Ionophores Based on Cationic Dye-Containing Ion Pairs and Their Use in Ion-Selective Electrodes

The use of ion-selective electrodes (ISEs) based on cationic dye-containing ion pairs in analytical chemistry was considered. The most important chemical analytical characteristics of the developed liquid and plasticized ISEs are presented. These electrodes offer promise for the creation of sensors for many inorganic and organic substances.     

Optimization of the Composition of Ca-Selective Membranes Based on Tridentate Phosphoryl-Containing Neutral Ionophores

The selectivity and sensitivity of ion-selective electrodes (ISEs) based on membranes with phosphoryl-containing ionophores and lipophilic anion exchangers were studied. The analytical properties of the ISEs can be significantly modified and their selectivity for alkali and alkaline-earth metals can be even reversed by changing the membrane composition.     

Potassium sodium chloride integrated microconduits in a potentiometric analytical system

The preparation and application of a K(+), Na(+) and Cl(-) integrated microconduit potentiometric analytical system with tubular ion-selective electrodes (ISEs), microvalve, chemfold, electrostatic and pulse inhibitors is described. Electrochemical characteristics of the tubular ISEs and integrated microconduit FIA-ISEs were studied. The contents of K(+), Na(+) and Cl(-) in soil, water and serum were determined with the device. The analytical results agreed well with those obtained by flame photometric and silver nitrate volumetric methods.     

A tutorial on the application of ion-selective electrode potentiometry: An analytical method with unique qualities,unexplored opportunities and potential pitfalls; Tutorial

Ion-selective potentiometry enjoys practical utility as a simple analytical technique to measure ionic constituents in complex samples. Advances in the field have improved the selectivity and decreased the detection limit of ion-selective electrodes (ISEs) by orders of magnitude such that trace analysis in micro and nanomolar concentrations is now possible with potentiometric sensors. This tutorial reviews the fundamental principles of ion-selective potentiometry, describes the practical considerations involved in the use of these sensors to measure real samples, and discusses the statistical evaluation of experimental results compared with alternative analytical techniques.     

Recent advances on potentiometric membrane sensors for pharmaceutical analysis

Prime concerns with modern developments are attributed to high level undetected but important biological substances or even toxicants cycled often among individual and populations; which in turn agonizes environmental monitoring, trace-gas detection, water treatment facilities, in vivo detection in biological fluids and other accomplishments. For the detection of such analytes, several analytical devices combined with biological component have been designed with a physiochemical detector component. Here, we essentially focus on drug-based potentiometric membrane sensors known as ion selective electrodes (ISEs). The functionality of ion-selective membrane is quite intricate, challenging, and our understanding is yet to be thrived with more interventions. ISEs have applied explications to enormous variety of analytical inquires as well as informative tools for probing host-guest chemistry. However, expansion of ISEs based applications is aimed to improve the system performance, acquiring enhanced understanding of their response mechanism, and finding new chemical or physical configurations mainly for human welfare. The major strength of ISEs is the precised analytical information, assured by using the ion-selective membrane electrodes used successfully for both in vitro and in vivo assays of pharmaceutical products as well as in clinical analyses. In this review, we attempt to provide a brief prologue to the applicability and advantages of potentiometric sensors in the analysis of pharmaceutically active compounds emphasizing their employment at molecular level for in situ selection of biologically important analytes.     

An Ion-Selective Electrode for Ethylenediaminetetraacetatobismuthate(III) Anions

The main characteristics of liquid-membrane ion-selective electrodes (ISEs) based on high-molecular quaternary ammonium salts (QASs) were studied. The electrodes are reversible to the ethylenediaminetetraacetatobismuthate(III) anion. It was found that the selectivity of the ISEs to the potential-determining ion depends on the symmetry of the QAS. A mechanism of the ISE membrane response was proposed.     

Membrane drotaverine-selective electrodes based on tetraphenylborate derivatives: Electrochemical, adsorption, and transport properties and analytical application

The potentiometric response of ion-selective electrodes (ISEs) based on different lipophilic derivatives of tetraphenylborate to drotaverine hydrochloride was studied. The composition of a polymeric membrane was optimized to obtain the best electroanalytical properties of ISEs. The transport properties of selective membranes, the permeability and the flow of ions through the interface, were studied. Linear correlations between the solubility of ionophoric membrane components, membrane transport, and electroanalytical properties were revealed. The kinetic studies of ion-exchange adsorption showed that two limiting stages of transfer, namely, diffusion through the boundary layer and diffusion throug the membrane phase, occurred. Procedures for the potentiometric determination of drotaverine hydrochloride in pharmaceutical forms were proposed.     

