Investigation of Protein Binding With All Solid‐State Ion‐Selective Electrodes

A potentiometric sensor for studying charge based adsorption of proteins was created using a single‐piece polyaniline‐PVC ion‐selective electrode (ISE). Three different ISEs, two for Na⁺ and one for Cl^? ion determination, were studied. The Na⁺‐ISEs consisted of a neutral calixarene‐based ionophore and one with a charged carrier dinonylnapthalenesulfonic acid (DNNSA) whereas for the Cl^? ISE, an anion exchanger tridodecylmethylammonium chloride (TDDMA⁺Cl^?), was used. The Na⁺ ISE with DNNSA as the charged carrier was successfully able to discriminate the binding of two different proteins (bovine serum albumin and lysozyme) based on their intrinsic charge.     

Na+-Selektive Monensin-PVC-Membranelektrode mit Festableitung

Zusammenfassung Eine Monensin-PVC-Membran zur Applikation an Festkontakt-Sensoren wurde entwickelt. Die Meßketten zeigen in Abhängigkeit von der Na⁺-Ionenaktivität ein Nernst-gemäßes elektromotorisches Verhalten. Für die Störionen aus der Reihe der Alkali- und Erdalkaliionen sind die Selektivitätskoeffizienten auch als Funktion ihrer Ionenradien angegeben.

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Na⁺ selective monensin PVC membrane electrode with solid contact

Summary A Monensin PVC membrane has been developed for application to solid contact sensors. Depending on the Na⁺ ion activity, the electrochemical cells show a Nernstlike electromotive behaviour. For interfering ions of the alkaline and alkaline earth series, the selectivity coefficients are also given as a function of their ion radii.

     

Sulfonated poly(ether ether ketone) as an alternative charged material to poly(vinyl chloride) in the design of ion-selective electrodes

To date, poly(vinyl chloride) (PVC) is the most used polymer in the design of ion selective electrode (ISE) membranes. This paper is focused on the use of sulfonated poly(ether ether ketone) (SPEEK) as an alternative material to PVC for the design of ISEs. SPEEK of the desired degree of sulfonation is synthesized from poly(ether ether ketone) (PEEK). An NH₄⁺-ISE has been chosen as a model electrode to study the efficiency of SPEEK as polymer matrix of the membrane. The material was evaluated in ionophore free ion exchanger membranes as well as in ion-selective electrodes membranes containing nonactine as ionophore. Analytical performance parameters of the prepared electrodes were evaluated. The electrodes show a slope between 50 and 60 mV dec⁻¹ depending on both the calibration medium and the membrane composition. A linear range of response between 10⁻⁴ and 1.0 M and a lifetime of 1-2 months were obtained. The interferences of cations such us Ca²⁺, Na⁺, Li⁺ and K⁺ over the prepared ISEs are studied as well. Although the plasticizer in the SPEEK based membrane matrix is not necessary, its presence improves the sensibility. This makes SPEEK a good potential choice over alternative membrane matrices reported in the literature and a promising platform for the establishment of membrane components.     

A study of metal complexes of a naturally occurring macrocyclic ionophore-monensin

The acid-base and complexing properties of a naturally occurring antibiotic ionophore-monensin (MonH)-were studied in anhydrous methanol solutions primarily by potentiometric measurements. The pK _a of the acid was found to be 10.30±0.05 at 25°C. Complexes of silver, thallium, and alkali ions with the undissociated ligand were also studied, and their stability constants were determined. The acid dissociation constant of MonH as well as the stability constants of Mon^– Na⁺ and MonH·NaClO₄ complexes were determined in the 5–45°C temperature range, and the enthalpy and entropy of the acidity and stability constants were determined from van't Hoff's plots. The formation of MonH and Mon^–Na⁺ species are both enthalpy and entropy stabilized, but the formation of the MonH·NaClO₄ complex is enthalpy stabilized but entropy destabilized.     

