Preparation and application of selenite ion selective electrode

A new selenite ion selective electrode using 4,6-dibromopiaselenole as active material, PVC as membrane matrix and dibutyl phthalate as plasticizer has been developed. An analytically useful potential change occurs from about 10(-6)-10(-1)M Se(IV), and the slope of the linear portion is -23.6 mV/10-fold change in Se(IV) concentration at a temperature of 21 degrees . The electrode shows fairly good selectivity for selenite ion over other anions and has been used for the successful determination of total selenium in human hair.     

Potentiometric anion selectivity of polymer-membrane electrodes based on cobalt, chromium, and aluminum salens

Metallo-salens of cobalt(II) (Co-Sal), chromium(III) (Cr-Sal), and aluminum(III) (Al-Sal) are used as the active ionophores within plasticized poly(vinyl chloride) membranes. It is shown that central metal-ion plays a critical role in directing the ionophore selectivity. Polymer-membrane electrodes based on Co-Sal, Cr-Sal, and Al-Sal are demonstrated to exhibit enhanced responses and selectivity toward nitrite/thiocyanate, thiocyanate, and fluoride anions, respectively. The improved anion selectivity of the three ionophore systems is shown to deviate significantly from the classical Hofmeister pattern that is based only on ion lipophilicity. For example, optimized membrane electrodes for nitrite ion based on Co-Sal exhibit logK(Nitrite,Anion)(pot) values of -5.22, -4.66, -4.48, -2.5 towards bromide, perchlorate, nitrate, and iodide anions, respectively. Optimized membrane electrodes based on Co-Sal and Cr-Sal show near-Nernstian responses towards nitrite (-57.9+/-0.9 mV/decade) and thiocyanate (-56.9+/-0.8 mV/decade), respectively, with fast response and recovery times. In contrast, Al-Sal based membrane electrodes respond to fluoride ion in a super-Nernstian (-70+/-3 mV/decade) and nearly an irreversible mode. The operative response mechanism of Co-Sal, Cr-Sal, and Al-Sal membrane electrodes is examined using the effect of added ionic sites on the potentiometric response characteristics. It is demonstrated that addition of lipophilic anionic sites to membrane electrodes based on the utilized metallo-salens enhances the selectivity towards the primary ion, while addition of cationic sites resulted in Hofmeister selectivity patterns suggesting that the operative response mechanism is of the charged carrier type. Electron spin resonance (ESR) data indicates that Co(II) metal-ion center of Co-Sal ionophore undergoes oxidation to Co(III). This process leads to formation of a charged anion-carrier that is consistent with the response behavior obtained for Co-Sal based membrane electrodes.     

Development of a Poly(vinyl chloride)-based Nitrate Ion-selective Electrode

The authors developed a nitrate ion-selective electrode(ISE) based on poly(vinyl chloride)(PVC) membrane with methyltrioctylammonium nitrate as a carrier and 1-decanol as a plasticizer. The performance of the nitrate-sensitive membranes was optimized by tuning the composition of components. The electrode exhibits a linear response with a Nernstian slope of (52±1.0) mV per decade for the nitrate ion concentration ranging from 5.8×10^-5 mol/L to 1.0 mol/L. The electrode can be used to detect a low concentration of nitrate ions down to 3×10^-5 mol/L in a pH range of 2.1-11.5 without any compensation. The advantage of the electrode includes simple preparation, short response time and good repeatability. The detection performance of the novel electrode on nitrate ions has been tested for water samples.     

Thiocyanate-selective electrode based on unsymmetrical benzoN(4) nickel(II) macrocyclic complexes

Unsymmetrical benzoN(4) nickel(II) macrocyclic complexes have been explored as an ionophore for preparing PVC-based membrane electrodes selective to SCN(-). The resulting electrode exhibited the best working concentration range (1.4x10(-7)-0.1 M) with a Nernstian slope of (-59.7+/-0.9 mV per decade) in the wide pH range of 3.5-10.5. The proposed electrode has a very fast response time (5 s) and high selectivity for thiocyanate over variety of anions. This sensor was successfully applied as an indicator electrode to potentiometric titration of thiocyanate ion with AgNO(3) and for direct determination of the amount of thiocyanate in urine and saliva samples in order to distinguish between smokers and nonsmokers.     

Clotrimazole-triiodide ion association as an ion exchanger for a triiodide ion-selective electrode.

