Evaluation of Gibbs free energy for the transfer of a highly hydrophilic ion from an acidic aqueous solution to an organic solution based on ion pair extraction

A method to determine the standard Gibbs free energy for the transfer, ΔG°_tr, of a highly hydrophilic metal ion from an aqueous solution, W, in the presence of high concentration of H⁺ to an organic solution, O, was proposed based on the theoretical consideration of the distribution process of ions between W and O. The usefulness of the proposed method was verified experimentally by comparing ΔG°_tr of Mg²⁺ determined by the method with that obtained by voltammetry for the ion transfer at the W|O interface. The O examined were nitrobenzene (NB) and 1,2-dichloroethane (DCE). By applying the proposed method, ΔG°_tr of NpO₂⁺, UO₂²⁺, NpO₂²⁺ and PuO₂²⁺ from an acidic W to NB were determined.     

Electrolysis at the Interface between Two Immiscible Electrolyte Solutions: Determination of Acetylcholine by Differential Pulse Stripping Voltammetry

Abstract

A three-electrode system with the hanging electrolyte drop electrode (HEDE) was developed for the analytical exploitation of electrolysis at the interface between two immiscible electrolyte solutions (ITIES). The use of the differential pulse stripping voltammetry (DPSV) for the quantitative determination of the species which participates in a charge transfer reaction at ITIES was demonstrated with acetylcholine cation transfer across the water/nitrobenzene interface. Trace concentration of acetylcholine in water in the part per million level (ppm) can be determined. It was concluded that the electrolysis at ITIES represents the perspective method of chemical analysis.     

Investigations of the ionic self-diffusion coefficients of the trivalent lanthanide 152Eu(III) in diluted Eu(ClO4)3 solutions in 1,4-dioxane + water mixtures at 298.15 K

The measurement of ionic self-diffusion coefficient D of the trivalent lanthanide ion ¹⁵²Eu(III) in asymmetrical electrolytes of Eu(ClO₄)₃ in hydro-organic water–dioxane mixtures (at a low dielectric constant) at 298.15?K, by the open-end capillary method gives evidence of the progressive association of ion pairs. The study of the different physicochemical properties in all the domains of composition shows the existence of three distinct behaviours. The application of association theory to such an asymmetrical electrolyte (3?:?1) with a polyvalent cation enables us to delimit the validity of the Bjerrum and Fuoss's association theories. Since there is similarity of the coordination chemistry of trivalent lanthanide and actinide ions, this study comes within the framework of previous works of the investigation of structure properties of the f-elements in solution carried out in some previous papers.     

Determination of Monensin by Voltammetry at the Interface between Two Immiscible Electrolyte Solutions

Abstract

The coccidiostat monensin can be determined by voltammetry at the interface between two immiscible electrolyte solutions (ITIES) in the concentration range between 0.05 mM to 3 mM. The peaks obtained with cyclic voltammetry at the water/nitrobenzene interface correspond to the transfer of sodium ions from the aqueous to the nonaqueous phase facilitated by complexation with monensin functioning as an ionophore and are proportional to its concentrations. The method was applied to the extracts from Streptomyces cultures.     

Facilitated Transfer of Alkali Metal Ions by a Tetraester Derivative of Thiacalix[4]arene at the Liquid–Liquid Interface

The facilitated transfer of alkali metal ions (Na⁺, K⁺, Rb⁺, and Cs⁺) by 25,26,27,28‐tetraethoxycarbonylmethoxy‐thiacalix[4]arene across the water/1,2‐dichloroethane interface was investigated by cyclic voltammetry. The dependence of the half‐wave transfer potential on the metal and ligand concentrations was used to formulate the stoichiometric ratio and to evaluate the association constants of the complexes formed between ionophore and metal ions. While the facilitated transfer of Li⁺ ion was not observed across the water/1,2‐dichloroethane interface, the facilitated transfers were observed by formation of 1 : 1 (metal:ionophore) complex for Na⁺, K⁺, and Rb⁺ ions except for Cs⁺ ion. In the case of Cs⁺ a 1 : 2 (metal:ionophore) complex was obtained from its special electrochemical response to the variation of ligand concentrations in the organic phase. The logarithms of the complex association constants, for facilitated transfer of Na⁺, K⁺, Rb⁺, and Cs⁺, were estimated as 6.52, 7.75, 7.91 (log β₁°), and 8.36 (log β₂°), respectively.     