Lipophilic salts as membrane additives and their influence on the properties of macro- and micro-electrodes based on neutral carriers

The influence of salts containing lipophilic cations and anions on the electrical resistance of the membranes of calcium ion-selective macro- and micro-electrodes based on a neutral carrier is described. The resistance of macroelectrodes was decreased by a factor of about 50 or of about 3 compared to membranes without and with potassium tetrakis- (p-chlorophenyl)borate, respectively. No significant reduction of the membrane resistance was achieved for microelectrodes. The lower detection limit and the Ca²⁺/K⁺ selectivity factor were improved for both types of electrode.     

Cs+ -selective membrane electrodes based on ethylene glycol-functionalized polymeric microspheres

A new strategy for improving the robustness of membrane-based ion-selective electrodes (ISEs) is introduced based on the incorporation of microsphere-immobilized ionophores into plasticized polymer membranes. As a model system, a Cs⁺-selective electrode was developed by doping ethylene glycol-functionalized cross-linked polystyrene microspheres (P-EG) into a plasticized poly(vinyl chloride) (PVC) matrix containing sodium tetrakis-[3,5-bis(trifluoromethyl)phenyl] borate (TFPB) as the ion exchanger. Electrodes were evaluated with respect to Cs⁺ in terms of sensitivity, selectivity, and dynamic response. ISEs containing P-EG and TFPB that were plasticized with 2-nitrophenyl octyl ether (NPOE) yielded a linear range from 10⁻¹ to 10⁻⁵ M Cs⁺, a slope of 55.4 mV/decade, and a lower detection limit (log a_Cs) of −5.3. In addition, these membranes also demonstrated superior selectivity over Li⁺, Na⁺, and alkaline earth metal ion interferents when compared to analogous membranes plasticized with bis(2-ethylhexyl) sebacate (DOS) or membranes containing a lipophilic, mobile ethylene glycol derivative (ethylene glycol monooctadecyl ether (U-EG)) as ionophore.     

Ionenselektive Coated Glass-Elektroden

Zusammenfassung Na⁺-, K⁺-, NH ₄ ⁺ - und Ca²⁺ selektive coated glass-Elektroden wurden entwickelt, bei denen eine ionenselektive Carrier-PVC-Membran auf eine ionenselektive Glasschicht aufgebracht wird, die über einen Innenelektrolyten mit der Ableitelektrode in Verbindung steht. Die Selektivität wird durch die aufgebrachte Carrier-PVC-Membran bestimmt, die zusätzlich Weichmacher zur Optimierung der Eigenschaften enthält.

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Ion-selective coated glass electrodes

Summary Na⁺, K⁺, NH ₄ ⁺ and Ca²⁺ selective electrodes have been developed by coating the ion-selective glass layer with a carrier PVC membrane. The glass is in contact with the conducting electrode through an inner electrolyte. The selectivity is determined by the PVC membrane, containing neutral carriers or electrically charged ligands and additionally plasticizers for optimizing the properties.

Dir Arbeit wird vom Bundesministerium für Forschung und Technologie der Bundesrepublik Deutschland gefördert.Prof. Dr. W. Simon stellte freundlicherweise die synthetischen neutralen Carrier für Na⁺ und Ca²⁺ zur Verfügung.     

3,7-Dioxaazelaamides as Ionophores for Lithium Ion Selective Liquid Membrane Electrodes

Lipophilic neutral carriers were synthesized which show Li⁺/Na⁺ selectivities of up to ca. 80 in highly lipophilic liquid membranes. The sensor membranes exhibit improved response times and increased lifetimes as compared to systems described earlier. They allow reliable measurements of Li⁺ in blood serum within the clinical concentration range. A 1:1 Li⁺/ionophore complex of one representative (N,N,N′,N′-tetracyclohexyl-5,5-dimethyl-3,7-dioxaazelaamide) has been prepared, and its structure was elucidated by X-ray analysis.     