A novel triiodide ion-selective electrode based on a clotrimazole-triiodide ion pair as a membrane carrier was prepared. It has a linear response to triiodide from 8 x 10(-6) to 5 x 10(-3) M with a slope of -68.9 mV per decade and a detection limit of 5 x 10(-6) M. The electrode response is independent of the pH of the solution in the pH range 2-9. It has a very short response time and can be used for at least 3 months without any considerable divergence in the potentials. The proposed sensor revealed very good selectivities for I3- over a variety of other anions. It was used as an indicator electrode in the potentiometric titration of triiodide ions and in an indirect potentiometric determination of clotrimazole in pharmaceutical preparations.     

Anion exchange membrane with viologen moiety as anion exchange groups and generation of photo-induced electrical potential from the membrane

An anion exchange membrane with a viologen moiety was prepared by the reaction of a film of chloromethylated polysulfone and 4,4′-bipyridine. The anion exchange membrane showed a high electrical resistance and a high transport number of anions due to the development of high crosslinking by the diamine. After the membrane had been swollen with ethylene glycol, photo-voltage and photo-current (82 mV, 410 nA at 200 kΩ load, 160 μm thick membrane) were generated from the membrane upon photo-irradiation.     

Nitrate-containing ionic liquids as active membrane components of nitrate-selection electrodes

Two dialkylimidazolium nitrate ionic liquids (ILs) have been tested for use as an active component of plasticized PVC membranes in nitrate ion selective electrodes (ISEs). The potentiometric reversibility and the main electrochemical characteristics of the ISEs in KNO₃ solutions have been studied. The test membranes contain 5% of the active component and demonstrate a near-Nernstian response to NO ₃ ^? . The use of a more hydrophobic IL based on dioctadecylimidazolium increases the sensitivity and decreases the detection limit: the slope of the electrode function is 57 mV/pC, and C _min = 3.7 · 10^?6 mol/L. The pH range of the membrane performance has been studied, and the potentiometric selectivity to NO ₃ ^? in the presence of several foreign anions has been determined. The new electrode exceeds the commercially available analogue (an ELIT 021 nitrate-selective electrode) in the detection limit and response time. The utility of the new electrode for the direct potentiometric determination of nitrate ILs in aqueous solutions has been demonstrated.     

Crystal Structure of[La(NO_3)_3(12-crown-4)-(H_2O)](12-crown-4)

ＣｒｙｓｔａｌＳｔｒｕｃｔｕｒｅｏｆ［Ｌａ（ＮＯ_３）_３（１２－ｃｒｏｗｎ－４）－（Ｈ_２Ｏ）］（１２－ｃｒｏｗｎ－４）ＭａｏＪｉａｎｇ－Ｇａｏ；ＪｉｎＺｈｏｎｇ－Ｓｈｅｎｇ；ＹｕＦｅｎｇ－Ｌａｎ（ＬａｂｏｒａｔｏｒｙｏｆＲａｒｅＥａｒｔｈＣｈｅｍｉ?..     

Recognition, encapsulation, and selective fluorescence sensing of nitrate anion by neutral C3-symmetric tripodal podands bearing amide functionality

A series of neutral C(3)-symmetric acyclic artificial receptors incorporating amide functionality has been designed, synthesized, and fully characterized. Upon protonation, these conformationally flexible N-bridged tripodal podands 1-5 form in situ cone shape conformation through hydrogen bonding and C-H···π interactions. The protonation-induced interior preorganized cavity is capable of entrapping nitrate anions through the amide N-H bonds to form discrete nitrate complexes (1a-5a), which were fully characterized by NMR, HRESI mass spectra, and single crystal structures. By incorporating suitable fluorophores at each branch of the tripod receptor, the resulting fluorescent receptor 5 selectively recognized nitrate anions by fluorescent quenching in a DMSO solution and displayed one of the highest binding affinities for nitrate anions reported so far in polar media. Receptor 5 represents a unique example of a neutral receptor for the recognition of nitrate anions in polar solvent media by its zwitterionic form. The possible mechanism of proton-induced preorganization of these flexible, acyclic receptors in a convergent cone conformation followed by nitrate complexation has been proposed to rationalize the effective nitrate recognition.     

Highly selective iodide membrane electrode based on a cerium salen.

