A study of liquid-membrane perchlorate-selective electrodes made from an organic radical ion salt

Liquid-membrane electrodes were prepared from solutions of N-ethyl-benzothiazole-2,2′-azaviolene perchlorate in 1,2-dichlorobenzene and in β,β′-dichlorodiethyl ether, and their response and selectivity characteristics were examined. Perchlorate response ranges of the order I–10^?6.5M and 1–10^?5.6M were shown to be attainable with the two systems, respectively. These values represent significant improvements over the range 1–10^?4.8M found for the solid-state electrode made from the same radical ion salt. Short response times and acceptably stable potentials were observed for both liquid-membrane sensors. Both showed high apparent selectivities for perchlorate over all the ten anions tested. Iodide and tetrafluoroborate were the most serious interferences in each case. The low interference shown by hydrogen and hydroxide ions indicated that perchlorate determinations may be performed within the pH range 1–12 with both electrodes.     

Anion selectivity studies on liquid membrane electrodes

Selectivity coefficients of liquid-membrane electrodes for common inorganic anions were measured in electrodes containing tris(l,10-phenanthroline)iron(II), tris(4,7-diphenyl-1,10-phenanthroline)iron(II) or tetraheptylammonium ion in nitrobenzene, and tris(4,7-diphenyl-1,10-phenanthroline)iron(II) ion in nitrobenzene, chloroform or n-amyl alcohol as the liquid membrane. With the exception of the amyl alcohol electrode, selectivity coefficients were relatively independent of membrane composition and followed a common sequence of decreasing selectivity: PF₆^?> ClO₄^?>SCN^?~I^?~BF₄^?>NO₃^?>Br^?>Cl^?. This sequence parallels the order of increasing anion hydration energy, suggesting that aqueous phase solvation energies play a predominant role in determining electrode selectivity for these ions. Time-dependent behavior of liquid-membrane electrodes on transfer between solutions containing different ions also is described. Instantaneous e.m.f. readings were used to determine selectivity coefficients.     

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.     

Ion-selective liquid electrodes: Problems of description and experimental determination of selectivity

Current state of selectivity theory for liquid-membrane ion-selective electrodes was considered. Analytical expressions for the selectivity coefficients of electrodes based on liquid ion exchangers, neutral carriers, and charged carriers were obtained using phase boundary potential model. The reasons responsible for the dependence of experimentally determined selectivity coefficients on the determination conditions are discussed. The main ways for the electrode design optimization providing dramatic improvement of the selectivity are considered.     

Selectivity coefficient changes for liquid-membrane electrodes

The effects of the activity levels of the measured ion and interfering ions, and of the detection limit of the electrode on the values of selectivity coefficients for liquid-membrane ion-selective electrodes are discussed. The coefficients were determined by the mixed-ion solution method. Depending on the activity of the interfering ion, the activity of the main ion for which the selectivity coefficient is determined may differ. The best conditions of measurement are those which involve the largest contribution from the term containing the selectivity coefficient in the Nikolsky equation; the measurements are then most precise, and the values of the selectivity coefficients describe the electrode behaviour most consistently. When the limit of detection of the electrode is comparable with the other terms, it must be taken into account in calculations. Under the optimal conditions, selectivity coefficients were calculated for the Orion calcium and divalent cation electrodes, with calcium as the main ion and alkali metal ions as interfering ions.     

Determination of sulpha-drugs with ion-selective membrane electrodes--II

Two liquid-membrane electrodes, one sensitive to Cu(2+) and the other to Ag(+), were used for the determination of various sulpha-drugs with pK(a) > or = 6 (as the sodium salts) by potentiometric titration with CuSO(4) and AgNO(3). The construction and basic characteristics of these two electrodes are discussed.     

13C-Kernresonanzspektroskopische und elektromotorische Untersuchungen der Wechselwirkung von neutralen Carriern mit Ionen in Membranen

Investigation of the interaction of neutral carriers with ions in membranes by ¹³C-NMR. and EMF.-measurements. Applying a simple model, information on the interaction of neutral carriers with cations as well as on the ion pair formation may be obtained through ¹³C-NMR. and potentiometric studies of PVC-supported ion selective liquidmembranes in contact with aqueous solutions. The results indicate that carriers for K⁺ (nonactin) and synthetic ionophores for Ca²⁺ show an association of the carrier-complexes with lipophilic anions. The extent of complex formation of the carrier in the presence of lipophilic anions in the sample solution is in agreement with earlier interpretations of the anion interference of cation selective liquid-membrane electrodes.     

