Recent advances in nanoelectrochemistry at the interface between two immiscible electrolyte solutions

The nanoscale interface between two immiscible electrolyte solutions (nanoITIES) is an emerging versatile analytical platform. Analytical advantages of chemical analysis using the nanoITIES include imaging with nanometer spatial resolution, probing fast dynamics with millisecond temporal resolution and fast response times, selectively detecting analytes, probing fundamental chemical processes (e.g., diffusion profiles), and versatile sensing of metal ions, proteins, neurotransmitters, ionic and neutral species, redox-active and non-redox active analytes, etc. We present here a brief theoretical background of the nanoITIES and experimental advances from the past five years. These advances include imaging of nanopores, probing diffusion profiles, biosensing, a new pH modulation mechanism for sensing neutral species, and studying exocytosis from Aplysia californica neurons.     

Electrolysis at the interface of two immiscible electrolyte solutions: Determination of ionophores

The principles of electrolysis and facilitated ion transfer at the interface of two immiscible electrolyte solutions are outlined. The method of determination of ionophores is exemplified by assay of monensin in cultures ofStreptomyces cinnamonensis.Dedicated to Professor W. Simon on the occasion of his 60th birthday     

Electrolysis at the interface between two immiscible electrolyte solutions by means of a hanging electrolyte drop electrode

A three-electrode system with a hanging electrolyte drop electrode is described. The system facilitates analytical exploitation of electrolysis at the interface between two immiscible electrolyte solutions. Its use is demonstrated for the determination of micromolar concentrations of tetraethylammonium cation by differential pulse stripping voltammetry, based on transfer of the cation from water to nitrobenzene.     

Determination of a polyhexamethylene guanidine by voltammetry at an interface between two immiscible electrolyte solutions

A possibility of the determination of polyhexamethylene guanidine (PHMG) by voltammetry at an interface between two immiscible electrolyte solutions water–o-nitrophenyl ether is shown. An electrochemical sensor based on a microperforated polymer film is created to implement the method. Factors affecting the formation of the analytical signal were studied, working conditions of voltammetric measurements were selected on their basis. The developed method was applied to the determination of PHMG in antiseptics.     

Size-selective voltammetry: modification of the interface between two immiscible electrolyte solutions by zeolite Y

Size- and charge-selective ion transfer across the zeolite-Y-modified interface between two immiscible electrolyte solutions (ZM-ITIES) is described. The zeolite-Y membrane is prepared from pressed disks by healing with tetraethyl orthosilicate (TEOS). Size- and charge-selective transfer of the tetraethylammonium cation, size-selective exclusion of tetrabutylammonium cation, and charge-selective exclusion of the tetrafluoroborate and perchlorate anions are demonstrated at the ZM-ITIES. The exclusion studies suggest that the membrane is coherent and contains a low density of pinholes, after healing with TEOS. Various factors affecting the ion transfer such as analyte concentration, supporting electrolyte concentration, and scan rate are investigated. The diffusion coefficient of tetraethylammonium ions within the zeolite-Y pores is found to be on the order of 10(-8) cm2 s(-1).     

Theory of electrochemistry at miniaturised interfaces between two immiscible electrolyte solutions

1. Download : Download high-res image (127KB)
2. Download : Download full-size image

     

Ion amperometry at the interface between two immiscible electrolyte solutions in view of realizing the amperometric ion-selective electrode

This article reviews the development in ion amperometry at the interface between two immiscible electrolyte solutions (ITIES) in view of realizing the amperometric ion-selective electrode (ISE). The concept of polarizability of ITIES in a multi-ion system is outlined. Principle aspects of ion amperometry at ITIES are discussed including the use of amperometry as a tool for the clarification of the ion sensing mechanism, and for determining the concentrations of ions in the solution. The reference is made to recent amperometric measurements at the supported liquid membrane (SLM) and polymer composite liquid membranes (PCLM), which, together with the micro-hole supported ITIES, appear to be particularly suitable for realization of the amperometric ISE.     

Ions at the water-oil interface: interfacial tension of electrolyte solutions

A theory, based on a modified Poisson-Boltzmann equation, is presented that allows us to calculate the excess interfacial tension of an electrolyte-oil interface accurately. The chaotropic (structure-breaking) ions are found to adsorb to the water-oil interface as the result of large polarizability, weak hydration, and hydrophobic and dispersion interactions. However, kosmotropic (structure-making) anions as well as potassium and sodium ions are found to be repelled from the interface. The adsorption of I(-) and ClO(4)(-) is found to be so strong as to lower the interfacial tension of the water-oil interface, in agreement with the experimental data. The agreement between the calculated interfacial tensions and the available experimental data is very good. The theory is used to predict the interfacial tensions of six other potassium salts, for which no experimental data is available at the moment.     

Thermodynamic analysis of the cation binding to a phosphatidylcholine monolayer at a polarised interface between two immiscible electrolyte solutions

Thermodynamic analysis of the polarised interface between two immiscible electrolyte solutions (ITIES) was outlined, which accounts for the adsorption of phosphatidylcholine (PC) both as a zwitterion and a cation formed by the aqueous cation association with the zwitterionic PC form, as well as for the aqueous cation transfer facilitated by PC leading to its depletion from the interface. Electrocapillary equation was derived clarifying the physical significance of the surface charge density; the differential capacity and the PC surface excess concentration. The potential dependence of the interfacial tension calculated using the Damaskin’s adsorption model of a compound adsorbed in two different forms was found to agree well with that measured for the polarised water|1,2-dichloroethane interface in the presence of dl-α-dipalmitoylphosphatidylcholine. Experimentally observed effect of the nature of the aqueous cation on the interfacial tension was ascribed to the difference in the PC association constant.     

