Contribution from the ion-exchange factor to the potential of a copper-containing electron-ion exchanger

The process of formation of the electrode potential of EI-21 electron-ion exchanger, composed of ultrafine copper particles and KU-23 sulfocationite, was studied. The potentials of a EI-21 powdery electrode with a platinum lead in copper(II) sulfate solutions of various concentrations (0.005–1.0 M) were measured using currentless-mode potentiometry. The potential of this electrode first shifted by 0.02–0.15 V in the negative direction with respect to a compact copper electrode, after which the shift eventually decreased to ?0.010 ± 0.003 V. It was demonstrated that the time evolution of the potential is determined by the interplay of electron and ion exchange. When EI-21 is placed onto a platinum lead, the role of the potential-determining reaction passes from Cu²⁺ + e^? ? Cu⁺ to Cu²⁺ + 2e^? ? Cu. At the same time, H⁺-Cu²⁺ ion exchange gives rise to a change in the ratio of the concentration of copper(II) ions in the internal and external solutions. The Donnan potential, which arises at the boundary between the electron-ion exchanger and the external solution, maintains a high concentration of copper(II) ions in the internal solution, a factor that facilitates the recrystallization of the particle distributed over the bulk of the exchanger. The process of recrystallization slows down with time to such an extent that the electrode potential stops changing, remaining at a level close to the equilibrium potential of the Cu²⁺/Cu pair. It was concluded that the internal stability of the system makes the potential of the EI-21 electrode sensitive to the dispersity of the metal component and the concentration of potential-determining metal ions in the external solution.     

Entrainment of ambient air into a spectrochemical inductively coupled argon plasma

A spectrochemical inductively coupled argon plasma (ICP) is normally operated in the open air. Therefore, it is suggested in the literature that entrainment of air molecules into such an ICP may cause loss of electrons, especially so at the plasma's edge. The present study discusses the significance of this effect. The density and temperature of electrons and nitrogen molecules around the edge of the plasma were measured by Thomson and rotational Raman scattering. A region where both electrons and nitrogen were present in detectable amounts (10¹⁹ and 10²⁴ m⁻³, respectively) could not be observed. Above the torch inner wall the nitrogen concentration drops rapidly towards the plasma. Measurements suggest that the nitrogen concentration at 1 mm from the plasma is only a few percent, and in the active zones of the plasma (far) below 0.1%. This is not enough to affect the plasma significantly. Moreover, electron loss due to diffusion of nitrogen into the plasma is calculated to be much slower than the loss observed in earlier studies. Hence, air entrainment is unlikely to play a significant role in the ICP. A possible alternative is the formation and destruction of molecular rare gas ions.     

Molecular dynamics simulation of solution structure and dynamics of aqueous sodium chloride solutions from dilute to supersaturated concentration

Constant-temperature and constant-pressure (NpT) molecular dynamics simulations were performed to study the effects of salt concentration ranging from dilute to supersaturated concentrations on solution structure and dynamical properties of aqueous sodium chloride solutions at 298 K. The rigid SPC/E model was used for water molecules, and sodium and chloride ions were modeled as charged Lennard–Jones particles. Na⁺–Cl⁻ radial distribution functions showed the presence of contact ion pairs and solvent separated ion pairs. The coordination numbers of Na⁺–Cl⁻ ion pairs increased with salt concentration up to saturated concentration, although the number of contact ion pairs was almost constant in supersaturated regions. The tracer diffusion coefficients of both ions decreased with salt concentration up to saturated concentration, while that of sodium ion was almost constant in supersaturated regions. The tracer diffusion coefficients of both ions were therefore quite close to each other. The constant number of the contact ion pairs and the almost equality of the tracer diffusion coefficients of both ions would lead to the formation of clusters in supersaturated solutions.     

Some spatial effects observed in the axially viewed filament argon microwave induced plasma with solution nebulization

Spatial profiles of analyte emission in an axially viewed argon filament microwave induced plasma sustained in the TE₁₀₁ rectangular cavity have been measured along a discharge tube cross-section for neutral atoms as well as ion lines of several elements. The filament diameter was approximately 1 mm. The analyte solution was introduced by means of an ultrasonic nebulizer without desolvation. The radial emission distribution depends on the operating parameters and is different for each of the analytes examined. Spatial distributions of excitation temperature (4000–6000 K) measured with Ar I lines by the Boltzmann plot method as well as electron temperature (6000–8000 K) by line to continuum emission ratio measurements at Ar I 430 nm and electron number density (1–1.5×10¹⁵ cm⁻³) by the Stark broadening method of the H_β line were determined to support the evidence of plasma processes. In the presence of excess sodium the enhancement of emission intensity and its shift to the plasma center appears to be the result of increased analyte penetration to the plasma. Changes in spatial emission profiles for Ca atoms and ions suggest that for this element ambipolar diffusion may be important as an additional interference mechanism. A possibility of minimizing spectral interferences from argon emission lines by choosing an off-axis plasma region for emission intensity measurements is indicated.     