A highly selective PVC membrane electrode based on a cerium-salen complex was prepared. The sensor displays an anti-Hofmeister selectivity sequence with a preference for iodide ion over many common organic and inorganic anions. The proposed electrode exhibits a near-Nernstian behavior over a wide concentration range (5.0 x 10(-2) - 8.0 x 10(-6) M) with a slope of 57.5 mV per decade, and a detection limit of 6.0 x 10(-6) M. The electrode has a very fast response time and can be used in the pH range of 3.0 - 1 1.0. It was applied, as an indicator electrode, in potentiometric titration of Ag+ ions.     

Selective thiocyanate poly(vinyl chloride) membrane based on a 1,8-dibenzyl-1,3,6,8,10,13-hexaazacyclotetradecane-Ni(II) perchlorate

A highly selective poly(vinyl chloride) (PVC) membrane electrode based on 1,8-dibenzyl-1,3,6,8,10,13-hexaazacyclotetradecane-Ni(II) as a membrane carrier with unique selectivity toward thiocyanate is reported. The influence of membrane composition, pH and foreign anions were investigated. The sensor exhibits a Nernstian response for thiocyanate over a wide concentration range of 3.3×10⁻⁶ to 0.10 M, with a slope 58.4±0.3 mV per decade. The limit of detection is 3.0×10⁻⁶ M SCN⁻. The sensor has a response time of <20 s and can be used for at least 2 months without any considerable divergence in potential. The proposed electrode shows fairly a good discriminating ability towards SCN⁻ ion in comparison to other anions. It was successfully applied to direct determination of thiocyanate in urine and saliva and it was also used as an indicator electrode in titration of thiocyanate with Ag⁺ ions.     

Probing the protic ionic liquid surface using X-ray reflectivity

The structure of the free liquid surface of three protic ionic liquids, ethylammonium nitrate (EAN), propylammonium nitrate (PAN), and ethylammonium formate (EAF), has been elucidated using X-ray reflectivity. The results show all three liquids have an extended interfacial region, spanning at least five ion pairs, which can be divided into two parts. Adjacent to the gas phase are aggregates consisting of multiple cations and anions. Below this are layers oriented parallel to the macroscopic surface that are alternately enriched and depleted in cation alkyl chains and polar domains of cation ammonium groups and their anions, gradually decaying to the isotropic sponge-like bulk structure. The most pronounced layering is observed for PAN, driven by strong solvophobic interactions, while reduced hydrogen bonding in EAF results in the least structured and least extensive interfacial region.     

Intensification of the Nitrate Anion Reduction on a Membrane Palladium Electrode

Polarization curves of electroreduction of nitrate anions in sulfuric acid aqueous solutions on a Pd/Pd palladium electrode with the opposite side kept at different constant potentials in the region of Pd–H -phase formation are compared. The reduction rate of nitrate anions is shown to be substantially higher on a membrane electrode, provided the conditions of hydrogen supply from the membrane's opposite side to the reaction zone are realized. This phenomenon is caused by the reduction of a chemisorbed intermediate (a certain N(III) form) by hydrogen diffused through the membrane. It is shown that the measurements of hydrogen diffusion currents through a membrane can be used in plotting hydrogen sorption isotherms in the Pd–H -phase.     

Anion recognition through amide-based dendritic molecule: a poly(vinyl chloride) based sensor for nitrate ion

Poly(vinyl chloride) (PVC)-based membranes of N,N-bis-succinamide-based dendritic molecule with tetrabutyl ammonium bromide (TBAB) as a cation inhibitor and dibutylphthalate (DBP), dioctylphthalate (DOP), dibutyl (butyl) phosphonate (DBBP) and 1-chloronaphthalene (CN) as plasticizing solvent mediators were prepared and used as nitrate ion-selective electrodes. Optimum performance was observed with the membrane having I-PVC-TBAB-DBP in the ratio 1:33:1:65 (w/w). The electrode has a linear response to nitrate with a detection limit of 3.9 × 10⁻⁵ ± 0.07 M and Nernstian compliance (57.0 ± 0.2 mV/decade) between pH 2.8 and 9.6 with a fast response time of about 20 s. The selectivity coefficient values of the order of 0.001 for mono-; bi- and trivalent anions; indicate high selectivity for nitrate ions over these anions. The preparation procedure of the electrode is very easy and inexpensive. The electrodes were used over a period of 45 days with good reproducibility. The analytical usefulness of the proposed electrode has been evaluated by its application in the determination of nitrate ions in waste water samples.     