Molecular design of calixarene-based ion-selective electrodes

In order to obtain insights into relationships between the calix[4]arene structure and the ion selectivity in the electrode system, 20 ionophoric calix[4]arenes were synthesized and their ion selectivity (with Na⁺ as a standard) estimated. Among these ionophoric calix[4]arenes, 25,26,27,28-tetrakis[(ethoxycarbonyl)methoxy]-p-t-octylcalix[4]arene afforded the highest logK _NA,M ^pot value (–3.1) in the presence of 2-fluorophenyl-2-nitrophenylether (10) as the best of 13 plasticizers. This is the first example in which the Na⁺/K⁺ selectivity exceeds a factor of 10³ in the electrode system based on the neutral carrier. The high Na⁺ selectivity is attributed to modification of the upper rim which ostensibly has no relation with the component of the cavity. This paper demonstrates the potential relationships between the unique structure of the calix[4]arene-based ligands and selectivity performance for the design of ion-selective electrodes.     

Microelectrode for potassium ions based on a neutral carrier and comparison of its characteristics with a cation exchanger sensor

A potassium-selective liquid-membrane microelectrode based on valinomycin is described. Tip diameters of about 2 μm as well as high discrimination against Na⁺, H₃O⁺, acetylcholine and some other quaternary ammonium ions, allow the intracellular measurement of potassium ion activity changes. The inherently high membrane resistance of the neutral carrier-based microelectrodes is reduced by adding a lipophilic charge carrier to the valinomycin. Results are compared with those of classical microelectrodes.     

Polymeric membrane electrodes with enhanced fluoride selectivity using Zr(IV)-porphyrins functioning as neutral carriers

Poly(vinyl chloride) polymeric membranes plasticized with o-NPOE (o-nitrophenyl octyl ether) or DOS (dibutyl sebacate) and containing Zr(IV)-octaethyl(OEP)- or Zr(IV)-tetraphenylporphyrins (TPP) along with lipophilic cationic additives (tridodecylmethylammonium chloride; TDMACl) are examined potentiometrically and optically with respect to their response toward fluoride. It is shown that these zirconium porphyrins can function as neutral anion carriers within the organic membranes of the electrodes. Spectrophotometric measurements of thin polymeric films indicate that the presence of lipophilic cationic sites in the form of TDMA⁺ and use of lower dielectric constant plasticizer (DOS) prevents formation of metalloporphyrin dimers in the organic polymer phase, which have been observed previously in polymeric membranes formulated with the same Zr(IV) porphyrins but with lipophilic anion site additives. By preventing dimer formation, rapid and Nernstian potentiometric response of the corresponding membrane electrodes toward fluoride ion is observed. Indeed, electrodes prepared with PVC/DOS membranes containing Zr(IV)-OEP and 15 mol% of TDMACl (relative to the ionophore) exhibit fast (t₉₅<15 s) and reversible response toward fluoride. The slope of calibration plots are near-Nernstian (−59.9 mV per decade). Such electrodes display the following selectivity pattern: ClO₄⁻>SCN⁻>F⁻>NO₃⁻>Br⁻>Cl⁻, which differs significantly from the classical Hofmeister series, with greatly enhanced potentiometric selectivity toward fluoride. The data presented herein, coupled with results from a previous study, confirm that Zr(IV) porphyrins can serve as either charged or neutral type anion carriers with respect to their enhanced interactions with fluoride when used as ionophores to prepare liquid-polymeric membrane electrodes, and that the nature of membrane additives and plasticizer dictates the response mechanism at play for given membrane formulations.     

Ion-selective electrodes for determination of organic ammonium ions: Ways for selectivity control