Diffusion potential is induced by coupled transport of ions through liquid membrane: nonlinear response to pH change in a reverse permeation system

In a cation exchange liquid membrane-aqueous alkali metal chloride system, diffusional flux of alkali metal ion driven by proton was observed. A supported liquid membrane formed on a Teflon filter by impregnating it with stearic acid-doped 1-octanol was used. The internal aqueous phase contained KCl and HCl, and the external aqueous phase also contained KCl. The initial concentrations of K⁺ ions of both phases were 1×10⁻¹ mol dm⁻³ for all the measurements. The concentration of HCl in the internal solution was kept at 1×10⁻² mol dm⁻³. The pH of the external solution was changed successively with HCl, appropriate buffer solution, or KOH. The pH dependence of membrane potential showed hysteresis loop in the range from neutral to alkaline pH, where reverse ion permeation was observed after the flux had been measured in the system with the external solution of an alkaline pH (pH 13). In the acidic range below neutral pH, the hysteresis of the membrane potential as well as reverse ion permeation was not observed. To elucidate the correlation between the appearance of hysteresis loop and the reverse ion permeation driven by proton across the membrane, the time course of the membrane potential in response to pH change was investigated. In the pH range where reverse permeation phenomena appeared, the time dependence of the membrane potential in nonsteady-state showed biphasic behavior. From the time course curve of the membrane potential, the total membrane potential was divided into the Donnan potential and the diffusion potential. From these findings, it was demonstrated that the diffusion potential was generated within the membrane only in the alkaline range where reverse ion permeation occurred. Analyzing the diffusional flux, the diffusion coefficient of potassium ion in the membrane was obtained taking the Donnan potential into account to be much greater than that in the membrane solvent. As a result of comparison of the diffusional fluxes measured by atomic absorption spectrometry and solution conductometry, the flux of the potassium ion was found to be significantly greater than that of the hydrogen ion in the opposite direction, especially at extremely high pH region. This implies the flows of hydroxide ions and neutralization reaction within the membrane facilitate the reverse ion permeation process of potassium ions.     

Volatile organic solvent-induced signal enhancements in inductively coupled plasma-mass spectrometry: a case study of methanol and acetone

Methanol and acetone were used to study effects of organic matrix on signal intensities of elements from ⁷Li to ²³⁸U and oxide yields in inductively coupled plasma-mass spectrometry (ICP-MS). Enhancement or suppression of analyte signals in the presence of methanol or acetone depends on the volatility and concentration of the compound and mass and ionization potential of elements concerned as well as ICP-MS operating conditions. Presence of a low concentration of methanol or acetone enhances the intensities of elements in order of decreasing mass. This is attributed to the spatial shift of the zone of maximum ion density, which, in turn, affects the extraction of ions from the plasma to the sampling cone. The possible effect of liquid methanol or acetone on nebulization and/or transport efficiency was avoided by using carry-over effect experiment. More volatile acetone more readily suppresses signals of all the elements under investigation. A higher concentration of methanol also suppresses intensities of the elements due to resultant cooling of the plasma. The enhancement effect of methanol and acetone appears to be more related to the amount of carbon present in the plasma than the difference between the functional groups of organic solvents. The oxide yield decreases in the presence of methanol, the magnitude of which depends on the nebulizer gas flow rate used. However, the reduced oxide yield is insufficient to account for the signal enhancement. Our results for ⁷⁵As and ⁷⁸Se agree with the C⁺-species–analyte atom charge transfer reaction hypothesis.     

A new method for measuring the diffusion coefficient in a gas phase

A new and fast method for measuring the diffusion coefficients of binary gas mixtures using ion mobility spectrometry (IMS) has been developed. In this method, the sample is injected as a short pulse into the flowing drift gas, forming a Gaussian concentration profile inside the drift region. This Gaussian cloud is irradiated with a fast moving swarm of electrons to create negative ions. The flash of electrons is so short that the negative ions do not move much during the exposure time. The ions then drift toward the detector, where they are collected. The collected ion signal pattern reflects the spatial distribution of the sample inside the cloud at the time of exposure. This is repeated in intervals of 300-400 ms to monitor the spatial spreading of the molecules in the drift region. Consecutive IMS spectra show the evolution of the cloud over time. The collected spectra are fit to Gaussian functions to extract diffusion coefficients. Using this method, the diffusion coefficient of O(2), CHCl(3), and C(2)H(2)Cl(2) were measured, and the results are in good agreement with the previously reported experimental data.     