Potentiometric detection of organic acids in ion-exclusion chromatography using different types of liquid-membrane electrodes

Four different liquid-membrane electrodes were tested in a potentiometric flow-cell, in combination with an LC ion chromatography system (Aminex HPX-87H column). This setup was used for the determination of weak organic acids. The flow-through detector was of the wall-jet type. Conditions were established to achieve the best separation and detection characteristics. The sensitivity, selectivity and response time of the different electrodes were compared. Calibration curves and detection limits were measured for several organic acids, and compared with conductometric, and with low-wavelength UV detection. The detection limits were improved by inserting a post-column ion-suppressor system between the column and the detector. Several biological samples were analyzed to demonstrate the possibilities of the potentiometric detector.     

Sims analysis of the distribution of hydrogen absorbed by gold electrodes during the evolution of hydrogen

Gold electrodes were charged with hydrogen by strong cathodic treatment in 0.5 M H₂SO₄. The concentration of hydrogen was then studied by SIMS both along the surface and in depth by etching in the ion beam. With electrodes consisting of a small number of crystals, the absence of abnormal hydrogen concentration at the grain boundaries seems to rule out diffusion along this route. The profiles observed seem to be consistent with a simple model of uniform bulk diffusion.     

Cation selectivity of 13-crown-4 and bis(13-crown-4) derivatives

The cation selectivity of liquid-membrane electrodes based on 18 derivatives of 13- crown-4 and bis(13-crown-4) is reported. When these compounds are dissolved in 1,2-dichlorobenzene, the electrodes exhibit MgCl⁺ selectivity which depends on the nature of the bonds connecting the crown ether rings.     

Membrane-dialzer injection loop for enhancing the selectivity of anion-responsive liquid-membrane electrodes in flow systems : Part 1. A sensing system for NOx and nitrite

A general approach for enhancing the selectivity of anion-responsive liquid-membrane electrodes is described. The method is based on use of the receptor channel of a flow-through dialyzer unit as the injection loop in a flow-injection system. An appropriate membrane in the dialyzer prevents ionic interferents from reaching an inselective electrode in the final flow stream. The concept is demonstrated by developing a highly selective semi-automated method for the determination of dissolved NO_x or nitrite at levels greater than 5 μM. Nitrogen dioxide is trapped across a teflon membrane in the dialyzer and converted to nitrate by a buffered peroxide recipient solution. This solution is injected and carried to a tubular nitrate electrode. The final selectivity and detection capabilities of this gas-sensing arrangement are examined and compared to those of the nitrate electrode alone and more conventional sensing systems based on pH electrodes. A dialyzer unit with wider channels improves the efficiency of gas transfer and thus the detection capabilities of the system.     

Theory and applications of ion-selective electrodes: Part 7

This review on ion-selective is arranged in the same way as earlier reviews of this series. The whole subject continues to grow steadily. The most discussed field is that of analysis of body-fluid cations. About 850 papers published between Spring 1985 and Spring 1987 are mentioned, covering the theory of membrane processes, technology, electrolysis at liquid/liquid interfaces, fixed-site electrodes, liquid-membrane electrodes, potentiometric biosensors and miscellaneous systems.     

Liquid-Membrane Transport of Rare Earth Metal Ions Facilitated by Di(2-Ethylhexyl) Phosphoric Acid: Comparison with the Results of Corresponding Centrifugal Partition Chromatography

Abstract

Selective liquid-membrane transport of rare earth metal ions were found to be effectively attained by the use of di(2-ethylhexyl)phosphoric acid (D2EHPA) carrier. This finding was obtained on the basis of the idea that liquid-membrane transport phenomena would be basically correlated with those of “separator-aided centrifugal partition chromatography”, a separation technique based on the counter-current continuous extraction method. For the rare earth metal ion samples direct comparison of liquid-membrane transport with the corresponding centrifugal partition chromatography by employing the same two-phase liquid systems both containing D2EHPA showed that a close parallelism in the results obtained with the two separation systems.     

