Mass Transfer from Ion-Sensing Component-Loaded Nanoemulsions into Ion-Selective Membranes: An Electrochemical Quartz Crystal Microbalance and Thin-Film Coulometry StudyClick to copy article linkArticle link copied!
- Canwei MaoCanwei MaoDepartment of Inorganic and Analytical Chemistry, University of Geneva, Quai Ernest-Ansermet 30, CH-1211Geneva, SwitzerlandMore by Canwei Mao
- Yoshiki SodaYoshiki SodaDepartment of Inorganic and Analytical Chemistry, University of Geneva, Quai Ernest-Ansermet 30, CH-1211Geneva, SwitzerlandMore by Yoshiki Soda
- Kye J. RobinsonKye J. RobinsonDepartment of Inorganic and Analytical Chemistry, University of Geneva, Quai Ernest-Ansermet 30, CH-1211Geneva, SwitzerlandMore by Kye J. Robinson
- Tara ForrestTara ForrestDepartment of Inorganic and Analytical Chemistry, University of Geneva, Quai Ernest-Ansermet 30, CH-1211Geneva, SwitzerlandMore by Tara Forrest
- Eric Bakker*Eric Bakker*Email: [email protected]Department of Inorganic and Analytical Chemistry, University of Geneva, Quai Ernest-Ansermet 30, CH-1211Geneva, SwitzerlandMore by Eric Bakker
Abstract
Recent work has shown that ion-selective components may be transferred from nanoemulsions (NEs) to endow polymeric membranes with ion-selective sensing properties. This approach has also been used for nanopipette electrodes to achieve single-entity electrochemistry, thereby sensing the ion-selective response of single adhered nanospheres. To this date, however, the mechanism and rate of component transfer remain unclear. We study here the transfer of lipophilic ionic compounds from nanoemulsions into thin plasticized poly(vinyl chloride) (PVC-DOS) films by chronoamperometry and quartz crystal microbalance. Thin-film cyclic coulovoltammetry measurements serve to quantify the uptake of lipophilic species into blank PVC-DOS membranes. Electrochemical quartz crystal microbalance data indicate that the transfer of the emulsion components is insignificant, ruling out simple coalescence with the membrane film. Ionophores and ion-exchangers are shown to transfer into the membrane at rates that correlate with their lipophilicity if mass transport is not rate-limiting, which is the case with more lipophilic compounds (calcium and sodium ionophores). On the other hand, with less lipophilic compounds (valinomycin and cation-exchanger salts), transfer rates are limited by mass transport. This is confirmed with rotating disk electrode experiments in which a linear relationship between the diffusion layer thickness and current is observed. The data suggests that once the nanoemulsion container approaches the membrane surface, transfer of components occur by a three-phase partition mechanism where the aqueous phase serves as a kinetic barrier. The results help better understand and quantify the interaction between nanoemulsions and ion-selective membranes and predict membrane doping rates for a range of components.
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You are free to share(copy and redistribute) this article in any medium or format and to adapt(remix, transform, and build upon) the material for any purpose, even commercially within the parameters below:
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Scheme 1
aThe rate-limiting step is postulated to be either (a) diffusional mass transport of the nanoemulsion, (b) fusion of the entire nanoemulsion phase with the membrane, or (c) delivery of the nanoemulsion components into the membrane by a partitioning mechanism.
Experimental Section
Chemicals and Instruments
Electrode Preparation
Mechanistic Ion Transfer Study
Results and Discussion
Scheme 2
Figure 1
Figure 1. Transfer process at 100 rpm rotating speed with DMF-based NEs encapsulated with TFPB– and monitored by thin-film cyclic voltammetry. (a) Consecutive voltammograms at 5 min intervals during emulsion doping, giving increasing currents with time. (b) Corresponding integrated charge (coulovoltammograms) for the experiment shown in a. (c) Resulting integrated charge as a function of doping time, giving a flux of 3.3 ± 0.2 pmol cm–2 s–1 of the ion-exchanger salt.
Figure 2
Figure 2. (a) An emulsion, free of TFPB–, is added to solution at the indicated time, giving the indicated frequency change that translates into a small mass change of 0.02 ng cm–2 s–1 indicating minimal fusion between the nanoemulsion phase and the membrane. (b) Frequency change (mass uptake) observed by QCM and (c) the corresponding current with time at 0.4 V upon introducing DMF-based nanoemulsions containing TFPB–. The lipophilicity of the salt was successively increased by adding electrolytes of increasing lipophilicity (LiCl, NaCl, TMACl, and TBACl as shown) at a 10 mM concentration to solution. The resulting doping rate does not depend on the lipophilicity, suggesting a mass transport-limited process.
Figure 3
Figure 3. Ion transfer amperometry at a thin membrane for the mass transfer of nanoemulsions containing TBA+TFPB– as cargo and a 10 mM TBACl solution as a function of the indicated electrode rotation speed (in rpm) to control the diffusion layer thickness. The solution is quiescent for the initial 3.5 min period. The experimental data (black trace) compares well to theory (red dashed line). In contrast, the flux observed for calcium ionophore uptake from the emulsion phase (Ca-IV, blue dashed line) is much smaller than that predicted based on diffusional mass transport.
Figure 4
Figure 4. Accumulated charge with time from ion transfer cyclic voltammograms for a thin-layer membrane containing 100 mmol kg–1 NaTFPB upon uptake of the ionophores (a) K-I, (b) Na-X, and (c) Ca-IV from the emulsion phase. Shown are the total charge for the two ion transfer peaks (squares), indicative of the cation-exchanger loss from the membrane, and the charge for the uncomplexed (so-called free) ion (black circles), which should decrease as the membrane takes up ionophores. Open circles indicate the charge for the ionophore-bound cation transfer peak, which is found to increase linearly with time and indicates the uptake rate for the ionophore.
component | K-I | TBA+TFPB– | Na-X | Ca-IV |
log P | 9.5 | 14.6 | 16.3 | 21.0 |
log J(mol cm–2 s–1) | –11.8 ± 0.3 | –11.5 ± 0.03 | –12.4 ± 0.2 | –13.7 ± 0.3 |
Conclusions
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsmeasuresciau.2c00053.
Detailed experimental information, calculation of the nanoemulsion concentration, analysis of mass transfer rates, and diffusion simulation (PDF)
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Acknowledgments
The authors thank the Swiss National Science Foundation (SNSF, grant number 200021_175622) for financial support of this work and the technical support from Thomas Cherubini. C.M. also appreciates the support from Daiting Han.
References
This article references 35 other publications.
- 1Hashemnejad, S. M.; Badruddoza, A. Z. M.; Zarket, B.; Ricardo Castaneda, C.; Doyle, P. S. Thermoresponsive Nanoemulsion-Based Gel Synthesized through a Low-Energy Process. Nat. Commun. 2019, 10, 2749, DOI: 10.1038/s41467-019-10749-1Google Scholar1https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB3M3psF2isQ%253D%253D&md5=589ae2b5d0e8e2d4f3a738fb0c525ae7Thermoresponsive nanoemulsion-based gel synthesized through a low-energy processHashemnejad Seyed Meysam; Badruddoza Abu Zayed Md; Ricardo Castaneda Carlos; Doyle Patrick S; Zarket BradyNature communications (2019), 10 (1), 2749 ISSN:.Thermoresponsive nanoemulsions find utility in applications ranging from food to pharmaceuticals to consumer products. Prior systems have found limited translation to applications due to cytotoxicity of the compositions and/or difficulties in scaling-up the process. Here, we report a route to thermally gel an oil-in-water nanoemulsion using a small amount of FDA-approved amphiphilic triblock Pluronic copolymers which act as gelling agents. At ambient temperature the suspension displays liquid-like behavior, and quickly becomes an elastic gel at elevated temperatures. We propose a gelation mechanism triggered by synergistic action of thermally-induced adsorption of Pluronic copolymers onto the droplet interface and an increased micelle concentration in the aqueous solution. We demonstrate that the system's properties can be tuned via many factors and report their rheological properties. The nanoemulsions are prepared using a low-energy process which offers an efficient route to scale-up. The nanoemulsion formulations are well-suited for use in cosmetics and pharmaceutical applications.
- 2Singh, Y.; Meher, J. G.; Raval, K.; Khan, F. A.; Chaurasia, M.; Jain, N. K.; Chourasia, M. K. Nanoemulsion: Concepts, Development and Applications in Drug Delivery. J. Controlled Release 2017, 252, 28– 49, DOI: 10.1016/j.jconrel.2017.03.008Google Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXktFWgurk%253D&md5=15e151ec10a01e8288723a33c2df9bdfNanoemulsion: Concepts, development and applications in drug deliverySingh, Yuvraj; Meher, Jaya Gopal; Raval, Kavit; Ali Khan, Farooq; Chaurasia, Mohini; Jain, Nitin K.; Chourasia, Manish K.Journal of Controlled Release (2017), 252 (), 28-49CODEN: JCREEC; ISSN:0168-3659. (Elsevier B.V.)Nanoemulsions are biphasic dispersion of two immiscible liqs.: either water in oil (W/O) or oil in water (O/W) droplets stabilized by an amphiphilic surfactant. These come across as ultrafine dispersions whose differential drug loading; viscoelastic as well as visual properties can cater to a wide range of functionalities including drug delivery. However there is still relatively narrow insight regarding development, manufg., fabrication and manipulation of nanoemulsions which primarily stems from the fact that conventional aspects of emulsion formation and stabilization only partially apply to nanoemulsions. This general deficiency sets up the premise for current review. We attempt to explore varying intricacies, excipients, manufg. techniques and their underlying principles, prodn. conditions, structural dynamics, prevalent destabilization mechanisms, and drug delivery applications of nanoemulsions to spike interest of those contemplating a foray in this field.
- 3Saberi, A. H.; Fang, Y.; McClements, D. J. Fabrication of Vitamin E-Enriched Nanoemulsions by Spontaneous Emulsification: Effect of Propylene Glycol and Ethanol on Formation, Stability, and Properties. Food Res. Int. 2013, 54, 812– 820, DOI: 10.1016/j.foodres.2013.08.028Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhs1Oqs7vF&md5=7f588fa3b058f5c918a25fe6cdd59e0eFabrication of vitamin E-enriched nanoemulsions by spontaneous emulsification: Effect of propylene glycol and ethanol on formation, stability, and propertiesSaberi, Amir Hossein; Fang, Yuan; McClements, David JulianFood Research International (2013), 54 (1), 812-820CODEN: FORIEU; ISSN:0963-9969. (Elsevier B.V.)Oil-in-water nanoemulsions are finding increasing application within pharmaceutical and functional food products as delivery systems to encapsulate lipophilic bioactive components, such as drugs, vitamins, and nutraceuticals. We investigated the influence of two water-sol. cosolvents, propylene glycol (PG) and ethanol, on the formation, stability, and properties of vitamin E acetate-loaded nanoemulsions (VE-NEs) prepd. by spontaneous emulsification. This method simply involves titrating an org. phase (VE + surfactant) into an aq. phase (water + cosolvent). The particle size and optical clarity of the nanoemulsions (10% + VE + 10% surfactant + 80% aq. phase) depended strongly on cosolvent type and concn. The smallest droplets (d < 50 nm) and highest transparency were obsd. when either 30% PG or 20% ethanol was present in the aq. phase. However, these nanoemulsions were highly unstable to droplet growth during storage, esp. at elevated temps., which was attributed to coalescence and Ostwald ripening. Diln. of the nanoemulsions (100 × with water) prior to storage considerably improved their long-term stability esp. at higher storage temps. Undiluted nanoemulsions exhibited a sharp and irreversible increase in turbidity upon heating: ≈ 53°C for the system contg. 30% PG and ≈ 38°C for the system contg. 20% ethanol. Dild. nanoemulsions had much better thermal stability, with a steep increase in turbidity occurring at ≈ 75.5°C for both systems. This study provides important information about the effect of cosolvents on the formation, stability, and phys. properties of VE-NEs suitable for use in pharmaceutical and food products.
- 4Kim, B.-K.; Boika, A.; Kim, J.; Dick, J. E.; Bard, A. J. Characterizing Emulsions by Observation of Single Droplet Collisions─Attoliter Electrochemical Reactors. J. Am. Chem. Soc. 2014, 136, 4849– 4852, DOI: 10.1021/ja500713wGoogle Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXktl2iur0%253D&md5=f9af73ddb463c1ce3deb13594236937bCharacterizing Emulsions by Observation of Single Droplet Collisions-Attoliter Electrochemical ReactorsKim, Byung-Kwon; Boika, Aliaksei; Kim, Jiyeon; Dick, Jeffrey E.; Bard, Allen J.Journal of the American Chemical Society (2014), 136 (13), 4849-4852CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The authors report an electrochem. study of the collisions of single droplets in an emulsion by two methods. In the 1st method, an electroactive redox species, for example, ferrocene, inside a toluene-in-H2O emulsion droplet (but not in the continuous phase) is measured by chronoamperometry during a collision with an ultramicroelectrode (UME). Here, a blip or spike type of collision signal is obsd., representing electrolysis of the droplet contents. In the 2nd method, electrochem. oxidn. of an electroactive redox species in the continuous aq. phase is hindered by a droplet blocking collision. In this case, a staircase current decrease is obsd. From an anal. of single soft particle collision data, one can find the emulsion droplet size distribution and the droplet contents.
- 5Xie, X.; Gutiérrez, A.; Trofimov, V.; Szilagyi, I.; Soldati, T.; Bakker, E. Charged Solvatochromic Dyes as Signal Transducers in PH Independent Fluorescent and Colorimetric Ion Selective Nanosensors. Anal. Chem. 2015, 87, 9954– 9959, DOI: 10.1021/acs.analchem.5b02566Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVKlsLvO&md5=e178b82e4e7529afc90708a33523eb14Charged Solvatochromic Dyes as Signal Transducers in pH Independent Fluorescent and Colorimetric Ion Selective NanosensorsXie, Xiaojiang; Gutierrez, Agustin; Trofimov, Valentin; Szilagyi, Istvan; Soldati, Thierry; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2015), 87 (19), 9954-9959CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Ionophore-based ion selective optical nanosensors that operate independently of the sample pH are developed here using elec. charged solvatochromic dyes as signal transducers. A series of dye mols. with a D-π-A structure was synthesized and characterized in various solvents and incorporated into ion selective nanospheres for K+, Na+, and H+. Since dye leakage was greatly suppressed when the solvatochromic dyes were encapsulated in the nanosphere core, ion sensing nanospheres were explored for cellular ion imaging in Dictyostelium discoideum live cells but spontaneous dye loss resulted in undesired staining of cells. The in vitro anal. of potassium in human plasma was successfully demonstrated with this approach. A theor. model was developed for the response of the ion selective nanosensors contg. charged solvatochromic dyes. The nanosensors exhibited a tunable response range, high sensitivity, and good stability.
