Evaluation of some new 14- and 15-crown-formazans as carriers in cesium ion selective electrodes

A number of new crown-formazans with 14 and 15 membered rings have been investigated as selective neutral carriers in cesium ion selective electrodes. Two plasticizers (NPOE and NPBnE) were studied. The new 14-crown-formazan 4a containing the 4-pyridyl N-oxide at the formazyl carbon exhibited the highest selectivity in cesium ion selective electrodes, especially towards the two low selectivity monovalent ions K⁺ and NH4⁺. Also, membranes containing the plasticizer NPBnE showed better cesium selectivity relative to most ions than those containing NPOE. Membranes containing 4a and variable compositions of plasticizers, potassium tetrakis-(p-chlorophenyl)borate (KTpClPB), and trioctylphosphine oxide (TOPO) were studied in order to prepare an electrode with the optimum cesium selectivity. The highest selectivity for cesium was achieved with the two electrodes designated d and e with membranes containing the ionophore 4a, NPBnE and KTpClPB with and without TOPO. Selectivities are reported relative to sodium, potassium, barium, calcium, ammonium, lithium, cobalt, and magnesium.     

Comparison of Multi‐walled Carbon Nanotubes and Poly(3‐octylthiophene) as Ion‐to‐Electron Transducers in All‐Solid‐State Potassium Ion‐Selective Electrodes

Multi‐walled carbon nanotubes (MWCNTs) were compared with poly(3‐octylthiophene) (POT) as ion‐to‐electron transducer in all‐solid‐state potassium ion‐selective electrodes with valinomycin‐based ion‐selective membranes. MWCNTs and POT were mixed with the other components of the potassium ion‐selective membrane cocktail (valinomycin, KTpClPB, o‐NPOE, PVC, THF) which was then applied on a glassy carbon (GC) substrate to prepare single‐piece ion‐selective electrodes (SPISEs). Results from potentiometric and impedance measurements showed that the MWCNT‐based electrodes have a more reproducuible standard potential and a lower overall impedance than the electrodes based on POT. Both types of electrodes showed similar sensitivity to potassium ions and no redox sensitivity.     

A comparative study of the effect of o-nitrophenyl octyl ether and o-nitrophenyl pentyl ether as plasticizers on the response and selectivity of carrier-based liquid membrane ion-selective electrodes

Lithium, potassium and caesium-selective microelectrodes were prepared by coating the tips of preconditioned silver wires, incorporated in a flow-cell, with PVC membranes containing four different ionophores. A dicarboxamide, a 14-crown-4 carboxylic acid, benzo-18-crown-6 and di-(tert-butylbenzo)-21-crown-7 ionophores were used in the electrode matrix. The first two ionophores were used in lithium ion-selective electrodes, the third in a potassium ion electrode and the fourth in a caesium ion electrode. Two different plasticizers, o-nitrophenyl octyl ether (NPOE) and o-nitrophenyl pentyl ether (NPP'E) were used. Enhancement of the signal and the slope of the calibration curve and improvement of the curve linearity were observed in all cases when NPP'E was used as plasticizer. A general trend of enhanced selectivity of the electrodes incorporating crown ether ionophores was also observed when NPP'E was the plasticizer.     

Synthesis and potentiometric selectivity study of new spiro-14-crown-4 derivatives

Abstract

Four new compounds with 14-crown-4 attached to spirocyclopentane or spirocyclohexane were synthesized and tested for potentiometric selectivity for lithium ion in polyvinyl chloride membrane electrodes. Four plasticizers were studied and the addition of tri-octylphosphine oxide (TOPO) was investigated. One ionophore exhibited a sodium/lithium selectivity, K^pot _Li,Na by the matched potential method of 0.0028 in the presence of 1% TOPO, using o-nitro-phenylphenyl ether as plasticizer. Selectivities are reported for sodium, potassium, nickel, cobalt, barium and calcium.     