The transfer of alkali metal ions across the water-nitrobenzene interface facilitated by neutral macrocyclic ionophores

The alkali metal ions transfer from water to the nitrobenzene phase containing macrocyclic neutral ionophores (crown polyethers, nonactin) has been investigated, applying the electrolysis at the interface of two immiscible electrolyte solutions (ITIES) in the single-sweep voltammetry mode. The stability constants of complexes formed in the non-aqueous phase have been determined from the peak voltammograms, as well as value of complex formation enthalpy. It has been concluded that the facilitated ion transfer in the temperature range 5–65°C is a diffusion-controlled process.     

Cyclic Voltammetry of Ion Transfer for Phenylpropanolamine Hydrochloride at Water|Nitrobenzene Interface

The transfer on phenylpropanolamine ion, PPAH⁺, has been studied at the Interface between Two Immiscible Solutions (ITIES). The polarizable potential range was determined by cyclic voltammetry at the interface between an aqueous solution of lithium chloride (LiCl) and a nitrobenzene (NB) solution of electrolyte tetrabutylammonium tetraphenylborate (TBATPB). The half‐wave potential of ion transfer for phenylpropanolamine accross the water|NB interface was found 465.3 mV. The peak separation, the diffusion coefficient, and the standard ion transfer potential of PPAH⁺ were observed to be 59.1 mV, 1.7 × 10^?6 cm²/s, and 104.6 mV, respectively. The temperature of experiment was kept constantly at 25 ± 1 °C using water flow thermostate.     

Estimation of Coupling Rate Constant of L‐Cysteine Radical Studied by Concentration‐Step Coulometry Using Porous Carbon Felt Electrode Impregnated with an Electrolyte

Controlled potential coulometry using carbon felt electrode impregnated with electrolytic solution realizes very rapid complete electrolysis and can be used to measure the faster reaction rate constant than that using conventional electrolytic cell. In this research, concentration step method was adopted to investigate coupling reaction rate of L ‐cysteine radical. The coupling reaction rate of L ‐cysteine radical becomes much larger than further electrode reaction rate of L ‐cysteine radical at high L ‐cysteine concentration, because the coupling reaction rate is proportional to the second order of L ‐cysteine radical concentration although the further electrode reaction rate is proportional to the first order of L ‐cysteine radical concentration. At a low constant potential value, apparent number of electrons (n_app) increased from 1 (L ‐cystine is produced) to 2 (L ‐cysteine sulfenic acid, RSOH, may be produced) according to decrease in concentration of L ‐cysteine to be electrolyzed. The second order rate constant of coupling reaction was estimated to be about 1200 dm³ mol^?1 s^?1 at 20 °C by curve fitting method for n_app vs. logarithm of L ‐cysteine concentration. Apparent number of electrons (n_app) consumed in the electrode oxidation of L ‐cysteine gradually increased as an applied potential increases, because the consecutive electrode reaction steps with different electrode reaction rates were involved in the electrode oxidation of L ‐cysteine. In the present method, the constant limited electrolytic current was observed at high electrode potential range, which suggests that electrode oxidation rate of L ‐cysteine is kinetically controlled.     

A new approach to micropatterning: application of potential-assisted ion transfer at the liquid-liquid interface for the local metal deposition

A new approach to micropatterning is demonstrated. The approach is based on driving an electrochemical process at the solid-liquid interface through the formation of a flux of ions from a micropipet that is held in close proximity to the surface. The flux of ions is generated by the so-called potential assisted ion transfer at the interface between two immiscible electrolyte solutions (ITIES). As a model system, the local deposition of silver was examined. Specifically, a constant potential, which was applied to a micropipet filled with an aqueous solution of silver ions, caused the transfer of Ag(+) into the outer nitrobenzene (NB) solution that consisted of an electrolyte, tetrabutylammonium tetrakis[4-chlorophenyl]borate (TBATPBCl). To facilitate the transfer of silver ions a macrocyclic ligand, that is, dibenzo-24-crown-8 (DB24C8), was added to the organic phase. The Faradaic current of this micro-ITIES was used as a means of controlling the tip-surface distance in scanning electrochemical microscopy (SECM) and depositing silver microstructures on a gold substrate.     

The double layer at the interface between two immiscible electrolyte solutions: Part II. Structure of the water/nitrobenzene interface in the presence of 1:1 and 2:2 electrolytes