- 6Soda, Y.; Robinson, K. J.; Nussbaum, R.; Bakker, E. Protamine/Heparin Optical Nanosensors Based on Solvatochromism. Chem. Sci. 2021, 12, 15596– 15602, DOI: 10.1039/D1SC04930EGoogle Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXisVykt73O&md5=9a7d9e6943b27c1ec585b403c6e6a84eProtamine/heparin optical nanosensors based on solvatochromismSoda, Yoshiki; Robinson, Kye J.; Nussbaum, Robin; Bakker, EricChemical Science (2021), 12 (47), 15596-15602CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)Optical nanosensors for the detection of polyions, including protamine and heparin, have to date relied upon ion-exchange reactions involving an analyte and an optical transducer. Unfortunately, due to the limited selectivity of the available ionophores for polyions, this mechanism has suffered from severe interference in complex sample matrixes. To date no optical polyion nanosensors have demonstrated acceptable performance in serum, plasma or blood. Herein we describe a new type of nanosensor based on our discovery of a "hyper-polarizing lipophilic phase" in which dinonylnaphthalenesulfonate (DNNS-) polarizes a solvatochromic dye much more than even an aq. environment. We have found that the apparent polarity of the org. phase is only modulated when DNNS- binds to large polyions such as protamine, unlike singly charged ions that lack the cooperative binding required to cause a significant shift in the distribution of the polarizing DNNS- ions. Our new sensing mechanism allows solvatochromic signal transduction without the transducer undergoing ion exchange. The result is significantly improved sensitivity and selectivity, enabling for the first time the quantification of protamine and heparin in human plasma using optical nanosensors that correlates with the current gold std. anal. method, the anti-Xa factor assay.
- 7Sabaragamuwe, S. G.; Conti, D.; Puri, S. R.; Andreu, I.; Kim, J. Single-Entity Electrochemistry of Nanoemulsion: The Nanostructural Effect on Its Electrochemical Behavior. Anal. Chem. 2019, 91, 9599– 9607, DOI: 10.1021/acs.analchem.9b00920Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXht1OqsbbE&md5=4a735aaa012ce31e20bf69ba51e2fd1bSingle-Entity Electrochemistry of Nanoemulsion: The Nanostructural Effect on Its Electrochemical BehaviorSabaragamuwe, Shashika Gunathilaka; Conti, Dylan; Puri, Surendra Raj; Andreu, Irene; Kim, JiyeonAnalytical Chemistry (Washington, DC, United States) (2019), 91 (15), 9599-9607CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)New electrochem. approaches have been applied to investigate nanoemulsions (NEs) for their nanostructures and the relevant electrochem. activity by single-entity electrochem. (SEE). Herein, we make highly monodisperse NEs with ∼40 nm diam., composed of biocompatible surfactants, castor oil as plasticizers, and ion exchangers. Dynamic light scattering (DLS) measurements with periodically varying surfactant to oil ratios provide us with a structural implication about uneven distributions of incorporating components inside NEs. To support this structural insight, we apply SEE and selectively monitor electron-transfer reactions occurring at individual NEs contg. ferrocene upon each collision onto a Pt ultramicroelectrode. The quant. anal. of the nanoelectrochem. results along with DLS and transmission electron microscopy (TEM) measurements reveal nanostructured compartments of incorporating components inside NEs and their effect on the electrochem. behavior. Indeed, a tunneling barrier inside NEs could be formed depending on the NE compn., thus detg. an electrochem. behavior of NEs, which cannot be differentiated by a general morphol. study such as DLS and TEM but by our SEE measurements. Furthermore, by employing the nanopipet voltammetry with an interface between two immiscible electrolyte solns. (ITIES) to mimic the NE interface, we could explicitly investigate that the electron-transfer reaction occurring inside NEs is facilitated by the ion-transfer reaction. Overall, these comprehensive electrochem. approaches enable us to elucidate the relation between structures and the electrochem. functionality of NEs and provide quant. criteria for the proper compns. of NEs regarding their activity in the electrochem. applications. Also, this finding should be a prerequisite for suitable biomedical/electrochem. applications of NEs.
- 8Soda, Y.; Gao, W.; Bosset, J.; Bakker, E. Emulsion Doping of Ionophores and Ion-Exchangers into Ion-Selective Electrode Membranes. Anal. Chem. 2020, 92, 14319– 14324, DOI: 10.1021/acs.analchem.0c02920Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitFSltLjP&md5=2184c2d7596301fdc25990637c4c0805Emulsion Doping of Ionophores and Ion-Exchangers into Ion-Selective Electrode MembranesSoda, Yoshiki; Gao, Wenyue; Bosset, Jerome; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2020), 92 (21), 14319-14324CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Ion-selective electrodes (ISEs) are widely used anal. devices to selectively measure ionic species. Despite significant advances in recent years, ion-selective membranes are still mostly prepd. in the same manner, by preloading the selective components into a solvent that is subsequently cast into a membrane or film. This paper describes an alternative method to prep. ISE membranes by mass transfer of the sensing components from an emulsion phase. Specifically, blank (undoped) plasticized poly(vinyl chloride) (PVC) membranes mounted into an electrode body are immersed into an aq. soln. contg. analyte ions and an appropriate emulsion of the desired sensing components to allow their transfer into the membrane. The concept is demonstrated with conventional membrane electrodes contg. an inner soln. as well as all-solid-state electrodes. It is shown to be universally useful for the realization of ISEs for K+, Na+, Ca2+, and NO3-.
- 9Apichai, S.; Wang, L.; Pankratova, N.; Grudpan, K.; Bakker, E. Ion-Exchange Microemulsions for Eliminating Dilute Interferences in Potentiometric Determinations. Electroanalysis 2018, 30, 2462– 2466, DOI: 10.1002/elan.201800366Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhsFOhs7jF&md5=3e6156efdf1d7351b454c1dfa9bd86d2Ion-Exchange Microemulsions for Eliminating Dilute Interferences in Potentiometric DeterminationsApichai, Sutasinee; Wang, Lu; Pankratova, Nadezda; Grudpan, Kate; Bakker, EricElectroanalysis (2018), 30 (10), 2462-2466CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)We report here for the first time on the use of functional microemulsions in potentiometric assays to remove dil. interferences from soln. when measuring high concns. of analyte. The microemulsions are similarly formulated to the ion-selective membrane used in the measurement and act as sacrificial material. They are here stabilized by the triblock copolymer pluronic F-127 and contain the chloride salt of the tridodecylmethylammonium cation, which also serves as anion-exchanger in the membrane electrode. Both membrane and microemulsion are preconditioned with chloride. If an anionic interference is present at moderate concn., the rapid equilibration with the functionalized microemulsion results in a quant. removal. The principle is explored with salicylate as common interference in the detection of chloride in physiol. samples. The data agree well to an equil. ion-exchange model for the microemulsion. Salicylate levels up to millimolar can be effectively removed. Unfortunately, quaternary ammonium salt from the microemulsion is found to contaminate the ion-selective membrane phase. Indeed, a cation-exchanging valinomycin membrane in contact with concd. anion-exchanging microemulsions shows a large potential increase. This indicates that the membrane changes from cation to anion permselectivity. This contamination of the membrane by the microemulsion phase must be overcome for a practical application of the approach.
- 10Tambe, D. E.; Sharma, M. M. The Effect of Colloidal Particles on Fluid-Fluid Interfacial Properties and Emulsion Stability. Adv. Colloid Interface Sci. 1994, 52, 1– 63, DOI: 10.1016/0001-8686(94)80039-1Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXmvFCjtA%253D%253D&md5=4d7eff32ffd55cfc7ac1a5535f6951e9The effect of colloidal particles on fluid-fluid interfacial properties and emulsion stabilityTambe, David E.; Sharma, Mukul M.Advances in Colloid and Interface Science (1994), 52 (), 1-65CODEN: ACISB9; ISSN:0001-8686.A review of relevant work done on the effects of colloidal particles on the rheol. properties of fluid-fluid interfaces and on emulsion stability. Results are presented which show that colloid particles stabilize emulsions primarily by providing steric hindrance to drop-drop coalescence and by modifying the rheol. properties of the interfacial region. The effectiveness of colloid particles in stabilizing emulsions depends largely on the formation of a sufficiently 'dense layer' of particles at the oil-H2O interface. The rheol. properties of the interfacial region also change as the concn. of particles at the interface increases and complete surface coverage is achieved. At sufficiently high concns. of particles, colloid-laden interfaces exhibit viscoelastic behavior. Viscoelastic interfaces enhance emulsion stability by increasing the magnitude of steric hindrance and by retarding the rate of liq. drainage between coalescing emulsion droplets. 80 Refs.
- 11Wang, X.; Collot, M.; Omran, Z.; Vandamme, T. F.; Klymchenko, A.; Anton, N. Further Insights into Release Mechanisms from Nano-Emulsions, Assessed by a Simple Fluorescence-Based Method. J. Colloid Interface Sci. 2020, 578, 768– 778, DOI: 10.1016/j.jcis.2020.06.028Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXht1Sru7rF&md5=84c99822b8eb0073bcb4b557ec031555Further insights into release mechanisms from nano-emulsions, assessed by a simple fluorescence-based methodWang, Xinyue; Collot, Mayeul; Omran, Ziad; Vandamme, Thierry F.; Klymchenko, Andrey; Anton, NicolasJournal of Colloid and Interface Science (2020), 578 (), 768-778CODEN: JCISA5; ISSN:0021-9797. (Elsevier B.V.)Nano-emulsion consists of a dispersion of oil droplets sizing below 200 nm, in aq. continuous phase, and generally stabilized by low-mol.-wt. surfactants. These stable nano-carriers are able to encapsulate and transport lipophilic mols. poorly sol. in water. However, the question on the leakage and release mechanisms of an active pharmaceutical ingredient, from oil nano-droplets to an acceptor medium has not been clearly addressed. Herein, we developed a simple fluorescence approach based on self-quenching of lipophilic fluorophore-based on Nile Red (NR668) to monitor cargo transfer from lipid nano-droplets to the acceptor medium. In this method, the fluorophore release can be monitored by the increase in its fluorescence quantum yield and the blue shift in its emission spectrum. The studies of the release process allow emphasizing an important role of the bulk aq. medium in controlling the droplet to droplet fluorophore transfer and the attained equil. The developed methodol. could be applied to monitor release of other lipophilic dyes and it could help to better understand the cargo release from nanocarriers.
- 12Ryu, V.; Corradini, M. G.; McClements, D. J.; McLandsborough, L. Impact of Ripening Inhibitors on Molecular Transport of Antimicrobial Components from Essential Oil Nanoemulsions. J. Colloid Interface Sci. 2019, 556, 568– 576, DOI: 10.1016/j.jcis.2019.08.059Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhs1ynsr7E&md5=473a69f2a4f97a406d6eb07405a0bc23Impact of ripening inhibitors on molecular transport of antimicrobial components from essential oil nanoemulsionsRyu, Victor; Corradini, Maria G.; McClements, David J.; McLandsborough, LynneJournal of Colloid and Interface Science (2019), 556 (), 568-576CODEN: JCISA5; ISSN:0021-9797. (Elsevier B.V.)The objective of this study was to provide insights into the mechanisms involved in the mass transport of antimicrobial compds. from essential oil nanoemulsions to bacterial cell membranes. Origanum oil-in-water nanoemulsions were produced using spontaneous emulsification by titrating a mixt. of essential oil, ripening inhibitor, and surfactant (Tween 80) into 5 mM sodium citrate buffer (pH 3.5). Stable nanoemulsions contg. relatively small droplets (d < 60 nm) were produced using this low-energy method. The nature of the ripening inhibitor used in the oil phase of the nanoemulsions affected the antimicrobial activity of the nanoemulsions: corn (LCT) > medium-chain triglycerides (MCT). Differences in antimicrobial activity were attributed to the differences in the rate of transfer of hydrophobic antimicrobial constituents from the nanoemulsion to the MCT emulsion, which was used to mimic the hydrophobic region of the bacterial cell membranes. Each antimicrobial nanoemulsion was sepd. from the MCT emulsion by a dialysis tubing. Dialysis tubing with two different pore sizes was used, one excluding nanoemulsion droplet and micelle delivery, allowing the delivery of antimicrobial compds. only through the aq. phase and the other by both the aq. phase and micelles. For origanum oil nanoemulsions, the delivery of all antimicrobial agents occurred more efficiently when micelles were present.
- 13Madawala, H.; Sabaragamuwe, S. G.; Elangovan, S.; Kim, J. In Situ Measuring Partition Coefficient at Intact Nanoemulsions: A New Application of Single-Entity Electrochemistry. Anal. Chem. 2021, 93, 1154– 1160, DOI: 10.1021/acs.analchem.0c04205Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXisV2qurrM&md5=a660d352b672721441ded0c1177196f0In Situ Measuring Partition Coefficient at Intact Nanoemulsions: A New Application of Single-Entity ElectrochemistryMadawala, Hiranya; Sabaragamuwe, Shashika Gunathilaka; Elangovan, Subhashini; Kim, JiyeonAnalytical Chemistry (Washington, DC, United States) (2021), 93 (2), 1154-1160CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The authors report a new application of the single-entity electrochem. (SEE) to in situ measure a partition coeff. at intact nanoemulsions (NEs). The partition coeff. at intact NEs is the most crucial physicochem. property to det. the uptake of delivery mols. inside NEs. It, however, was not unequivocally elucidated by currently existing techniques based on ex situ measurements. Herein, the authors apply the single-entity electrochem. (SEE) to directly and quant. measure the partition coeff. at NEs in situ. The authors use NEs featured with amphiphilic triblock copolymer (Pluronic F-127) as a model system to ext./preconc. 2-aminobiphenyl (2-ABP) dissolved in the H2O and demonstrate a new application of SEE to in situ quant. est. the amts. of 2-ABP distributed into each intact NE. The authors' SEE measurements reveal that the partitioning is governed by extn. of 2-ABP inside NEs rather than its adsorption on the NE surface, and this extn. is remarkably efficient with up to ~ 8 orders of magnitude of the preconcn. factor, thus leading to the unprecedentedly large partition coeff. of 1.9 (±1.4) x 1010. This result implies that not only the thermodn. distribution but also the intermol. interaction of extd. compds. inside NEs could play a significant role in the apparent partition coeff. (P = 1.9 (±1.4) x 1010). The exptl. detd. partition coeff. was validated by mol. dynamics (MD) simulations with showing a stabilizing role of intermol. interaction in the partitioned system. The authors further verified the authors' methodol. with other compds. exhibiting arom. properties, e.g., ferrocenemethanol. Significantly, the authors' new approach can be readily applicable to study practical NEs com. marketed for drug, food, and cosmetics.
- 14He, W.; Wang, C.; Wang, H.; Jian, M.; Lu, W.; Liang, X.; Zhang, X.; Yang, F.; Zhang, Y. Integrated Textile Sensor Patch for Real-Time and Multiplex Sweat Analysis. Sci. Adv. 2019, 5, eaax0649 DOI: 10.1126/sciadv.aax0649Google ScholarThere is no corresponding record for this reference.