New polymeric membrane cadmium(II)-selective electrodes using tripodal amine based ionophores

Fabrication of PVC membrane electrodes incorporating selective neutral carriers for Cd(2+) was reported. The ionophores were designed to have different topologies, donor atoms and lipophilicity by attaching tripodal amine (TPA) units to the lipophilic anthracene (ionophore I) and p-tert-butylcalix[4]arene (ionophores II, III and IV). The synthesized ionophores were incorporated to the plasticized PVC membranes to prepare Cd(II) ion selective electrodes (ISEs). The membrane electrodes were optimized by changing types and amounts of ionic sites and plasticizers. The selectivity of the membranes fabricated from the synthesized ionophores was evaluated, the relationship between structures of ionophores and membrane characteristics were explored. The ionophore IV which composed of two opposites TPA units on the calix[4]arene compartment showed the best selectivity toward Cd(2+). The best membrane electrode was fabricated from ionophore IV (10.2 mmol kg(-1)) with KTpClPB (50.1 mol% related to the ionophore) as an ion exchanger incorporated in the DOS plasticized PVC membrane (1:2; PVC:DOS). The Cd-ISE fabricated from ionophore IV exhibited good properties with a Nernstian response of 29.4±0.6 mV decade(-1) of activity for Cd(2+) ions and a working concentration range of 1.6×10(-6)-1.0×10(-2)M. The sensor has a fast response time of 10s and can be used for at least 1 week without any divergence in potential. The electrode can be used in the pH range of 6.0-9.0. The proposed electrodes using ionophores III and IV were employed as a probe for determining Cd(2+) from the oxidation of CdS QDs solution and the real treatment waste water sample with excellent results.     

Novel proton-conducting polymer inclusion membranes

The preparation and characterization of new polymer inclusion membranes (PIMs) for proton transport is described. PIMs were prepared with different polymeric cellulose-based compounds and PVC as supports, tris(2-butoxyethyl)phosphate (TBEP) and 2-nitrophenyl octyl ether (NPOE) as plasticizers and dinonylnaphthalenesulfonic acid (DNSA) and dinonylnaphthalenedisulfonic acid (DNDSA) as carriers. The effects of the nature and content of the supports, plasticizers and carriers on membrane proton conductivity was studied using electrochemical impedance spectroscopy (EIS). This technique was also used to evaluate the chemical stability of a CTA–NPOE–DNDSA membrane while its selectivity was monitored with respect to sodium and calcium ions through counter-transport experiments. DSC and TGA techniques were used to determine the thermal stability of these membranes. A PIM based on CTA–DNDSA–NPOE showed the highest proton conductivity (3.5 mS/cm) with no variation of its behavior during 2 months of evaluation. FTIR characterization did not show structural changes of the membrane in this period of time. Thermal analysis indicates that it is stable up to 180 °C. An empirical functional relationship between PIM resistance and composition indicates that increasing plasticizer and carrier concentrations enhances the conductivity of the membranes, while increasing CTA content tends to decrease this property. Transport experiments showed a good selectivity of the CTA–DNDSA–NPOE membrane for protons over calcium or sodium ions.     

Hyamine 1622 - Selective PVC Membrane Electrodes Based on bis (Crown Ether)s

Abstract

Hyamine 1622 - selective PVC membrane electrodes based on bis (crown ether)s containing the benzo - 18 - crown - 6 moiety were prepared, using o - nitrophenyloctylether (NPOE) or dipentylphthalate (DPP) as the plasticizer of the PVC membrane. Selectivity coefficients for various interfering ions (inorganic and organic cations), were determined by the mixed solution method. The selectivity of the respective electrodes was found to be affected by the kind of plasticizer employed, and NPOE seemed to be a more suitable plasticizer than DPP. The NPOE electrode system based on the bis (crown ether) that has 11 atoms between the two benzo-18-crown-6 moieties offers the advantage of greater selectivity. The electrodes show excellent electrode properties, and the electrode response was stable in a wide pH range.     