Quality control criteria for solid-contact, solvent polymeric membrane ion-selective electrodes

After a long history and conflicting views, solid-contact (SC) solvent polymeric membrane ion-selective electrodes (ISEs) emerged as reliable potentometric-sensing devices with unique advantages. From the large variety of proposed SCs inherently conductive polymers emerged as the materials of choice. In our view, the most attractive feature of SC ISEs is their compatibility with thin- and thick-film microfabrication technologies that can provide cheap, mass-produced sensors and sensor arrays that can be integrated with the measuring, data acquisition, and control electronics in a straightforward way. However, despite the impressive properties of certain SC electrodes and their potential advantages, they remained primarily in the research laboratories. To make the jump from the research laboratories into commercial devices, it would be essential to prove that miniaturized SC ISEs can indeed match or surpass the performance characteristics of the conventional, liquid-contact macroelectrodes. In addition, it would be important to settle on the quality control criteria and testing protocols for assessing the performance characteristics of SC electrodes. It could help in interpreting the sometimes-inconsistent experimental data. Once cheap, miniaturized, SC ISEs will mach the performance characteristics of macroscopic-size electrodes, it is expected to have an important impact in a variety of applications requiring robust, maintenance-free, or single-use ISEs, e.g., in homecare or bedside diagnostics, environmental analysis, and quality control assessment. In addition, reliable SC ISEs are expected to revitalize the field of ion-selective field effect transistors and open new possibilities in combination with nanowire-based devices.     

Recent trends in potentiometric sensor arrays--a review

Nowadays there exists a large variety of ion sensors based on polymeric or solid-state membranes that can be used in a sensor array format in many analytical applications. This review aims at providing a critical overview of the distinct approaches that were developed to build and use potentiometric sensor arrays based on different transduction principles, such as classical ion-selective electrodes (ISEs) with polymer or solid-state membranes, solid-contact electrodes (SCE) including coated wire electrodes (CWE), ion-sensitive field-effect transistors (ISFETs) and light addressable potentiometric sensors (LAPS). Analysing latest publications on potentiometric sensor arrays development and applications certain problems are outlined and trends are discussed.     

Ionophore-Based Ion-Selective Electrodes in Non-Zero Current Modes: Mechanistic Studies and the Possibilities of the Analytical Application

Journal of Analytical Chemistry - This mini review briefly describes (i) literature data on the non-zero current measurements with ionophore-based ion-selective electrodes (ISEs) aimed at...     

Highly sensitive ion-selective electrodes based on dithiacrown ethers for the determination of mercury in fish samples

Electrochemical properties of membranes based on macrocyclic compounds containing two sulfur atoms in a polyether ring were studied. The use of these compounds as ionophores of membranes of ion-selective electrodes (ISEs) reversible with respect to mercury(II) was examined. The ISEs developed were used for the determination of mercury in samples of fish and soil.     

Evidence of a water layer in solid-contact polymeric ion sensors

This paper presents the very first direct structural evidence for the formation of a 100 +/- 10 A water layer in coated-wire polymeric-membrane ion-selective electrodes (ISEs).     

Strong molecular aggregation of neutral carriers bearing perfluoroalkyl chains in liquid-crystalline ion-sensor membranes.

A liquid-crystalline benzocrown ether, 4'-[(4'-1,1,2,2-tetrahydroperfluorooctyloxy)biphenyloxycarbonyl]benzo-15-crown-5, was used as a neutral carrier of ion-selective electrodes (ISEs) to elucidate the effect of highly ordered assembling of the neutral carrier on the sensor properties through fluorophilic interactions. The properties for the membrane and the resulting ISEs based on a benzocrown ether bearing a perfluoroalkyl chain were compared with those based on the corresponding crown ether bearing an alkyl chain. Atomic force microscopy and fluorescence measurements suggested that the neutral carrier bearing a perfluoroalkyl chain formed highly aggregational states in the membranes of ISEs.     

Highly Selective Ion-Sensitive Electrodes Based on Dibenzo-Crown Ethers Containing Functional Groups for the Determination of Potassium in Biological Fluids

The electrochemical properties of membranes based on dibenzo-crown ethers bearing hydroxyl and chloromethyl groups in polyether rings were studied. These substances were tested as membrane ionophores for ion-selective electrodes (ISEs) reversible to potassium ion. The developed ISEs were used for determining potassium in blood plasma samples. The generalized results of determining potassium in the blood of different patients with cardiovascular diseases revealed quantitative regularities that allowed the diseases to be diagnosed early.     

Surface chemistry and potential response of copper sulfide based ion-selective membrane in ligand solutions

Dissolution of membraneous composite ions of copper sulfide precipitate-based ion-selective electrodes (ISEs) has been measured in various ligand solutions by ICP atomic emission spectrometry and atomic absorption spectrometry from the solution side and by X-ray photoelectron spectrometry on the electrode surface. Asymmetric dissolution, amount of copper dissolved is higher than that of sulfur, was generally observed. The copper dissolution is correlated with the potential response as well as conditional stability constants. The results are discussed in terms of the charge separation caused by the asymmetric dissolution and electrostatic interaction of charged ligands with the space charge on the electrode surface in view of microscopic characterization of ISEs in metal buffer solutions in general. The results were also used to clarify the reason for some discrepancies of complex stability constants obtained by precipitate-based ISEs and other methods.Dedicated to Professor W. Simon on the occasion of his 60th birthday     

Effect of dissolved CO2 on the potential stability of all-solid-state ion-selective electrodes.