- 15Mao, C.; Robinson, K. J.; Yuan, D.; Bakker, E. Ion–Ionophore Interactions in Polymeric Membranes Studied by Thin Layer Voltammetry. Sens. Actuators, B 2022, 358, 131428 DOI: 10.1016/j.snb.2022.131428Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XivVymt7c%253D&md5=0da19efb7c8d1f37756a160dabde4b09Ion-ionophore interactions in polymeric membranes studied by thin layer voltammetryMao, Canwei; Robinson, Kye J.; Yuan, Dajing; Bakker, EricSensors and Actuators, B: Chemical (2022), 358 (), 131428CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)In ion sensing applications, selective ion-receptor complexation is the mol. basis for endowing the sensing material with selectivity. In this work, thin polymeric membrane-based ion transfer voltammetry is used to investigate ion-receptor complexation, using a range of elec. neutral ionophores and surfactants as examples. Previous studies lacked a convincing approach to eliminate the influence from transducing layer, resulting in deviations of the obsd. binding consts. compared to potentiometric methods. A recently developed method allows for subtracting the potential changes of the transducing layer, thereby overcoming this challenge. Using this approach, a range of ionophores are assessed. Valinomycin for the detection of potassium gave a logarithmic complex formation const. in the membrane of 9.69 ± 0.25 with a 1:1 stoichiometry. Lithium ionophore VI for lithium gave a logarithmic stability const. of 5.97 ± 0.06 with 1:2 complexes; while sodium ionophore X for sodium (7.57 ± 0.03, 1:1) and calcium ionophore IV for calcium (21.57 ± 0.25, 1:3) were also characterized, in addn. to their complexes with potential interfering ions. The complex formation of three surfactants with potassium are also explored in membranes contg. valinomycin, with Brij-35 (4.88 ± 0.08, 1:1), Triton X-100 (5.63 ± 0.10, 1:1), F-127 (4.63 ± 0.49, 1:1). Limitations of the approach are discussed, which includes the need for electrochem. reversibility and a sufficiently high lipophilicity to adequately retain the components in the membrane.
- 16Bruckenstein, S.; Shay, M. Experimental Aspects of Use of the Quartz Crystal Microbalance in Solution. Electrochim. Acta 1985, 30, 1295– 1300, DOI: 10.1016/0013-4686(85)85005-2Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28Xht1amsA%253D%253D&md5=360e8960c06534dabe72b345ac6abfc6Experimental aspects of use of the quartz crystal microbalance in solutionBruckenstein, S.; Shay, M.Electrochimica Acta (1985), 30 (10), 1295-300CODEN: ELCAAV; ISSN:0013-4686.Transistor-transistor-logic based circuitry is described for measuring the resonant frequency of an oscillating quartz crystal having 1 face in contactwith an electrolyte. The circuitry facilitates application of the quartz crystal microbalance technique to in situ electrogravimetric studies of submonolayer and many monolayer thick electrodeposited and electrosorbed films. The effect of the temp. and viscosity of the soln. , and height of liq. above the crystal were investigated and the results correlated with theory. An in situ soln. method for detg. the mass sensitivity of the crystal is described and the latter sensitivity is shown to be the same as the calcd. vacuum sensitivity. The effect of double layer structure and specific adsorption is discussed.
- 17Sauerbrey, G. Verwendung von Schwingquarzen Zur Wägung Dünner Schichten Und Zur Mikrowägung. Zeitschrift für Phys. 1959, 155, 206– 222, DOI: 10.1007/BF01337937Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaG1MXoslSjtQ%253D%253D&md5=ff97a9cc63637eb9823aebfeb57a367bThe use of quartz oscillators for weighing thin layers and for microweighingSauerbrey, GuntherZeitschrift fuer Physik (1959), 155 (), 206-22CODEN: ZEPYAA; ISSN:0044-3328.The frequency of a quartz plate is altered if a layer of foreign material is deposited on the quartz, e.g. by evapn. Since changes in frequency can be measured very accurately, the phenomenon can be used for weighing thin layers. The change in frequency is proportional to the d. of the foreign layer and the proportionality const. can be calcd. from the characteristic frequency of the quartz plate. The accuracy of the method is limited by the temp. variation of the characteristic frequency of the quartz oscillator. For a temp. fluctuation of 1° the accuracy is ±4.10-9 g./cm. This corresponds to a mean thickness of the layer of 0.4 A. at a d. of 1 g./cc. The method can also be used for direct microweighing, e.g. by evapg. a drop of a soln. on the quartz plate.
- 18Niu, L.; Kvarnström, C.; Ivaska, A. Mixed Ion Transfer in Redox Processes of Poly(3,4-Ethylenedioxythiophene). J. Electroanal. Chem. 2004, 569, 151– 160, DOI: 10.1016/j.jelechem.2004.01.029Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXltFOltbY%253D&md5=4d70a1688f042e4a33f255648a405262Mixed ion transfer in redox processes of poly(3,4-ethylenedioxythiophene)Niu, Li; Kvarnstrom, Carita; Ivaska, AriJournal of Electroanalytical Chemistry (2004), 569 (2), 151-160CODEN: JECHES ISSN:. (Elsevier)A model considering the transfer of counterions and solvent mols. is presented to explain the complicated ion transfer in polymer films during electrochem. redox processes. The developed mixed ion transfer model is used to analyze the ion transfer behavior of poly(3,4-ethylenedioxythiophene) during doping and dedoping processes. Both anions and cations are involved in n-doping as well as in p-doping processes. The behavior of different electrolyte ions was also studied. The developed model shows that solvent mols. are also transferred in conjunction with the ion transfer.
- 19Bard, A. J.; Faulkner, L. R. Electrochemical Methods: Fundamentals and Applications,2nd Edition; John Wiley & Sons, Incorporated, 2000.Google ScholarThere is no corresponding record for this reference.
- 20Forrest, T.; Zdrachek, E.; Bakker, E. Thin Layer Membrane Systems as Rapid Development Tool for Potentiometric Solid Contact Ion-selective Electrodes. Electroanalysis 2020, 32, 799– 804, DOI: 10.1002/elan.201900674Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXmt1Witw%253D%253D&md5=de93414bee9fa59be8a7c21b450da899Thin Layer Membrane Systems as Rapid Development Tool for Potentiometric Solid Contact Ion-selective ElectrodesForrest, Tara; Zdrachek, Elena; Bakker, EricElectroanalysis (2020), 32 (4), 799-804CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)The use of thin membrane layer ion-selective electrodes (of ∼200 nm thickness) as rapid diagnosis tool is proposed. While conventional solid contact systems (with a membrane of ∼250 μm thickness) may exhibit a satisfactory stability for regular lab. use, a signal degrdn. can still be distinguished over a longer period of time but this requires tedious and time consuming tests. By diminishing the thickness of the membrane by a factor of 103 approx., diffusion processes happen faster, and the lifetime is significantly reduced. This would ordinarily be a strong drawback but not if the aim is to detect a membrane deterioration in a shorter time frame. This characteristic makes thin membrane systems an ideal tool for rapid complications identification in the development process of conventional solid contact electrodes. The approach is demonstrated here in the development of an all new solid contact probe for anions. PEDOT-C14, a conducting polymer, was used for the first time in a solid contact electrode with an anion exchange membrane for the detection of nitrate. The thin layer configuration was used to optimize the polymn. parameters as well as the membrane compn. without having to run week-long trials. A stable conventional solid contact electrode was in the end successfully developed and exhibited a lower detection limit of 10-5.5 M for nitrate with a stable Nernstian response for several days.
- 21Kabagambe, B.; Izadyar, A.; Amemiya, S. Stripping Voltammetry of Nanomolar Potassium and Ammonium Ions Using a Valinomycin-Doped Double-Polymer Electrode. Anal. Chem. 2012, 84, 7979– 7986, DOI: 10.1021/ac301773wGoogle Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xht1SitLbN&md5=bad6a704035c11aff8aa3b1d731a52aeStripping Voltammetry of Nanomolar Potassium and Ammonium Ions Using a Valinomycin-Doped Double-Polymer ElectrodeKabagambe, Benjamin; Izadyar, Anahita; Amemiya, ShigeruAnalytical Chemistry (Washington, DC, United States) (2012), 84 (18), 7979-7986CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Here, the authors report on the 1st application of an ionophore-doped double-polymer electrode for ion-transfer stripping voltammetry (ITSV) to explore the nanomolar limit of detection (LOD) and multiple-ion detectability. The authors developed a theor. model for ITSV at a thin ionophore-doped membrane on the solid supporting electrode to demonstrate that its LOD is controlled by the equil. preconcn. of an aq. analyte ion as an ionophore complex into the thin polymer membrane and is lowered by the formation of a more stable ion-ionophore complex. The theor. predictions were confirmed using valinomycin as a K+-selective ionophore, which forms a ∼ 60 times more stable complex with K+ than with NH4+, as confirmed by cyclic voltammetry. A LOD of 0.6 nM K+ was achieved by ITSV using com. ultrapure water as a K+-free media, where NH4+ contamination at a higher concn. was also detected by ITSV. The dependence of the ITSV response on the preconcn. time was monitored under the rotating-electrode configuration and analyzed theor. to directly det. ∼100 nM NH4+ and ∼5 nM K+ contaminations in com. ultrapure water and lab.-purified water, resp., without the background ITSV measurement of an analyte-free blank soln.
- 22Kim, Y.; Rodgers, P. J.; Ishimatsu, R.; Amemiya, S. Subnanomolar Ion Detection by Stripping Voltammetry with Solid-Supported Thin Polymeric Membrane. Anal. Chem. 2009, 81, 7262– 7270, DOI: 10.1021/ac900995aGoogle Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXptlGnsrs%253D&md5=1c3e200aa50de6dffea2be5b9a0fa120Subnanomolar Ion Detection by Stripping Voltammetry with Solid-Supported Thin Polymeric MembraneKim, Yushin; Rodgers, Patrick J.; Ishimatsu, Ryoichi; Amemiya, ShigeruAnalytical Chemistry (Washington, DC, United States) (2009), 81 (17), 7262-7270CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Subnanomolar limits of detection (LODs) were obtained for stripping voltammetry based on ion transfer at the interface between the aq. sample and the thin polymeric membrane supported with a solid electrode. It was predicted theor. that a lower LOD can be obtained for a more lipophilic analyte ion, which can be preconcd. at a higher equil. concn. in the solid-supported thin polymeric membrane to enhance a stripping current response. This study is the 1st to exptl. confirm the general theor. prediction for both cationic and anionic analytes. Proof-of-concept expts. demonstrate that a subnanomolar LOD of (8 ± 4) × 10-11 M Pr4N+ is significantly lower than a LOD of less lipophilic Et4N+. Importantly, stripping voltammetry of the cationic analytes is enabled by newly introducing an oxidatively doped poly(3,4-ethylenedioxythiophene) film as the intermediate layer between a plasticized poly(vinyl chloride) membrane and a Au electrode. However, an undoped poly(3-octylthiophene) film was used as an intermediate layer for voltammetric detection of a lipophilic inorg. anion, hexafluoroarsenate, an arsenical biocide found recently in wastewater. A LOD of (9 ± 2) × 10-11 M hexafluoroarsenate thus obtained by ion-transfer stripping voltammetry is comparable to a LOD of 80 pM by inductively coupled plasma mass spectrometry with anion-exchange chromatog. Great sensitivity for a lipophilic ion is potentially useful for environmental anal. because high lipophilicity of an ion is relevant to its bioaccumulation and toxicity.
- 23Mao, C.; Yuan, D.; Wang, L.; Bakker, E. Separating Boundary Potential Changes at Thin Solid Contact Ion Transfer Voltammetric Membrane Electrodes. J. Electroanal. Chem. 2021, 880, 114800 DOI: 10.1016/j.jelechem.2020.114800Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXit12nsb3N&md5=5c4a6990d93dda1c73b4aaee99d17b2dSeparating boundary potential changes at thin solid contact ion transfer voltammetric membrane electrodesMao, Canwei; Yuan, Dajing; Wang, Lu; Bakker, EricJournal of Electroanalytical Chemistry (2021), 880 (), 114800CODEN: JECHES; ISSN:1873-2569. (Elsevier B.V.)Thin ion-selective membrane films deposited on solid electrode substrate are useful tools to study ion transfer processes. This is because the exptl. conditions may be chosen such that diffusion processes within the membrane and contacting aq. soln. are not rate limiting. In an ideal case, therefore, equil. considerations may be used to describe the resulting ion transfer voltammograms. For example, the electrochem. oxidn. of an elec. neutral redox mol. in the membrane results in a cationic oxidized form. To preserve electroneutrality, a cation is transferred out of the membrane into soln., freeing the cation-exchanger of the membrane to become the counterion of the oxidized redox mol. This work describes a model system that agrees well with thermodn. theory, using the lipophilic (1-dodecyl-1H-1,2,3-triazol-4-yl)ferrocene as redox mol. and a monovalent ref. cation for ion transfer. The full peak width at half max. was found as 0.110 V, in agreement with theory, and with peak current proportional to scan rate supporting thin layer behavior. The charge passed during the voltammetric scan was related to ion-exchanger concn. available for ion extn. as a function of potential. Subtraction of the ion transfer potential using the ref. ion from the exptl. one for each charge increment gave the potential change for the electrochem. ion-to-electron transducer. In one application, the potential change of the polymeric transducing layer poly(3-octylthiophene) (POT) film upon electrochem. oxidn. within the membrane was characterized. A nonlinear potential-charge curve was obsd., in contrast to earlier assumptions.
- 24Cuartero, M.; Crespo, G. A.; Bakker, E. Ionophore-Based Voltammetric Ion Activity Sensing with Thin Layer Membranes. Anal. Chem. 2016, 88, 1654– 1660, DOI: 10.1021/acs.analchem.5b03611Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitV2ntr%252FO&md5=fc1a1919bd579e1e69a5fc6e773d616bIonophore-Based Voltammetric Ion Activity Sensing with Thin Layer MembranesCuartero, Maria; Crespo, Gaston A.; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2016), 88 (3), 1654-1660CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)As shown in recent work, thin layer ion-selective multi-ionophore membranes can be interrogated by cyclic voltammetry to detect the ion activity of multiple species simultaneously and selectively. Addnl. fundamental evidence is put forward on ion discrimination with thin multi-ionophore-based membranes with thicknesses of 200 ± 25 nm and backside contacted with poly-3-octylthiophene (POT). An anodic potential scan partially oxidizes the POT film (to POT+), thereby initiating the release of hydrophilic cations from the membrane phase to the sample soln. at a characteristic potential. Varying concn. of added cation-exhanger demonstrates that it limits the ion transfer charge and not the deposited POT film. Voltammograms with multiple peaks are obsd. with each assocd. with the transfer of one type of ion (lithium, potassium, and sodium). Exptl. conditions (thickness and compn. of the membrane and concn. of the sample) are chosen that allow one to describe the system by a thermodn. rather than kinetic model. As a consequence, apparent stability consts. for sodium, potassium, and lithium (assuming 1:1 stoichiometry) with their resp. ionophores are calcd. and agree well with the values obtained by the potentiometric sandwich membrane technique. As an anal. application, a membrane contg. three ionophores was used to det. lithium, sodium, and potassium in artificial samples at the same location and within a single voltammetric scan. Lithium and potassium were also detd. in undiluted human plasma in the therapeutic concn. range.