Solvent‐Polymeric ISEs Tailored for Measurements in Solutions Containing Tetrabutylammonium,Cesium, and Calcium Ions

Ion‐selective electrodes are described, with membranes tailored for measurements of tetrabutylammonium ions in aqueous and formamide solutions, and for measurements of cesium and calcium ions in the presence of tetrabutylammonium. It is shown that reliable measurements of cesium ions are possible when a correction is introduced for interference from tetrabutylammonium, using Nikolsky selectivity coefficient. A novel membrane composition is described which ensures high selectivity to calcium ions over tetrabutylammonium.     

Functional layers for chemical sensors based on conducting polypyrrole

Functional thin layers based on polypyrrole were used in electrochemical sensors as mixed conducting interfaces between ion‐selective membranes and the wiring. In particular, new types of ion‐selective electrodes for potentiometric measurement of pH value and concentration of sulfate ions in solutions were developed. The resulting electrodes do not need any inner liquid junction. First determinations of the sensor parameters sensitivity, selectivity and long term stability indicate a good performance of the prepared sensors. The results imply that interfaces, containing polypyrrole, could be an interesting basis for the construction of a new type of all‐solid‐state ion‐selective electrodes.     

Study on Hydrogen Ion-Selective Solid Contact Electrodes Based on Decamethylcyclopentasiloxane

Hydrogen ion-selective solid contact electrode based on decamethylcyclopentasiloxane (DMCS) as ionophore was fabricated. The membrane solution was prepared by mixing DMCS, polyvinyl chloride (PVC), potassium tetrakis p-chlorophenyl borate (KTpClPB) and various plasticizers. The best performance was obtained with the sensor based on NPOE (o-nitrophenyl octyl ether) and the conducting polymer layer of poly(pyrrole), doped with NaClO₄. The electrode exhibited Nernstian-response in the range of pH 1.9–9.8 with a slope of 57.6 ± 0.2 mV per decade and fast response time within 15 s. This electrode showed good selectivity and was successfully used as an indicator electrode in the potentiometric titration.     

Elaboration and characterisation of a plasticized cellulose triacetate membrane containing trioctylphosphine oxyde (TOPO): Application to the transport of uranium and molybdenum ions

A cellulose triacetate (CTA) membrane containing trioctylphosphine oxyde (TOPO) as carrier and 2-nitrophenyloctyl ether (NPOE) as a plasticizer was prepared. The membrane CTA + NPOE + TOPO was characterised using chemical techniques as well as Fourier Transform InfraRed (FTIR) spectroscopy, X-ray diffraction and Scanning Electron Microscopy (SEM). The CTA membrane is characterised by well-defined pores; these pores are completely filled with the NPOE and carrier. Surfaces of membranes with TOPO are smooth. The systems constituted by the mixture of CTA + NPOE, CTA + NPOE + TOPO do not give any diffraction. This can be due to the absence of crystallization within the membrane. On the other hand, this result should be attributable to the amorphous state of the structure, which permits us to eliminate the mechanism of transfer of the ions by electron jump. A comparative study of transport across a polymer inclusion membrane (PIM) and a supported liquid membrane (SLM) containing the same carrier in chloroform has shown that uranium or molybdenum transport efficiency was increased using PIM instead of SLM. PIM showed higher stability than SLM, the flux of transport remain constant in the former case after 2 weeks.     

Atropine-selective membrane electrodes and relative selectivity concept

TFPB was introduced as a charged ionophore for atropine selective electrodes. Typical Nernstian responses were found (57.78, 58.95 and 58.41 mV/decade) for PVC-membrane electrodes incorporating NPOE, DOS, and DDP as plasticizers. They exhibited practical linear ranges of 9.1 x 10(-3) - 10(-6), 9.1 x 10(-3) - 10(-6) and 9.1 x 10(-3) - 10(-7) M, respectively. It works in the sub-micro scale of atropine concentrations. The optimum pH-range was 3.18 - 8.97. The selectivity coefficient values were estimated for different organic and inorganic cations. They were interpreted by using the "Relative Selectivity Concept", which was introduced for the first time. The new concept was applied for comparing the selectivity properties of previously reported electrodes. The effect of the presence of ephedrine, caffeine, glucose, Na(+), Ca(2+), and Mg(2+) on the calibration graphs of the electrodes was studied.     

