Simple Ion Transfer Research Articles

Detection of benzalkonium chloride and polyhexamethylene guanidine hydrochloride using novel organic gel-based amperometric electrode and HILIC DAD

This article describes the simultaneous determination of cationic surfactants benzalkonium chloride (ADBAC) and polyhexamethylene guanidine hydrochloride (PHMG) in stock solutions and commercial disinfectants using a novel voltammetric ion-selective electrode with a gel-like polymer composite membrane. The ADBAC and PHMG sensing methodology is based on a simple polyelectrolyte ion transfer reaction across the water/polyvinyl chloride-2-nitrophenyloctyl ether (PVC-NPOE) gel interface and was first investigated using cyclic voltammetry. Our novel electrode gave a current response proportional to ADBAC and PHMG ions ranging from 10 to 70 mg·L−1 and 25 to 120 mg·L−1, respectively, and the calculated detection limits were 1.24 mg·L−1 for ADBAC and 1.77 mg·L−1 for PHMG. As a comparative method for the determination and separation of ADBAC and PHMG, hydrophilic interaction chromatography (HILIC DAD) was used in combination with diode-array detection. LOD, LOQ, and RSD for recovery were determined for both methods, and a study of the analytical performance for both methods showed that the electrochemical method was more sensitive but had a larger error and a narrower range of linearity. The applicability of both methods to the routine analysis of disinfectants is discussed.

Oleic and nitro-oleic acid behavior at an electrified water-1,2-dichloroethane interface

In this work, oleic and 9/10-nitro oleic acid were studied at a polarized water-1,2-dichloroethane interface. We found that both fatty acids can undergo a simple interfacial ion transfer reaction that is mainly limited by diffusion. The possibility of spontaneous partitioning of the fatty acid into the organic phase and acting as a ligand for the facilitated sodium ion transfer was excluded. The ionic currents originating from the chemical species interfacial transfer were recorded starting from a pH of around 8.5, which agreed with their poor acidity. The acid-base properties of fatty acids were studied with pKa 9.7 (for oleic acid) and 8.5 for the 9/10-nitro derivative. The formal Galvani potential difference of the fatty acids ion transfer reaction was used to calculate the water-1,2-dichloroethane partition coefficients. The results indicated similar water solubility for 9/10-nitro oleic acid (logP' −3.47) and oleic acid (logP' −3.42), where 9/10-nitro oleic acid is slightly more hydrophilic. The partial water solubility of the fatty acids was confirmed by the measurement of ionic currents, which did not increase linearly with their increasing aqueous phase concentration. The obtained results were correlated with the dynamic light scattering of the fatty acids, indicating the formation of supramolecular structures. 9/10-Nitro oleic acid is an endogenously produced signaling molecule involved in cell redox homeostasis. The results obtained here could contribute to further (bio)chemical studies on fatty acid nitroalkenes.

Electrodeless Synthesis of Low Dispersity Au Nanoparticles and Nanoclusters at an Immiscible Micro Water/Ionic Liquid Interface.

Owing to their biocompatibility, optical, and catalytic properties, Au nanoparticles (NPs) have been the subject of much research. Since smaller NPs have enhanced catalytic properties and NP morphology greatly impacts their effectiveness, controlled and reproducible methods of generating Au NPs are still being sought. Herein, Au NPs were electrochemically generated at a water|ionic liquid (w|IL) immiscible micro-interface, 25 µm in diameter, using a redox active IL and compared to results at a water|oil (w|o) one. The liquid|liquid interface is advantageous as it is pristine and highly reproducible, as well as an excellent means of species and charge separation. In this system, KAuCl4 dissolved in the aqueous phase reacts under external potential control at the water|P8888TB (tetraoctylphosphonium tetrakis(pentafluorophenyl)borate) with trioctyl(ferrocenylhexanoyl)phosphonium tetrakis(pentafluorophenyl)borate (FcIL), an electron donor and redox active IL. FcIL was prepared with a common anion to P8888TB, which greatly enhances its solubility in the bulk IL. Simple ion transfer of AuCl4− and AuCl(4−γ)(OH)γ− at the w|P8888TB micro-interface were characterized voltammetrically as well as their heterogeneous electron transfer reaction with FcIL. This interfacial reaction generates Au NPs whose size can be thermodynamically controlled by modifying the pH of the aqueous phase. Critically, at low pH, nanoclusters, <1.7 nm in diameter, were generated owing to inhibited thermodynamics in combination with the supramolecular fluidic nature of the IL microenvironment that was observed surrounding the as-prepared NPs.

