Ionophore extrem hoher Lipophilie als selektive Komponenten für Flüssigmembranelektroden

Selective ionophores of extreme lipophilicity for liquid membrane electrodes Lipophilic ionophores of the type diether diamides have been prepared. Their lipophilicity is up to 7 orders of magnitude higher than the one of the most lipophilic ion carriers used as selective components in liquid membrane electrodes reported so far. For such ion carriers of extremely high lipophilicity kinetic limitations of the carrier induced ion transfer between aqueous and membrane phase usually dominate and heavily disturb the electromotive behavior of the membrane electrode. These limitations are absent only in those cases where most of the lipophilic segments of the carrier may remain in the membrane phase while the segments with the coordination sites are exposed to the aqueous phase during the transfer process.     

Electromotive behaviour of anion selective membranes with triorganotin acetates as ionophores and nucleophiles as additives

The electromotive behaviour of neutral carrier based Cl^–-selective electrodes can be improved if lipophilic nucleophiles are added to the membrane phase containing triorganotin acetates as anion carriers. The addition of about 50 mol-% octadecanethiol to diethyl-n-hexyltin acetate as ionophore leads to improved sensor response times and to slopes of the electrode response function close to the Nernstian behaviour.     

Carbonate ion electrode based on HTPP sites

Several quaternary phosphonium salts have been used as the site materials for construction of carbonate ion electrodes. Among them the electrode based on hexadecyltriphenylphosphonium salt showed best performance characteristics. The Nerstian response range of the electrode is from 1 × 10^?2 down to 6.3 × 10^?7 mol · dm^?3 with a detection limit of 1.8 × 10^?7 mol · dm³. The selectivity order of ions can be altered by the introduction of trifluoroacetyl-tert-butylbenzene as a solvent mediator. The strong solvatoin of the primary ion of interest in the membrane phase by the solvent mediator favors the improvement of the selectivity of the proposed electrode.     

Interpretation of the selectivity and detection limit of liquid ion-exchanger electrodes

An equation has been derived which describes the e.m.f. of a liquid ion-exchanger membrane electrode in conditions of low concentration levels of the primary and interfering ions. The equation is based on the assumption that if the external solution contains no excess of ions which may exchange with the organic phase, then the concentration of the exchanger at the interface decreases, and this is responsible for formation of a diffusion layer inside the membrane. Therefore the potential response depends on the initial concentration of the ion-exchanger in the membrane phase, on the thicknesses of the diffusion layer on both sides of the interface, and on the diffusion coefficients of the species in both phases. This equation explains the non-Nernstian behaviour of the electrode in the presence of interferents, as well as the variation of the conditional selectivity coefficients. The parameters mentioned also influence the detection limit of an electrode. The electrode behaviour has been tested in unstirred solutions and in solutions stirred at different rates. Through its influence on the diffusion layer thickness, the stirring also influences the electrode potential and the characteristics of the electrode.     

Interference of permeable anions in potassium-sensitive membrane electrodes based on valinomycin and dimethyldibenzo-30-crown-10

Responses of potassium-sensitive electrodes with valinomycin and dimethyldibenzo-30-crown-10 in the poly(vinyl chloride) membrane plasticized with dipentyl phthalate in solutions containing lipophilic anions, i.e., perchlorate and picrate have been measured. Using a general theoretical treatment, the role of possible ion pair formation in the membrane phase in the e.m.f./activity dependences is discussed. The electrode with a crown-compound is characterized by a broader region of cation response with an almost Nernstian slope. The possibility of extending the analytically useful range of these electrodes has been verified by using the membrane phase containing C₁₂—C₁₄ phthalates.     

Ionic Diffusion Through Unblended PVC Membranes

Abstract

This work deals with the study of the diffusion of Cl^? ion through pure unblended polyvinylchloride (PVC) membranes of different thickness. Several PVC -tetrahydrofuran ratios and also different internal diameter glass disks have been used to change the thickness of the membrane. A chloride ion selective electrode also constructed in the laboratory is used as the detector. The electrode behaviour was studied by running up a calibration graph prior to membrane positioning. A mean slope of 57 ±1 mV/log.C at 28.0 ± 0.5 °C was obtained and the range of potential values were then known. The detector was very well washed and immediately a membrane was placed directly on its surface and assembled to a rotating disk electrode in order to get a diffusion cell. The receiving compartment in this system has a negligible volume. Therefore, the response of the chloride ion selective electrode is directly proportional to the flux of material through the membrane rather than to the receiving compartment concentration. An almost linear relationship between the Cl^? ion concentration in the range 0.0010 – 0.10 M and its flux through the unblended PVC membrane was found. The chloride ion flux through the PVC membrane in solutions with the ion strength adjusted to 0.1 M was twice to that value obtained without ion strength adjustor (ISA) in the solution. Average rate transport in the range 3.5?10^?7 to 9.6?10^?7 mol/s Cl^? was found at a rotation speed of 1280 rpm.     

