Determination Of Ion Mobilities Research Articles

Identification of thermodiffusion coefficients in an aqueous potassium ferri/ferrocyanide thermocell using open-circuit voltage data

Ion thermodiffusion coefficients are crucial to analyse effects of thermodiffusion in thermocells and these values are difficult to measure experimentally. To determine these coefficients, this paper adopts parameter identification and studies their identifiability. Time dependence of open-circuit voltage is measured in an aqueous potassium ferri/ferrocyanide thermocell as data set. A one-dimensional numerical model is established according to theories of electrochemistry and non-equilibrium thermodynamics. Identification of thermodiffusion coefficients is conducted using genetic algorithm in eight parameter spaces, which are divided according to signs of three parameters. Thermodiffusion is suggested to induce a 9.38% drop in voltage. The best identification results are −8.30 × 10−12, −6.56 × 10−12, −3.48 × 10−12 m2/(s K) for ferricyanide, ferrocyanide and potassium ion, respectively. However, five optimal parameters in other parameter spaces have close fitness, implying multimodality of identification. And only one of these parameters is practically identifiable using this method. To improve identification results, more accurate estimation of inner temperature difference and determination of ion mobilities are necessary. Besides, electric current data has the potential to determine the actual combination of thermodiffusion coefficients from these six optimal results.

Collision Cross Sections of Charge-Reduced Proteins and Protein Complexes: A Database for Collision Cross Section Calibration.

The use of charge-reducing reagents to generate lower-charge ions has gained popularity in the field of native mass spectrometry (MS) and ion mobility mass spectrometry (IM-MS). This is because the lower number of charged sites decreases the propensity for Coulombic repulsions and unfolding/restructuring, helping to preserve the native-like structure. Furthermore, lowering the charge state consequently increases the mass-to-charge values (m/z), effectively increasing spacing between signals originating from small mass differences, such as different proteoforms or protein-drug complexes. IM-MS yields collision cross section (CCS, Ω) values that provide information about the three-dimensional structure of the ion. Traveling wave IM (TWIM) is an established and expanding technique within the native MS field. TWIM measurements require CCS calibration, which is achieved via the use of standard species of known CCS. Current databases for native-like proteins and protein complexes provide CCS values obtained using normal (i.e., non-charge-reducing) conditions. Herein, we explored the validity of using "normal" charge calibrants to calibrate for charge-reduced proteins and show cases where it is not appropriate. Using a custom linear field drift cell that enables the determination of ion mobilities from "first principles", we directly determined CCS values for 19 protein calibrant species under three solution conditions (yielding a broad range of charge states) and two drift gases. This has established a database of CCS and reduced-mobility (K0) values, along with their associated uncertainties, for proteins and protein complexes over a large m/z range. TWIM validation of this database shows improved accuracy over existing methods in calibrating CCS values for charge-reduced proteins.

On the origin of membrane potential in membranes with polarizable nanopores

We report a new mechanism for the generation of membrane potential in polarizable nanoporous membranes separating electrolytes with different concentrations. The electric field generated by diffusion of ions with different mobilities induces a non–uniform surface charge, which results in charge separation inside the nanopore. The corresponding Donnan potentials appear at the pore entrance and exit leading to a dramatic enhancement of membrane potential in comparison with an uncharged non–polarizable membrane. At high concentration contrast, the interaction between electric field and uncompensated charge at a low concentration side results in the development of electrokinetic vortices. The theoretical predictions are based on the Space–Charge model, which is extended to nanopores with polarizable conductive surface for the first time. This model is validated against full Navier–Stokes, Nernst–Planck, and Poisson equations, which are solved in a high aspect ratio nanopore connecting two reservoirs. The experimental measurements of membrane potential of dielectric and conductive membranes in KCl and NaCl aqueous solutions confirm the theoretical results. The membranes are prepared from Nafen nanofibers with ∼10nm in diameter and modified by depositing a conductive carbon layer. It is shown theoretically that the membrane potential enhancement becomes greater with decreasing the electrolyte concentration and pore radius. A high sensitivity of membrane potential to the ratio of ion diffusion coefficients is demonstrated. The described phenomenon may find applications in precise determination of ion mobilities, electrochemical and bio–sensing, as well as design of nanofluidic and bioelectronic devices.

Investigation of Electric Field Induced Ion Migration in Semiconductor Encapsulation Materials without the Interference of Electron Conductivity

Ion migration can cause severe damage to high power semiconductor devices. One of the main sources of mobile ions is the encapsulation material such as molding compounds. Within this work a method will be described to evaluate the risk of field induced ion migration of different molding compounds depending on the temperature and field strength. This method allows the qualitative and quantitative determination of ion mobility in molding compounds, without the interference of electron conductivity.

