Ionophores In Ion-selective Electrodes Research Articles

Silver(I)-selective electrodes based on rare earth element double-decker porphyrins

Various double-decker porphyrins accommodating rare earth elements (Sm, Tb, Y) were investigated as ionophores in potentiometric ion sensors. The studied ion-selective electrodes based on double-decker porphyrins were primarily selective to Ag+ ions. The experimentally derived selectivity coefficients were compared to theoretical predictions based on density functional theory (DFT) calculations of the metal-binding energies (ΔE) of double-decker porphyrin-metal ion complexes. Although DFT calculations were performed in vacuo, without taking into account ion-solvent and ion-membrane interactions, this computational approach showed relatively good correlation with the experimentally observed selectivity patterns of the ion-selective electrodes. Thus, DFT calculations were found to be a useful predictive tool when designing new ionophores for ion-selective electrodes.

New bis(azobenzocrown)s with dodecylmethylmalonyl linkers as ionophores for sodium selective potentiometric sensors.

Novel biscrowns 1 and 2 were synthesized from 13-membered azobenzocrown ethers containing bromoalkylenoxy chains in para position relative to the azo group. The synthesized diester molecules are dodecylmethylmalonic acid derivatives differing by the linker length. The synthesized compounds have the potential of being used as sodium ionophores in ion-selective electrodes. They were characterized and used as ionophores in classic and miniature, solid contact (screen-printed and glassy carbon) membrane ion-selective electrodes. Compound 3, a similar monoester derivative of 13-membered azobenzocrown, was synthesized and used in membrane electrodes for comparison. Lipophilicity of new ionophores was determined by TLC. Lipophilicity of bis(azobenzocrown)s was found to be within the range of logPTLC = 12–13. It was observed that the particularly important selectivity coefficients logK Na,K determined for new electrodes, being logK Na,K = −2.5 and −2.6 (SSM, 0.1 M), are better than those of the electrodes featuring seven out of the nine commercially available sodium ionophores. It was concluded that the ionophore 1 creates, in acetone, with sodium iodide, complex of 1:1 stoichiometry (sandwich complex) with stability constant (logK) ca. 3.0.

To the memory of Hugo Schiff: Applications of Schiff bases in potentiometric sensors

The review summarizes the potentiometric methods of analysis based on Schiff bases as ionophores for ion-selective electrodes. The review covers the literature published since 1980.

Lead(II) and copper(II) ion-selective electrodes based on two heterocyclic compounds

In this paper, two nitrogen, sulphur or oxygen containing heterocyclic compounds were used as ionophores in ion-selective electrodes. In these two ion-selective electrodes, 2,6-di(5-methyl-1,3,4-oxadiazol-5-yl)pyridine (DMOP) gives the best Pb2+ sensitivity and 2,5-di(2′-methylpyridinethio)thiadiazole (DPTD) gives the best sensitivity for Cu2+. These electrodes are composed of KTpClPB as anion excluder and DOS as plasticizer. The two membrane electrodes show Nernstian or near-Nernstian response towards Pb2+ or Cu2+ (29.3 and 27.3 mV/decade, respectively) over the concentration range 10−5∼10−2 and 10−6∼10−3 M, respectively. The response time was less than 20 sec and a good reproducibility over a period of 2 months was observed. The electrodes exhibited good selectivities over a number of alkali, alkaline earth and transition metal ions. The proposed electrodes have also been used for the direct determination of Pb2+ and Cu2+ ions in real samples.

Synthesis and properties of calix[4]arene telluropodant ethers as Ag+ selective sensors and Ag+, Hg2+ extractants.

Three novel phenyltelluroalkoxyl functionalized tweezer-like calix[4]arenes 6–8 and two monophenyltelluropropoxyl functionalized calix[4]arenes 10 (cone conformer) and 12 (partial cone conformer) were synthesized and characterized. They are good Ag+-selective ionophores in ion-selective electrodes evaluated by electromotive force measurements of polymer membrane electrodes. The tweezer-like ionophores 6–8 showed excellent extraction ability towards Ag+ and Hg2+.