Simultaneous electropolymerization/Au nanoparticle generation at an electrified liquid/liquid micro-interface

Free-standing nanocomposite thin-films for bioimplantation and (electro)catalysis are still an immature field despite the need for new materials. Herein, the micro liquid|liquid interface between water|1,2-dichloroethane (w|DCE) positioned at the tip of a pulled pipette has been exploited to generate a free-standing thin-film incorporating Au NPs electrogenerated in situ by reduction of a gold salt in the aqueous phase and using 2,2′:5′,2″-terthiophene (TT) as monomer/electron donor dissolved in the DCE phase. Low pH of the aqueous phase generated incomplete, poorly formed films, as evidenced by TEM and AFM images of the final film. At high pH the half-wave potential of the electron transfer wave shifted to lower potentials (∼0.35 V versus simple ion transfer of AuCl4–) with repeated cyclic voltammetric cycling indicating improved thermodynamics. Imaging of films produced at pH's >5.5 were robust. These results indicate the need of a Brønsted base to capture protons and facilitate TT+•, radical cation coupling. TEM and AFM imaging are complemented by in situ impedance spectroscopy measurements that show an increase in the capacitive nature of the interface as [TT] and pH increases along with increased cycling of the potential. Curve fitting using equivalent circuit models required the addition of a second capacitator element to mimic the generation of a porous film at the liquid|liquid interface, i.e., a liquid|solid|liquid interface. By reducing the required overpotential, one can prevent overoxidation of the monomer/polymer. AFM measurements of formed thin-films mechanically deposited onto silicon substrates were found to be ∼0.4 μm in thickness with Au NP radius increasing concomitantly with distance away from the w|DCE interface.

Electrochemical Study of Ion Transfers Processes at the Interfaces between Water and Trifluorotoluene and Its Derivatives

AbstractAs one phase constituting of a liquid/liquid (L/L) interface, suitable organic solvents are of great significance for the study of electrochemistry at a L/L interface. In this work, the thermodynamic and kinetic parameters of simple ion transfer (IT) at the water/trifluorotoluene (W/TFT) interface were measured using micro‐ and nanopipettes voltammetry, respectively. In addition to the study of model ions, we have also explored some ions whose transfer potentials are close to the two ends of the potential window. Inspired by the work of the W/TFT interface, we also further developed two novel L/L interfaces and investigated various simple IT reactions based on the W/o‐ and p‐methylbenzotrifluoride (W/o‐ and p‐MBTF) interfaces. The transfer potential and Gibbs energy of ITs across the W/o‐and p‐MBTF interface were determined by the analysis of the electrochemical voltametric curves. Special attention should be paid to that we can observe the IT peak or steady‐state of tetraamyl ammonium (TAA+) at W/o‐ and p‐MBTF interfaces with no difficulty, which is rather challenging at other L/L interfaces. Compared to the classical W/1,2‐dichloroethane (DCE) and W/nitrobenzene (NB) interfaces, the W/TFT and its derivatives interfaces exhibit low toxicity, favourable stability, and wider potential windows, which can be better choices for replacing the traditional organic solvents in the electrochemical study at a L/L interface.

