Solid-contact pH-selective electrode using multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNT) are shown to be efficient transducers of the ionic-to-electronic current. This enables the development of a new solid-contact pH-selective electrode that is based on the deposition of a 35-μm thick layer of MWCNT between the acrylic ion-selective membrane and the glassy carbon rod used as the electrical conductor. The ion-selective membrane was prepared by incorporating tridodecylamine as the ionophore, potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate as the lipophilic additive in a polymerized methylmethacrylate and an n-butyl acrylate matrix. The potentiometric response shows Nernstian behaviour and a linear dynamic range between 2.89 and 9.90 pH values. The response time for this electrode was less than 10 s throughout the whole working range. The electrode shows a high selectivity towards interfering ions. Electrochemical impedance spectroscopy and chronopotentiometry techniques were used to characterise the electrochemical behaviour and the stability of the carbon-nanotube-based ion-selective electrodes.     

A simple approach for fabricating solid-contact ion-selective electrodes using nanomaterials as transducers

A simple and robust approach for the development of solid-state ion-selective electrodes (ISEs) using nanomaterials as solid contacts is described. The electrodes are fabricated by using the mixture of an ionic liquid (IL) and a nanomaterial as intermediate layer, formed by melting the IL. Tetradodecylammonium tetrakis(4-chlorophenyl)borate (ETH 500) is chosen as an model of IL to provide strong adhesion between the inner glassy carbon electrode and the intermediate layer. Nanomaterials including single-walled carbon nanotubes (SWCNTs) and graphene were used as active ion-to-electron transducers between the glassy carbon electrode and the ionophore-doped ISE membrane. By using the proposed approach, the solid-contact Cu²⁺- and Pb²⁺-selective electrodes based on ETH 500/SWCNTs and ETH 500/graphene as transducers, respectively, have been fabricated. The proposed electrodes show detection limits in the nanomolar range and exhibit a good response time and excellent stability.     

Investigation of methods of enzyme immobilization on a coated-wire electrode for the development of micro-biosensors

Tridodecylamine- and carboxyl-substituted poly(vinyl chloride)-based hydrogen ion-selective coated-wire electrodes are investigated as transducers for micro-biosensors. Various methods for immobilization of enzyme on the electrode were evaluated by using penicillinase as a model enzyme. The best method was immobilization with glutaraldehyde on the electrode previously modified with bovine serum albumin in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide to increase the amount of immobilized enzyme. A stable, large potential change is obtainable even in salt-containing samples with this sensor. The possibility of the practical use of such a micro-biosensor is suggested.     

Solid-contact Cu(II) ion-selective electrode based on 1,2-di-(<Emphasis Type="Italic">o</Emphasis>-salicylaldiminophenylthio)ethane

The development of Cu(II) solid-contact ion-selective electrodes, based on 1,2-di-(o-salicylaldiminophenylthio)ethane as a neutral carrier, is presented. For the electrodes construction, unmodified carbon ink (type 1 electrode) and polymer membrane-modified carbon ink (type 2 electrode) were used as solid support and transducer layer. Also, carbon ink composite polymer membrane electrode (type 3 electrode) was prepared. The analytical performance of the electrodes was evaluated with potentiometry, while bulk and interfacial electrode features were provided with electrochemical impedance spectroscopy. It is shown that modification of carbon ink with polymer membrane cocktail decreases the bulk contact resistance of the transducer layer and polymer membrane, thus enhancing the analytical performance of the electrode in terms of sensitivity, linear range, and stability of potential. The optimized electrodes of types 2 and 3 exhibit a wide linear range with detection limits of 1.8 × 10⁻⁶ and 1.6 × 10⁻⁶ M, respectively. They are suitable for determination of Cu²⁺ in analytical measurements by direct potentiometry and in potentiometric titrations, within pH between 2.3 and 6.5. The electrodes are selective for Cu²⁺ over a large number of tested transition and heavy metal ions.     

Synthesis and Ionophoric Properties of α,ω-Diphosphorylated Aza Podands: II. Kabachnik-Fields Reaction as a Method for Design of α,ω-Diphosphorylated Aza Podands and Their Use for Determination of Metal Ions

Methods of the design of podands with α-aminomethylphosphine oxide terminal groups with the purpose of investigation of the ionophoric properties of the podands and their use as components of ion-selective electrodes are analyzed. The most convenient procedure is a one-pot synthesis based on the Kabachnik-Fields reaction in a system comprising a dialkyl(aryl)phosphinous acid, formaldehyde, and a diamine. An alternative procedure is two-stage and involves the reaction of a primary amine with a phosphinous acid and formaldehyde to form an α-aminomethyldialkyl(aryl)phosphine oxide in the first stage and cross-linking of two molecules of this compound via reaction with a dihalooligoether of the corresponding length in the second. Advantages and disadvantages of both procedures are considered. Electrode-active properties of the prepared aza podands are studied to show that ion-selective electrodes on their basis can be used for selective determination of low concentrations of alkali and alkaline-earth metal ions.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 2, 2005, pp. 244–252.Original Russian Text Copyright © 2005 by Garifzyanov, Vasil’ev, Cherkasov.For communication I, see [1].     