Solid-contact pH-selective electrode using multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNT) are shown to be efficient transducers of the ionic-to-electronic current. This enables the development of a new solid-contact pH-selective electrode that is based on the deposition of a 35-μm thick layer of MWCNT between the acrylic ion-selective membrane and the glassy carbon rod used as the electrical conductor. The ion-selective membrane was prepared by incorporating tridodecylamine as the ionophore, potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate as the lipophilic additive in a polymerized methylmethacrylate and an n-butyl acrylate matrix. The potentiometric response shows Nernstian behaviour and a linear dynamic range between 2.89 and 9.90 pH values. The response time for this electrode was less than 10 s throughout the whole working range. The electrode shows a high selectivity towards interfering ions. Electrochemical impedance spectroscopy and chronopotentiometry techniques were used to characterise the electrochemical behaviour and the stability of the carbon-nanotube-based ion-selective electrodes.     

Kinetische Betrachtung der Verteilung von elektrisch neutralen Ionophoren zwischen einer Flüssigmembran und einer wässerigen Phase

Kinetic Study of the Distribution of Electrically Neutral Ionophores between a Solvent Polymeric Membrane and an Aqueous Phase The kinetic behaviour of a series of ligands in the transfer from a solvent polymeric membrane into a stirred aqueous phase was investigated and compared with theoretical kinetic models. It was found that the transfer of ligands with low lipophilicity was controlled by the diffusion in the membrane phase, and that of ligands with high lipophilicity was controlled by the exchange reaction at the phase boundary and/or the diffusion through the unstirred Nernst diffusion layer. The diffusion coefficients in the membrane decrease drastically on increase of the content of the polymer in the membrane and are nearly independent of the size and lipophilicity of the ligand, whereas the overall transfer coefficient through the boudary region does not depend on the polymer content but decreases with increasing lipophilicity of the ionophore.     

Determination of experimental parameters in the Fe(III)/Fe(II) system in 1 M H2SO4, with a polycrystalline gold electrode, taking advantage of its non-linear behaviour

In this work, the values of the heterogeneous standard rate constant and the transfer coefficient of the electrochemical system Fe(III)/Fe(II) in 1 M H₂SO₄ at a polycrystalline gold electrode were determined. The response spectrum to an ac potential of such amplitude as to make the behaviour of the electrode process non-linear was analysed. The experimental study was complemented by a theoretical study of the Fe(III)/Fe(II) system using numerical methods. Comparison of the experimental and theoretical data enabled the kinetic parameters of this electrode process to be determined.     

Ion-selective characteristics of heavy metal myristate liquid membrane electrodes

Liquid membrane electrodes of myristate soaps of heavy metals, namely copper, cadmium, zinc, nickel, cobalt, strontium and barium in a benzene-n-butanol mixture were prepared. Each electrode showed nernstian response in common metal ion test solution. The range of concentration of the test solution for the Nernstian behaviour lies between 10^?4 and 10^?1M. With a dissimilar metal ion in test solution the metal soap liquid membrane electrode indicates deviations from Nernst's equation depending on the nature of the metal ion, suggesting different selectivities for different ions. The selectivity ratios are therefore calculated.     

Solid Contact Nitrate Ion‐Selective Electrode Based on Ionic Liquid with Stable and Reproducible Potential

A simple, fast and cheap method of preparation of solid contact nitrate ion‐selective electrode is proposed. The electrode membrane phase consist of only three components: PVC, plasticizer and ionic liquid (IL).The ionic liquid trihexyltetradecylphosphonium chloride is used in triple function as ionophore, as lipophilic ionic component in order to reduce membrane resistance, and as transducer media in order to stabilize the potential of internal Ag/AgCl electrode. The electrical properties of the membrane were studied by electrochemical impedance spectroscopy and the influence of the interfacial water film was evaluated by potentiometric water layer test.     

An All‐solid‐state Polymeric Membrane Ca2+‐selective Electrode Based on Hydrophobic Alkyl‐chain‐functionalized Graphene Oxide

An all‐solid‐state polymeric membrane Ca²⁺‐selective electrode based on hydrophobic octadecylamine‐functionalized graphene oxide has been developed. The hydrophobic composite in the ion‐selective membrane not only acts as a transduction element to improve the potential stability for the all‐solid‐state Ca²⁺‐selective electrode, but also is used to immobilize Ca²⁺ ionophore with lipophilic side chains through hydrophobic interactions. The developed all‐solid‐state Ca²⁺‐selective electrode shows a stable potential response in the linear range of 3.0×10⁻⁷–1.0×10⁻³ M with a slope of 24.7±0.3 mV/dec, and the detection limit is (1.6±0.2 )×10⁻⁷ M (n =3). Additionally, due to the hydrophobicity and electrical conductivity of the composite, the proposed all‐solid‐state ion‐selective electrode exhibits an improved stability with the absence of water layer between the ion‐selective membrane and the underlying glassy carbon electrode. This work provides a simple, efficient and low‐cost methodology for developing stable and robust all‐solid‐state ion‐selective electrode with ionophore immobilization.     