- 25Bandey, H. L.; Martin, S. J.; Cernosek, R. W.; Hillman, A. R. Modeling the Responses of Thickness-Shear Mode Resonators under Various Loading Conditions. Anal. Chem. 1999, 71, 2205– 2214, DOI: 10.1021/ac981272bGoogle Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXis1WgsLo%253D&md5=9c3ef38e0b41c68800db263d0f08437eModeling the Responses of Thickness-Shear Mode Resonators under Various Loading ConditionsBandey, Helen L.; Martin, Stephen J.; Cernosek, Richard W.; Hillman, A. RobertAnalytical Chemistry (1999), 71 (11), 2205-2214CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A general model is developed to describe the elec. responses of thickness-shear mode resonators subject to a variety of surface conditions. The model incorporates a phys. diverse set of single-component loadings, including rigid solids, viscoelastic media, and fluids (Newtonian or Maxwellian). The model allows any no. of these components to be combined in any configuration. Such multiple loadings are representative of a variety of phys. situations encountered in electrochem. and other liq.-phase applications, as well as gas-phase applications. In the general case, the response of the composite load is not a linear combination of the individual component responses. Application of the model is discussed in a qual. diagnostic fashion to gain insight into the nature of the interfacial structure, and in a quant. fashion to ext. appropriate phys. parameters such as liq. viscosity and d. and polymer shear moduli.
- 26Chan, A. D. C.; Harrison, D. J. NMR Study of the State of Water in Ion-Selective Electrode Membranes. Anal. Chem. 1993, 65, 32– 36, DOI: 10.1021/ac00049a008Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38Xms1eksLg%253D&md5=1359f6c1df62599873ec16361bea04e7NMR study of the state of water in ion-selective electrode membranesChan, Andy D. C.; Harrison, D. JedAnalytical Chemistry (1993), 65 (1), 32-6CODEN: ANCHAM; ISSN:0003-2700.Variable-temp. 1H and 2D NMR studies of H2O and D2O uptake in poly(vinyl chloride) (PVC) based ion-selective membranes were employed to evaluate the state of water. The data show that water (heavy or light) in the membranes is present as freezable water, indicating it is present as droplets or clusters. The water freezes between 0 and -15°, and calcns. suggest the min. droplet diam. is about 0.016 μm, but a large size range exists. The light scattering centers obsd. during water uptake must be due to these droplets, at least in part. The NMR chem. shift of water is a function of the concn. of KB(C6H5)4 added to the membrane, and the range of chem. shifts demonstrates there are a range of environments for water.
- 27Grause, G.; Hirahashi, S.; Toyoda, H.; Kameda, T.; Yoshioka, T. Solubility Parameters for Determining Optimal Solvents for Separating PVC from PVC-Coated PET Fibers. J. Mater. Cycles Waste Manag. 2017, 19, 612– 622, DOI: 10.1007/s10163-015-0457-9Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVGhsL3F&md5=744a4f693901234b524f314d5af6cba4Solubility parameters for determining optimal solvents for separating PVC from PVC-coated PET fibersGrause, Guido; Hirahashi, Suguru; Toyoda, Hiroshi; Kameda, Tomohito; Yoshioka, ToshiakiJournal of Material Cycles and Waste Management (2017), 19 (2), 612-622CODEN: JMCMFW; ISSN:1438-4957. (Springer Japan)Poly(vinyl chloride) (PVC) in PVC-coated poly(ethylene terephthalate) (PET) fabrics can be sepd. through dissoln. in a suitable solvent, leaving only the PET fibers. We investigated the soly. of PVC in 30 solvents using swelling tests. The results were compared with those obtained using the Hansen, Gutmann, Swain, ET(30), and Kamlet-Taft parameters. For this purpose, Gaussian plots of the PVC swellability vs. soly. parameter were used to decide the applicability of the soly. parameter system. Only Gutmann's electron acceptor-donor parameter (AN + DN) and the Kamlet-Taft parameters β and π* could describe the PVC-solvent system satisfactorily. THF (THF), Me Et ketone (MEK), N,N-dimethylformamide (DMF), cyclohexanone, and cyclopentanone were tested for sepg. PVC from PET at different temps. THF dissolved PVC at 20 °C, while cyclohexanone and cyclopentanone did so at 40 °C. Traces of PVC remained on the PET fibers when DMF was used. Complete dissoln. of PVC was not achieved at any temp. with MEK. The present work shows that soly. parameters are a helpful tool for the search for suitable solvents. It shows also that soly. parameters have to be selected carefully, since their usefulness depends strongly on the polymer properties.
- 28Robinson, K.; Mao, C.; Bakker, E. Surfactants for Optode Emulsion Stabilization without Sacrificing Selectivity or Binding Constants. Anal. Chem. 2021, 93, 15941– 15948, DOI: 10.1021/acs.analchem.1c03232Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXisFWrsL7K&md5=c78957566c620d2fd977daa4d79bb337Surfactants for Optode Emulsion Stabilization without Sacrificing Selectivity or Binding ConstantsRobinson, Kye; Mao, Canwei; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2021), 93 (48), 15941-15948CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We compare here the effect of surfactants on ion-selective membranes measured via voltammetry and optode emulsions measured optically. Cyclic voltammetry on a thin-film ion-selective membrane is shown to be a useful screening technique for the estn. of effective complex formation consts. and selectivity coeffs. for different surfactants with various cations. This technique is particularly useful for its ability to identify sep. ion-transfer events (free, surfactant complexed, ionophore complexed) for a specific membrane. However, we also caution against the over-reliance on this technique as changes in membrane characteristics are obsd. following surfactant partitioning. Of the surfactants explored here, a zwitterionic sulfobetaine-based surfactant was found to stabilize sensors without reducing effective binding consts. and selectivity, with greatly superior characteristics to other commonly utilized surfactants. Those include Brij-35, F-127, and Triton X-100, all of which showed significant binding to so-called free ions in the membrane, resulting in peak potential shifts of 199 ± 10, 180 ± 24, 278 ± 11 mV, resp., for potassium following the subtraction of transducing layer effects. This peak shift translated to a much larger undesired free ion response in optode emulsions. The selectivity in emulsion-based systems was also shown to decrease in the presence of nonionic surfactants compared to that contg. the zwitterion.
- 29Bakker, E.; Pretsch, E. Lipophilicity of Tetraphenylborate Derivatives as Anionic Sites in Neutral Carrier-Based Solvent Polymeric Membranes and Lifetime of Corresponding Ion-Selective Electrochemical and Optical Sensors. Anal. Chim. Acta 1995, 309, 7– 17, DOI: 10.1016/0003-2670(95)00077-DGoogle Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXmtVygsro%253D&md5=092477e1de78c54275c66558fd2c1a33Lipophilicity of tetraphenylborate derivatives as anionic sites in neutral carrier-based solvent polymeric membranes and lifetime of corresponding ion-selective electrochemical and optical sensorsBakker, Eric; Pretsch, ErnoeAnalytica Chimica Acta (1995), 309 (1-3), 7-17CODEN: ACACAM; ISSN:0003-2670. (Elsevier)The leaching process of lipophilic anionic additives (e.g., tetraphenylborates) from neutral carrier based membranes into an aq. sample is quantified. While the necessary lipophilicity (i.e., equil. partition coeff.) of the additive for a certain lifetime of the sensor is identical to the one of neutral compds. described earlier, its quantification needs to consider the coextn. equil. with the counterions between both phases. It is shown theor. and with liq.-liq. extn. expts. that the lifetime of the sensor depends for a given tetraphenylborate both on the nature of the counterion and its concn. in the aq. and org. phase. Also, the complexation of the cationic counterion by the ionophore will shift the partition equil. of the anionic site in direction of the membrane phase, thus rendering the additive more lipophilic. By using previously measured ion-exchange consts. detd. on thin membrane phases (optical sensors) together with the extn. data presented here, quant. lipophilicity data is indirectly accessible. Ionophores forming highly stable complexes with the sample cation (e.g., valinomycin for K+ or ETH 1001 for Ca2+) induce a sufficiently high lipophilicity of the tetraphenylborate deriv. according to the criteria presented here. However, only the most lipophilic tetraphenylborates (i.e., tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) show acceptably slow leaching behavior in membranes contg. no ionophore.
- 30Kubjnyi, H. Drug Partitioning: Relationships between Forward and Reverse Rate Constants and Partition Coefficient. J. Pharm. Sci. 1978, 67, 262– 263, DOI: 10.1002/jps.2600670237Google ScholarThere is no corresponding record for this reference.
- 31Egorov, V. V.; Novakovskii, A. D.; Zdrachek, E. A. A Simple Dynamic Diffusion Model of the Response of Highly Selective Electrodes: The Effect of Simulation Parameters and Boundary Conditions on the Results of Calculations. Russ. J. Electrochem. 2018, 54, 381– 390, DOI: 10.1134/S1023193518040031Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXotF2nt70%253D&md5=efd97478de852d068c082bb4850d52e5A Simple Dynamic Diffusion Model of the Response of Highly Selective Electrodes: The Effect of Simulation Parameters and Boundary Conditions on the Results of CalculationsEgorov, V. V.; Novakovskii, A. D.; Zdrachek, E. A.Russian Journal of Electrochemistry (2018), 54 (4), 381-390CODEN: RJELE3; ISSN:1023-1935. (Pleiades Publishing, Ltd.)For a tetrabutylammonium-selective electrode with a ion-exchange membrane, in the real-work scenario corresponding to the detn. of selectivity coeffs. by the IUPAC-recommended method of sep. solns., it is shown that of the results of calcns. obtained within the framework of the dynamic diffusion model based on the use of the finite-difference technique substantially depend on of the chosen boundary conditions and the values of arbitrarily set simulation parameters. The key parameter that dets. the quality of simulation results is the thickness of the elementary layer in the membrane phase, esp. for low diffusion coeffs. It is found that the use of thin elementary layers in membranes and thick elementary layers in the aq. phase makes it possible to combine the high quality with the high calcn. rate. In simulating the long-term expts., account should be taken of the accumulation of the potential-detg. ion in the aq. soln. vol. as a result of its displacement by a foreign ion from the membrane. A good correspondence between calcn. data and exptl. results is demonstrated.
- 32Ma, Y.; Liu, C.; Wang, L. Defined Ion-Transfer Voltammetry of a Single Microdroplet at a Polarized Liquid/Liquid Interface. Anal. Chem. 2022, 94, 1850– 1858, DOI: 10.1021/acs.analchem.1c04809Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XptlShtQ%253D%253D&md5=0f57d68534746a329013a548ae9b7d4eDefined Ion-Transfer Voltammetry of a Single Microdroplet at a Polarized Liquid/Liquid InterfaceMa, Yamin; Liu, Cheng; Wang, LishiAnalytical Chemistry (Washington, DC, United States) (2022), 94 (3), 1850-1858CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A strategy for the fast anal. of ion transfer/facilitated ion transfer toward a tiny (femtoliter) water-in-oil droplet has been established. This scenario is embodied by the fusion of a w/o microdroplet at the micro liq./liq. (L/L) interface, with the use of Fourier transform fast-scan cyclic voltammetry (FT-FSCV) to express the apparent half-wave potentials of anions or cations encapsulated inside the w/o microdroplet. First, the half-wave potential is in strict accordance with the transfer Gibbs free energy of either cations or anions. Second, the half-wave potential has been found to be pos. proportional to the logarithmic concn. of ions, shedding thermodn. insight into ion transfer. Third, as an instance of multivalent biopolymers, the transfer of protamine inside the single w/o microdroplet has been investigated. Obvious discrepancies in the behaviors of the fusion impacts at different pH, as well as in the absence and presence of the cationic surfactant DNNS-, are revealed. The internal mechanism of protamine transfer has been thoroughly investigated. This work proposes a strategy to sensitively and quickly det. the transfer Gibbs energy and the concn. of ions encapsulated in a single microdroplet, and it provides the possibility of analyzing the interfacial transfer properties of trace biomacromols. inside an aq. micro- or nanoscale droplet.
- 33Moon, H.; Park, J. H. In Situ Probing Liquid/Liquid Interfacial Kinetics through Single Nanodroplet Electrochemistry. Anal. Chem. 2021, 93, 16915– 16921, DOI: 10.1021/acs.analchem.1c04071Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXis1CrurjO&md5=cd0f6e9d48a3947d2f09d34c7e01fbb6In Situ Probing Liquid/Liquid Interfacial Kinetics through Single Nanodroplet ElectrochemistryMoon, Hyeongkwon; Park, Jun HuiAnalytical Chemistry (Washington, DC, United States) (2021), 93 (50), 16915-16921CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)In this study, we report the new application of single nanodroplet electrochem. to in situ monitor the interfacial transfer kinetics of electroactive species across liq./liq. interface. Interfacial kinetic information is crucial in drug delivery and membrane transport. However, interfacial information has been mainly studied thermodynamically, such as partition coeff., which could not manifest a speed of transfer. Herein, we measure the phase-transfer kinetic const. via the steady-state electrochem. of an extd. redox species in a single nanodroplet. The redox species were transferred from the continuous oil phase to the water nanodroplet by partition equil. The transferred redox species are selectively electrolyzed within the droplet when the droplet contacts with an ultramicroelectrode, while the electrochem. reaction of the redox species outside the droplet (i.e., org. solvent) is effectively suppressed by adjusting the electrolyte compn. The redox species in the water droplets can quickly attain a steady state during electrolysis owing to an extensive mass transfer by radial diffusion, and the steady-state current can be analyzed to obtain kinetic information with help from the finite-element method. Finally, a quick calcn. method is suggested to est. the kinetic const. of phase transfer without simulation.
- 34Deng, H.; Dick, J. E.; Kummer, S.; Kragl, U.; Strauss, S. H.; Bard, A. J. Probing Ion Transfer across Liquid–Liquid Interfaces by Monitoring Collisions of Single Femtoliter Oil Droplets on Ultramicroelectrodes. Anal. Chem. 2016, 88, 7754– 7761, DOI: 10.1021/acs.analchem.6b01747Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFeku7bP&md5=3460466fbb237a5409b4bf07af17a946Probing Ion Transfer across Liquid-Liquid Interfaces by Monitoring Collisions of Single Femtoliter Oil Droplets on UltramicroelectrodesDeng, Haiqiang; Dick, Jeffrey E.; Kummer, Sina; Kragl, Udo; Strauss, Steven H.; Bard, Allen J.Analytical Chemistry (Washington, DC, United States) (2016), 88 (15), 7754-7761CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We describe a method of observing collisions of single femtoliter (fL) oil (i.e., toluene) droplets that are dispersed in water on an ultramicroelectrode (UME) to probe the ion transfer across the oil/water interface. The oil-in-water emulsion was stabilized by an ionic liq., in which the oil droplet trapped a highly hydrophobic redox probe, rubrene. The ionic liq. also functions as the supporting electrolyte in toluene. When the potential of the UME was biased such that rubrene oxidn. would be possible when a droplet collided with the electrode, no current spikes were obsd. This implies that the rubrene radical cation is not hydrophilic enough to transfer into the aq. phase. We show that current spikes are obsd. when tetrabutylammonium trifluoromethanesulfonate or tetrahexylammonium hexafluorophosphate are introduced into the toluene phase and when tetrabutylammonium perchlorate is introduced into the water phase, implying that the ion transfer facilitates electron transfer in the droplet collisions. The current (i)-time (t) behavior was evaluated quant., which indicated the ion transfer is fast and reversible. Furthermore, the size of these emulsion droplets can also be calcd. from the electrochem. collision. We further investigated the potential dependence on the electrochem. collision response in the presence of tetrabutylammonium trifluoromethanesulfonate in toluene to obtain the formal ion transfer potential of tetrabutylammonium across the toluene/water interface, which was detd. to be 0.754 V in the inner potential scale. The results yield new phys. insights into the charge balance mechanism in emulsion droplet collisions and indicate that the electrochem. collision technique can be used to probe formal ion transfer potentials between water and solvents with very low (ε < 5) dielec. consts.