Novel Cesium‐Selective Electrodes Based on Lipophilic 1,3‐Bisbridged Cofacial‐calix[6]crowns

Five bisbridged calix[6]crowns have been investigated as Cs⁺ ionophore in PVC membrane electrodes. As ionophores, three 1,3‐bisbridged calix[6]crown‐4‐ethers( I–III ), 1,3‐bisbridged calix[6]crown‐5‐ether( IV ), and 1,3‐bisbridged calix[6]crown‐6‐ether( V ) have been evaluated. The membranes all give good Nernstian response in the concentration range from 1×10^?7 to 1×10^?1 M of cesium ion. The best detection limits (?log aequation/tex2gif-inf-1.gif=7.08–7.36) are obtained for electrode membranes containing 1,3‐bisbridged cofacial‐calix[6]crown‐4‐ethers( I‐III ), and the values are the lowest compared with those reported previously. The highest selectivity coefficients [ 3.74(Cs/K), 2.63(Cs/Rb)] are obtained for the membrane of 1,3‐bisbridged calix[6]crown‐4‐ether( II ), and these values are also the highest compared with previous reports for Cs⁺‐ISEs. The highest selectivity towards cesium ion is attributed to the geometrically cofacial positions of two crown‐ethers in calix[6]crowns in order to provide the complex of cesium ion and eight oxygens of cofacial crowns.     

Quantitive binding constants of H(+)-selective chromoionophores and anion ionophores in solvent polymeric sensing membranes

The binding properties of neutral or charged chromoionophores and anion ionophores in solvent polymeric membranes were characterized in situ by the so-called sandwich membrane method. Acidity constants (pK(a)) of eight chromoionophores (ETH 5294, ETH 2439, ETH 5350, ETH 5418, ETH 5315, ETH 7061, ETH 7075, ETH 2412) were measured in bis(2-ethylhexyl)sebacate (DOS) and o-nitrophenyloctylether (NPOE) plasticized poly(vinyl chloride) (PVC) membranes commonly used in optical and potentiometric ion sensors. The pK(a) values of all chromoionophores in DOS membranes are by 2-3 orders of magnitude smaller than in NPOE membranes. The weak alkali metal ion binding properties with neutral H(+)-chromoionophore and anion binding with electrically charged chromoionophores were also studied quantitatively. The complex formation constants of the commercially available Co(III)cobyrinate nitrite ionophore and the organomercury chloride ionophore, ETH 9009, were also measured. The very low stability constant observed for ETH 9009 (logbeta(2)=3.60+/-0.03 in PVC-DOS and 3.61+/-0.01 in PVC-NPOE) was explained by the decomposition of the ionophore in contact with chloride samples. On the other hand, the electrically charged nitrite ionophore showed strong complexation with nitrite ions, with logbeta=10.58 and 10.59 in DOS and NPOE membranes, respectively. In contrast to cation ionophores, the stability constant of the NO(2)(-) ionophore does not change with different plasticizers.     

聚冠醚的合成和性质——Ⅵ.聚冠醚为载体的碱金属离子选择性电极

本文报道以含有12-冠-4、15-冠-5和18-冠-6结构单元的双酚A型聚冠醚为载体的钠、钾和铯离子选择性电极的制备及电极响应特性的研究。结果表明三种电极都有较好的Nernstian响应特性和对碱金属及碱土金属的良好选择性。     

Potentiometric determination of coextraction constants of potassium salts in ion-selective electrodes utilizing a nitrobenzene liquid membrane phase