Dissociation of acetic acid in 50 mass % ethylene carbonate-water from 20 to 55°C

The dissociation constant of acetic acid in 50 mass % ethylene carbonate-water solvents has been determined at eight temperatures from 20 to 55°C by emf measurements of cells without liquid-junction containing hydrogen electrodes and silver-silver chloride electrodes. Acetic acid is weaker in the mixed solvent than in pure water. At 25°C, pK is 5.645 as compared with 4.756 in water, in spite of the fact that the dielectric constants of the two media do not differ materially. Standard changes in Gibbs energy, enthalpy, entropy, and heat capacity for the dissociation processes at 25°C were evaluated. The decrease in acidic strength when ethylene carbonate is added to the water medium appears to be largely the results of a destabilization of the two ionic species, especially a partial desolvation of the hydrogen ion.     

Effects of concentration of neutral carrier and addition of organophosphorus compounds on alkali metal ion-selectivity of the dibenzo-14-crown-4 liquid-membrane electrode

The lithium ion selectivity of the dibenzo-14-crown-4 (DB14C4) liquid-membrane electrode increases with the concentration of DB14C4 om the membrane. The lithium ion selectivity was enhanced by an addition of organophosphorus compounds such as trioctyl phosphine oxide.     

Glycopyrronium-selective electrodes

Liquid-membrane and PVC-membrane glycopyrronium-selective electrodes have been developed. They are based on the ion-pair complexes of glycopyrronium with dicyclohexylnaphthalenesulphonate, di-isopentylnaphthalenesulphonate, di-isobutylnaphthalenesulphonate and tetraphenylborate. Their response is nearly Nernstian over the pH-range 4–8, and the detection limits range from 10⁻⁶M to 10⁻⁵M. For the liquid-membrane electrodes, with homologous membrane solvents, the response slopes are linearly related to the inverse of the dielectric constant of the membrane solvent, according to the formula S = C_o − C₁/ε. A similar relation exists between the slopes for both types of electrode and the dielectric constants of mixed-solvent backgrounds. The electrodes can be used in the potentiometric determination of glycopyrrolate.     

Tributyl- and Triphenyltin Benzoates,Phenylacetates, and Cinnamates as Anion Carriers: an Electrochemical Assessment Coupled to Structural NMR Studies and AM1 Calculations

A series of tributyl and triphenyltin benzoates, phenylacetates, and cinnamates, with different electron-withdrawing substituents, were evaluated for their selectivity as anion carriers and for their application in liquid-membrane potentiometric ion-selective electrodes. The tributyltin carboxylates exhibited good sensitivity and significant chloride selectivities, while the corresponding triphenyltin benzoates were much less active. The observed potentiometric response differences were related to Sn-atom Lewis acidity, as assessed by binding constants of chloride to the tin carriers determined from ¹¹⁷Sn-NMR titration experiments and theoretical simulations of the resulting titration curves. The thermodynamic characteristics as well as the expected chloride-carrier adducts in relation to starting substrates were analyzed theoretically by AM1 calculations.     

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.     

Non-Aqueous Titrations Using A New Solid—Membrane Cupric Ion Electrode

Abstract

Use of the new, solid-membrane cupric electrode for non-aqueous titrations, a significant advancement over the earlier liquid-membrane electrode, is illustrated. The solid-membrane cupric electrode was used for the complexometric titration of cupric ion with several ligands in methanol, acetone and acetonitrile.     

Determination of the performance of glass electrodes in aqueous solutions in the physiological ph range and at the physiological sodium ion concentration

A method for testing glass electrodes in the physiological pH range (6.4–7.6) and at the physiological sodium ion concentration (0.15 mol l^-1), based on indirect comparison of potentials with the hydrogen gas electrode, is developed according to a scheme described earlier. The hydrogen ion sensitivity and the sodium ion error of a glass electrode can be determined with three different aqueous solutions of amine buffers and their hydrochlorides; two of these have different pH values and one also contains a sodium salt (at the higher pH value). A cell without a liquid/liquid junction, containing silver/silver chloride reference electrodes, is used at 37° C. The accuracy of both determinations is ±0.2 mV (±0.003 pH). The results for some commercial glass electrodes tested with this method are presented.