- 35Yang, W.; Zhai, J.; Xie, X. Rhodamine Dye Transfer from Hydrogel to Nanospheres for the Chemical Detection of Potassium Ions. Analyst 2019, 144, 5617– 5623, DOI: 10.1039/C9AN01079CGoogle Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsVKntL%252FO&md5=b9dffa44281bd62b8286b80c36e12049Rhodamine dye transfer from hydrogel to nanospheres for the chemical detection of potassium ionsYang, Wei; Zhai, Jingying; Xie, XiaojiangAnalyst (Cambridge, United Kingdom) (2019), 144 (18), 5617-5623CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)Smart hydrogels incorporating various functional nanomaterials are becoming popular tools for chem. sensing. Here, ion-exchange nanospheres composed of the block copolymer Pluronic F-127 played the role of a scavenger for a signal transducer dye (Rhodamine 800) in a three-phase based optical detection system for potassium ions. Rhodamine 800, a pos. charged dye, was incorporated into a hydrogel together with the potassium ionophore valinomycin and an ion-exchanger (Na+R-). The concn. of Rhodamine 800 in the aq. sample was kept low by the nanospheres contg. Na+R-. Consequently, the detection limit (0.3 μM) of the three-phase based system was shifted 2 orders of magnitude lower compared with those of previously reported two-phase based sensing systems. The concept of controlling the dye transfer among the three phases provided a new train of thought for the design of ionophore-based chem. sensors.
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Abstract
Scheme 1
Scheme 1. Hypothesis of the Transfer Mechanism of Nanoemulsions Delivering Their Cargo to an Ion-Selective MembraneaaThe rate-limiting step is postulated to be either (a) diffusional mass transport of the nanoemulsion, (b) fusion of the entire nanoemulsion phase with the membrane, or (c) delivery of the nanoemulsion components into the membrane by a partitioning mechanism.
Scheme 2
Scheme 2. Mechanism of Monitoring the Mass Transfer of a Lipophilic Cation-Exchanger Salt R-M+ from a Nanoemulsion into a Thin Pristine Membrane where I and II Show the Membrane Composition Before and After the Start of the Mass Transfer Process from EmulsionFigure 1
Figure 1. Transfer process at 100 rpm rotating speed with DMF-based NEs encapsulated with TFPB– and monitored by thin-film cyclic voltammetry. (a) Consecutive voltammograms at 5 min intervals during emulsion doping, giving increasing currents with time. (b) Corresponding integrated charge (coulovoltammograms) for the experiment shown in a. (c) Resulting integrated charge as a function of doping time, giving a flux of 3.3 ± 0.2 pmol cm–2 s–1 of the ion-exchanger salt.
Figure 2
Figure 2. (a) An emulsion, free of TFPB–, is added to solution at the indicated time, giving the indicated frequency change that translates into a small mass change of 0.02 ng cm–2 s–1 indicating minimal fusion between the nanoemulsion phase and the membrane. (b) Frequency change (mass uptake) observed by QCM and (c) the corresponding current with time at 0.4 V upon introducing DMF-based nanoemulsions containing TFPB–. The lipophilicity of the salt was successively increased by adding electrolytes of increasing lipophilicity (LiCl, NaCl, TMACl, and TBACl as shown) at a 10 mM concentration to solution. The resulting doping rate does not depend on the lipophilicity, suggesting a mass transport-limited process.
Figure 3
Figure 3. Ion transfer amperometry at a thin membrane for the mass transfer of nanoemulsions containing TBA+TFPB– as cargo and a 10 mM TBACl solution as a function of the indicated electrode rotation speed (in rpm) to control the diffusion layer thickness. The solution is quiescent for the initial 3.5 min period. The experimental data (black trace) compares well to theory (red dashed line). In contrast, the flux observed for calcium ionophore uptake from the emulsion phase (Ca-IV, blue dashed line) is much smaller than that predicted based on diffusional mass transport.
Figure 4
Figure 4. Accumulated charge with time from ion transfer cyclic voltammograms for a thin-layer membrane containing 100 mmol kg–1 NaTFPB upon uptake of the ionophores (a) K-I, (b) Na-X, and (c) Ca-IV from the emulsion phase. Shown are the total charge for the two ion transfer peaks (squares), indicative of the cation-exchanger loss from the membrane, and the charge for the uncomplexed (so-called free) ion (black circles), which should decrease as the membrane takes up ionophores. Open circles indicate the charge for the ionophore-bound cation transfer peak, which is found to increase linearly with time and indicates the uptake rate for the ionophore.
References
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- 1Hashemnejad, S. M.; Badruddoza, A. Z. M.; Zarket, B.; Ricardo Castaneda, C.; Doyle, P. S. Thermoresponsive Nanoemulsion-Based Gel Synthesized through a Low-Energy Process. Nat. Commun. 2019, 10, 2749, DOI: 10.1038/s41467-019-10749-11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB3M3psF2isQ%253D%253D&md5=589ae2b5d0e8e2d4f3a738fb0c525ae7Thermoresponsive nanoemulsion-based gel synthesized through a low-energy processHashemnejad Seyed Meysam; Badruddoza Abu Zayed Md; Ricardo Castaneda Carlos; Doyle Patrick S; Zarket BradyNature communications (2019), 10 (1), 2749 ISSN:.Thermoresponsive nanoemulsions find utility in applications ranging from food to pharmaceuticals to consumer products. Prior systems have found limited translation to applications due to cytotoxicity of the compositions and/or difficulties in scaling-up the process. Here, we report a route to thermally gel an oil-in-water nanoemulsion using a small amount of FDA-approved amphiphilic triblock Pluronic copolymers which act as gelling agents. At ambient temperature the suspension displays liquid-like behavior, and quickly becomes an elastic gel at elevated temperatures. We propose a gelation mechanism triggered by synergistic action of thermally-induced adsorption of Pluronic copolymers onto the droplet interface and an increased micelle concentration in the aqueous solution. We demonstrate that the system's properties can be tuned via many factors and report their rheological properties. The nanoemulsions are prepared using a low-energy process which offers an efficient route to scale-up. The nanoemulsion formulations are well-suited for use in cosmetics and pharmaceutical applications.
- 2Singh, Y.; Meher, J. G.; Raval, K.; Khan, F. A.; Chaurasia, M.; Jain, N. K.; Chourasia, M. K. Nanoemulsion: Concepts, Development and Applications in Drug Delivery. J. Controlled Release 2017, 252, 28– 49, DOI: 10.1016/j.jconrel.2017.03.0082https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXktFWgurk%253D&md5=15e151ec10a01e8288723a33c2df9bdfNanoemulsion: Concepts, development and applications in drug deliverySingh, Yuvraj; Meher, Jaya Gopal; Raval, Kavit; Ali Khan, Farooq; Chaurasia, Mohini; Jain, Nitin K.; Chourasia, Manish K.Journal of Controlled Release (2017), 252 (), 28-49CODEN: JCREEC; ISSN:0168-3659. (Elsevier B.V.)Nanoemulsions are biphasic dispersion of two immiscible liqs.: either water in oil (W/O) or oil in water (O/W) droplets stabilized by an amphiphilic surfactant. These come across as ultrafine dispersions whose differential drug loading; viscoelastic as well as visual properties can cater to a wide range of functionalities including drug delivery. However there is still relatively narrow insight regarding development, manufg., fabrication and manipulation of nanoemulsions which primarily stems from the fact that conventional aspects of emulsion formation and stabilization only partially apply to nanoemulsions. This general deficiency sets up the premise for current review. We attempt to explore varying intricacies, excipients, manufg. techniques and their underlying principles, prodn. conditions, structural dynamics, prevalent destabilization mechanisms, and drug delivery applications of nanoemulsions to spike interest of those contemplating a foray in this field.
- 3Saberi, A. H.; Fang, Y.; McClements, D. J. Fabrication of Vitamin E-Enriched Nanoemulsions by Spontaneous Emulsification: Effect of Propylene Glycol and Ethanol on Formation, Stability, and Properties. Food Res. Int. 2013, 54, 812– 820, DOI: 10.1016/j.foodres.2013.08.0283https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhs1Oqs7vF&md5=7f588fa3b058f5c918a25fe6cdd59e0eFabrication of vitamin E-enriched nanoemulsions by spontaneous emulsification: Effect of propylene glycol and ethanol on formation, stability, and propertiesSaberi, Amir Hossein; Fang, Yuan; McClements, David JulianFood Research International (2013), 54 (1), 812-820CODEN: FORIEU; ISSN:0963-9969. (Elsevier B.V.)Oil-in-water nanoemulsions are finding increasing application within pharmaceutical and functional food products as delivery systems to encapsulate lipophilic bioactive components, such as drugs, vitamins, and nutraceuticals. We investigated the influence of two water-sol. cosolvents, propylene glycol (PG) and ethanol, on the formation, stability, and properties of vitamin E acetate-loaded nanoemulsions (VE-NEs) prepd. by spontaneous emulsification. This method simply involves titrating an org. phase (VE + surfactant) into an aq. phase (water + cosolvent). The particle size and optical clarity of the nanoemulsions (10% + VE + 10% surfactant + 80% aq. phase) depended strongly on cosolvent type and concn. The smallest droplets (d < 50 nm) and highest transparency were obsd. when either 30% PG or 20% ethanol was present in the aq. phase. However, these nanoemulsions were highly unstable to droplet growth during storage, esp. at elevated temps., which was attributed to coalescence and Ostwald ripening. Diln. of the nanoemulsions (100 × with water) prior to storage considerably improved their long-term stability esp. at higher storage temps. Undiluted nanoemulsions exhibited a sharp and irreversible increase in turbidity upon heating: ≈ 53°C for the system contg. 30% PG and ≈ 38°C for the system contg. 20% ethanol. Dild. nanoemulsions had much better thermal stability, with a steep increase in turbidity occurring at ≈ 75.5°C for both systems. This study provides important information about the effect of cosolvents on the formation, stability, and phys. properties of VE-NEs suitable for use in pharmaceutical and food products.
- 4Kim, B.-K.; Boika, A.; Kim, J.; Dick, J. E.; Bard, A. J. Characterizing Emulsions by Observation of Single Droplet Collisions─Attoliter Electrochemical Reactors. J. Am. Chem. Soc. 2014, 136, 4849– 4852, DOI: 10.1021/ja500713w4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXktl2iur0%253D&md5=f9af73ddb463c1ce3deb13594236937bCharacterizing Emulsions by Observation of Single Droplet Collisions-Attoliter Electrochemical ReactorsKim, Byung-Kwon; Boika, Aliaksei; Kim, Jiyeon; Dick, Jeffrey E.; Bard, Allen J.Journal of the American Chemical Society (2014), 136 (13), 4849-4852CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The authors report an electrochem. study of the collisions of single droplets in an emulsion by two methods. In the 1st method, an electroactive redox species, for example, ferrocene, inside a toluene-in-H2O emulsion droplet (but not in the continuous phase) is measured by chronoamperometry during a collision with an ultramicroelectrode (UME). Here, a blip or spike type of collision signal is obsd., representing electrolysis of the droplet contents. In the 2nd method, electrochem. oxidn. of an electroactive redox species in the continuous aq. phase is hindered by a droplet blocking collision. In this case, a staircase current decrease is obsd. From an anal. of single soft particle collision data, one can find the emulsion droplet size distribution and the droplet contents.
- 5Xie, X.; Gutiérrez, A.; Trofimov, V.; Szilagyi, I.; Soldati, T.; Bakker, E. Charged Solvatochromic Dyes as Signal Transducers in PH Independent Fluorescent and Colorimetric Ion Selective Nanosensors. Anal. Chem. 2015, 87, 9954– 9959, DOI: 10.1021/acs.analchem.5b025665https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVKlsLvO&md5=e178b82e4e7529afc90708a33523eb14Charged Solvatochromic Dyes as Signal Transducers in pH Independent Fluorescent and Colorimetric Ion Selective NanosensorsXie, Xiaojiang; Gutierrez, Agustin; Trofimov, Valentin; Szilagyi, Istvan; Soldati, Thierry; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2015), 87 (19), 9954-9959CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Ionophore-based ion selective optical nanosensors that operate independently of the sample pH are developed here using elec. charged solvatochromic dyes as signal transducers. A series of dye mols. with a D-π-A structure was synthesized and characterized in various solvents and incorporated into ion selective nanospheres for K+, Na+, and H+. Since dye leakage was greatly suppressed when the solvatochromic dyes were encapsulated in the nanosphere core, ion sensing nanospheres were explored for cellular ion imaging in Dictyostelium discoideum live cells but spontaneous dye loss resulted in undesired staining of cells. The in vitro anal. of potassium in human plasma was successfully demonstrated with this approach. A theor. model was developed for the response of the ion selective nanosensors contg. charged solvatochromic dyes. The nanosensors exhibited a tunable response range, high sensitivity, and good stability.
- 6Soda, Y.; Robinson, K. J.; Nussbaum, R.; Bakker, E. Protamine/Heparin Optical Nanosensors Based on Solvatochromism. Chem. Sci. 2021, 12, 15596– 15602, DOI: 10.1039/D1SC04930E6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXisVykt73O&md5=9a7d9e6943b27c1ec585b403c6e6a84eProtamine/heparin optical nanosensors based on solvatochromismSoda, Yoshiki; Robinson, Kye J.; Nussbaum, Robin; Bakker, EricChemical Science (2021), 12 (47), 15596-15602CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)Optical nanosensors for the detection of polyions, including protamine and heparin, have to date relied upon ion-exchange reactions involving an analyte and an optical transducer. Unfortunately, due to the limited selectivity of the available ionophores for polyions, this mechanism has suffered from severe interference in complex sample matrixes. To date no optical polyion nanosensors have demonstrated acceptable performance in serum, plasma or blood. Herein we describe a new type of nanosensor based on our discovery of a "hyper-polarizing lipophilic phase" in which dinonylnaphthalenesulfonate (DNNS-) polarizes a solvatochromic dye much more than even an aq. environment. We have found that the apparent polarity of the org. phase is only modulated when DNNS- binds to large polyions such as protamine, unlike singly charged ions that lack the cooperative binding required to cause a significant shift in the distribution of the polarizing DNNS- ions. Our new sensing mechanism allows solvatochromic signal transduction without the transducer undergoing ion exchange. The result is significantly improved sensitivity and selectivity, enabling for the first time the quantification of protamine and heparin in human plasma using optical nanosensors that correlates with the current gold std. anal. method, the anti-Xa factor assay.
