

由预处理后的虾壳制备几丁质,以盐酸水解制得D-氨基葡萄糖盐酸盐,优化水解工艺,得到最佳工艺条件:水解盐酸浓度11.7mol/L,水解温度95℃,水解时间4h,收率63%,采用紫外分光光度法测定样品中D-氨基葡萄糖盐酸盐的含量为94.6%。     

Electro-oxidation and determination of gemcitabine hydrochloride,an anticancer drug at gold electrode

Electrochemical behavior of an anticancer drug, gemcitabine hydrochloride (GMB) was studied in 10.4 pH with 0.2 M phosphate buffer solution as supporting electrolyte at 25 ± 0.1 °C at gold electrode (GE) using different voltammetric techniques. The electrochemical process was observed to be diffusion controlled, irreversible and involving one-electron oxidation. Under optimal conditions, the peak current was proportional to GMB concentration in the range of 0.1–15 μM with a detection limit of 0.06 μM by differential pulse voltammetry. The method was developed for the determination of GMB in pharmaceutical formulations and urine as a real sample.     

Electrochemical sensors based on platinum electrodes modified with hybrid inorganic-organic coatings for determination of 4-nitrophenol and dopamine

New electrochemical sensors for dopamine (DA) and phenol derivative, based on hybrid inorganic redox material-organic conducting polymers, were developed. Hybrid inorganic-organic coatings based on Prussian blue, polyazulene, poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3-[(E)-2-azulene-1-yl)vinyl]thiophene) have been prepared by electrochemical methods in various configurations onto Pt substrate. Dopamine and 4-nitrophenol (4-NP) have been determined by square wave voltammetry using both mono and bilayer modified electrodes. The modified electrodes exhibited a linear response over wide range of 4-nitrophenol concentrations from 30 to 90 μM, with a detection limit of 8.23 μM (s/n = 3). A linear trend for the responses for dopamine concentrations ranging from 2 to 100 μM, with a sensitivity of 0.116 μA/μM, has been also obtained.     

填充聚氯乙烯硬质塑料地砖配方与生产工艺的研究

本文系统地研究了增韧剂氯化聚烯烃(M_1)和腈基橡胶(M_2),增塑剂邻苯二甲酸二辛酯(P)以及几种不同填料对硬质PVC填充体系力学性能的影响。结果表明,增韧剂M_1、M_2能显著改善高填充PVC体系的冲击强度,其最适宜用量为5～10PHR;增塑剂P可改善高填充PVC体系的加工流动性,也能改善体系的冲击强度,其用量以5～10PHR为宜,填料的密度越大,粒径越细,填充体系的冲击强度和拉伸强度越高,加工性能也越好;随填料含量的提高,体系的力学性能和加工性能下降;填料的改性结果以F_1为最好,F_3次之,F_2最差。     

热收缩膜专用PVC树脂的生产

针对PVC热收缩膜的加工特点,从调整颗粒形态、控制增塑剂吸收量、降低鱼眼数和控制挥发物含量等方面介绍了热收缩膜专用PVC树脂的生产方法。