Ion-selective sensors for determining Au(CN)<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> with membranes based on the ionic liquid tetradecylphosphonium dicyanoaurate

A polymeric membrane for an ion-selective electrode is proposed on the basis of supramolecular systems including a polymeric compound (polyvinyl chloride, PVC) and an ionophore (ionic liquid tetradecylphosphonium dicyanoaurate) in which ionic liquid is simultaneously used as a PVC plasticizer. The selectivity, linear response range, and potential stability of ion-selective electrodes with the optimum membrane composition are measured. The detection limit for Au(I) with the developed electrode is 4.5 × 10^?7 M.     

Potentiometric determination of cetylpyridinium chloride using a new type of screen-printed ion selective electrodes

A new type of screen-printed ion-selective electrode for the determination of cetylpyridinium chloride (CPC) is presented. These new electrodes involve in situ, modified and unmodified screen-printed ion-selective electrodes for the determination of CPC. The screen-printed electrodes (SPEs) show a stable, near-Nernstian response for 1 × 10⁻² to 1 × 10⁻⁶ M CPC at 25 °C over the pH range 2-8 with cationic slope 60.66 ± 1.10. The lower detection limit is found to be 8 × 10⁻⁷ M and response time of about 3 s and exhibit adequate shelf-life (6 months). The fabricated electrodes can be also successfully used in the potentiometric titration of CPC with sodium tetraphenylborate (NaTPB). The analytical performances of the SPEs are compared with those for carbon paste electrode (CPE) and polyvinyl chloride (PVC) electrodes. The method is applied for pharmaceutical preparations with a percentage recovery of 99.60% and R.S.D. = 0.53. The frequently used CPC of analytical and technical grade as well as different water samples has been successfully titrated and the results obtained agreed with those obtained with commercial electrode and standard two-phase titration method. The sensitivity of the proposed method is comparable with the official method and ability of field measurements.     

Hydrophobic ionic liquids in plasticized membranes of ion-selective eletctrodes

Ionic liquids with substituted imidazole, pyridine, and pyrrolidine cations and hydrophobic anions are studied as ionophores of PVC membranes of ion-selective electrodes plasticized with 2-nitrophenyloctyl ether. These membranes show a response to hydrophobic organic cations. In solutions of cationic surfactants, the slope of the electrode function is close to the theoretical one and the limit of detection does not exceed n × 10⁻⁶ M. Ion-selective electrodes for anions are developed using a trioctylmethylammonium salicylate ionic liquid. The electrode on its basis shows a stable potentiometric response to the salicylate anion in a wide range of concentrations and is characterized by good selectivity in the presence of foreign anions.     

A liquid-state copper(II) ion-selective electrode containing a complex of Cu(II) with salicylaniline

A new liquid-state ion-selective electrode based on a complex of Cu(II) with salicylaniline is described. The electrode shows linear dependence of potential on the activity of Cu(2+) in the range from 5 x 10(-6) to 0.1M, with a slope of 28.3 mV/pCu at 18 degrees . The electrode shows a better selectivity relative to Ag(I) and Hg(II) than other copper(II) ion-selective electrodes. The possibilities for using the electrode for determination of copper in the presence of interfering cations are described.     

Multi-flow-through sensor for simultaneous cation determination

The activity of several metal ions can be detected potentiometrically using glass electrode measuring chains, which have normally a cylindrical design. To analyse different cations simultaneously, on one hand several single indicator electrodes can be integrated in a prefabricated flow-through equipment, where they can be measured versus electrochemical reference electrodes. On the other hand, by principle it is possible to construct tubular flow-through electrodes. In the present case, glass electrodes are double-walled, so that the liquid internal reference system consisting of reference solution and reference element can be placed.In the case of multi-analysis, for constructional reasons it would be necessary to combine several of such flow-through electrodes by complicated connecting elements. In this paper a multi-flow-through electrode is described, which can be fabricated in one piece by substitution of the liquid by a solid reference half cell. The contact of ion-selective glasses with semiconducting zinc oxide leads to a reversible phase interface, so that a high stability of the individual half cell potentials is achieved. Nearly all electrode properties are in a good agreement with those of traditional cation selective electrodes. The pH electrodes, for example, exhibit almost linear response in a range of pH 1–10 with a slope of 57–59 mV/pH at θ = 25 °C.     

