Arginine Determination with Ion-Selective Membrane Electrodes

Abstract

A new method for the determination of the amino acid arginine utilizes a dual enzyme catalyzed reaction monitored with an ammonium ion selective membrane electrode of the antibiotic type. The technique gives a linear correlation between arginine concentration and electrode response over the 3 × 10^?3 M to 3 × 10^?5 M range and a useful, but non-linear, response over a wider range. Major interferences are urea, K⁺, and NH₄ ⁺, but Na⁺ does not interfere in the physiological concentration range.     

Determination of Antiseptic Dyes with Ion-Selective Electrodes

The possibility of determining Methylene Blue and Brilliant Green antiseptic dyes in solutions with the use of ion-selective electrodes based on trioctyl oxybenzosulfonic acid was examined. Data on application of the electrodes fabricated to analysis of powdered dyes are presented. A gravimetric method for analysis for Brilliant Green was suggested and used as a comparative technique.     

New Ion-Selective Electrodes for Determination of Bupivacaine and Oxybuprocaine

Abstract

PVC membrane electrodes selective for hydrochlorides of the anaesthetics bupivacaine (BpC) and oxybuprocaine (ObC) are prepared. The electrodes have a near Nernstian slope (58 mV for BpC and 51 mV for ObC electrodes) over the range of 1.6 × 10^?5-10^?1M and 1.3 × 10^?1M for BpC and ObC electrodes, respectively. The change in pH of the test solution within the ranges 2.5–6.0 and 3.0–7.4 does not affect the EpC-and ObC-electrodes, respectively. The electrodes have very long life times (10 days for BpC, and 3 months for ObC) and exhibit good seletivity for the investigated compounds with respect to a large number of inorganic cations and organic substances of biological importance. The isothermal coefficients of the electrodes are calculated from the standard electrode potentials at different temperatures. BpC and ObC are determined successfully in some pharmaceutical preparations using the calibration graph technique and potentiometric titration.     

Ion-Selective Electrodes

Summary Current investigations and hypotheses by the authors on the theory and mechanism of operation of ion-selective electrodes are reviewed. Some trends in the applications of ion-selective electrodes are discussed, with particular reference to the interests of the authors.

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Zusammenfassung Die laufenden Untersuchungen der Autoren und daraus abgeleitete Hypothesen zur Theorie und Wirkungsweise ionen-selektiver Elektroden wurden dargelegt. Einige Entwicklungen der Anwendung solcher Elektroden wurden im Zusammenhang mit den Arbeiten der Verfasser diskutiert.

     

Determination of Some Thiobarbiturates with Ion-Selective Membrane Electrodes

Abstract

A liquid membrane Ag⁺-selective electrode of our construction and a commercial solid membrane Ag⁺/S^2--selective electrode were used for the determination of thiobarbiturates by potentiometrie titration with AgNO₃ solution or by direct potentlometry. The potentio-setrio data correlated vd. th IR spectra allowed the elucidation of the reaction mechanism.     

Application of Ion-Selective Electrodes as Reference Electrodes

Abstract

Reference electrodes limiting interfering effects of conventional reference electrodes on the measurement involving ion-selective electrodes have been developed. They are constructed of a plastic body with porous plug or sleeve junction. Solid state, low impedance, ion-selective electrodes (cupric, cadmium, fluoride) in the equilibrium of corresponding ion solution are used as the half-cells. The absence of interfering ions in the electrolyte allows the determination of the ion of interest at extremely low levels without interference. The electrodes have good reproducibility and stable intercomparison potentials of ± 0.2 mV. The performance of the electrodes has been tested for the measurement of sub-ppm halide levels. Data on stability, reproducibility, effects of temperature, ionic strengthand pH is presented and compared to that of conventional reference electrodes.     

Separate Determination of Homologous Sodium Alkyl Sulfates with Ion-Selective Electrodes

The possibility of the separate determination of homologous sodium alkyl sulfates with ion-selective electrodes and using multisensor analysis was studied. The optimum component ratios were found for the analysis of model mixtures with ion-selective electrodes. It was shown that nonlinear regression analysis and artificial neural networks can be used for processing analytical signals from a set of weakly selective sensors for anionic surfactants.     

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.     

Determination of β-Lactam Antibiotics by Potentiometry with Ion-Selective Electrodes

Ion-selective electrodes for antibiotics from the penicillin series, with membranes based on three different classes of ionophores (anion exchangers, aza compounds, and metal phthalocyanines), were proposed. The electrochemical and performance characteristics of the sensors were studied and compared.     

Liquid Ion-Selective Electrodes for Determining Nonionic Surfactants

It was shown that nonionic surfactants (NS) can be determined by potentiometry using liquid NS-selective electrodes. The effect of medium acidity and foreign substances on the operation of liquid NS-selective electrodes was studied. Some properties of NS-selective electrodes were determined.     