Electrochemical diffusion potential in a flame plasma: theory and experiment

A flame doped with an appropriate additive to produce positive ions and free electrons is a quasineutral, weak, continuum plasma. When bounded by a metallic burner upstream and a metal plate downstream, the two electrodes and flame plasma can be viewed as a gas-phase electrochemical cell. When the ion (and electron) density varies continuously along the flame axis, an expression for the diffusion potential can be derived in terms of the concentration gradient. The familiar logarithmic dependence on the ion concentration is obtained. A plasma sheath develops at the metal plate electrode; it sustains a potential difference which can be modeled by a Boltzmann distribution of the electrons in the sheath. Since the plate has to be cooled in practice, the average sheath temperature is less than the flame temperature because the sheath occurs inside the thermal boundary layer which covers the plate electrode. Inevitably, the reduced sheath temperature affects the sheath voltage. Experimental measurements of the “cell” voltage are made for the two cases of a positive concentration gradient using a sodium plasma, and a negative gradient by doping the flame with methane. As predicted theoretically, the cell voltages have opposite signs. However, the magnitude of the cell voltage seems to depend significantly on the sheath temperature which appears to decrease steadily with increasing distance downstream from the burner. It is also possible that the measured cell voltages involve unknown surface contact potentials. When compared with solution concentration cells, gas-phase flame systems exhibit both similarities and differences.     

Diffusion of ionic species labeled with35S in various aqueous electrolyte solutions at 25°C

Composite diffusion coeffcients have been measured for the various species labeled with³⁵S which are present in a number of aqueous solutions due to the introduction of the labeled material as³⁵SO ₄ ^2– . The solutions were of two components consisting of water and either sodium sulfate. The diffusion coeffcient measured for sodium chloride solutions is similar to literature data for the corresponding diffusion in sodium sulfate solutions. The results for sulfuric acid and ammonium hydrogen sulfate have been interpreted using literature data for the relative concentrations of the hydrogen sulfate and sulfate ions to obtain estimates for the diffusion coefficents of those ions. The results for perchloric acid, regarded as representing the diffusion coefficient of the hydrogen sulfate ion, have a much different concentration dependence to that observed for the estimates for that ion in sulfuric acid and ammonuim hydrogen sulfate. The difference is attributed to the effect of the perchlorate ion on the water structure.     

Preparation of W1/O/W2 emulsion to limit the diffusion of Fe3+ in the Fricke gel 3D dosimeter

The irradiation of tumors in radiotherapy requires accurate 3D dosimetry. The Fricke 3D dosimeters, which were considered to be high potential of application in 3D dosimetry, suffer from a reduced temporal integrity of dose distribution caused by Fe³⁺ ions diffusion. To overcome the drawback, we firstly synthesized a kind of amphiphilic molecules with critical micelle concentration of 0.45 g/L and hydrophile‐lipophile balance value of 10, then prepared multiple emulsions by self‐assembling those molecules in Fricke solution under liquid paraffin, and finally obtained Fricke hydrogel embedded with the multiple emulsions. The diffusion coefficient of Fe³⁺ ions in the embedded Fricke hydrogel was measured to be 0.17 mm²/h. The hydrogel dosimeter exhibits considerable potential for use in dose verification applications.     

Analyte ionization in the inductively coupled plasma

Spatially resolved ion-atom emission intensity ratios for Sr, Ca, Mg, Cd and Zn have been measured at rf power settings of 1.00, 1.25, 1.50, 1.75 and 2.0 kW at a vertical height of 16 mm above the load coil. Measured values of electron density have been used to construct a theoretical local thermal equilibrium (LTE) framework, and ion-atom emission intensity ratios calculated from this framework have been compared to experimentally measured values. The measured ion-atom emission intensity ratios were found to be within an order of magnitude of these calculated LTE ratios.The experimental degree of ionization for these five elements was determined for the various rf input powers. These values have been compared to the analagous LTE values. Both degree of ionization and departure from LTE were found to be strongly correlated with the ionization potential of the element.The radial spatial dependence of the degree of ionization for Cd at an rf power of 1.25 kW has been measured for aerosol flow rates of 0.6, 0.8 and 1.21 m⁻¹ for vertical heights of 4, 8, 12, 16 and 20 mm above the load coil. The spatial distribution of electron number density was measured at an rf power of 1.25 kW and at aerosol flow rates of 0.6, 0.8 and 1.21 m⁻¹ and a correlation between degree of ionization and electron density identified. Finally the relative concentration of Cd ions has been calculated from ion spatial emission profiles and plasma operating conditions which produce a maximum in the ion density identified.     