Ion-transfer electrochemistry at arrays of nanoscale interfaces between two immiscible electrolyte solutions arranged in hexagonal format

• Nanoscale interfaces between two immiscible electrolyte solutions were studied. • Arrays of pores were formed by focused ion beam milling. • Hexagonal array format was characterised by ion transfer voltammetry. • Comparison of experiment and numerical simulation was undertaken with good agreement. • nanoITIES arrays in hexagonal format reach independent diffusion at large separations. The electrochemical behaviour of hexagonally arranged nanopore arrays was studied by simple ion transfer across the interface between two immiscible electrolyte solutions (ITIES) formed between water and 1,2-dichloroethane. The hexagonal nanoITIES arrays were supported at nanopores fabricated by focused ion beam milling into 50 nm thick silicon nitride films. Six arrays with different pore centre-to-centre distance ( r c ) to radius ( r a ) ratios were prepared. Within these arrays, the diffusion-limited steady-state currents ( i ss ) of tetrapropylammonium cation (TPrA + ) ion transfer increased concomitantly with increasing r c / r a ratio, reaching a plateau at r c / r a ≥ 96, which is greater than that previously reported for square-patterned nanoITIES arrays ( r c / r a ≥ 56). The diffusion regime and i ss associated with simple ion transfer across a nanopore array was also examined using numerical simulations, via COMSOL Multiphysics software, incorporating a 3-dimensional geometry and employing finite element analysis. Simulated linear sweep voltammograms of TPrA + transfer demonstrated a unique diffusional behaviour dependent on hexagonal nanopore spacing and the r c / r a ratio, analogous to the experimental voltammograms. Overlay of simulated and experimental voltammograms for each r c / r a ratios showed good agreement. These results indicate that a new design criterion is required to achieve independent diffusion at hexagonal nanointerface arrays, in order to maximize nanodevice performance in electrochemical sensor technologies.

Effect of aggregation on the simple ion transfer across oil|water interfaces

The theory of cyclic voltammetry of simple ion transfer across a liquid|liquid (L|L) interface including the effect of aggregation is developed. We focus on two different situations: ion transfer followed by an aggregation process in the organic phase, and a disaggregation process in the aqueous phase followed by ion transfer. We use parameters typical of the areas of study of molecular aggregation and polymer formation, namely average aggregate size and polydispersity index. These parameters allow us to analyse, in a simple and rigorous way, the interconversion between monomer and aggregate species, both at the aqueous or organic side of the L|L interface and in the interfacial region during the potential scan. Our results show that aggregation occurring in the organic phase facilitates ion transfer across the L|L interface. In contrast, when the aggregates are present in the aqueous phase, they must be disaggregated so that the monomers can be transferred, hence the transfer energy increases. Both processes significantly alter the shape of voltammograms. The peak current and mid-peak potential are analysed as a function of initial concentrations, aggregation constants and maximum number of monomers forming each aggregate. These results are compared with approximate analytical equations, which can be used to guide further experiments and extract information from experimental responses.

Electrified Soft Interface as a Selective Sensor for Cocaine Detection in Street Samples.

A straightforward, direct, and selective method is presented for electrochemical cocaine identification in street samples. The sensing mechanism is based on a simple ion transfer reaction across the polarized liquid–liquid interface. The interfacial behavior of a number of cutting agents is also reported. Interfacial miniaturization has led to improved electroanalytical properties of the liquid–liquid interface based sensor as compared with the macroscopic analogue. The reported method holds great potential to replace colorimetric tests with poor selectivity for on-site street sample analysis.

(Invited) Contactless Photo-Electrochemistry of Dye-Sensitized TiO2 Nanoparticles Floating at Electrified Water-Oil Interfaces