A Liquid-State Tetrafluoroborate Ion-Selective Electrode Based on Brilliant Green Tetrafluoroborate

Abstract

A liquid-state ion-selective electrode which is sensitive to tetrafluoroborate ion, and which is based on Brilliant green tetrafluoroborate, has been developed. A chlorobenzene solution of the basic dye salt is absorbed into natural rubber sheeting which acts as the membrane in the electrode. At concentrations of tetrafluoroborate ion between 10^?4 and 10^?1 M a near Nernstian slope of 58.5 mV per decade change of concentration was obtained at 25°C; the potential response became steady within 1 minute at each concentration. Selectivity constants are given for a range of anions of which only perchlorate interferes markedly (K_{BF 4}-_{/ClO 4}- = 1.0 to 1.6).     

Potentiometric and voltammetric responses of carbon fibre electrodes

The potentiometric response of several carbon fibres to hydrogen ion concentration (ph) was investigated. The effects of electrochemical pretreatment and the presence of complexes in the sample solution were studied. In solutions free of complexing anions, the response of pristine fibres ranged from 42.0 to 58.0 mV ph^?1, with a mean of 48.5 mV ph^?1. After electrochemical pretreatment, a mean slope of 52.0 ± 2.0 mV ph^?1 was obtained. In the presence of EDTA, Tris, citrate, oxalate and tartrate, slopes of 59.0 mV ph^? were obtained with pretreated fibres compared with zero slopes or highly curved plots obtained in the absence of pretreatment. The differential pulse voltammetry of iron (III) in a peroxide-containing electrolyte and of molybdate in nitrate- and chlorate-containing electrolytes was examined. At a conventionally sized glassy carbon electrode, the effect on the peak current of increasing the concentration of these ions was broadly in line with depolarizer/electrolyte systems in which catalytic currents occur. At carbon fibre electrodes, these catalytic currents were either absent (for molybdenum/nitrate and iron (III)/peroxide) or severely diminished (for molybdenum/chlorate).     

A bromide selective polymeric membrane electrode based on Zn(II) macrocyclic complex

A novel bromide ion-selective PVC membrane sensor based on 2,3,10,11-tetraphenyl-1,4,9,12-tetraazacyclohexadeca-1,3,9,11-tetraene zinc(II)complex (I) as carrier has been developed. The electrode exhibited wide working concentration range 2.2 × 10⁻⁶ to 1.0 × 10⁻¹ M and a limit of detection as 1.4 × 10⁻⁶ M with a Nernstian slope of 59.2 ± 0.5 mV per decade. The response time of electrode was 20 s over entire concentration range. The electrode possesses the advantages of low resistance, fast response and good selectivities for bromide over a variety of other anions and could be used in a pH range of 3.5–9.5. It was successfully used as an indicator electrode in the potentiometric titration of bromide ions with silver ion and also in the determination of bromide in real samples.     

Electro-adsorption of polyethyleneimine on the anion exchange membrane: Application to the nitrate removal from loaded solutions

Anion exchange membrane has been modified by fixation of polyethyleneimine. The modification has been carried out aiming to achieve a separation of anions according to their hydration radii and their sizes. The performances of the modified membranes were compared with the unmodified one by applying Donnan dialysis of nitrate ion using Cl⁻ in the strip compartment. The transfer of nitrate ions in the presence of chloride was enhanced by using immersion modified membrane. The presence of a thin layer of PEI on the strip side of the membrane improves Cl⁻ transference, by creating a chemical potential difference which increases the transfer.     

A quinoline based bis-urea receptor for anions: a selective receptor for hydrogen sulfate

A dipodal bis-urea receptor has been synthesized from the reaction of 8-amino quinoline and 1,4-phenylene diisocyanate in dichloromethane, and the anion binding ability of the receptor has been studied using fluoride, chloride, bromide, iodide, perchlorate, nitrate, dihydrogen phosphate and hydrogen sulfate by UV-Vis titrations in DMSO. The results show that the receptor binds each of the anions with a 1:1 stoichiometry, showing high affinity and moderate selectivity for hydrogen sulfate among the anions studied. Ab initio calculations based on density functional theory (DFT) suggest that an anion (X(-)) is bonded within the cleft formed by the two arms of the receptor through two NH...X(-) and two aromatic CH...X(-) interactions. The results from solution and theoretical studies suggest that binding is predominantly influenced by hydrogen bonding interactions and the basicity of anions.