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.     

Measuring quaternary ammonium cleaning agents with ion selective electrodes

Data for coated-wire, ion selective electrodes (ISEs) are presented for cationic surfactant ions found in common cleaners including benzyldimethyltetradecylammonium, benzyldimethyldodecylammonium, and benzyldimethylhexadecylammonium. The ion exchangers dinonylnaphthalene sulfonic acid, tetraphenyborate, and tetrakis(4-chlorophenyl)borate are examined, showing dinonylnaphthalene sulfonic acid to be the favored species. The ISEs exhibit approximately Nernstian behavior down to the 10⁻⁶ M limit of detection with lifetimes in excess of 50 days when used continuously, and a shelf life of over 100 days. Reaching the upper detection limit at the critical micelle concentration requires use of polymeric-membrane reference electrodes including a new membrane cocktail, which allow response measurements of an order of magnitude higher than the traditional fritted-glass reference electrode. The surfactant ISEs show excellent selectivity over the common metal ions Na⁺, K⁺, Mg²⁺, Ca²⁺, and Cu²⁺ with selectivity coefficients less than 10^−5.3. The ISEs are also selective over the lower molecular weight quaternary ammonium ions tetradecyltrimethylammonium, dodecyltrimethylammonium, benzyldimethyl(2-hydroxyethyl)ammonium, and tetrabutylammonium with selectivity coefficients ranging from 10^−1.7 to 10^−5.5. Use of a single electrode to determine accurately the total cationic surfactant concentration in common cleaning solutions is accomplished with information about concentration dependent interferences and a modified Nikolsky–Eisenman model. Finally, quaternary ammonium surfactants have a deleterious effect on the measurements of pH and common ions like K⁺, Mg²⁺ and Ca²⁺ with polymeric ISEs. This makes it critical to include surfactant electrodes in a detector array when cleaning agents are present.     

Asymmetric membranes with modified gold films as selective gates for metal ion separations

Thin layers of gold (700 Å) were deposited on manufactured alumina pourous supports to yield nanopores with openings of <7 nm. A self-assembled monolayer (SAM) of alkyl thiols was then attached to provide a hydrophobic support for trialkyl phosphine oxide-based metal ion carriers. The resulting gated membranes provided a barrier to ions including H⁺, and Ca²⁺, NO₃⁻, and CH₃COO⁻. When an aqueous feed solution of 4.2 mM uranyl nitrate and 1 M lithium nitrate pH 4, and a receiving solution of 1 M sodium acetate pH 5.5 were used 100% of the metal was transported across the membrane by facilitated transport via the phosphate or phosphine oxide carrier. The thin gates transported metal ions as neutral nitrate complexes with fluxes high enough to be limited by the alumina support. The flux rates of 200,000 metal ions per pore per second are only a factor of 5 below that observed for the potassium channel. High selectivity of U over Eu is observed until the [U] is <0.84 mM in the feed solution, despite the fact the Eu actually transports faster when U is not present. This work demonstrates that selectivity can be added without impeding transport by using thin selective layers.     

Cesium-selective optode membrane based on the lipophilic calix[4]biscrown in the 1,3-alternate conformation

One type of lipophilic calix[4]biscrowns in the 1,3-alternate conformation which are highly selective complexant for cesium has been used to construct cesium poly(vinyl chloride) (PVC) membrane optode. The reversible sensing system has been formed by incorporating the lipophilic neutral H⁺—selective chromoionophore ETH5294 in the plasticized PVC membrane with 1,3-calix[4]bisnaphtyl-crown-6. The measuring range of cesium ions can be conditioned by buffering different pH in the cesium solutions. At pH 7.0, the measuring range of the optode membrane for cesium ions is from 1×10⁻⁶ to 1×10⁻² M. The response behavior of optode membrane including response time, selectivity, reproducibility and lifetime, has been described in detail.     

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.     

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.     

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。     

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.     

铋(Ⅲ)-卤素络阴离子选择电极的研究

我们曾报导了PVC膜四碘络铋离子选择电极的研制。现又研制了铋(Ⅲ)-溴,铋(Ⅲ)-氯的络阴离子PVC膜选择电极。本文比较了三种铋(Ⅲ)-卤素络阴离子选择电极的主要性能,并对络阴离子电极配位体的选择条件及阳离子的干扰规律进行了讨论。     

Detection of metal ions using ion-channel sensor based on self-assembled monolayer of thioctic acid

Gold electrodes were chemically modified with thioctic acid monolayer designed to mimic biological ion-channel membranes. The technique was then used in the determination of alkali, alkaline earth, thallium(I), and lanthanum metal cations as analytes. Cyclic voltammograms (CV) of [Fe(CN)6]³⁻ an electroactive marker, were measured in the presence of the various types of analyte cations. In the absence of the analyte cation, electrostatic repulsion between the marker anions and the carboxylate groups of the receptor monolayer hindered the approach of the marker anion to the electrode surface and hence hindered its reduction. The modified electrodes responded well to the metal cations except the alkali metal cations. The sensors could detect the trivalent cation La³⁺ at concentrations as low as 10⁻⁸ M. The response of the sensor to the metal cations increase in the order alkali metal3+ can be discriminated in the ratio 1:100. This makes it possible to determine the trivalent ion in a sample matrix containing monovalent and divalent cations. Thallium(I) ion showed marked deviation in its response as compared to monovalent ions of the alkali metals. The ion-channel sensor based on self-assembled monolayer of thioctic acid therefore offers a potential alternative technique for the selective determination of metal ions.     