Certain soft interfaces formed between aqueous and organic electrolyte solutions of low miscibility (e.g., trifluorotoluene) are electrochemically active in the sense that it is possible to precisely control the Galvani potential difference between the two adjacent liquids (i.e., to “polarise” or electrify the interface), and thus drive charge transfer reactions. In comparison to solid electrode-electrolyte interfaces, where typically only electron transfer may be probed, charge transfer reactions at soft interfaces may include simple ion transfer, assisted ion transfer, heterogeneous electron transfer, or photoinduced heterogeneous electron transfer (PET), see Figure 1 [1]. PET represents a novel method of potentially harnessing solar energy at electrified soft interfaces. By exploiting (i) energy trapped from visible light by a photoactive interfacial film (e.g., a porphyrin dye or a dye-sensitized TiO2 nanoparticle) and (ii) the electrochemical driving force provided by electrification of the soft interface, a solar fuel such as H2 or H2O2 may be evolved by PET across the soft interface using a weak electron donor in the oil phase, e.g., ferrocene. Crucially, all photo-electrochemical techniques applied at traditional solid electrode-electrolyte interfaces (voltammetry, impedance, photo-current transients, etc.) are applicable at polarised soft interfaces [2-3]. The photochemical properties of TiO2 nanoparticles have been extensively studied in homogeneous phases for a variety of processes including water splitting and the photocatalytic destruction of pollutants. Mesoporous films based on TiO2 nanoparticles have also been studied as photoactive materials. In this regard, dye sensitization of wide bandgap semiconductors has been extensively studied in the field of photovoltaics. Despite the overwhelming literature on the photochemistry of TiO2 colloids, little is yet known about the properties of these particles floating as “photo-electrodes” at molecular water-oil interfaces, with only a small number of published articles on the topic [4-7]. In this presentation the photo-electrochemistry of TiO2 nanoparticles floating at electrified water-oil interfaces under blue LED illumination will be detailed. The experimental techniques employed (cyclic voltammetry, photocurrent transient data) will be able to provide valuable fundamental information on the rates of charge transfer between redox species in solution and the semiconductors floating at the interface. The studies will explore new possibilities for contactless photo-electrochemistry of nanoparticles in the presence of a static electric field, with potential applications in solar energy conversion to solar fuels and storage (ECS) and photocatalytic pollutant degradation.

Theory of electrochemistry at miniaturised interfaces between two immiscible electrolyte solutions

In this current opinion article on the electrochemistry of micro- and nano-interfaces between two immiscible electrolyte solutions, we present a summary of theoretical descriptions to-date, rather than only of work in the past ca. 2 years. The opinion summarises the current state of art in the theory used to interpret and analyse this form of experimental electrochemistry, specifically addressing only simple ion transfer processes.

Electrochemical signature of hen egg white lysozyme at the glycerol-modified liquid-liquid interface

Electrochemical characterization of hen egg white lysozyme (HEWL) at a glycerol-modified interface between two immiscible electrolyte solutions (ITIES) was conducted using a microporous silicon membrane-supported gelled-1,6-dichlorohexane|water-glycerol interface. The electrochemical response of HEWL under these conditions is of interest for the system’s potential application to the formation of isorefractive emulsified-ITIES, which offer practical opportunities for spectrophotometric analysis of interfacial processes. Importantly, the voltammetric signature for HEWL seen under glycerol-rich conditions was similar but with some differences from that for glycerol-free conditions. Specifically, the potential at which facilitated transfer of the organic phase electrolyte anion tetrakis-(4-chlorophenyl) borate (TPBCl−) occurred was shifted to lower potential with increasing glycerol concentration. However, features in the voltammetry associated with adsorption/desorption processes were observed to remain constant. The simple ion transfer response of tetraethylammonium cations (TEA+) at the same glycerol-modified ITIES provides insight into the nature of changes that determine the atypical HEWL signature. Lower ion transfer current with respect to increasing glycerol concentration and a shift in transfer potential were the key findings here. The results indicate that the electrochemistry which determines the HEWL signature is similar in environments that are rich in glycerol or purely aqueous.