311 - A new model of membrane transport: electrolysis at the interface of two immiscible electrolyte solutions

A simple membrane model is the interface between water and an organic liquid immiscible with water, with a strongly hydrophilic electrolyte dissolved in the aqueous phase and a strongly hydrophobic electrolyte in the organic phase. This interface can be electrochemically polarized in the same way as the interface electrode |electrolyte solution using various modes of voltammetry or the galvanostatic method. A four-electrode potentiostatic system is required for such studies. An electrolyte dropping electrode, analogous to Heyrovsky's DME, was also constructed. The voltammograms fully resemble those obtained with metallic electrodes.The faradaic proceses studied so far are mainly connected with the transfer of hydrophobic ions across the interface. These processes are quite rapid and the half-wave potential of a particular ion is related to its standard Gibbs transfer energy. Observed electron-transfer effects model redox processes at membranes.Macrocyclic ionophores facilitate transfer of alkali metal ions across this interface. Very fast ion transfer as well as complex formation was observed in the systems under investigation so that, generally, the diffusion of the ionophore toward the interface and of the complex into the organic phase is the rate-controlling step, no surface reaction retarding the overall process.Apart from the investigation of membrane processes, this approach can be used for elucidation of processes in ion-selective electrodes and in phase-transfer catalysis.     

Ion transfer kinetics at the interface between two immiscible electrolyte solutions supported on a thick-wall micro-capillary. A mini review

Synopsis: This mini review presents recent advances and our comments on the research subject of graphene-conducting polymer nanocomposite-based supercapacitors. We emphasize material design, controlled assembly and nanoscale engineering of relevant composites, and their applications in flexible and bendable supercapacitors.

1. Download : Download high-res image (165KB)
2. Download : Download full-size image

     

Determination of interfacial tension between two immiscible polymers with and without surfactants at the interface

A second-order drop deformation method for inferring interfacial tension between two immiscible polymers is proposed and shown to improve the accuracy of tension estimate appreciably. A small step-strain method, which uses a strong flow (capillary number >1) and short flow time approximately O(0.1s), is successfully developed to avoid complications caused by the surfactants for surfactant-laden drops. This method is demonstrated to give good tension estimates for a range of viscosity ratios and surface coverage.     

The double layer and ion adsorption at the interface between two non miscible solutions: Part I. Interfacial tension measurements for the water-nitrobenzene tetraalkylammonium bromide systems

The classical treatment of the double layer has been extended to the interface between two immiscible solutions. The model presented is composed of an inner compact layer, characterized by a dipolar potential drop, between two diffuse type layers. The systems studied are composed of C₂ to C₅ quaternary ammonium bromides at partition equilibrium between water and nitrobenzene for which the inner potential difference, for a given electrolyte, is independent, at least in the lower concentration range, of the concentration. Drop weight interfacial measurements and the use of the Gouy-Chapman approach show that the tetraethyl-, tetrapropyl- and tetrabutylammonium ions are not adsorbed within the inner compact layer, and the dipolar potential drop of this layer can then be determined. Tetrapentylammonium ions on the contrary are specifically adsorbed but the amount of adsorbed ions within the compact inner layer cannot be evaluated because of the impossibility, in this case, of determining the dipolar potential drop.     

Investigation of ion transfer across the membrane-stabilized interface of two immiscible electrolyte solutions: Part I

Anion transfer across the water/nitrobenzene interface has been investigated with the two electrolyte solutions separated by a hydrophilic cellulose membrane. The transfer was found to be reversible at low sweep rates. The apparent diffusion coefficient was about 10⁻⁶ cm² s⁻¹ for ClO⁻₄ within the membrane.     

Electrolysis at the interaface of two immiscible electrolyte solutions and extraction kinetics

The problem of the interfacial step of salt extraction has been solved using the ideas of the kinetics of individual ion transfer across the interface of two immiscible electrolyte solutions (ITIES). A new concept, the extraction potential has been introduced. The values of extraction rate constants for several tetraalkylammonium picrates have been presented.     

Potentiometric investigation of the effect of the pH on the ionic transfer of some amino acids at the interface between two immiscible electrolyte solutions

The effect of the pH on the ionic transfer of glycine and beta-alanine at the interface between two immiscible electrolyte solutions (ITIES) was investigated by a simple potentiometric method. Upon addition of small amounts of solution containing the investigated amino acids, a variation of the potential drop across the interface was recorded, which was found to be pH-dependent. This behavior was explained in terms of a preferential orientation of the amino acid molecules at the ITIES, induced by the different lipoficility of the functional groups. The results enabled the measurement of this voltage variation to be used as the basis for a simple and rapid method for determining the isoelectric point of the investigated compounds. The agreement between the pH(i) values thus estimated and those reported in the literature suggests the possibility of using the method for the interpretation of processes occurring at the level of biological membranes.