Triethylene Glycol Ether End-grafted Carbosilane Dendrimer: A Potential Ionophore for Potassium Ion Recognition

The performance of a newly synthesized carbosilane dendrimer bearing four triethylene glycol ether (TEG) units, Si(CH2CH2CH2Si(Me)2CH2CH2CH2(OCH2CH2)3Me)4 (1), as ionophores in ion-selective electrodes has been investigated. Optimization of the plasticized polyvinyl chloride membrane composition has produced electrodes that exhibit a Nernstian response for potassium ions. The best general characteristics exhibited by the electrodes were found when the membrane composition ratio of DPE:1:NaTPB:PVC 60:3:2:35 (wt%) was used. The response of the electrode was linear with a Nernstian slope of 58.3 mV/decade over the K+ ion concentration range of 1.9x10(-7) to 1.0x10(-1) M with a detection limit of 3.1x10(-7) M. The response time to achieve a 95% steady potential for the K+ concentration ranging from 1.0x10(-1) to 1.0x10(-8) M was less than 10 s, and it was found that the electrode is suitable for use within a pH range of 5.5-8.5. The selectivity coefficients (log KPotK+,Mn+)), which were determined by the fixed interference method, showed good selectivity for K+ against most of the interfering cations. The influence of this selective ion-binding behavior using electrospray ionization time-of-flight (ESI-TOF) mass spectrometric studies is discussed.

Potentiometric Determination of Silver(I) by Selective Membrane Electrode Based on Derivative of Porphyrin

The performance of silver metal complexes with meso-tetraphenylporphyrin ([H2T(4-CH3)]PP) as ionophores for ion-selective electrodes was studied. The electrode exhibited linear response with Nernstian slope of 59.2 +/- 1.0 mV per decade within the concentration range of 1.0 x 10(-7)-1.0 x 10(-1) M silver ions. The limit of detection as determined from the intersection of the extrapolated linear segments of the calibration plot, was 1.0 x 10(-7) M. The response time of the electrode was < 10 s over the entire concentration range. The silver-selective electrode exhibited good selectivity for Ag(I) with respect to alkali, alkaline earth and heavy metal ions. The electrodes could be used at least three months without a considerable divergence in their potential. The electrodes are suitable for use in aqueous solutions in a wide pH range of 3.0-9.0. They were used as indicator electrodes in titration of Ag(I) with sodium iodide solution and were successfully applied to direct determination of silver in real samples.

P-(3-Carboxy- and 3-carboxymethyl-1-adamantyl)calix[4]arenes: synthesis and arming with amino acid units

Adamantylcalix[4]arenes carboxylated at the upper rim have been synthesized by a convenient one-step procedure from p-H-calix[4]arene and carboxylated 1-adamantanols. Selective and exhaustive lower rim alkylation along with upper rim modification by amino acid fragments have been carried out. Preliminary evaluation of the novel N-linked peptidocalixarenes as ionophores for ion-selective electrodes is reported.

Highly selective ion-sensitive electrodes based on dibenzo-crown ethers containing functional groups for the determination of potassium in biological fluids

The electrochemical properties of membranes based on dibenzo-crown ethers bearing hydroxyl and chloromethyl groups in polyether rings were studied. These substances were tested as membrane ionophores for ion-selective electrodes (ISEs) reversible to potassium ion. The developed ISEs were used for determining potassium in blood plasma samples. The generalized results of determining potassium in the blood of different patients with cardiovascular diseases revealed quantitative regularities that allowed the diseases to be diagnosed early.

Polymeric Membrane Ion-Selective Electrodes Based on Molecular Asterisk Ionophores

Ion-selective electrodes (ISEs) have been developed that incorporate a novel supramolecular class of ionophores called molecular asterisks. These ionophores are constructed with “arms” of repeating phenylene sulfide units that radiate outward from a core of either benzene or coronene. The flexibility of the arms, as well as the open exterior geometry and multiple soft Lewis base functionalities make these molecules potential candidates as ionophores for ISEs particularly for soft Lewis acids like transition metals. Studies with molecular asterisk-based ISEs show that these ionophores display a high selectivity relative to ion-exchanging ionophores toward Ag+ over a number of other cations. According to theoretical prediction, these ISEs demonstrate a super-Nernstian region of response toward silver from 10−6 to 10−5 M with a Nernstian response above 10−5 M, when primary ion is absent from the internal filling solution. Additionally, it was determined that both the nature of the core entity and the length (or generation) of the arms play a role in governing selectivity of these ionophores.

The first synthesis of a calix[4](diseleno)crown ether as a sensor for ion-selective electrodes

Two calix[4](diseleno)crown ethers 3 and 4 were synthesized by reaction of the disodium salt of 1,3-propanediselanol with the preorganized 1,3-dibromoethoxylcalix[4]arenes 1 and 2 . Compound 3 forms an interesting infinite sheet aggregate via self-inclusion and intermolecular Se⋯Se interactions in the solid state. Preliminary evaluation of 3 and 4 as ionophores for ion-selective electrodes (ISEs) is reported.