Calculation of Ion Mobilities and their Effects on Gas Discharge of AC Plasma Display Cells

We have found that ion mobilities in a gas mixture greatly affect discharge characteristics of a plasma display cell. Therefore, correct ion mobilities are required to obtain meaningful simulation results on plasma display cells. Since plasma display panels use microdischarges in the Xe mixed gas to generate vacuum ultraviolet light to excite phosphor for visible light emission, the condition of the discharge gas mixtures is one of the main factors that determine luminous efficacy. Thus, intensive studies on the discharge gas mixture are essential to optimize it and the accurate determination of ion mobilities in it is necessary. We have discussed how to determine necessary values of ion mobilities in various discharge gas mixtures including the three-species He–Ne–Xe mixture. Calculated ion mobilities and their effect on the discharge of an AC plasma display cell have also been presented and discussed. We have revealed that the enhanced ion mobilities in the gas mixture resulting from adding He gas to the conventional Ne–Xe mixture play an important role in increasing the luminous efficacy of a plasma display cell sustained in the He–Ne–Xe mixture by decreasing the cathode fall potential.

Electroosmotic effects in the determination of ion mobilities of carrier-free radionuclides in free aqueous electrolyte solutions

A device for on-line electromigration studies of radio-elements in free electrolytes has been tested by measuring the absolute individual ion mobilities of no-carrier-added single charged anions [99mTc]TcO4 - and [18F]F- and differently charged cations [137Cs]Cs+, [57Co]Co2+ and [241Am]Am3+ in inert aqueous electrolytes at 298.1 K. The observed ion mobilities were found to be influenced by electroosmosis in the migration tube. A relation to correct this effect is proposed. In addition, it was shown that the effect of electroosmosis may be suppressed by chemical treatment of the surface of the migration tube.

Time-of-flight ion mobility measurements in epoxy-amine systems during curing

The technique based on the time-of-flight (TOF) concept was proposed for determination of ion mobility in epoxy resins under isothermal curing conditions. This study extends our earlier investigations on this subject. Ionic conductivity dc measurements also were carried out in order to gain better understanding of the evolution of the ionic conductivity and mobility. The experiments have been performed for selected epoxy-amine systems that gellify and vitrify: diglycidyl ether of bisphenol A (DGEBA) with 4,4'-methylenebis [3-chloro-2,6-diethylaniline] (MCDEA) and for reacting medium that gellify only: diglycidyl ether of 1,4-butanediol (DGEBD) with 4,9-dioxa-1,12-dodecane diamine (4D). The differences found between the time dependency of the ionic conductivity and mobility during curing are explained by the decrease of the concentration of ionic charge carriers during the reaction. We conclude that the decrease of the ionic charge carrier density during the reaction, limits the applicability of the basic assumption of electrical techniques for reaction monitoring, that the ionic conductivity is related directly to the medium viscosity.

Determination of ion mobilities by IBM PC controlled nuclear electromigratic method

An IBM PC controlled nuclear electromigratic measuring system was developed to determine ion mobilities of different radioactive isotopes. The software and interface are shown in detail.

Determination of ion mobilities of radionuclides in a free electrolyte. Methods and experimental organization

A new variant of a technique for determining ion mobilities by means of horizontal zone electrophoresis in free solutions is developed. Setup circuit is presented. Some details of experiment and results of measuring limiting mobilities of131I-and160Tb3+ are given. On these examples the reproductibility was checked.

Determination of ion mobility from ionic injection current at strong diffusion

A method of using the ionic injection current in polymers to determine the ion mobility at strong diffusion is described. The mobilities of hydrogen and hydroxyl ions in polyester polymer have been determined by this method. Using a simple model of ionic conduction the thermal dependence of ion mobility is discussed.

Ionization of Liquids by Radiation. I. Methods for Determination of Ion Mobilities and Ion Yields at Low Voltage

Experimental methods are described in detail for determination of ion mobilities and of the zero-field conductivity induced by irradiation of insulating liquids with x rays. The yield of separated ions is thereby obtained with an accuracy of ±11% and is found to be 0.10 ion pairs per 100 eV for hexane at 23°C. The physical processes resulting from absorption of high-energy radiation are less well understood for liquids than for gases. Though it has long been thought that most ions produced in liquids disappear immediately by initial recombination, with only a small fraction of the excitation events leading to real charge separation, no actual measurement of the yield of separated charges was available when we first undertook to make this determination (late in 1961). From the magnitude of this value for different liquids and its dependence on temperature we may hope to deduce something about the behavior of slow electrons in liquids and the geometrical distribution of the radiation-induced electric charges.