Response Amplification of an Ion-Selective Electrode

Abstract

The response of an ion-selective electrode can be amplified by connecting the cell, which is composed of an ion-selective electrode and a reference electrode, in series. For a cell using 1, 2 or 3 valinomycin electrodes connected in series, the response slopes to 1 × 10^?5 ?1 × 10^?1 M K⁺ were 58, 116 and 174 mV/activity decade (a.d.) at 25°C, respectively. This amplification method would especially be useful for accurate determinations with electrodes in the range of low concentrations outside the Nernstian response or for determinations of polyvalent ions, in which both cases exhibit small emf response changes in changing the ion concentration.     

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.     

The Ternary Coppersilver Selenide—A New Homogeneous Solid State Ion-Selective Electrode for Copper (II)

Abstract

The performance characteristics of a copper (II) ion-selective electrode, based on pressed-pellet membrane of ternary CuAgSe, are reported. The sensing material is isostructural with the natural mineral β -eucairite and shows high corrosion resistivity which results in stable and reproducible electrode performance upon ageing. The electrodes exhibit a linear Nernstian response dawn to 5.10^?8 M in non buffered medium and down to 10^?13M in copper-glycine ion buffer. Data on the electrode stability for a period of two and a half years, on the electrode response time, pH-dependence, selectivity etc. are also presented.     

Automation of Direct Potentiometry

Abstract

A simple, versatile, automated direct potentiometry is described. It offers a wide range of possible applications for all types of ion-selective electrodes, including the glass electrode. The apparatus consists of two Fisher turntable sample changers connected to an Orion automatic switch, Orion pH/mV meter, and Orion printer system via a control module. The optimum sampling rate is 20 samples per hour F^? and NH⁺ in water samples were determined by using commercially available ion-selective electrodes.     

Lead-Selective Membrane Electrode Based on Dibenzopyrydino-18-Crown-6

Abstract

A lead ion-selective electrode based on dibenzopyridino-18-crown-6 as membrane carrier was successfully prepared. The electrode exhibits a Nernstian response for Pb²⁺ ions over a wide concentration range. Influences of the nature of plasticizer, the concentrations of internal solutions in the electrodes and the composition of the membrane were investigated. The lead ion-selective electrode exhibited comparatively good selectivities with respect to alkali, alkaline earth and some transition and heavy metal ions.     

Construction of Gel Type Reference and Combination Ion-Selective Electrodes

Abstract

A simple and an inexpensive procedure for the construction of the reference electrodes and of the conversion of ion-selective electrodes to the “combination” types is described. It allows the manipulation of the reference electrode filling solution according to the needs of a particular measurement. The electrodes have good reproducibility and stable inter-comparison potentials of ± 0.2 mV. The performance characteristics of these electrodes are satisfactory for potentiometric measurements.     

Sulfonamides as Ionophores for Ise. III. Guanidinium Ion-Selective Electrodes Based on Lipophilic Bis-Sulfonamide Podands

Abstract

PVC membrane ion-selective electrodes based on bis-sulfonamide podands and DOS (Bis(2-ethylhexyl)-sebacate) as plasticizer are described. They were found to behave as guanidinium ion sensors, exhibiting high selectivity for guanidinium ions over potassium ions.     

Studies on the Preparation and Analytical Applications of Various Metal Ion-Selective Membrane Electrodes Based on Polymeric,Inorganic and Composite Materials—A Review

Ion-selective membrane electrodes commonly known as electrochemical sensors are important in view of the ability to make direct or indirect measurement of various metal ions. The fact is that the use of ion-selective electrodes for such type of measurements requires relatively inexpensive equipment, which makes ion-selective electrodes attractive to scientists in many disciplines. Thus, potentometric sensors can offer an inexpensive and convenient method for the analysis of heavy metal ions in solutions providing acceptable sensitivity and selectivity. For this purpose, many organic, inorganic, chelating, intercalating and composite materials were studied as electroactive materials for the preparation of ion-selective membrane electrodes. The present study provides a detailed review of literature for the fabrication, characterization and analytical applications of ion-selective membrane electrode based on different electro active components.     

Perchlorate Ion-Selective Electrodes with the Liquid Membranes of the O-Phenanthroline Chelate or its Related Compounds

Abstract

The metal chelates of o-phenanthroline, a, a′-dipyridyl or bathophenanthroline were used as the ion exchanger in the liquid membrane of the perchlorate ion-selective electrode. The electrode with a nitrobenzene membrane containing tris(bathophenanthroline)ferrous perchlorate is the highest sensitive one and gives a linear Nernstian response up to about 1 × 10 ^?5 M perchlorate. The membrane electrode having the ferrous ion-chelate of o-phenanthroline as an ion exchanger shows an excellent selectivity for perchlorate ion over nitrate or iodide Ion. The effects of the chelate concentration in the membrane and the central metal species of the chelate are examined on the electrode performance.     

A new Chloride-Selective Carrier and its Evaluation in Ion-Selective Electrodes

 A new chloride selective carrier, the tributyltin cinnamate, is evaluated for its analytical characteristics when incorporated in liquid polymeric membranes of ion-selective electrodes. The electrode constructed based on this carrier exhibited an improved selectivity towards chloride as compared to those based on the existing chloride carriers, completely satisfying the selectivity for direct blood measurements. Additionally, the response time of the sensor is fast, while the good signal stability allows for the application as a stand-alone device or as a detector in FIA system. The electrode exhibited analytical characteristics suitable for its employment in a variety of real-sample analysis.     