New Hypothesis for SOFC Ceramic Oxygen Electrode Mechanisms

There is a lot of discussion and little agreement about the mechanisms for the oxygen reduction/oxide ion oxidation reaction ceramic electrodes in solid oxide cells, such as perovskite electrodes like the lanthanum strontium manganate – yttria stabilized zirconia composite electrode or mixed ion and electron conducting electrodes like (La1-xSrx)sCoO3- d (LSC). Many mechanisms with similarities such as electron transfer being rate determining and involving surface oxide vacancies have been proposed. Often the proposals were based on studies of oxygen isotope (16O – 18O) exchange at perovskite and fluorite structured metal oxide surfaces, which actually is not an electrically driven process. Even though oxygen exchange - on a non-polarized surface of a ceramic that is not electrically connected to an electrolyte - has electrochemical character, it does not necessarily behave the same way as an electrochemically polarized electrode. Furthermore, most proposed mechanisms assumed that the oxygen electrode reaction took place on a real perovskite surface, but during recent years, it has become generally accepted that perovskites and many other Ruddlesden-Popper phases have a thin (few nanometer) and continuous surface layer of A-site oxides, e.g. SrO and La2O3in the case of the popular mixed conducting LSC. This layer is observed to increasingly impede the kinetics of the reversible oxygen electrode as the AO layer grows thicker. As the electrode reaction does not stop, but just decreases with increasing SrO thickness, we take these literature reports as an indication that the electrode reaction takes place through an AO layer even though the AO bulk phase is both ion and electron insulating. Our hypothesis is that a thin AO layer, like a 1 nm thick SrO layer, is electron and ion conducting due to space charge layers both on the oxygen gas side and on the perovskite side of it. Thus, the SrO layer will probably contain O- and O2 -ions, which act as electron holes, and request oxygen vacancies, which enables the oxide ion conductivity. This otherwise insulating layer then becomes a mixed conductor. We further hypothesize that the actual specific conductivity by oxygen ions as well as by electrons will be very sensitively dependent on the oxygen vacancy concentration in, and the electron Fermi level of, the perovskite layer. Apart from the change in defect chemistry with polarization of the perovskite electrode, the SrO layer will also change stress state because of stoichiometric expansion/contraction of the perovskite due to the change in the perovskite stoichiometry with polarization. Straining of the SrO lattice may also change its conductivity. On this background, another rate limiting process is suggested: O2(gas) + 2 e-(surface) → 2 O-(ads,SrO) fast (1) O-(ads, SrO) + VO(surface) → O-(SrO,subsurface) slow (2) O-(SrO) + e- → O2-(LSC) fast (3) This mechanism is sketched in the Figure. The slow rate determining process of eq. 2 is not limited by slow electron transfer and it is not a simple ion transfer, but rather a kind of diffusion or conduction process through the thin segregated SrO surface layer. This hypothesis seems to be able to qualitatively explain a number of otherwise puzzling observations reported in the literature. This will be explained in the paper together with more details. The Figure shows a much simplified sketch of the proposed mechanism for the (La0.6Sr0.4)0.98CoO3- d oxygen electrode. The electrons may meet the O- - ions inside the SrO layer. VO means oxide vacancies and is not attempting to account for the charge imbalance. Figure 1

Ion-transfer voltammetric determination of folic acid at meso-liquid-liquid interface arrays.

Voltammetric studies on the simple ion transfer (IT) behaviors of an important water-soluble B-vitamin, folic acid (FA), at the liquid-liquid (L-L) interface were firstly performed and then applied as a novel detection method for FA under physiological conditions. Meso-water-1,6-dichlorohexane (W-DCH) and meso-water-organogel interface arrays were built by using a hybrid mesoporous silica membrane (HMSM) with a unique structure of pores-in-pores and employed as the new platforms for the IT voltammetric study. In view of the unique structure of the HMSM, the impact of the ionic surfactant cetyltrimethylammonium bromide (CTAB), self-assembled within the silica nanochannels of the HMSM, was investigated. In particular, its effect on the IT voltammetric behavior and detection of FA at meso-L-L interface arrays was systematically examined by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and differential pulse stripping voltammetry (DPSV). It was found that all the voltammetric responses of CV, DPV, and DPSV and the corresponding detection limit of FA at such meso-L-L interface arrays are closely related to the CTAB in the HMSM. Significantly, the calculated detection limit of FA could be improved to 80 nM after the combination of the DPSV technique with the additional preconcentration of FA in the silica-CTAB nanochannels, achieved through an anion-exchange process between FA(-) and the bromide of CTAB in HMSM. This provides a new and attractive strategy for the detection of those biological anions.