Preparation and properties of a carbonate ion-selective membrane electrode

A liquid membrane ion-selective electrode has been prepared for the measurement of carbonate ion activities in solutions containing high levels of hydrogen carbonate and chloride. The electrode exhibits Nernstian response in the approximate range 1O^-2–1O^-7M carbonate, and has a fast response and low noise level under most conditions. In the physiologically important pH region, hydroxide ion does not interfere. Detailed information is given on the composition and properties of the active membrane phase.     

Kinetics of intermediate phase growth at the interface of fluoride-conducting solid electrolytes with metal electrodes

The effect of the reference electrode (Ag, AgCl∣KF + KCl or Sn, SnF₂) on the kinetics of new phase growth at interfaces formed by LaF₃:Eu²⁺ or CeF₃:Sr²⁺ single crystal solid electrolytes with metal electrodes of Ag and Bi is studied by chronoamperometry and linear scan voltammetry. It is shown that when a solid-phase reference electrode is used, the current transients reflect hindrances associated with instantaneous two- or three-dimensional nucleation as well as limitations for fluoride ion diffusion in the solid electrolyte.     

Highly Selective Potentiometric Oxalate Ion Sensors Based on Ni(Ⅱ) Bis-(m-aminoacetophenone)ethylenediamine

A plasticized PVC (polyvinyl chloride) membrane based oxalate ion selective electrode has been developed by using the condensation product of m‐aminoacetophenone and ethylenediamine. The transition metal complexes of the ligand N,N′‐bis(m‐aminoacetophenene)ethylenediamine (L) were synthesized and incorporated as ionophore for the synthesis of oxalate ion selective electrodes. Most appropriate result in terms of dynamic range, detection limit and response behavior was determined for the Ni(II) bis‐(m‐aminoacetophenone)ethylenediamine complex. The electrode demonstrated higher selectivity for oxalate ion with improved performance as compared to other carriers reported in past. The electrode shows Nernstian slope of (?28.5±0.4) mV·decade^?1 with improved linear range of 1×10^?1?1×10^?7 mol·L^?1, with a comparatively lower detection limit in the pH range of 5–10.5, giving a relatively fast response within 10 s and reasonable reproducibility. The selectivity coefficient was calculated using matched potential method and fixed interference method. The lifetime of the electrode was found to be nearly 2 months. The response mechanism and the interaction of oxalate ion with the complexes have been discussed by UV‐visible spectroscopic technique. Further the electrode was also successfully applied to determine the oxalate content in water samples.     

The role of PVC in ion selective electrode membranes

The behaviour of a solution of NaBPh₄ in a PVC membrane plasticized by di-octyl sebacate is compared with a solution of NaBPh₄ in pure liquid di-octyl sebacate. In the liquid the NaBPh₄ is present as ion pairs with ~ 0.2% of these dissociated in a 1 mM solution. By contrast in the membrane 1 mM solution is 74% dissociated. This difference in behaviour arises chiefly from the higher dielectric constant of the membrane phase.     

锂离子电池多孔电极理论的回顾与新思考

本文总结了Newman多孔电极理论的基本内容,提出若干改进思路. 提出基于离子-空穴耦合传输机制描述浓电解质中的离子输运过程,在此基础上引入离子-电子耦合转移反应的思想处理电极材料中的离子传输问题,并通过计算嵌锂材料的离子扩散系数验证其合理性. 总结了描述多孔电极多尺度结构的相关理论和技术,表明均质化方法和基于结构重建的介观模拟方法均能给出比较合理的有效输运参数,从而提高多孔电极理论模拟结果的准确性.     

The behaviour of copper(II)-selective electrodes in chloride-containing solutions

Calibration curves for copper(II) in solutions containing various chloride ion concentrations are examined in detail. The mechanism of the interferences on the behaviour of the copper(II)-selective electrode is discussed. The anomalous slopes observed can be explained by considering the sensitivity of the electrode membrane to the silver ions released from the electrode surface by chemical interaction with the solution. The effects of the formation of silver-chloride complexes and of the changes in the membrane are described.     

Analytical Evaluation of the Silver Sulfide Membrane Electrode

Abstract

A membrane electrode selective for sulfide and silver ion has been described. No interferences were found for sulfide ion measurements, and only mercuric ion had a measurable interference with silver ion. Other characteristics of this electrode which are evaluated include speed of response and temperature coefficients. The use of the silver sulfide membrane electrode as an end-point detector in potentiometric titrations under oxidizing conditions is illustrated.     

Membranelektrode zur selektiven,potentiometrischen Erfassung organischer Kationen

A liquid ion exchanger membrane electrode responding preferentially to large onium ions is described. Selectivities of the sensor for different cations vary by factors of up to 10¹⁴ and the selectivity constants correlate closely with the corresponding exchange constants of the extracation system involved. For most cations the electrode shows theoretical response at activities >10^?6M and has a life time of at least 4 months.