Lithium Ion Selective Electrode Based on Ionomycin Methyl Ester

Abstract

An ion-selective electrode based on ionomycin methyl ester, a derivative of the naturally occurring carboxylic polyether antibiotic ionomycin, is described which exhibits high Li⁺ selectivity. The selectivity coefficients of the electrode based on ionomycin methyl ester, log K^pot _LiNa and log K^pot _LiK are -1.3 and -1.9, respectively.     

Determination of Inorganic and Organic Thiophosphates with Ion-Selective Membrane Electrodes

Abstract

The conditions for the determination of sodium thiophosphate and sodium S-(2-amino-ethyl)-thiophos-phate in the presence of phosphate ion using ion-selective membrane electrodes are described. Both thiophosphates (inorganic and organic) are hydrolyzed in acidic medium. The phosphate ion is determined with Pb(II) using a Pb²⁺ – selective membrane electrode.

Cysteamine is determined by potentiometric titration with Hg(I1) using a Ag⁺/S^2? – crystal membrane electrode or by direct potentiometry with a Cu²⁺ selective membrane electrode. The results were verified by the iodination method.     

Sodium Ion-Selective Chalcogenide Glass Electrodes

Abstract

Analytical characteristics and sensing mechanism of sodium ion-selective electrodes based on NaCl-Ga₂S₃-GeS₂ glasses have been investigated. Chalcogenide glass electrodes containing 10 mol.% NaCl in the membrane showed near-Nernstian response in the concentration range from 10-³ to 1 M sodium nitrate solution. These sensors were superior to the conventional pNa oxide glass electrodes in selectivity in the presence of hydrogen ions and in Na⁺ ion sensitivity in fluoride media. Prolonged solution treatment for several days reduces, however, the detection limit of the sensors and the slope of the electrode response. Ionic processes at the membrane surface have been investigated using XPS technique and ²²Na tracer measurements. It was shown that sodium ion-exchange governed Na⁺ ion response of chalcogenide     

Ion-selective sensors for determining Au(CN)<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> with membranes based on the ionic liquid tetradecylphosphonium dicyanoaurate

A polymeric membrane for an ion-selective electrode is proposed on the basis of supramolecular systems including a polymeric compound (polyvinyl chloride, PVC) and an ionophore (ionic liquid tetradecylphosphonium dicyanoaurate) in which ionic liquid is simultaneously used as a PVC plasticizer. The selectivity, linear response range, and potential stability of ion-selective electrodes with the optimum membrane composition are measured. The detection limit for Au(I) with the developed electrode is 4.5 × 10^?7 M.     

Urea Biosensors Based on PVC Membrane Ion-Selective Electrodes

Abstract

This paper presents a general method of enzyme immobilization at the surface of ion selective membranes. Covalent binding of enzymes directly on the electrode surface is a very effective method that results in stable enzymatic membranes. As an example the construction of enzymatic sensors for urea determination based on ammonium and hydrogen carbonate ion selective electrodes is presented. The optimum working conditions for these biosensors were found. Bioelectrodes based on an ammonium sensor show very good analytical parameters: dynamic stability - over 2 months without decrease of sensitivity, response time - shorter then 20 s. high sensitivity, determination range from 0.3 to 70 mM. In the contrast to the ammonium ion based biosensors, those constructed on the basis of anion selective electrodes have worse analytical parameters. It is mainly due to poor selectivity and instability of an applied ion selective electrode. In spite of this, both types of urea biosensors were used for measurements in the differential potentiometry mode. The application of such system increased the sensitivity of urea determination.     

Studies with the Selectrode: Determination of Oxalate Ion Activity

Abstract

A solid state oxalate sensor is reported utilizing a commercial ion-selective electrode, the Selectrode^TM. Comparative measurements in aqueous solution of similar carboxylate ions and common inorganic anions, indicates appreciabl'e selectivity for oxalate. The Selectrode^TM was activated with a mixture of silver sulphide, lead sulphide, and lead oxalate.     

An Organic Cation-Selective Electrode: Potentiometric Determination of Acetylcholine Activity

Abstract

The performance characteristics of the first ion-selective electrode specifically designed for the quantitation of an organic cation are described. The liquid membrane electrode exhibits rapid and near Nernstian response to acetylcholine ion activity from 10^?1 to 10^?5 M. High selectivity over Na⁺, K⁺ and NH₄ ⁺ is observed.     

The Stability Constants of Some Benzo-15-Crown-5 And Naphtho-15-Crown-5 Derivatives

Abstract

The stability constants for the complexes of several benzo-15-crown-5 and naphtho-15-crown-5 derivatives containing various substituents in the aromatic ring have been determined in methanol. The potentiometric method with glass ion-selective electrodes has been employed. The stability constants have been compared to the selectivity coefficients (log k^pot _K,Na ) of membrane electrodes based on the mentioned compounds. No significant relationship has been stated.     

The Analysis of Fluoride in the Acetic Acid Leach Solution of Fluorspar with an Ion-Selective Electrode

Abstract

An analytical procedure for the determination of fluoride ion left in the acetic acid leach solution of the U. S. Customs method for fluorspar is presented. The technique described employs an Orion fluoride ion-selective electrode. A semilogarithmic plot of fluoride ion concentration versus millivolt response yields a linear calibration curve. The new procedure s shown to compare favorably with the Customs method in economy analysis time, accuracy and precision.     

Metal Ion Uptake and Voltammetry on a Dithiocarbamate Containing Polymer Modified Electrode

Abstract

There is a need to expand the range of working electrodes which can be us in analytical voltammetry.

In this work, the synthesis of a thio containing (poly) N-Ethyl Tyramine electrode is described. Cyclic voltammetry, SEM and EPMA were used to characterise the modified electrode.

The ability of this electrode to uptake copper, nickel, mercury or cobalt ions from solution was investigated. Detection limits of the order of 0.1 ppm were estimated using differential pulse voltammetry.