The influence of the ISE membrane composition on the selectivity for primary, secondary, tertiary, and quaternary alkylammonium cations, as well as for cations of physiologically active amines, has been investigated. Factors studied include the effect of plasticizer (2-nitrophenyl octyl ether, o-NPOE; dibutyl phthalate, DBP; dinonyl adipate, DNA; tris(2-ethylhexyl) phosphate, TEHP) and ion exchanger (potassium tetrakis(4-chlorophenyl)borate, K(TpClPB); potassium tris(nonyloxy)benzenesulfonate, K(TNOBS)), as well as that of the lipophilic cationic additive (tetradecylammonium nitrate, (TDA)NO(3)) and neutral carrier (dibenzo-18-crown-6) presence in membrane. It has been established that plasticizer nature affects K(i,j)(pot) values both when the target and/or foreign ions have non-ionic polar groups capable of specific interaction with plasticizer, and when the only difference consists in the substitution degree of their ionic groups. K(i,j)(pot) values for quaternary alkylammonium cations over primary-tertiary ones change in the following order: TEHP>DBP approximately DNA>o-NPOE. The highest K(i,j)(pot) value change is achieved for the primary-quaternary alkylammonium cation pair, amounting to 3 and 4.7 orders for membranes containing K(TNOBS) and K(TpClPB) as ion exchangers, respectively. In its turn, the ion exchanger influence on the selectivity depends on plasticizer nature, it being maximal for o-NPOE (about 2 orders) and practically non-existent for TEHP. On the whole, as compared to K(TpClPB)-based ISEs, those based on K(TNOBS) show higher selectivity for primary-tertiary alkylammonium cations over quaternary ones. Incorporation of (TDA)NO(3) into membrane causes further improvement of selectivity for primary-tertiary alkylammonium cations in the case of K(TNOBS) only. The maximal total effect of the ion exchanger and lipophilic ionic additive is observed for ISEs with DNA-plasticized membranes and is over 3 orders. The influence of crown ether on the selectivity also depends significantly upon ion exchanger and plasticizer nature. For ISEs with o-NPOE-plasticized membranes the K(i,j)(pot) value changes can be as great as 3 (ion exchanger K(TNOBS)) and even 4.5 (ion exchanger K(TpClPB)) orders. On the contrary, for ISEs with TEHP-plasticized membranes the crown ether effect on the selectivity is unessential. The results obtained are explained by peculiarities of organic ammonium cations solvating by plasticizer and association of cations with ion exchangers.     

Study of Cobalt(III) Corrole as the Neutral Ionophore for Nitrite and Nitrate Detection via Polymeric Membrane Electrodes

Cobalt(III) 5,10,15‐tris(4‐tert‐butylphenyl) corrole was synthesized and incorporated into plasticized poly(vinyl chloride) membranes and studied as a neutral carrier ionophore via potentiometry. This cobalt(III) complex has binding affinity to nitrite, and the resulting membrane electrode yields reversible and Nernstian response toward nitrite. Enhanced nitrite selectivity is observed over other anions, including lipophilic anions such as thiocyanate and perchlorate when an appropriate amount of lipophilic cationic sites are added to the membrane phase. Detection limit to nitrite is ca. 5 µM. Using tributylphosphate as the plasticizer with the cobalt(III) corrole species yields electrodes with enhanced nitrate selectivity.     

Cationic Surfactant Ion-Selective PVC Membrane Electrode Containing Macrocyclic Diimine Crown Ether

ABSTRACT

DP⁺ ion-selective PVC membrane electrode based on 2,3,11,12-dibenzo-5,9-diaza-4,9(10)-cis-diimino-1,13-dioxacyclopentadecane as a novel macrocyclic diimine crown ether is proposed. o-Nitrophenyl octyl ether as plasticizer and potassium tetrakis(4-chlorophenyl)borate as lipophilic salt were used. The electrode exhibits a Nernstian response for 1.0 x 10^?2-1.0 x 10^?6 mol 1^?1 DPCl with a slope of 58 mVdecade^?1. The detection limit is 2.5 x 10^?7 mol 1^?1. The electrode response was stable over a wide pH range (3-11). The lifetime of the electrode was about 2 months. The electrode shows a high selectivity towards inorganic cations. Among the organic cations tested, only hexadecyltrimethylammonium ion interferes. The electrode was suitable for determining the critical micelle concentration and as an end-point detector in the potentiometric titration of the cationic surfactants.     