Impact of an ionic surfactant on the ion transfer behaviors at meso-liquid/liquid interface arrays

Abstract The influence of ionic surfactants, cetyltrimethylammonium bromide (CTAB), self-assembled within silica-nanochannels of a hybrid mesoporous silica membrane (HMSM) on simple ion transfer (IT) behaviors at the meso-water/1,2-dichloroethane (W/DCE) interface arrays supported by such a HMSM was investigated by voltammetry for the first time. Significantly, it is found that the CTAB in HMSM can dramatically enhance the peak-current responses corresponding to ITs of some anions and even lower their Gibbs transfer energies from W to DCE, which could be ascribed to an anion-exchange process between anions and the bromide of CTAB associated with partial ion-dehydration induced by the CTAB. This work will provide a new strategy to study anion transfer processes and improve the electroanalytical performance for anion detection at the liquid/liquid interface.

Electrochemical behaviors of protonated diamines at the micro-water/1,2-dichloroethane interface

The simple ion transfer (IT) and facilitated ion transfer (FIT) of a series of protonated diamines ([H3N(CH2)nNH3]2+ (DA2+) or [H2N(CH2)nNH3]+ (DA+), n=2, 3, 4, 6, 8) at the micro-water/1,2-dichloroethane (μ-W/DCE) interface supported at the tip of a micropipette are reported. The effect of pH on both transfer processes has been studied in detail. For the IT process at low pH, DA2+ is dominated whereas at high pH it is mostly due to the DA+ transfer. The experimental results also demonstrate that dibenzo-18-crown-6 (DB18C6, L) can facilitate the transfer of protonated diamines at such interface. The complexation between ion and ligand is 1:1 at all experimental pH when CDAz+≫CL (where z can be 0, 1 or 2 depending on the pH of solutions). For CDAz+≪CL, the ion to ligand stoichiometry is 1:1 when pH is high, and is 1:2 when pH is low. The association constants for both cases are also calculated. Among these five diamines, the association constant for protonated 1,3-propanediamine has the biggest values.

Electrochemical Study of the Anticancer Drug Daunorubicin at a Water/Oil Interface: Drug Lipophilicity and Quantification

In this work, the ion transfer mechanism of the anticancer drug daunorubicin (DNR) at a liquid/liquid interface has been studied for the first time. This study was carried out using electrochemical techniques, namely cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The lipophilicity of DNR was investigated at the water/1,6-dichlorohexane (DCH) interface, and the results obtained were presented in the form of an ionic partition diagram. The partition coefficients of both neutral and ionic forms of the drug were determined. The analytical parameter for the detection of DNR was also investigated in this work. An electrochemical DNR sensor is proposed by means of simple ion transfer at the water/DCH interface, using DPV as the quantification technique. Experimental conditions for the analytical determination of DNR were established, and a detection limit of 0.80 μM was obtained.

Determination of alkali metal ion transfers at liquid|liquid interfaces stabilized by a micropipette

The extremely stable microinterface between two immiscible electrolytic solutions (micro-ITIES) housed at the tip of a 25μm diameter capillary, has given access to simple ion transfer of alkali metal ions for the first time at conventional supporting electrolyte concentrations (∼5mM). This was made possible by a uniquely designed pipette holder that uses a syringe to back-fill the aqueous phase and also helps to adjust and maintain the ITIES at the capillary tip, which was continuously monitored using a CCD camera attached to a custom-designed microscope. The formal transfer potential, Δowϕiz+o′ for each of the ions (Li+, Na+, K+, Rb+ and Cs+) was determined by means of cyclic voltammetry along with differential pulse voltammetry. This thermodynamic constant is of great value as a point of reference for the quantitative evaluation of metal ion extraction through interfacial complexation at an ITIES. Since these ions typically limit the polarizable potential window, in the past Δowϕiz+o′ was estimated using the current–potential response at the edge of the voltammogram, a method developed through numerical calculations. Δowϕiz+o′ was also determined at a microhole ITIES, requiring minimal concentrations of the analyte and no supporting electrolyte.