From fast galvanostatic pulse measurements at 25°C the capacitance of the water/nitrobenzene interface was evaluated as a function of the interfacial potential difference Δ_o^w? for systems consisting of NaBr, LiCl or MgSO₄ in water and tetrabutylammonium tetraphenylborate, tetraphenylarsonium tetraphenylborate or tetraphenylarsonium dicarbollylcobaltate in nitrobenzene. The modified Verwey—Niessen model, in which an inner layer of solvent molecules separates two space-charge regions (the diffuse double layer), describes the structure of the water/nitrobenzene interface well at electrolyte concentrations above ca. 0.02 mol dm^?3, provided that the ions are allowed to penetrate into the inner layer over some distance. For all the systems studied the zero-charge potential difference was found at Δ^w_o?_pzc ≈ 0 on the basis of the standard potential difference Δ^w_o?⁰_TMA + = 0.035 V for tetramethylammonium cation which was used as a reference ion. At zero surface charge a comparison was made with the theoretical capacitance calculated using the mean spherical approximation for a model consisting of two ion and dipole mixtures facing each other. The effect of ion penetration on the interfacial capacitance was estimated from the solution of the linearized Poisson-Boltzmann equation for a triple dielectric model with a continuous distribution of the point ions. The concentration-independent inner layer potential difference and capacitance can only be inferred from the capacitance data if the ion size effect is taken into account. A non-iterative procedure based on the hypernetted-chain equation was used for the evaluation of the potential drop across the diffuse double layer. The extend of the penetration into the inner layer appears to be a function of ion solvation, e.g. the more hydrated ion the less extensive ion penetration is likely.     

Transfer of lanthanum ion across the adsorption of emulsifier OP at the water-nitrobenzene interface

The transfer of lanthanum ion facilitated by diantipyrylmathane (DAM) across the water/nitrobenzene (w/nb) interface and the adsorption of emulsifier OP at the w/nb interface has been studied by the cyclic voltammetry.The mechanism of the charge transfer reactions is discussed.It has been concluded that the transfer of rare earth metal ion (La3+) facilitated by neutral ionophore (DAM) at the w/nb interface is E mechanism and the nonionic surfactant (emulsifier OP) can participate in the charge transfer process as an ionophore,charge transfer catalyst and inhibitor.     

Electrochemical dediazoniation of arenediazonium ions and subsequent radical polymerization at the liquid-liquid interface

Arenediazonium ions are dediazoniated through reduction by decamethylferrocene in the 1,2-dichloroethane (DCE) after the electrochemical transfer of the arenediazonium ions from the aqueous side of the interface between the DCE and the aqueous phase (W). Cyclic voltammetry of the ion transfer clearly shows that this process is described as an E _r C _i process, that is, the diffusion-limited transfer of the ions across the interface followed by the irreversible dediazoniation in the DCE phase. Arene radicals formed in DCE can initiate the radical polymerization of styrene at the interface. The polystyrene formed in the interfacial region significantly impedes the transfer of tetraethylammonium ions across the DCEIW interface. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 1, pp. 80–84. The text was submitted by the authors in English.     

Ion-transport and diffusion coefficients of non-plasticised methacrylic-acrylic ion-selective membranes

The ion-transport behaviour of methacrylic-acrylic-based polymers for ion-selective electrode (ISE) membranes was investigated by a spectrophotometric method to determine the apparent diffusion coefficient. By observing the degree of deprotonation of the chromoionophore or chromogenic ionophore, the extent of penetration of cations into the polymer films was determined. The transport of the cations into the optode films depended on the stoichiometry of complexation by the ionophores. The apparent diffusion coefficients, estimated from the deprotonation data were of the order of 10⁻¹² to 10⁻¹¹ cm² s⁻¹. These values indicate that the apparent ion mobility in the methacrylic-acrylic ISE membranes is approximately a thousand times lower than that in plasticised PVC ISE membranes. For some ionophores, the value of the apparent diffusion coefficient could be modulated according to the ionophore content in the membrane and the data obtained for a calixarene containing membrane were tested against a model for facilitated diffusion with chained carriers. The data did not fit a model where intramolecular diffusion was limiting, but were consistent with a first-order rate-limiting mechanism involving an intermediate 1:2 complex between ion and ionophore. In this instance, the lowest values for D_app were thus not necessarily obtained for lowest ionophore loading and in the range examined, a trend of decreasing D_app with increasing ionophore was noted.     

New Insights into Buffer-Ionic Salt Interactions: Solubilities,Transfer Gibbs Energies,and Transfer Molar Volumes of TAPS and TAPSO from Water to Aqueous Electrolyte Solutions

The solubilities of N-[tris(hydroxymethyl)methyl]-3-aminopropanesulfonic acid (TAPS) or N-[tris(hydroxymethyl)methyl]-3-amino-2-hydroxypropanesulfonic acid (TAPSO) in water and in aqueous solutions of CH₃COOK (KAc), KBr, KCl, or NaCl were determined from density measurements at 298.15 K. The solubilities of TAPS in aqueous solution decrease with increasing concentration of the salts (salting-out effect), whereas those of TAPSO increase with increasing concentration of the salts (salting-in effect). The solubility and density data were further used to calculate the apparent transfer Gibbs energies, Δ_tr G, and transfer molar volumes, D_trV_f^o\Delta_{\mathrm{tr}}V_{\phi}^{\mathrm{o}}, of these buffers from water to aqueous electrolyte solutions at 298.15 K. The contributions of various functional groups of TAPS, TAPSO, and the related buffers (tris(hydroxymethyl)aminomethane, TRIS, and N-tris[hydroxymethyl]-4-amino-butanesulfonic acid, TABS) to the transfer properties were systematically estimated from the calculated Δ_tr G and D_trV_f^o\Delta_{\mathrm{tr}}V_{\phi}^{\mathrm{o}}.     