How Far the Ion-Selectivity Should be Improved; a Task Oriented Limit of Ion-Selective Electrode Design

Abstract

A simple formula is proposed for the definition and the calculation of the highest acceptable selectivity coefficient values of ion-selective electrodes. On the basis of the formula which is based on the consideration of the precision of the direct potentiometric measuring techniques one can easily decide whether the selectivity of an electrode is sufficient or not for solving a well defined analytical task correctly. On the other, hand it indicates clearly for ion-selective electrode developing teams or manufacturers how far the ion-selectivity of an electrode should be improved for a certain type of analytical application.

Characteristic selectivity values for a few concrete analytical sample types are given in table together with the selectivity coefficients of the corresponding, existing ion-selective electrodes.     

Nitrate and ammonium ion-selective electrodes as sensors. I. In bacterial growth curves for isolation of nitrate and nitrite reductases from Escherichia coli

Ammonium and nitrate ion-selective electrodes were applied as sensors in bacterial growth curves for the isolation of nitrate and nitrite reductase. A nitrate ion-selective electrode was used as a successful new technique for the assay of nitrate reductase activity: the decrease in nitrate concentration was followed continuously. Likewise, an ammonium ion-selective electrode was used to follow the increase in ammonium ion concentration. Excellent agreement with spectrophotometric procedures ( < 5%) was obtained.     

General survey and microanalytical aspects of ion-selective electrodes

Summary A survey is presented of recent developments in the field of ion-selective electrodes. Special emphasis is placed on problems of electrode miniaturization and ISFET production. Different electrode types in present use are described and theories for the interpretation of electrode mechanisms are outlined. It is pointed out that the electrode potentials are due to the formation of a space charge. Different applications of ion-selective electrodes are dealt with and the problems connected with the determination of small concentrations are discussed. Attention is given to the selection of conditions under which a reliable measurement of extremely small amounts or extremely small concentrations can be ensured.     

Design and performance of some microflow-cell potentiometric transducers

The paper presents and compares the design of three potentiometric transducers: ion-selective field effect transistor (ISFET), solid-state Ag/AgCl electrode and miniaturized classical Ag/AgCl electrode. The reported transducers were fabricated using different, less or more complicated and expensive, technologies. The transducers were constructed to be compatible with the sensor housing of the flow-cell, designed previously. Moreover, the back-side contact structures of the two planar devices, where electrical connectors and the sensing layer are on the opposite sides, facilitated their application in the flow analysis. Exemplary potassium-selective microsensors based on developed transducers were prepared, applying plasticized PVC and polysiloxane membranes containing valinomycine. The determined microsensor performances allowed comparison of their usefulness for multiparameter flow analysis.     

Ion-selective electrodes for determination of phenylalanine based on uranyl complexes of phosphoryl-containing podands

The possibility of phenylalanine determination using membrane ion-selective electrodes based on uranyl complexes with phosphoryl-containing podands was shown. The variation of the procedure of membrane preparation (either entrapping the preliminarily synthesized uranyl-podand complex in the membrane phase or conditioning of the podand-containing membrane in the uranyl solution) was found to have practically no effect on the electrode properties. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1729–1732, October, 2000.     

A copper ion-selective electrode with high selectivity prepared by sol-gel and coated wire techniques

A sol-gel electrode and a coated wire ion-selective poly(vinyl chloride) membrane, based on thiosemicarbazone as a neutral carrier, were successfully developed for the detection of Cu (II) in aqueous solutions. The sol-gel electrode and coated electrode exhibited linear response with Nernstian slopes of 29.2 and 28.1 mV per decade respectively, within the copper ion concentration ranges 1.0×10^–5–1.0×10^–1 M and 6.0×10^–6–1.0×10^–1 M for coated and sol-gel sensors. The coated and sol-gel electrodes show detection limits of 3.0×10^–6 and 6.0×10^–6 M respectively. The electrodes exhibited good selectivities for a number of alkali, alkaline earth, transition and heavy metal ions. The proposed electrodes have response times ranging from 10–50 s to achieve a 95% steady potential for Cu²⁺ concentration. The electrodes are suitable for use in aqueous solutions over a wide pH range (4–7.5). Applications of these electrodes for the determination of copper in real samples, and as an indicator electrode for potentiometric titration of Cu²⁺ ion using EDTA, are reported. The lifetimes of the electrodes were tested over a period of six months to investigate their stability. No significant change in the performance of the sol-gel electrode was observed over this period, but after two months the coated wire copper-selective electrode exhibited a gradual decrease in the slope. The selectivity of the sol-gel electrode was found to be better than that of the coated wire copper-selective electrode. Based on these results, a novel sol-gel copper-selective electrode is proposed for the determination of copper, and applied to real sample assays.     