Tripodal compound 1,1,1-tris(N-ethyl-N-phenylamino-carboxylmethoxymethyl) propane as an ionophore for alkali and alkaline earth metal cations-selective electrode

A new tripodal compound, 1,1,1-tris(N-ethyl-N-phenylamino-carboxylmethoxymethyl) propane, has been synthesized and evaluated as an ionophore in PVC membrane electrode for the analysis of alkali and alkaline earth metal cations. The influence of the nature of the plasticizers (o-NPOE, DBP and DOP) and of the amount of incorporated ionophore on the characteristics of the electrode was discussed. Selectivity coefficients against alkali and alkaline earth metal cations were calculated. The electrodes based on the tripodal compound with o-NPOE and DBP as plasticizer gave good performance (slope, limits of detection) to lithium and sodium ions. The electrode plasticized with o-NPOE also exhibited near-Nernstian response to divalent ions: Ca(2+), Sr(2+) and Ba(2+). The electrode prepared with 3.9 mg ionophore, 185 mg o-NPOE, 92 mg PVC and 0.46 mg KTpClPB can be used as a Ca(2+) electrode. The influence of pH has also been studied. The electrodes exhibited better potential stability and operational lifetime of more than 3 months.     

Electrochemical studies on ion-selective polymer membrane electrodes

The selectivity and response of neutral carrier based polymer membrane electrodes are investigated via exchange current measurements for systems containing valinomycin, dibenzo-18-crown-6, and plasticizer alone in a polyvinyl chloride matrix. Using a transient galvanostatic step method, apparent exchange current densities of 1.3 X 10^?3 A/cm², 5.4 X 10^?6 A/cm², and 2.2 X 10^?9 A/cm² were obtained with K⁺ as the primary ion for the three types of membranes, respectively. Preliminary results indicate that the exchange current data obtained with this technique are complementary to the potentiometric response observed for the membranes studied.     

中性载体可咯化合物应用于银离子电位传感器的研究

研制了一种以5,10,15-三(五氟苯基)可咯[H_3(tpfc)]为活性组分物质、以邻硝基苯辛醚o-NPOE为增塑剂、以四苯硼钠为亲脂性大阴离子添加剂的PVC膜电极(4种物质的质量比为3:3:62:32),电极能斯特斜率为54.8 mV/decade、工作浓度范围为5.1×10~(-6)～0.1 mol/L,pH为4.0～8.0,响应时间不超过30 s,该电极对银离子能抵抗来自Hg~(2+)、Pb~(2+)等离子干扰,表现出较高的选择性.这种传感器可用于对实际矿石样品进行检测.     

Investigation of ion-selective electrodes based on quaternary phosphonium salts: Part 2. A tetrachlorothallate(III) Ion-Selective Electrode

A tetrachlorothallate(III)-selective electrode based on the tetradecylphosphonium tetrachlorothallate(III) ion-pair complex in a PVC membrane is described. The mechanism of the influence of the hydrochloric acid content of sample solutions is discussed in detail. Electrode membranes made with and without dubutyl phthalate as plasticizer were investigated. The membranes without plasticizer are better with regard to selectivity and limit of detection (2 × 10^?7 mol 1^?1).     

Iron (III) Ion Selective Electrode Based on Dithia 12-Crown-4

An iron (III) ion selective PVC membrane electrode based on 1,7-dithia 12-crown-4 as a neutral carrier was prepared. Monovalent responses with a Nerstian slope of 56+1 mV/decade was observed for the Fe (III) ion-selective electrode within the concentration range 10^?3–10^?5 M Fe (NO₃)₃. The monovalent responses may be attributed to the formation of Fe (OH)₂⁺ or Fe (OH)₂(H₂O)⁺₄ species in aqueous solutions and the absorption of these ions into the PVC electrode membrane. The electrode exhibited good selectivity for Fe (III) in comparison with various alkali, alkali-earth and some heavy metal ions. The effects of the composition of the membrame, addition of STPB (sodium tetraphenyl borate), the concentration of internal solution of the electrode and anions in the test solutions were discussed.