Application of Thiouronium Derivatives as Anion Ionophores for Ion Selective Electrodes

Abstract Novel anion ionophores based on thiouronium derivatives were synthesized, and their application to ion selective electrodes (ISEs) was examined. The electrodes clearly exhibited an anti-Hofmeister selectivity pattern with enhanced selectivity for the iodide anion.

Improved silver ion-selective electrodes using novel 1,3-bis(2-benzothiazolyl)thioalkoxy- p-tert-butylcalix[4]arenes

1,3-Bis(2-benzothiazolyl)thioalkoxycalix[4]arenes 1 and 2 have been synthesized and found to adopt a cone conformation. Compounds 1 and 4 were characterized by X-ray analysis. Preliminary evaluation of 1 and 2 as ionophores for ion-selective electrodes is reported.

New Cyclodextrin-Based Ion-Selective Electrodes for Determining Activity Coefficients of Biologically Important Onium Ions

Ion-selective electrodes (ISEs), apart from fluoride, calcium, and a few others, have not often been used to obtain thermodynamic information on electrolytes. Here, novel cyclodextrin-based ISEs are used to determine activity coefficients of some onium chlorides in aqueous solution. Cyclodextrins, rendered lipophilic by alkylation, have been incorporated into polymeric membranes and used as ionophores in ISEs for sensing the substituted ammonium (onium) ions, choline, acetylcholine, and acetyl-β-methylcholine. Potentiometric measurements using these cyclodextrin-based ISEs allow the determination of ratios of activity coefficients in solutions. Choosing one solution as reference and using a theoretical model (e.g., Pitzer equations), it is possible to evaluate activity coefficients of individual solutions. Results for choline chloride compare well with limited data in the literature. This is the first time, that ISEs have been used to measure activity coefficients of biologically important ions.

Structural aspects of host molecules acting as ionophores in ion-selective electrodes

Structural aspects of ligand molecules acting as neutral ionophores in ion-selective membrane electrodes are discussed and examples of Li-selective ionophores are presented. The relationship between the structure of ionophore and its complex determined by X-ray and NMR study and the selectivity of ISE was determined.

Selectivity enhancement on a poly(butadiene-maleic acid)-coated cation phase induced by ethylene oxide-based complexing agents

Crown ethers as well as acyclic compounds bearing ethylene oxide units are well-known as complexing agents for different cations. They are mainly used as ionophores in ion selective electrodes. In ion chromatography some studies have been preformed using crown ether stationary phases. Using crown ethers as eluent components for the separation of alkali and alkaline earth metal cations on a poly(butadiene-maleic acid)-coated phase, it is possible to tune the selectivity to the special needs of the sample. An eluent with addition of 18-crown-6 elutes potassium after magnesium and calcium with an improved separation of sodium and ammonium compared to the same eluent without addition of 18-crown-6. In contrast, the addition of a polyethylene glycol improves the sodium ammonium separation without changing the elution order.

Naphtho-crown ethers as ionophores in ion-selective electrodes

Poly (vinyl chloride) membrane electrodes based on three naphtho-crown ethers (naphtho-15-crown-5, naphtho-18-crown-6 and dinaphtho-30-crown-10) are characterized. These ionophores may provide inexpensive alternatives to valinomycin for potassium-selective electrodes. All three crowns give near-Nernstian responses to potassium under appropriate conditions and excellent selectivity for potassium over sodium can be obtained. With naphtho-18-crown-6, an improved response to cesium is observed as the ionophore concentration in the membrane is increased. The characteristics of each electrode are dependent on the concentration of crown and the choice of plasticizer.

Comparative evaluation of neutral, and proton-ionizable crown ether compounds as lithium ionophores in ion-selective electrodes and in solvent extraction

Comparative evaluation of neutral, and proton-ionizable crown ether compounds as lithium ionophores in ion-selective electrodes and in solvent extraction

Sulfonamides as ionophores for ion-selective electrodes. II. Macrocyclic ligands containing two sulfonamide groups as ionophores

Ten macrocyclic compounds (1–10), each containing two sulfonamide groups have been incorporated into PVC membrane electrodes as ionophores. Their selectivity towards alkali and alkaline earth metal cations has been studied and compared to selectivities found in cation transport experiments.

Design features of ionophores for ion selective electrodes

Abstract