A theoretical treatment of potentiometric data is applied to calculate coextraction constants (K_IA) for three potassium salts from water into a liquid nitrobenzene phase. The experiment involves treating nitrobenzene as a membrane and contacting it with two aqueous solutions of different ion activities. In the presence of either a cation or anion exchanger, the ratio of activities of ions in the two aqueous phases gives rise to a potential difference across the membrane that depends upon the nature and charge of the counter ion of the ion-exchanger in excess. Here, the cation exchanger was chosen to be potassium tetrakis(4-chlorophenyl)borate (KTpClPB) and the anion exchanger was tetradodecylammonium chloride (TDDACl). TDDACl was incrementally added to the nitrobenzene phase containing a fixed concentration of KTpClPB, and the corresponding emf was recorded as a function of concentration of TDDACl. The membrane changes from one with cation exchanger properties (excess KTpClPB) to one with anion exchanger properties (excess TDDACl). The potential difference and shape of the titration curve can be predicted by theory based on the phase boundary potential model. Log(K_IA) values calculated for KCl, KNO₃ and KClO₄ in nitrobenzene were found as: −10.53 (± 0.09), −8.16 (± 0.05) and −5.63 (± 0.03) respectively, in accordance with the Hofmeister series of lipophilicity, and similar to those observed in PVC membranes containing other plasticizers. The method presented here offers the advantage over other methods to calculate K_IA, in that it is relatively experimentally simple without compromising the accuracy of the calculated coextraction constants. The ability to titrate directly into the liquid membrane phase affords a higher precision compared to the preparation of a series of PVC/plasticizer membranes with different compositions.     

Construction of a Highly Selective and Sensitive La(III) Sensor Based on N‐(2‐Pyridyl)‐N′‐(4‐methoxyphenyl)‐thiourea for Nano Level Monitoring of La(III) Ions

N‐(2‐Pyridyl)‐N′‐(4‐methoxyphenyl)‐thiourea (PMPT) was found to be a suitable neutral ion carrier for the construction of a highly selective and sensitive La(III) membrane sensor. Poly(vinyl chloride) (PVC) based membranes of PMPT with potassium tetrakis (p‐chlorophenyl) borate (KTpClPB) as an anionic excluder and oleic acid (OA), dibutyl phthalate (DBP), benzyl acetate (BA) and o‐nitrophenyloctyl ether (NPOE) as plasticizing solvent mediators were constructed and investigated as La(III) membrane sensors. A membrane composed of PMPT‐PVC‐KTpClPB‐BA with the ratio 8.0 : 35.0 : 3.0 : 54.0 works well over a very wide concentration range (4.0×10^?8 to 1.0×10^?1 M) with a Nernstian slope of 19.6±0.2 mV per decade of activity between pH values of 4.0 and 9.0. The detection limit of the sensor was calculated to be 2.0×10^?8 M (ca. 3.0 ppb). The sensor displays very good discrimination toward La(III) ions with regard to most common metal ions and lanthanide ions. The proposed sensor shows a short response time for whole concentration range (ca. 12 s). For evaluation of the analytical applicability of the La(III) sensor, it was successfully used as an indicator electrode for the titration of La(III) ions with EDTA. It was also applied to the determination of fluoride content of two mouth wash preparation samples and monitoring of La(III) ions in some binary and ternary mixtures.     

Seventeen new 14- and 15-crown-formazans: their synthesis and evaluation in spectrophotometric determination of lithium

A number of new crown-formazans with 14 and 15 membered rings have been synthesized, characterized and investigated as selective spectrophotometric chelating agents for lithium. The effect of sodium ion concentration on the background lithium signal was studied. A comparative study for the sensitivity of these new crown-formazans in spectrophotometric determinations was studied and compared with those reported previously. The three new 14- and 15-crown-formazans 4a-c containing the pyridyl N-oxide at the formazyl carbon showed the highest selectivity to lithium determination in the presence of sodium ion.     

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.     

Selective transport of cesium ion in polymeric CTA membrane containing calixcrown ethers

A series of calixcrown ethers for which the cavity size of the crown ring is varied from crown-6 to crown-7 to crown-8 were examined for the transport abilities toward alkali metal ions. These ligands were incorporated into supported liquid membranes (SLMs) and into polymer inclusion membranes (PIMs) composed of cellulose triacetate (CTA) as a support and 2-nitrophenyl octyl ether (NPOE) and tris(2-butoxyethyl) phosphate (TBEP) as a plasticizer. In both membrane systems, calixcrown-6 showed the best selectivity toward a cesium ion over other alkali metal ions. The polymeric CTA membrane showed more rapid transport rate as well as higher durability than did the SLMs.