Electrochemical Properties of Superoxide Ion in Aprotic Media

The electrochemical response of the oxygen/superoxide ion (O₂/O ₂ ^.- ) couple at glassy carbon electrode in N,N-dimethylformamide (DMF) is investigated by cyclic voltammetry. The electrode reaction mechanisms of superoxide ion with hydroquinone and ethyl acetate are discussed in detail. The macroscale generation of superoxide ion is carried out by means of controlled-potential electrolysis. The UV spectrum of superoxide ion in DMF, obtained for the first time, exhibits a single absorption band with _max at 273 nm within 190–500 nm.     

A Novel Hg(II) PVC Membrane Sensor Based on Simple Ionophore Ethylenediamine Bis‐Thiophenecarboxaldehyde

Abstract

A mercury (II) ion‐selective polyvinyl chloride (PVC) membrane sensor based on ethylenediamine bisthiophenecarboxaldehyde (EDBT) as a novel nitrogen‐ and sulfur‐containing sensing material was successfully developed. The ionophore was produced through Schiff's base formation between ethylenediamine and 2‐thiophenecarboxaldehyde. These two reagents have the advantages of low cost and simple chemical compounds. Ortho‐nitro phenyl pentyl ether (o‐NPPE) as solvent and sodium tetraphenyl borate (NaTPB) as a lipophilic salt were chosen. The sensor exhibited a good linear response of 30.0±0.4 mV per decade within the concentration range of 10^?7–10^?2 and a detection limit of 7.0×10^?8 mol L^?1 Hg(II). The sensor showed good selectivity and fast response for the mercury (II) ion with respect to some alkali, alkaline earth, transition, and heavy metal ions. The EDBT–based sensor was suitable for aqueous solutions of pH range from 2.0 to 4.5. It can be used for about 3 months without any considerable divergence in potential. The formation constant of ionophore complex with Hg(II) ion was calculated by using the segmented sandwich membrane method. The structure of both the ionophore and its Hg(II) complex were examined using infrared spectra and elemental analysis. The proposed sensor was applied for the determination of Hg(II) content in some dental amulgum alloys and as an indicator electrode for potentiometric titration of Hg(II) ion with EDTA solution, as well as with I^?, OH^?, and IO₃ ^? ions. In addition, the solubility products of the previous ions were determined by using this sensor.     

Kinetics of electrode reaction coupled to ion transfer across the liquid/liquid interface

In the theoretical model it is assumed that a graphite disk electrode is covered by a thin film of solution of decamethylferrocene (dmfc) and some electrolyte CX in nitrobenzene and immersed in an aqueous solution of the electrolyte MX. Oxidation of dmfc is accompanied by the transfer of anion X ⁻ from water into nitrobenzene since it is also assumed that cations dmfc ⁺ and C ⁺ are insoluble in water and cation M ⁺ is insoluble in nitrobenzene. Kinetic parameters of the electrode reaction can be determined if the total potential difference across the nitrobenzene/water interface is maintained constant by adding the electrolytes CX and MX in concentrations which are much higher than the initial concentration of dmfc in nitrobenzene.     

Charge transfer across a polymer gel/liquid interface: determination of ionophores

An electrochemical method for the determination of the ionophores monensin and lasalocid was developed, based on the polarization of an agar gel/nitrobenzene electrolyte interface. The measured current corresponding to the facilitated ion transfer across this interface is directly proportional to the concentration of an ionophore dissolved in the organic phase. Using cyclic voltammetry in a three-electrode system the detection limit for both ionophores is about 3 × 10^?5 M.     

液——液界面双电层统计力学处理

应用巨正则系综统计法处理液／液界面（ＩＴＩＥＳ）双电层体系。根据ＭＶＮ模型,假定溶液中离子可穿入界面内层（定向溶剂分子层）,由体系（内层）巨正则配分函数导出内层微分电容（Ｃ１）统计表达式,拟合计算Ｃ１随该层表面电荷密度（σｍ）变化关系。理论同时表明,Ｃ１与σｍ涨落存在确定关系