Gas phase hydrogen deuterium exchange reactions of a model peptide: FT-ICR and computational analyses of metal induced conformational mutations

We utilized gas phase hydrogen/deuterium (H/D) exchange reactions and ab initio calculations to investigate the complexation between a model peptide (Arg-Gly-AspRGD) with various alkali metal ions. The peptide conformation is drastically altered upon alkali metal ion complexation. The associated conformational changes depend on both the number and type of complexing alkali metal ions. Sodium has a smaller ionic diameter and prefers a multidentate interaction that involves all three amino acids of the peptide. Conversely, potassium and cesium form different types of complexes with the RGD. The [RGD + 2Cs − H]⁺ species exhibit the slowest H/D exchange reactivity (reaction rate constant of 6 × 10⁻¹³ cm³molecule⁻¹s⁻¹ for the fastest exchanging labile hydrogen with ND₃). The reaction rate constant of the protonated RGD is two orders of magnitude faster than that of the [RGD + 2Cs − H]⁺. Addition of the first cesium to the RGD reduces the H/D exchange reaction rate constant (i.e., D₀) by a factor of seven whereas sodium reduces this value by a factor of thirty. Conversely, addition of the second alkali metal ions has the opposite effect; the rate of D₀ disappearance for all [RGD + 2Met − H]⁺ species (MetNa, K, and Cs) decreases with the alkali metal ion size.     

PANI-SnP复合膜电极在镍镉废水中电控离子交换性能

采用滴涂法在铂基底制备了电活性聚苯胺-磷酸锡(PANI-SnP)复合膜电极,考察了该电极在Ni²⁺、Cd²⁺溶液的电控离子交换性能. 用傅立叶变换红外光谱和扫描电镜分析观察复合膜的组成及表面形貌;在0.1 mol·L^-1 Ni(NO₃)₂、Cd(NO₃)₂溶液,通过循环伏安法比较了PANI膜、SnP膜及PANI-SnP复合膜电极的电化学性能,并结合电化学石英晶体微天平技术重点考察了PANI-SnP复合膜的离子交换机制;同时,通过循环伏安法调控复合膜电极的氧化还原电位,结合X射线能谱和X射线光电子能谱分别测定了其氧化和还原状态的元素组成. 结果表明,PANI-SnP复合膜电极在Ni²⁺、Cd²⁺溶液均有良好的氧化还原电活性和可逆离子交换性能,其Cd²⁺离子选择性优于Ni²⁺离子,通过电控离子交换可使Cd²⁺离子从镍镉废水高效分离.     

Nickel hexacyanoferrate membrane as a coated wire cation-selective electrode

Nickel hexacyanoferrates containing alkali metal cations as counter ions were used to prepare ion-selective electrodes for potentiometric sensing of intercalated species in the coated wire electrode (CWE) configuration. All the electrodes developed display a quasi-Nernstian response towards potassium ion, whereas the highest sensitivity is generally achieved when Cs+ is the counter cation in the sensing material. The selectivity constants of the electrodes were calculated by the matched potential method considering K+ as the primary ion. The selectivity order is Cs+ > K+ > Na+ > Li+ and reflects the effective dimension of the hydrated cations.     

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.     

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.     

电活性铁氰化镍膜电极对稀土钇的电控离子分离

通过电沉积方法分别在镀铂石英晶片和铂基底上制备了电活性铁氰化镍膜,并考察了膜电极在含钇离子溶液中的电控离子交换性能. 在0.1 mol·L^-1的硝酸钇溶液中,使用循环伏安法及石英晶体微天平技术测试考察了铁氰化镍膜对钇离子的置入释放性能及对应的质量变化,同时比较了铁氰化镍膜电极在Y(NO₃)₃和Sr(NO₃)₂溶液中的电化学性能. 在0.1 mol·L^-1 [Y(NO₃)₃ + Sr(NO₃)₂]混合溶液中,通过循环伏安法分析了薄膜对Y³⁺/Sr²⁺离子的选择性. 用扫描电子显微镜观察了铁氰化镍膜的表面形貌,并通过X射线光电子能谱仪测定了膜在氧化和还原状态下的元素组成. 结果表明,铁氰化镍膜在含Y³⁺溶液中具有良好的离子交换行为,其中氧化过程薄膜质量减少,对应着钇离子的释放;还原过程薄膜质量增加,对应钇离子的置入;在0.0 V或0.9 V调控膜电极的氧化还原状态实现对钇离子的有效分离.     

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.