- 7Sabaragamuwe, S. G.; Conti, D.; Puri, S. R.; Andreu, I.; Kim, J. Single-Entity Electrochemistry of Nanoemulsion: The Nanostructural Effect on Its Electrochemical Behavior. Anal. Chem. 2019, 91, 9599– 9607, DOI: 10.1021/acs.analchem.9b009207https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXht1OqsbbE&md5=4a735aaa012ce31e20bf69ba51e2fd1bSingle-Entity Electrochemistry of Nanoemulsion: The Nanostructural Effect on Its Electrochemical BehaviorSabaragamuwe, Shashika Gunathilaka; Conti, Dylan; Puri, Surendra Raj; Andreu, Irene; Kim, JiyeonAnalytical Chemistry (Washington, DC, United States) (2019), 91 (15), 9599-9607CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)New electrochem. approaches have been applied to investigate nanoemulsions (NEs) for their nanostructures and the relevant electrochem. activity by single-entity electrochem. (SEE). Herein, we make highly monodisperse NEs with ∼40 nm diam., composed of biocompatible surfactants, castor oil as plasticizers, and ion exchangers. Dynamic light scattering (DLS) measurements with periodically varying surfactant to oil ratios provide us with a structural implication about uneven distributions of incorporating components inside NEs. To support this structural insight, we apply SEE and selectively monitor electron-transfer reactions occurring at individual NEs contg. ferrocene upon each collision onto a Pt ultramicroelectrode. The quant. anal. of the nanoelectrochem. results along with DLS and transmission electron microscopy (TEM) measurements reveal nanostructured compartments of incorporating components inside NEs and their effect on the electrochem. behavior. Indeed, a tunneling barrier inside NEs could be formed depending on the NE compn., thus detg. an electrochem. behavior of NEs, which cannot be differentiated by a general morphol. study such as DLS and TEM but by our SEE measurements. Furthermore, by employing the nanopipet voltammetry with an interface between two immiscible electrolyte solns. (ITIES) to mimic the NE interface, we could explicitly investigate that the electron-transfer reaction occurring inside NEs is facilitated by the ion-transfer reaction. Overall, these comprehensive electrochem. approaches enable us to elucidate the relation between structures and the electrochem. functionality of NEs and provide quant. criteria for the proper compns. of NEs regarding their activity in the electrochem. applications. Also, this finding should be a prerequisite for suitable biomedical/electrochem. applications of NEs.
- 8Soda, Y.; Gao, W.; Bosset, J.; Bakker, E. Emulsion Doping of Ionophores and Ion-Exchangers into Ion-Selective Electrode Membranes. Anal. Chem. 2020, 92, 14319– 14324, DOI: 10.1021/acs.analchem.0c029208https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitFSltLjP&md5=2184c2d7596301fdc25990637c4c0805Emulsion Doping of Ionophores and Ion-Exchangers into Ion-Selective Electrode MembranesSoda, Yoshiki; Gao, Wenyue; Bosset, Jerome; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2020), 92 (21), 14319-14324CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Ion-selective electrodes (ISEs) are widely used anal. devices to selectively measure ionic species. Despite significant advances in recent years, ion-selective membranes are still mostly prepd. in the same manner, by preloading the selective components into a solvent that is subsequently cast into a membrane or film. This paper describes an alternative method to prep. ISE membranes by mass transfer of the sensing components from an emulsion phase. Specifically, blank (undoped) plasticized poly(vinyl chloride) (PVC) membranes mounted into an electrode body are immersed into an aq. soln. contg. analyte ions and an appropriate emulsion of the desired sensing components to allow their transfer into the membrane. The concept is demonstrated with conventional membrane electrodes contg. an inner soln. as well as all-solid-state electrodes. It is shown to be universally useful for the realization of ISEs for K+, Na+, Ca2+, and NO3-.
- 9Apichai, S.; Wang, L.; Pankratova, N.; Grudpan, K.; Bakker, E. Ion-Exchange Microemulsions for Eliminating Dilute Interferences in Potentiometric Determinations. Electroanalysis 2018, 30, 2462– 2466, DOI: 10.1002/elan.2018003669https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhsFOhs7jF&md5=3e6156efdf1d7351b454c1dfa9bd86d2Ion-Exchange Microemulsions for Eliminating Dilute Interferences in Potentiometric DeterminationsApichai, Sutasinee; Wang, Lu; Pankratova, Nadezda; Grudpan, Kate; Bakker, EricElectroanalysis (2018), 30 (10), 2462-2466CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)We report here for the first time on the use of functional microemulsions in potentiometric assays to remove dil. interferences from soln. when measuring high concns. of analyte. The microemulsions are similarly formulated to the ion-selective membrane used in the measurement and act as sacrificial material. They are here stabilized by the triblock copolymer pluronic F-127 and contain the chloride salt of the tridodecylmethylammonium cation, which also serves as anion-exchanger in the membrane electrode. Both membrane and microemulsion are preconditioned with chloride. If an anionic interference is present at moderate concn., the rapid equilibration with the functionalized microemulsion results in a quant. removal. The principle is explored with salicylate as common interference in the detection of chloride in physiol. samples. The data agree well to an equil. ion-exchange model for the microemulsion. Salicylate levels up to millimolar can be effectively removed. Unfortunately, quaternary ammonium salt from the microemulsion is found to contaminate the ion-selective membrane phase. Indeed, a cation-exchanging valinomycin membrane in contact with concd. anion-exchanging microemulsions shows a large potential increase. This indicates that the membrane changes from cation to anion permselectivity. This contamination of the membrane by the microemulsion phase must be overcome for a practical application of the approach.
- 10Tambe, D. E.; Sharma, M. M. The Effect of Colloidal Particles on Fluid-Fluid Interfacial Properties and Emulsion Stability. Adv. Colloid Interface Sci. 1994, 52, 1– 63, DOI: 10.1016/0001-8686(94)80039-110https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXmvFCjtA%253D%253D&md5=4d7eff32ffd55cfc7ac1a5535f6951e9The effect of colloidal particles on fluid-fluid interfacial properties and emulsion stabilityTambe, David E.; Sharma, Mukul M.Advances in Colloid and Interface Science (1994), 52 (), 1-65CODEN: ACISB9; ISSN:0001-8686.A review of relevant work done on the effects of colloidal particles on the rheol. properties of fluid-fluid interfaces and on emulsion stability. Results are presented which show that colloid particles stabilize emulsions primarily by providing steric hindrance to drop-drop coalescence and by modifying the rheol. properties of the interfacial region. The effectiveness of colloid particles in stabilizing emulsions depends largely on the formation of a sufficiently 'dense layer' of particles at the oil-H2O interface. The rheol. properties of the interfacial region also change as the concn. of particles at the interface increases and complete surface coverage is achieved. At sufficiently high concns. of particles, colloid-laden interfaces exhibit viscoelastic behavior. Viscoelastic interfaces enhance emulsion stability by increasing the magnitude of steric hindrance and by retarding the rate of liq. drainage between coalescing emulsion droplets. 80 Refs.
- 11Wang, X.; Collot, M.; Omran, Z.; Vandamme, T. F.; Klymchenko, A.; Anton, N. Further Insights into Release Mechanisms from Nano-Emulsions, Assessed by a Simple Fluorescence-Based Method. J. Colloid Interface Sci. 2020, 578, 768– 778, DOI: 10.1016/j.jcis.2020.06.02811https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXht1Sru7rF&md5=84c99822b8eb0073bcb4b557ec031555Further insights into release mechanisms from nano-emulsions, assessed by a simple fluorescence-based methodWang, Xinyue; Collot, Mayeul; Omran, Ziad; Vandamme, Thierry F.; Klymchenko, Andrey; Anton, NicolasJournal of Colloid and Interface Science (2020), 578 (), 768-778CODEN: JCISA5; ISSN:0021-9797. (Elsevier B.V.)Nano-emulsion consists of a dispersion of oil droplets sizing below 200 nm, in aq. continuous phase, and generally stabilized by low-mol.-wt. surfactants. These stable nano-carriers are able to encapsulate and transport lipophilic mols. poorly sol. in water. However, the question on the leakage and release mechanisms of an active pharmaceutical ingredient, from oil nano-droplets to an acceptor medium has not been clearly addressed. Herein, we developed a simple fluorescence approach based on self-quenching of lipophilic fluorophore-based on Nile Red (NR668) to monitor cargo transfer from lipid nano-droplets to the acceptor medium. In this method, the fluorophore release can be monitored by the increase in its fluorescence quantum yield and the blue shift in its emission spectrum. The studies of the release process allow emphasizing an important role of the bulk aq. medium in controlling the droplet to droplet fluorophore transfer and the attained equil. The developed methodol. could be applied to monitor release of other lipophilic dyes and it could help to better understand the cargo release from nanocarriers.
- 12Ryu, V.; Corradini, M. G.; McClements, D. J.; McLandsborough, L. Impact of Ripening Inhibitors on Molecular Transport of Antimicrobial Components from Essential Oil Nanoemulsions. J. Colloid Interface Sci. 2019, 556, 568– 576, DOI: 10.1016/j.jcis.2019.08.05912https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhs1ynsr7E&md5=473a69f2a4f97a406d6eb07405a0bc23Impact of ripening inhibitors on molecular transport of antimicrobial components from essential oil nanoemulsionsRyu, Victor; Corradini, Maria G.; McClements, David J.; McLandsborough, LynneJournal of Colloid and Interface Science (2019), 556 (), 568-576CODEN: JCISA5; ISSN:0021-9797. (Elsevier B.V.)The objective of this study was to provide insights into the mechanisms involved in the mass transport of antimicrobial compds. from essential oil nanoemulsions to bacterial cell membranes. Origanum oil-in-water nanoemulsions were produced using spontaneous emulsification by titrating a mixt. of essential oil, ripening inhibitor, and surfactant (Tween 80) into 5 mM sodium citrate buffer (pH 3.5). Stable nanoemulsions contg. relatively small droplets (d < 60 nm) were produced using this low-energy method. The nature of the ripening inhibitor used in the oil phase of the nanoemulsions affected the antimicrobial activity of the nanoemulsions: corn (LCT) > medium-chain triglycerides (MCT). Differences in antimicrobial activity were attributed to the differences in the rate of transfer of hydrophobic antimicrobial constituents from the nanoemulsion to the MCT emulsion, which was used to mimic the hydrophobic region of the bacterial cell membranes. Each antimicrobial nanoemulsion was sepd. from the MCT emulsion by a dialysis tubing. Dialysis tubing with two different pore sizes was used, one excluding nanoemulsion droplet and micelle delivery, allowing the delivery of antimicrobial compds. only through the aq. phase and the other by both the aq. phase and micelles. For origanum oil nanoemulsions, the delivery of all antimicrobial agents occurred more efficiently when micelles were present.
- 13Madawala, H.; Sabaragamuwe, S. G.; Elangovan, S.; Kim, J. In Situ Measuring Partition Coefficient at Intact Nanoemulsions: A New Application of Single-Entity Electrochemistry. Anal. Chem. 2021, 93, 1154– 1160, DOI: 10.1021/acs.analchem.0c0420513https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXisV2qurrM&md5=a660d352b672721441ded0c1177196f0In Situ Measuring Partition Coefficient at Intact Nanoemulsions: A New Application of Single-Entity ElectrochemistryMadawala, Hiranya; Sabaragamuwe, Shashika Gunathilaka; Elangovan, Subhashini; Kim, JiyeonAnalytical Chemistry (Washington, DC, United States) (2021), 93 (2), 1154-1160CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)The authors report a new application of the single-entity electrochem. (SEE) to in situ measure a partition coeff. at intact nanoemulsions (NEs). The partition coeff. at intact NEs is the most crucial physicochem. property to det. the uptake of delivery mols. inside NEs. It, however, was not unequivocally elucidated by currently existing techniques based on ex situ measurements. Herein, the authors apply the single-entity electrochem. (SEE) to directly and quant. measure the partition coeff. at NEs in situ. The authors use NEs featured with amphiphilic triblock copolymer (Pluronic F-127) as a model system to ext./preconc. 2-aminobiphenyl (2-ABP) dissolved in the H2O and demonstrate a new application of SEE to in situ quant. est. the amts. of 2-ABP distributed into each intact NE. The authors' SEE measurements reveal that the partitioning is governed by extn. of 2-ABP inside NEs rather than its adsorption on the NE surface, and this extn. is remarkably efficient with up to ~ 8 orders of magnitude of the preconcn. factor, thus leading to the unprecedentedly large partition coeff. of 1.9 (±1.4) x 1010. This result implies that not only the thermodn. distribution but also the intermol. interaction of extd. compds. inside NEs could play a significant role in the apparent partition coeff. (P = 1.9 (±1.4) x 1010). The exptl. detd. partition coeff. was validated by mol. dynamics (MD) simulations with showing a stabilizing role of intermol. interaction in the partitioned system. The authors further verified the authors' methodol. with other compds. exhibiting arom. properties, e.g., ferrocenemethanol. Significantly, the authors' new approach can be readily applicable to study practical NEs com. marketed for drug, food, and cosmetics.
- 14He, W.; Wang, C.; Wang, H.; Jian, M.; Lu, W.; Liang, X.; Zhang, X.; Yang, F.; Zhang, Y. Integrated Textile Sensor Patch for Real-Time and Multiplex Sweat Analysis. Sci. Adv. 2019, 5, eaax0649 DOI: 10.1126/sciadv.aax0649There is no corresponding record for this reference.
- 15Mao, C.; Robinson, K. J.; Yuan, D.; Bakker, E. Ion–Ionophore Interactions in Polymeric Membranes Studied by Thin Layer Voltammetry. Sens. Actuators, B 2022, 358, 131428 DOI: 10.1016/j.snb.2022.13142815https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XivVymt7c%253D&md5=0da19efb7c8d1f37756a160dabde4b09Ion-ionophore interactions in polymeric membranes studied by thin layer voltammetryMao, Canwei; Robinson, Kye J.; Yuan, Dajing; Bakker, EricSensors and Actuators, B: Chemical (2022), 358 (), 131428CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)In ion sensing applications, selective ion-receptor complexation is the mol. basis for endowing the sensing material with selectivity. In this work, thin polymeric membrane-based ion transfer voltammetry is used to investigate ion-receptor complexation, using a range of elec. neutral ionophores and surfactants as examples. Previous studies lacked a convincing approach to eliminate the influence from transducing layer, resulting in deviations of the obsd. binding consts. compared to potentiometric methods. A recently developed method allows for subtracting the potential changes of the transducing layer, thereby overcoming this challenge. Using this approach, a range of ionophores are assessed. Valinomycin for the detection of potassium gave a logarithmic complex formation const. in the membrane of 9.69 ± 0.25 with a 1:1 stoichiometry. Lithium ionophore VI for lithium gave a logarithmic stability const. of 5.97 ± 0.06 with 1:2 complexes; while sodium ionophore X for sodium (7.57 ± 0.03, 1:1) and calcium ionophore IV for calcium (21.57 ± 0.25, 1:3) were also characterized, in addn. to their complexes with potential interfering ions. The complex formation of three surfactants with potassium are also explored in membranes contg. valinomycin, with Brij-35 (4.88 ± 0.08, 1:1), Triton X-100 (5.63 ± 0.10, 1:1), F-127 (4.63 ± 0.49, 1:1). Limitations of the approach are discussed, which includes the need for electrochem. reversibility and a sufficiently high lipophilicity to adequately retain the components in the membrane.