Ion-Selective Electrodes for the Determination of Antimony and Thallium Based on Water-Insoluble Basic Dye Salts

Abstract

Hexachloroantimonate(V) and tetrachlorothallate(III) salts of Sevron Red L (C.I. Basic Red 17), Sevron Red GL (C.I. 11,085), Flavinduline O (C.I. 50,000) and Phenazinduline O have been applied in liquid-state ion-selective electrodes for the determination of antimony and thallium. The slope of potential versus pM graphs approach full Nernstian response in the range 10 M (Sb) and 10^?6 M (T1) to 10^?2 M. An unusual feature of the electrodes is their response to antimony(III) as well as to antimony(V).     

Ion-Selective Electrodes Based on Adamantylcalix[4,8]arenes for the Determination of Alkali Cations

Calix[4,8]arenes bearing adamantyl substituents in the upper rim and ethoxycarbonylmethoxy groups in the lower rim of the macrocycle were proposed as ionophores in membranes of ion-selective electrodes (ISEs) for determining alkali cations. Depending on the number of phenolic fragments (n) in the calixarene molecule, ISEs respond to either sodium (n = 4) or cesium (n = 8) ions. Sensors based on membranes that, along with ionophores, contain tetraphenyl borate ions as a lipophilic additive are selective for Na and Cs ions in the presence of other alkali metals. They exhibit almost theoretical responses over the concentration range from 1 × 10^–4 to 1 × 10^–1 M at pH 5.5–12 for Na-SE and pH 3–11 for Cs-SE, respectively.     

Determination of Nitrilotriacetic Acid (NTA) with Ion-Selective Membrane Electrodes

Abstract

A solid membrane copper ion selective electrode was used for the determination of NTA via complexometric titration with copper(II). Interferences, of the type commonly found in detergents, were investigated.     

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 Electrodes Prepared with Polyaniline Membranes

Polyaniline is a conductive polymer that has electrochemical activity. For this reason, it has many different uses in electrochemical area. In this study, polyaniline was prepared by electrochemical oxidation of aniline in concentrated H₂SO₄ and HCl solutions. Then, membranes were obtained from a mixture of these polymers and paraffin at a weight ratio of 50%. Ion-selective electrodes were prepared with these membranes and AgCl/Ag electrodes. Properties of prepared membranes were investigated with potentiometric measurements made in HCl, KCl, H₂SO₄, and HClO₄ solutions of different concentrations. The E–logc plots obtained with these ion-selective electrodes were found to be linear in a distinct concentration range. Their slopes depend on the membrane type and the doping ion in the test solution. The difference between these membranes was explained according to the morphological structures of polyaniline membranes.     

Ion-Selective Electrodes Based on Bilayer Film Coating

The electrode characteristics of ion-selective electrodes (ISEs) for K⁺, Na⁺, NH₄ ⁺, and Ca²⁺ based on bilayer film coatings, where the inner layer films are electroactive electropolymerized ones and the outer layer films are composed of conventional ion-sensitive materials, have been examined. These ISEs of the coated-wire electrode type have no conventional internal reference solution and reference electrode, but the inner films may be considered to function as the “internal standard solution.” The ion selectivity coefficients and the activity range showing Nernstian response were almost comparable to those of conventional liquid-membrane electrodes. The bilayer-coated ISEs showed insensitivity to O₂ and CO₂, long-term stability, and little drift. It was also found that the electrode performance is practically unchanged after sterilization in an autoclave. The results demonstrate that the bilayer-coated ISEs examined are promising for the determination of K⁺, Na⁺, NH₄ ⁺, or Ca²⁺ activity in biological and environmental systems.     

Ion-Selective Electrode for the Determination of Sulfadimezine

The main electroanalytical properties of ion-selective electrodes for determining sulfadimezine were studied. Quaternary ammonium salts containing different functional substituents were tested as ionophore groups in ion exchangers. The association constants of ionophores in membrane media, solubility products, and partition coefficients in the aqueous solution–membrane solvent system were calculated.     

Ion-Selective Electrode for the Determination of Furaltadone

ABSTRACT

A Furaltadone (FD) ion-selective PVC membrane electrode based on the ion-pair complex of FD with sodium tetraphenylborate was prepared with dioctyl phthalate as a plasticiser. The electrode exhibits a linear response with an approximate Nernstian slope (50 mV decade^?1 at 20 ⁰C) with the concentration range 2.18 x 10^?5–2.18 x 10^?4 FD. The effects of ionic strength and pH of the test solution on the electrode performance were studied. The electrode exhibited very good selectivity for FD with respect to a large number of inorganic and organic cations of biological importance. The standard addition method and potentiometric titration were used to determine the FD in pure solution and in pharmaceutical preparations with satisfactory results.     

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.     

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.