The influence of dissolved CO2 on the potentiometric responses of all-solid-state ion-selective electrodes (ISEs) was systematically examined with four different types of electrodes fabricated by pairing pH-sensitive and pH-insensitive metal electrodes (Pt and Ag/AgCl, respectively) with pH-sensitive and pH-insensitive ion-selective membranes (H+-selective membrane based on tridodecylamine and Na+-selective membrane based on tetraethyl calix[4]arenetetraacetate, respectively). The experimental results clearly showed that the carbonic acid formed by the diffused CO2 and water vapor at the membrane/metal electrode interface varies the phase boundary potentials both at the inner side of the H+-selective membrane (deltaE(in)mem) and at the metal electrode surface (deltaEelec). The potential changes, deltaE(in)mem and deltaEelec, occurring at the facing boundaries, are opposite in their sign and result in a canceling effect if both the membrane and metal surface are pH-sensitive. Consequently, the H+-selective membrane coated on a pH-sensitive electrode (Pt) tends to exhibit a smaller CO2 interference than that on a pH-insensitive electrode (Ag/AgCl). When the all-solid-state Na+ and K+ ISEs were fabricated with both pH-insensitive metal electrode and ion-selective membrane, they did not suffer from CO2 interference. It was also confirmed that plasticization of the PVC leads to increased CO2 permeation. Various types of intermediate layers were examined to reduce the CO2 interference problem in the fabrication of H+-selective all-solid-state ISEs. The results indicated that the H+-selective electrode needs an intermediate layer that maintains a constant pH unless the carbonic acid formation at the interfacial area is effectively quenched.     

A solid-state ion-selective electrode with an ionic-electronic transducer for determining chlordiazepoxide

A solid-state ion-selective electrode for determining chlordiazepoxide is described. A characteristic feature of the electrode is the presence of an intermediate conducting polymeric layer (transducer) of poly(o-aminophenol) between the ion-selective membrane with ionic conduction and a Pt conductor. The properties of ion-selective electrodes with transducers are compared with those of ISEs without transducers (coated-wire electrodes, CWEs). The most important distinctive features of ion-selective electrodes with transducers are the high stability of their potentials in time and their small sizes. The main performance characteristics of the electrode and the scope of its application are found.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 1, 2005, pp. 74–78.Original Russian Text Copyright © 2005 by Gorelov, Ryasenskii, Kartamyshev, Fedorova.     

Glass and polymeric membrane electrodes for the measurement of pH in milk and cheese

While there is a considerable interest in the food industry in determining various analytes using ion-selective electrodes (ISEs), only few reports describe their use for direct measurements in food. In this study, the suitability of glass electrodes and ionophore-based solvent polymeric ISEs for the determination of pH in Process cheese, Cheddar cheese and milk was investigated. The liquid junction potential between a 3 M KCl bridge electrolyte and diluted as well as undiluted Process cheese was found to be negligible. Reference electrodes with ceramic plug and sleeve-type junctions performed well, although precautions needed to be taken to prevent plugging at the junctions. While the protein rennet casein posed no problems in pH measurements, the extraction of neutral lipophilic compounds or hydrophobic peptides into solvent polymeric membranes was evident, resulting in some loss of selectivity for monovalent cations upon exposure to cheese. However, it was found that ISEs based on tridodecylamine (R₃N) as ionophore and o-nitrophenyl octyl ether (oNPOE) as plasticizer can be used to accurately measure the pH of milk and, after desensitization of the electrodes in a cheese emulsion, of diluted Process cheese. Since pH measurements with a glass electrode showed that emulsions of cheese moderately diluted to a cheese content of 70% have the same pH as undiluted cheeses, it is possible to determine the pH in cheese with ionophore-based ISEs. R₃N membranes also performed well in undiluted milk.     

Estimation of chloride in oxidizing media by means of ion-selective electrodes

Chloride concentrations down to the ppm level in a large excess of chlorate or perchlorate can be quantitatively estimated by use of chloride ion-selective electrodes (ISEs). Similarly traces of chloride in chromic acid solutions can be estimated with a heterogeneous silicone-rubber based chloride ISE. However, homogeneous chloride ISEs pose a problem for practical applications, because their response in chromic acid solutions changes with time owing to chemical attack on the membrane surface. In permanganate solutions, both homogeneous and heterogeneous type electrodes can be used for monitoring chloride ions. The Orion electrode, however, was found to show a slightly super-Nernstian response in such solutions. The presence of 10(-3)M iron(III) had no adverse effect on the performance of these electrodes in permanganate solutions.