- 16Bruckenstein, S.; Shay, M. Experimental Aspects of Use of the Quartz Crystal Microbalance in Solution. Electrochim. Acta 1985, 30, 1295– 1300, DOI: 10.1016/0013-4686(85)85005-216https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28Xht1amsA%253D%253D&md5=360e8960c06534dabe72b345ac6abfc6Experimental aspects of use of the quartz crystal microbalance in solutionBruckenstein, S.; Shay, M.Electrochimica Acta (1985), 30 (10), 1295-300CODEN: ELCAAV; ISSN:0013-4686.Transistor-transistor-logic based circuitry is described for measuring the resonant frequency of an oscillating quartz crystal having 1 face in contactwith an electrolyte. The circuitry facilitates application of the quartz crystal microbalance technique to in situ electrogravimetric studies of submonolayer and many monolayer thick electrodeposited and electrosorbed films. The effect of the temp. and viscosity of the soln. , and height of liq. above the crystal were investigated and the results correlated with theory. An in situ soln. method for detg. the mass sensitivity of the crystal is described and the latter sensitivity is shown to be the same as the calcd. vacuum sensitivity. The effect of double layer structure and specific adsorption is discussed.
- 17Sauerbrey, G. Verwendung von Schwingquarzen Zur Wägung Dünner Schichten Und Zur Mikrowägung. Zeitschrift für Phys. 1959, 155, 206– 222, DOI: 10.1007/BF0133793717https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaG1MXoslSjtQ%253D%253D&md5=ff97a9cc63637eb9823aebfeb57a367bThe use of quartz oscillators for weighing thin layers and for microweighingSauerbrey, GuntherZeitschrift fuer Physik (1959), 155 (), 206-22CODEN: ZEPYAA; ISSN:0044-3328.The frequency of a quartz plate is altered if a layer of foreign material is deposited on the quartz, e.g. by evapn. Since changes in frequency can be measured very accurately, the phenomenon can be used for weighing thin layers. The change in frequency is proportional to the d. of the foreign layer and the proportionality const. can be calcd. from the characteristic frequency of the quartz plate. The accuracy of the method is limited by the temp. variation of the characteristic frequency of the quartz oscillator. For a temp. fluctuation of 1° the accuracy is ±4.10-9 g./cm. This corresponds to a mean thickness of the layer of 0.4 A. at a d. of 1 g./cc. The method can also be used for direct microweighing, e.g. by evapg. a drop of a soln. on the quartz plate.
- 18Niu, L.; Kvarnström, C.; Ivaska, A. Mixed Ion Transfer in Redox Processes of Poly(3,4-Ethylenedioxythiophene). J. Electroanal. Chem. 2004, 569, 151– 160, DOI: 10.1016/j.jelechem.2004.01.02918https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXltFOltbY%253D&md5=4d70a1688f042e4a33f255648a405262Mixed ion transfer in redox processes of poly(3,4-ethylenedioxythiophene)Niu, Li; Kvarnstrom, Carita; Ivaska, AriJournal of Electroanalytical Chemistry (2004), 569 (2), 151-160CODEN: JECHES ISSN:. (Elsevier)A model considering the transfer of counterions and solvent mols. is presented to explain the complicated ion transfer in polymer films during electrochem. redox processes. The developed mixed ion transfer model is used to analyze the ion transfer behavior of poly(3,4-ethylenedioxythiophene) during doping and dedoping processes. Both anions and cations are involved in n-doping as well as in p-doping processes. The behavior of different electrolyte ions was also studied. The developed model shows that solvent mols. are also transferred in conjunction with the ion transfer.
- 19Bard, A. J.; Faulkner, L. R. Electrochemical Methods: Fundamentals and Applications,2nd Edition; John Wiley & Sons, Incorporated, 2000.There is no corresponding record for this reference.
- 20Forrest, T.; Zdrachek, E.; Bakker, E. Thin Layer Membrane Systems as Rapid Development Tool for Potentiometric Solid Contact Ion-selective Electrodes. Electroanalysis 2020, 32, 799– 804, DOI: 10.1002/elan.20190067420https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXmt1Witw%253D%253D&md5=de93414bee9fa59be8a7c21b450da899Thin Layer Membrane Systems as Rapid Development Tool for Potentiometric Solid Contact Ion-selective ElectrodesForrest, Tara; Zdrachek, Elena; Bakker, EricElectroanalysis (2020), 32 (4), 799-804CODEN: ELANEU; ISSN:1040-0397. (Wiley-VCH Verlag GmbH & Co. KGaA)The use of thin membrane layer ion-selective electrodes (of ∼200 nm thickness) as rapid diagnosis tool is proposed. While conventional solid contact systems (with a membrane of ∼250 μm thickness) may exhibit a satisfactory stability for regular lab. use, a signal degrdn. can still be distinguished over a longer period of time but this requires tedious and time consuming tests. By diminishing the thickness of the membrane by a factor of 103 approx., diffusion processes happen faster, and the lifetime is significantly reduced. This would ordinarily be a strong drawback but not if the aim is to detect a membrane deterioration in a shorter time frame. This characteristic makes thin membrane systems an ideal tool for rapid complications identification in the development process of conventional solid contact electrodes. The approach is demonstrated here in the development of an all new solid contact probe for anions. PEDOT-C14, a conducting polymer, was used for the first time in a solid contact electrode with an anion exchange membrane for the detection of nitrate. The thin layer configuration was used to optimize the polymn. parameters as well as the membrane compn. without having to run week-long trials. A stable conventional solid contact electrode was in the end successfully developed and exhibited a lower detection limit of 10-5.5 M for nitrate with a stable Nernstian response for several days.
- 21Kabagambe, B.; Izadyar, A.; Amemiya, S. Stripping Voltammetry of Nanomolar Potassium and Ammonium Ions Using a Valinomycin-Doped Double-Polymer Electrode. Anal. Chem. 2012, 84, 7979– 7986, DOI: 10.1021/ac301773w21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xht1SitLbN&md5=bad6a704035c11aff8aa3b1d731a52aeStripping Voltammetry of Nanomolar Potassium and Ammonium Ions Using a Valinomycin-Doped Double-Polymer ElectrodeKabagambe, Benjamin; Izadyar, Anahita; Amemiya, ShigeruAnalytical Chemistry (Washington, DC, United States) (2012), 84 (18), 7979-7986CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Here, the authors report on the 1st application of an ionophore-doped double-polymer electrode for ion-transfer stripping voltammetry (ITSV) to explore the nanomolar limit of detection (LOD) and multiple-ion detectability. The authors developed a theor. model for ITSV at a thin ionophore-doped membrane on the solid supporting electrode to demonstrate that its LOD is controlled by the equil. preconcn. of an aq. analyte ion as an ionophore complex into the thin polymer membrane and is lowered by the formation of a more stable ion-ionophore complex. The theor. predictions were confirmed using valinomycin as a K+-selective ionophore, which forms a ∼ 60 times more stable complex with K+ than with NH4+, as confirmed by cyclic voltammetry. A LOD of 0.6 nM K+ was achieved by ITSV using com. ultrapure water as a K+-free media, where NH4+ contamination at a higher concn. was also detected by ITSV. The dependence of the ITSV response on the preconcn. time was monitored under the rotating-electrode configuration and analyzed theor. to directly det. ∼100 nM NH4+ and ∼5 nM K+ contaminations in com. ultrapure water and lab.-purified water, resp., without the background ITSV measurement of an analyte-free blank soln.
- 22Kim, Y.; Rodgers, P. J.; Ishimatsu, R.; Amemiya, S. Subnanomolar Ion Detection by Stripping Voltammetry with Solid-Supported Thin Polymeric Membrane. Anal. Chem. 2009, 81, 7262– 7270, DOI: 10.1021/ac900995a22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXptlGnsrs%253D&md5=1c3e200aa50de6dffea2be5b9a0fa120Subnanomolar Ion Detection by Stripping Voltammetry with Solid-Supported Thin Polymeric MembraneKim, Yushin; Rodgers, Patrick J.; Ishimatsu, Ryoichi; Amemiya, ShigeruAnalytical Chemistry (Washington, DC, United States) (2009), 81 (17), 7262-7270CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)Subnanomolar limits of detection (LODs) were obtained for stripping voltammetry based on ion transfer at the interface between the aq. sample and the thin polymeric membrane supported with a solid electrode. It was predicted theor. that a lower LOD can be obtained for a more lipophilic analyte ion, which can be preconcd. at a higher equil. concn. in the solid-supported thin polymeric membrane to enhance a stripping current response. This study is the 1st to exptl. confirm the general theor. prediction for both cationic and anionic analytes. Proof-of-concept expts. demonstrate that a subnanomolar LOD of (8 ± 4) × 10-11 M Pr4N+ is significantly lower than a LOD of less lipophilic Et4N+. Importantly, stripping voltammetry of the cationic analytes is enabled by newly introducing an oxidatively doped poly(3,4-ethylenedioxythiophene) film as the intermediate layer between a plasticized poly(vinyl chloride) membrane and a Au electrode. However, an undoped poly(3-octylthiophene) film was used as an intermediate layer for voltammetric detection of a lipophilic inorg. anion, hexafluoroarsenate, an arsenical biocide found recently in wastewater. A LOD of (9 ± 2) × 10-11 M hexafluoroarsenate thus obtained by ion-transfer stripping voltammetry is comparable to a LOD of 80 pM by inductively coupled plasma mass spectrometry with anion-exchange chromatog. Great sensitivity for a lipophilic ion is potentially useful for environmental anal. because high lipophilicity of an ion is relevant to its bioaccumulation and toxicity.
- 23Mao, C.; Yuan, D.; Wang, L.; Bakker, E. Separating Boundary Potential Changes at Thin Solid Contact Ion Transfer Voltammetric Membrane Electrodes. J. Electroanal. Chem. 2021, 880, 114800 DOI: 10.1016/j.jelechem.2020.11480023https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXit12nsb3N&md5=5c4a6990d93dda1c73b4aaee99d17b2dSeparating boundary potential changes at thin solid contact ion transfer voltammetric membrane electrodesMao, Canwei; Yuan, Dajing; Wang, Lu; Bakker, EricJournal of Electroanalytical Chemistry (2021), 880 (), 114800CODEN: JECHES; ISSN:1873-2569. (Elsevier B.V.)Thin ion-selective membrane films deposited on solid electrode substrate are useful tools to study ion transfer processes. This is because the exptl. conditions may be chosen such that diffusion processes within the membrane and contacting aq. soln. are not rate limiting. In an ideal case, therefore, equil. considerations may be used to describe the resulting ion transfer voltammograms. For example, the electrochem. oxidn. of an elec. neutral redox mol. in the membrane results in a cationic oxidized form. To preserve electroneutrality, a cation is transferred out of the membrane into soln., freeing the cation-exchanger of the membrane to become the counterion of the oxidized redox mol. This work describes a model system that agrees well with thermodn. theory, using the lipophilic (1-dodecyl-1H-1,2,3-triazol-4-yl)ferrocene as redox mol. and a monovalent ref. cation for ion transfer. The full peak width at half max. was found as 0.110 V, in agreement with theory, and with peak current proportional to scan rate supporting thin layer behavior. The charge passed during the voltammetric scan was related to ion-exchanger concn. available for ion extn. as a function of potential. Subtraction of the ion transfer potential using the ref. ion from the exptl. one for each charge increment gave the potential change for the electrochem. ion-to-electron transducer. In one application, the potential change of the polymeric transducing layer poly(3-octylthiophene) (POT) film upon electrochem. oxidn. within the membrane was characterized. A nonlinear potential-charge curve was obsd., in contrast to earlier assumptions.
- 24Cuartero, M.; Crespo, G. A.; Bakker, E. Ionophore-Based Voltammetric Ion Activity Sensing with Thin Layer Membranes. Anal. Chem. 2016, 88, 1654– 1660, DOI: 10.1021/acs.analchem.5b0361124https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitV2ntr%252FO&md5=fc1a1919bd579e1e69a5fc6e773d616bIonophore-Based Voltammetric Ion Activity Sensing with Thin Layer MembranesCuartero, Maria; Crespo, Gaston A.; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2016), 88 (3), 1654-1660CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)As shown in recent work, thin layer ion-selective multi-ionophore membranes can be interrogated by cyclic voltammetry to detect the ion activity of multiple species simultaneously and selectively. Addnl. fundamental evidence is put forward on ion discrimination with thin multi-ionophore-based membranes with thicknesses of 200 ± 25 nm and backside contacted with poly-3-octylthiophene (POT). An anodic potential scan partially oxidizes the POT film (to POT+), thereby initiating the release of hydrophilic cations from the membrane phase to the sample soln. at a characteristic potential. Varying concn. of added cation-exhanger demonstrates that it limits the ion transfer charge and not the deposited POT film. Voltammograms with multiple peaks are obsd. with each assocd. with the transfer of one type of ion (lithium, potassium, and sodium). Exptl. conditions (thickness and compn. of the membrane and concn. of the sample) are chosen that allow one to describe the system by a thermodn. rather than kinetic model. As a consequence, apparent stability consts. for sodium, potassium, and lithium (assuming 1:1 stoichiometry) with their resp. ionophores are calcd. and agree well with the values obtained by the potentiometric sandwich membrane technique. As an anal. application, a membrane contg. three ionophores was used to det. lithium, sodium, and potassium in artificial samples at the same location and within a single voltammetric scan. Lithium and potassium were also detd. in undiluted human plasma in the therapeutic concn. range.
- 25Bandey, H. L.; Martin, S. J.; Cernosek, R. W.; Hillman, A. R. Modeling the Responses of Thickness-Shear Mode Resonators under Various Loading Conditions. Anal. Chem. 1999, 71, 2205– 2214, DOI: 10.1021/ac981272b25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXis1WgsLo%253D&md5=9c3ef38e0b41c68800db263d0f08437eModeling the Responses of Thickness-Shear Mode Resonators under Various Loading ConditionsBandey, Helen L.; Martin, Stephen J.; Cernosek, Richard W.; Hillman, A. RobertAnalytical Chemistry (1999), 71 (11), 2205-2214CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A general model is developed to describe the elec. responses of thickness-shear mode resonators subject to a variety of surface conditions. The model incorporates a phys. diverse set of single-component loadings, including rigid solids, viscoelastic media, and fluids (Newtonian or Maxwellian). The model allows any no. of these components to be combined in any configuration. Such multiple loadings are representative of a variety of phys. situations encountered in electrochem. and other liq.-phase applications, as well as gas-phase applications. In the general case, the response of the composite load is not a linear combination of the individual component responses. Application of the model is discussed in a qual. diagnostic fashion to gain insight into the nature of the interfacial structure, and in a quant. fashion to ext. appropriate phys. parameters such as liq. viscosity and d. and polymer shear moduli.
- 26Chan, A. D. C.; Harrison, D. J. NMR Study of the State of Water in Ion-Selective Electrode Membranes. Anal. Chem. 1993, 65, 32– 36, DOI: 10.1021/ac00049a00826https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38Xms1eksLg%253D&md5=1359f6c1df62599873ec16361bea04e7NMR study of the state of water in ion-selective electrode membranesChan, Andy D. C.; Harrison, D. JedAnalytical Chemistry (1993), 65 (1), 32-6CODEN: ANCHAM; ISSN:0003-2700.Variable-temp. 1H and 2D NMR studies of H2O and D2O uptake in poly(vinyl chloride) (PVC) based ion-selective membranes were employed to evaluate the state of water. The data show that water (heavy or light) in the membranes is present as freezable water, indicating it is present as droplets or clusters. The water freezes between 0 and -15°, and calcns. suggest the min. droplet diam. is about 0.016 μm, but a large size range exists. The light scattering centers obsd. during water uptake must be due to these droplets, at least in part. The NMR chem. shift of water is a function of the concn. of KB(C6H5)4 added to the membrane, and the range of chem. shifts demonstrates there are a range of environments for water.