Electrochemical sensors for sulfur- and lead-containing gases

The possibility of using solid-electrolyte transducers with nonstoichiometric electrodes was studied, and the effect of the material and nonstoichiometry of lead monochalkogenides as measurement electrodes on the work of transducers was considered. The reliability of the results obtained was substantiated by comparing the calculated thermodynamic properties of the measurement electrodes with the corresponding reference values. The effect of nonstoichiometry was assessed from coulometric titration curves. It was noticed that the defect type affects the sensitivity of the transducer. The effect of the surface of the measurement electrode on the process of gas analysis was assessed. The applicability region for the transducers under study was indicated.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 2, 2005, pp. 193–197.Original Russian Text Copyright © 2005 by Leushina, Makhanova.Presented at the International Forum Analytics and Analysts, Voronezh, 2003.This revised version was published online in April 2005 with corrections to the author names and book review format.     

The ion adsorption effect on selectivity of liquid state, O,O'-didecylodithiophosphate chelate based ion-selective electrodes

Ion-selective electrodes with liquid membranes including O,O′-didecylo-dithiophosphate complexes of Tl(I), Pb(II), Cd(II) and Ni(II) are characterised and results of the study on their selectivity are reported. A short review of problems related to determination and interpretation of selectivity coefficients of ion-selective electrodes is presented with particular emphasis on the drawbacks of the hitherto used methods. A new method is proposed, which in the experimental part is close to that of mixed solutions recommended by IUPAC but can be applied also when the latter is of no use. The method proposed for determination of selectivity coefficients simultaneously allows concluding about the mechanism of potential generation. A few examples of relations between selectivity coefficients of the electrodes and concentrations of disturbing ions in solutions, are given. An interpretation of the above relations as results of the processes of ion adsorption at the interface of the electrode membrane and water solution is proposed. The results obtained have confirmed the hypothesis given by Pungor, according to which the main role in the mechanism of generation of ion-selective electrodes potential is played by the processes of ion chemisorption at the interface of the membrane and water solution.     

Flow-injection approach for the determination of the dynamic response characteristics of ion-selective electrodes. Part 1. Theoretical considerations

A single-line flow-injection system with a straight tube reactor is proposed for investigating the dynamic response behaviour of ion-selective electrodes. The principle of the method is based on the fact that the concentration—time curve at the electrode surface can be described theoretically in the flow-injection system under certain practically realizable conditions. The response of the ion-selective electrode to that input signal can be measured experimentally. Thus, knowing the input and the output signal of an ion-selective electrode, an appropriate model describing its dynamic behaviour can be selected among the relevant models existing in the literature. Theoretical expressions for predicting the transient response of ion-selective electrodes in the flow system when the rate-determining step is an ion-transport process through a diffusion layer or a kinetic process were elaborated.     

Effect of dissolved CO2 on the potential stability of all-solid-state ion-selective electrodes.

The influence of dissolved CO2 on the potentiometric responses of all-solid-state ion-selective electrodes (ISEs) was systematically examined with four different types of electrodes fabricated by pairing pH-sensitive and pH-insensitive metal electrodes (Pt and Ag/AgCl, respectively) with pH-sensitive and pH-insensitive ion-selective membranes (H+-selective membrane based on tridodecylamine and Na+-selective membrane based on tetraethyl calix[4]arenetetraacetate, respectively). The experimental results clearly showed that the carbonic acid formed by the diffused CO2 and water vapor at the membrane/metal electrode interface varies the phase boundary potentials both at the inner side of the H+-selective membrane (deltaE(in)mem) and at the metal electrode surface (deltaEelec). The potential changes, deltaE(in)mem and deltaEelec, occurring at the facing boundaries, are opposite in their sign and result in a canceling effect if both the membrane and metal surface are pH-sensitive. Consequently, the H+-selective membrane coated on a pH-sensitive electrode (Pt) tends to exhibit a smaller CO2 interference than that on a pH-insensitive electrode (Ag/AgCl). When the all-solid-state Na+ and K+ ISEs were fabricated with both pH-insensitive metal electrode and ion-selective membrane, they did not suffer from CO2 interference. It was also confirmed that plasticization of the PVC leads to increased CO2 permeation. Various types of intermediate layers were examined to reduce the CO2 interference problem in the fabrication of H+-selective all-solid-state ISEs. The results indicated that the H+-selective electrode needs an intermediate layer that maintains a constant pH unless the carbonic acid formation at the interfacial area is effectively quenched.