Electrochemical behaviour of myoglobin at an array of microscopic liquid–liquid interfaces

Electrochemistry at liquid–liquid interfaces, or at interfaces between two immiscible electrolyte solutions (ITIES), provides a basis for the non-redox detection of biological molecules, based on ion-transfer or adsorption processes. The electroactivity of myoglobin at an array of micron-sized liquid–organogel interfaces was investigated. The μITIES array was patterned with a silicon membrane consisting of an array of eight pores with radii of ∼12.8μm and a pore to pore separation of ∼400μm. Using cyclic voltammetry at the ITIES, the protein was shown to adsorb at the interface and facilitate the transfer of the organic phase electrolyte anions to the aqueous side of the interface. The electrochemical current response was linear with concentration in the range of 1–6μM, with corresponding surface coverage of 10–50pmolcm−2. The reverse peak currents was found to be proportional to the voltammetric scan rate, indicating a desorption process. The detection of the protein was only possibly when the pH of the aqueous phase solution was below the pI of the protein. The steady-state simple ion transfer behaviour of tetraethylammonium cation was decreased on the forward sweep, providing a qualitative indication of the presence of adsorbed protein at the interface. Increasing the ionic strength of the aqueous phase resulted in enhanced peak currents, possibly due to aggregation of protein precipitates in the aqueous solution. UV/Vis absorbance spectroscopy was used to investigate the effects of various aqueous electrolyte solutions on the structure of the protein, and it was shown that at low pH the protein is at least partially denatured. These results provide the basis for label-free detection of myoglobin at the ITIES.

Simple Ion Transfer at Liquid|Liquid Interfaces

The main aspects related to the charge transfer reactions occurring at the interface between two immiscible electrolyte solutions (ITIES) are described. The particular topics to be discussed involve simple ion transfer. Focus is given on theoretical approaches, numerical simulations, and experimental methodologies. Concerning the theoretical procedures, different computational simulations related to simple ion transfer are reviewed. The main conclusions drawn from the most accepted models are described and analyzed in regard to their relevance for explaining different aspects of ion transfer. We describe numerical simulations implementing different approaches for solving the differential equations associated with the mass transport and charge transfer. These numerical simulations are correlated with selected experimental results; their usefulness in designing new experiments is summarized. Finally, many practical applications can be envisaged regarding the determination of physicochemical properties, electroanalysis, drug lipophilicity, and phase-transfer catalysis.

Hydrophobic alkylphosphonium ionic liquid for electrochemistry at ultramicroelectrodes and micro liquid|liquid interfaces

Combining a large asymmetric alkylphosphonium cation, trihexyltetradecylphosphonium, with the tetrakis(pentafluorophenyl)borate anion affords a very hydrophobic room temperature ionic liquid (RTIL) possessing a melting point below room temperature. The viscosity and conductivity of this RTIL have been measured along with cyclic voltammetry (CV) of the ferrocene/ferrocenium redox couple at an ultramicroelectrode from 25 to 90 °C. The RTIL demonstrates a polarized potential window (PPW) at the water|IL interface as large as 0.8 V; indicating the large hydrophobicity of its component ions. Simple ion transfer (IT), at the micro water|IL interface (25 μm in diameter) housed at the tip of a micropipette was calibrated using the tetraphenylarsonium tetraphenylborate TATB assumption. The Galvani transfer potentials of several IT reactions at the interface were determined. It was discovered that large peak-to-peak separation in CVs obtained at the solid–liquid and liquid–liquid junction was mainly due to the slow electron transfer (ET) and IT kinetics. This is confirmed by overlapping experimental and theoretical CVs obtained from finite element analysis simulations. Standard rate constants ( k°) of 5 × 10 −4 cm s −1 were garnered at these interfaces.