- 27Grause, G.; Hirahashi, S.; Toyoda, H.; Kameda, T.; Yoshioka, T. Solubility Parameters for Determining Optimal Solvents for Separating PVC from PVC-Coated PET Fibers. J. Mater. Cycles Waste Manag. 2017, 19, 612– 622, DOI: 10.1007/s10163-015-0457-927https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVGhsL3F&md5=744a4f693901234b524f314d5af6cba4Solubility parameters for determining optimal solvents for separating PVC from PVC-coated PET fibersGrause, Guido; Hirahashi, Suguru; Toyoda, Hiroshi; Kameda, Tomohito; Yoshioka, ToshiakiJournal of Material Cycles and Waste Management (2017), 19 (2), 612-622CODEN: JMCMFW; ISSN:1438-4957. (Springer Japan)Poly(vinyl chloride) (PVC) in PVC-coated poly(ethylene terephthalate) (PET) fabrics can be sepd. through dissoln. in a suitable solvent, leaving only the PET fibers. We investigated the soly. of PVC in 30 solvents using swelling tests. The results were compared with those obtained using the Hansen, Gutmann, Swain, ET(30), and Kamlet-Taft parameters. For this purpose, Gaussian plots of the PVC swellability vs. soly. parameter were used to decide the applicability of the soly. parameter system. Only Gutmann's electron acceptor-donor parameter (AN + DN) and the Kamlet-Taft parameters β and π* could describe the PVC-solvent system satisfactorily. THF (THF), Me Et ketone (MEK), N,N-dimethylformamide (DMF), cyclohexanone, and cyclopentanone were tested for sepg. PVC from PET at different temps. THF dissolved PVC at 20 °C, while cyclohexanone and cyclopentanone did so at 40 °C. Traces of PVC remained on the PET fibers when DMF was used. Complete dissoln. of PVC was not achieved at any temp. with MEK. The present work shows that soly. parameters are a helpful tool for the search for suitable solvents. It shows also that soly. parameters have to be selected carefully, since their usefulness depends strongly on the polymer properties.
- 28Robinson, K.; Mao, C.; Bakker, E. Surfactants for Optode Emulsion Stabilization without Sacrificing Selectivity or Binding Constants. Anal. Chem. 2021, 93, 15941– 15948, DOI: 10.1021/acs.analchem.1c0323228https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXisFWrsL7K&md5=c78957566c620d2fd977daa4d79bb337Surfactants for Optode Emulsion Stabilization without Sacrificing Selectivity or Binding ConstantsRobinson, Kye; Mao, Canwei; Bakker, EricAnalytical Chemistry (Washington, DC, United States) (2021), 93 (48), 15941-15948CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We compare here the effect of surfactants on ion-selective membranes measured via voltammetry and optode emulsions measured optically. Cyclic voltammetry on a thin-film ion-selective membrane is shown to be a useful screening technique for the estn. of effective complex formation consts. and selectivity coeffs. for different surfactants with various cations. This technique is particularly useful for its ability to identify sep. ion-transfer events (free, surfactant complexed, ionophore complexed) for a specific membrane. However, we also caution against the over-reliance on this technique as changes in membrane characteristics are obsd. following surfactant partitioning. Of the surfactants explored here, a zwitterionic sulfobetaine-based surfactant was found to stabilize sensors without reducing effective binding consts. and selectivity, with greatly superior characteristics to other commonly utilized surfactants. Those include Brij-35, F-127, and Triton X-100, all of which showed significant binding to so-called free ions in the membrane, resulting in peak potential shifts of 199 ± 10, 180 ± 24, 278 ± 11 mV, resp., for potassium following the subtraction of transducing layer effects. This peak shift translated to a much larger undesired free ion response in optode emulsions. The selectivity in emulsion-based systems was also shown to decrease in the presence of nonionic surfactants compared to that contg. the zwitterion.
- 29Bakker, E.; Pretsch, E. Lipophilicity of Tetraphenylborate Derivatives as Anionic Sites in Neutral Carrier-Based Solvent Polymeric Membranes and Lifetime of Corresponding Ion-Selective Electrochemical and Optical Sensors. Anal. Chim. Acta 1995, 309, 7– 17, DOI: 10.1016/0003-2670(95)00077-D29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXmtVygsro%253D&md5=092477e1de78c54275c66558fd2c1a33Lipophilicity of tetraphenylborate derivatives as anionic sites in neutral carrier-based solvent polymeric membranes and lifetime of corresponding ion-selective electrochemical and optical sensorsBakker, Eric; Pretsch, ErnoeAnalytica Chimica Acta (1995), 309 (1-3), 7-17CODEN: ACACAM; ISSN:0003-2670. (Elsevier)The leaching process of lipophilic anionic additives (e.g., tetraphenylborates) from neutral carrier based membranes into an aq. sample is quantified. While the necessary lipophilicity (i.e., equil. partition coeff.) of the additive for a certain lifetime of the sensor is identical to the one of neutral compds. described earlier, its quantification needs to consider the coextn. equil. with the counterions between both phases. It is shown theor. and with liq.-liq. extn. expts. that the lifetime of the sensor depends for a given tetraphenylborate both on the nature of the counterion and its concn. in the aq. and org. phase. Also, the complexation of the cationic counterion by the ionophore will shift the partition equil. of the anionic site in direction of the membrane phase, thus rendering the additive more lipophilic. By using previously measured ion-exchange consts. detd. on thin membrane phases (optical sensors) together with the extn. data presented here, quant. lipophilicity data is indirectly accessible. Ionophores forming highly stable complexes with the sample cation (e.g., valinomycin for K+ or ETH 1001 for Ca2+) induce a sufficiently high lipophilicity of the tetraphenylborate deriv. according to the criteria presented here. However, only the most lipophilic tetraphenylborates (i.e., tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) show acceptably slow leaching behavior in membranes contg. no ionophore.
- 30Kubjnyi, H. Drug Partitioning: Relationships between Forward and Reverse Rate Constants and Partition Coefficient. J. Pharm. Sci. 1978, 67, 262– 263, DOI: 10.1002/jps.2600670237There is no corresponding record for this reference.
- 31Egorov, V. V.; Novakovskii, A. D.; Zdrachek, E. A. A Simple Dynamic Diffusion Model of the Response of Highly Selective Electrodes: The Effect of Simulation Parameters and Boundary Conditions on the Results of Calculations. Russ. J. Electrochem. 2018, 54, 381– 390, DOI: 10.1134/S102319351804003131https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXotF2nt70%253D&md5=efd97478de852d068c082bb4850d52e5A Simple Dynamic Diffusion Model of the Response of Highly Selective Electrodes: The Effect of Simulation Parameters and Boundary Conditions on the Results of CalculationsEgorov, V. V.; Novakovskii, A. D.; Zdrachek, E. A.Russian Journal of Electrochemistry (2018), 54 (4), 381-390CODEN: RJELE3; ISSN:1023-1935. (Pleiades Publishing, Ltd.)For a tetrabutylammonium-selective electrode with a ion-exchange membrane, in the real-work scenario corresponding to the detn. of selectivity coeffs. by the IUPAC-recommended method of sep. solns., it is shown that of the results of calcns. obtained within the framework of the dynamic diffusion model based on the use of the finite-difference technique substantially depend on of the chosen boundary conditions and the values of arbitrarily set simulation parameters. The key parameter that dets. the quality of simulation results is the thickness of the elementary layer in the membrane phase, esp. for low diffusion coeffs. It is found that the use of thin elementary layers in membranes and thick elementary layers in the aq. phase makes it possible to combine the high quality with the high calcn. rate. In simulating the long-term expts., account should be taken of the accumulation of the potential-detg. ion in the aq. soln. vol. as a result of its displacement by a foreign ion from the membrane. A good correspondence between calcn. data and exptl. results is demonstrated.
- 32Ma, Y.; Liu, C.; Wang, L. Defined Ion-Transfer Voltammetry of a Single Microdroplet at a Polarized Liquid/Liquid Interface. Anal. Chem. 2022, 94, 1850– 1858, DOI: 10.1021/acs.analchem.1c0480932https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XptlShtQ%253D%253D&md5=0f57d68534746a329013a548ae9b7d4eDefined Ion-Transfer Voltammetry of a Single Microdroplet at a Polarized Liquid/Liquid InterfaceMa, Yamin; Liu, Cheng; Wang, LishiAnalytical Chemistry (Washington, DC, United States) (2022), 94 (3), 1850-1858CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)A strategy for the fast anal. of ion transfer/facilitated ion transfer toward a tiny (femtoliter) water-in-oil droplet has been established. This scenario is embodied by the fusion of a w/o microdroplet at the micro liq./liq. (L/L) interface, with the use of Fourier transform fast-scan cyclic voltammetry (FT-FSCV) to express the apparent half-wave potentials of anions or cations encapsulated inside the w/o microdroplet. First, the half-wave potential is in strict accordance with the transfer Gibbs free energy of either cations or anions. Second, the half-wave potential has been found to be pos. proportional to the logarithmic concn. of ions, shedding thermodn. insight into ion transfer. Third, as an instance of multivalent biopolymers, the transfer of protamine inside the single w/o microdroplet has been investigated. Obvious discrepancies in the behaviors of the fusion impacts at different pH, as well as in the absence and presence of the cationic surfactant DNNS-, are revealed. The internal mechanism of protamine transfer has been thoroughly investigated. This work proposes a strategy to sensitively and quickly det. the transfer Gibbs energy and the concn. of ions encapsulated in a single microdroplet, and it provides the possibility of analyzing the interfacial transfer properties of trace biomacromols. inside an aq. micro- or nanoscale droplet.
- 33Moon, H.; Park, J. H. In Situ Probing Liquid/Liquid Interfacial Kinetics through Single Nanodroplet Electrochemistry. Anal. Chem. 2021, 93, 16915– 16921, DOI: 10.1021/acs.analchem.1c0407133https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXis1CrurjO&md5=cd0f6e9d48a3947d2f09d34c7e01fbb6In Situ Probing Liquid/Liquid Interfacial Kinetics through Single Nanodroplet ElectrochemistryMoon, Hyeongkwon; Park, Jun HuiAnalytical Chemistry (Washington, DC, United States) (2021), 93 (50), 16915-16921CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)In this study, we report the new application of single nanodroplet electrochem. to in situ monitor the interfacial transfer kinetics of electroactive species across liq./liq. interface. Interfacial kinetic information is crucial in drug delivery and membrane transport. However, interfacial information has been mainly studied thermodynamically, such as partition coeff., which could not manifest a speed of transfer. Herein, we measure the phase-transfer kinetic const. via the steady-state electrochem. of an extd. redox species in a single nanodroplet. The redox species were transferred from the continuous oil phase to the water nanodroplet by partition equil. The transferred redox species are selectively electrolyzed within the droplet when the droplet contacts with an ultramicroelectrode, while the electrochem. reaction of the redox species outside the droplet (i.e., org. solvent) is effectively suppressed by adjusting the electrolyte compn. The redox species in the water droplets can quickly attain a steady state during electrolysis owing to an extensive mass transfer by radial diffusion, and the steady-state current can be analyzed to obtain kinetic information with help from the finite-element method. Finally, a quick calcn. method is suggested to est. the kinetic const. of phase transfer without simulation.
- 34Deng, H.; Dick, J. E.; Kummer, S.; Kragl, U.; Strauss, S. H.; Bard, A. J. Probing Ion Transfer across Liquid–Liquid Interfaces by Monitoring Collisions of Single Femtoliter Oil Droplets on Ultramicroelectrodes. Anal. Chem. 2016, 88, 7754– 7761, DOI: 10.1021/acs.analchem.6b0174734https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFeku7bP&md5=3460466fbb237a5409b4bf07af17a946Probing Ion Transfer across Liquid-Liquid Interfaces by Monitoring Collisions of Single Femtoliter Oil Droplets on UltramicroelectrodesDeng, Haiqiang; Dick, Jeffrey E.; Kummer, Sina; Kragl, Udo; Strauss, Steven H.; Bard, Allen J.Analytical Chemistry (Washington, DC, United States) (2016), 88 (15), 7754-7761CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)We describe a method of observing collisions of single femtoliter (fL) oil (i.e., toluene) droplets that are dispersed in water on an ultramicroelectrode (UME) to probe the ion transfer across the oil/water interface. The oil-in-water emulsion was stabilized by an ionic liq., in which the oil droplet trapped a highly hydrophobic redox probe, rubrene. The ionic liq. also functions as the supporting electrolyte in toluene. When the potential of the UME was biased such that rubrene oxidn. would be possible when a droplet collided with the electrode, no current spikes were obsd. This implies that the rubrene radical cation is not hydrophilic enough to transfer into the aq. phase. We show that current spikes are obsd. when tetrabutylammonium trifluoromethanesulfonate or tetrahexylammonium hexafluorophosphate are introduced into the toluene phase and when tetrabutylammonium perchlorate is introduced into the water phase, implying that the ion transfer facilitates electron transfer in the droplet collisions. The current (i)-time (t) behavior was evaluated quant., which indicated the ion transfer is fast and reversible. Furthermore, the size of these emulsion droplets can also be calcd. from the electrochem. collision. We further investigated the potential dependence on the electrochem. collision response in the presence of tetrabutylammonium trifluoromethanesulfonate in toluene to obtain the formal ion transfer potential of tetrabutylammonium across the toluene/water interface, which was detd. to be 0.754 V in the inner potential scale. The results yield new phys. insights into the charge balance mechanism in emulsion droplet collisions and indicate that the electrochem. collision technique can be used to probe formal ion transfer potentials between water and solvents with very low (ε < 5) dielec. consts.
- 35Yang, W.; Zhai, J.; Xie, X. Rhodamine Dye Transfer from Hydrogel to Nanospheres for the Chemical Detection of Potassium Ions. Analyst 2019, 144, 5617– 5623, DOI: 10.1039/C9AN01079C35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsVKntL%252FO&md5=b9dffa44281bd62b8286b80c36e12049Rhodamine dye transfer from hydrogel to nanospheres for the chemical detection of potassium ionsYang, Wei; Zhai, Jingying; Xie, XiaojiangAnalyst (Cambridge, United Kingdom) (2019), 144 (18), 5617-5623CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)Smart hydrogels incorporating various functional nanomaterials are becoming popular tools for chem. sensing. Here, ion-exchange nanospheres composed of the block copolymer Pluronic F-127 played the role of a scavenger for a signal transducer dye (Rhodamine 800) in a three-phase based optical detection system for potassium ions. Rhodamine 800, a pos. charged dye, was incorporated into a hydrogel together with the potassium ionophore valinomycin and an ion-exchanger (Na+R-). The concn. of Rhodamine 800 in the aq. sample was kept low by the nanospheres contg. Na+R-. Consequently, the detection limit (0.3 μM) of the three-phase based system was shifted 2 orders of magnitude lower compared with those of previously reported two-phase based sensing systems. The concept of controlling the dye transfer among the three phases provided a new train of thought for the design of ionophore-based chem. sensors.
Supporting Information
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsmeasuresciau.2c00053.
Detailed experimental information, calculation of the nanoemulsion concentration, analysis of mass transfer rates, and diffusion simulation (PDF)
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