On the Initial Stages of Electrooxidation of Aqueous Maleic Acid on Bi‐Doped PbO2

Oxidation of maleic acid in aqueous solution on bismuth‐doped lead oxide has been studied. The effects of hydrodynamic conditions on the oxidation rate have been identified. The number of electrons transferred during the initial stages of oxidation as well as the apparent heterogeneous rate constant was obtained from the combined analysis of rotating ring‐disk currents and the decrease of concentration at constant potential, determined from UV‐vis measurements. The number of electrons involved during electrochemical oxidation was found to be 12, indicating full mineralization to CO₂, and the heterogeneous rate constant for oxidation at 1.6 V was 9.8×10⁵ cm s^?1.     

Cellulose and chitin nanomaterials for capturing silver ions (Ag+) from water via surface adsorption

The study explores the potential of cellulose nanocrystals (CNC), cellulose nanofibers (CNF) and chitin nanocrystals (ChNC) isolated from bioresidues to remove silver ions from contaminated water. Zeta sizer studies showed negatively charged surfaces for CNC and CNF isolated from cellulose sludge in the acidic and alkaline pHs, whereas ChNC isolated from crab shell residue showed either positive or negative charges depending on pH conditions. Model water containing silver ions showed a decrease in Ag⁺ ion concentration (measured by inductively coupled plasma-optical emission spectrometer; inductively coupled plasma mass spectrometry), after treatment with CNC, CNF and ChNC suspensions. The highest Ag⁺ ion removal was measured near neutral pH for CNC, being 34.4 mg/g, corresponding to 64 % removal. ChNC showed 37 % and CNF showed 27 % removal of silver ions. The WDX (wavelength dispersive X-ray analysis) and XPS (X-ray photoelectron spectroscopy) analysis confirmed the presence of silver ions on the surface of the nanocellulose and nanochitin after adsorption. Surface adsorption on the nanoparticles via electrostatic interactions is considered to be the prominent mechanism of heavy metal ion capture from aqueous medium, with CNC with negative surface charge and negatively charged functional groups being most favourable for the adsorption of positively charged Ag⁺ ions compared to other native bionanomaterials.     

A segmented radiofrequency-only quadrupole collision cell for measurements of ion collision cross section on a triple quadrupole mass spectrometer

The gas collision cell of a triple quadrupole mass spectrometer has been modified to consist of ten short quadrupole rod segments that allow an axial field to be applied to the cell in order to make measurements of ion mobility. The radiofrequency (rf)-quadrupole field provides effective radial confinement that greatly reduces diffusional losses at low pressure. The mobilities of mass-selected ions from an ionspray source have been measured at a pressure of 8 × 10^?3 torr at electric fields of 0. 1 to 3 V/cm, and used to calculate the collision cross sections of the ions. The measured cross sections compare well with those measured by other techniques.     

Proton conductive thin films prepared by plasma polymerization

Proton conductive membranes were prepared as thin films of about 10 μm thickness by an ion beam assisted plasma polymerization process. Argon ions were generated in a high frequency plasma and accelerated towards a PTFE target where CF fragments were released as a consequence of the ion impact. Various sulfur components (SO₂, CF₃SO₃H or ClSO₃H) were added to achieve proton conductivity by the formation of sulfonic acid groups. The CF fragments combined with the sulfur components to form a coherent thin film on a substrate. Mass spectrometric investigations revealed, however, that sulfur oxygen compounds were extremely delicate towards reduction to sulfur carbon compounds like CS₂ or SCF₂. The best membrane conductivities (>10⁻⁴ S/cm) and highest ion exchange capacities (0.15 mmol/g) were achieved with chlorosulfonic acid involved in the plasma polymerization process. Ultra-thin layers of these of these plasma polymers (ca. 300 nm) were subsequently deposited onto Nafion^® membranes in order to suppress methanol permeation for a potential application in a direct methanol fuel cell (DMFC). The ratio of proton conductivity and methanol diffusion coefficient was employed for an assessment of the transport characteristics of the coated membrane. Diffusion coefficients were determined in a flow cell coupled to a mass spectrometer. The plasma polymer coating decreased both the methanol permeation and the proton conductivity. With a proton conductive plasma polymer coating the decrease of methanol diffusion could outweigh the loss of proton conductivity. Plasma coating offers a way to suppress methanol crossover in DMFCs and to maintaining the proton conductivity.     

Ion pairing between dissolved poly(o-phenylenediamine) and halogenide ions

An electrically conductive polymer, poly(o-phenylenediamine) (PoPD), is soluble in dimethylsulfoxide (DMSO) without any pretreatment. Cyclic voltammograms of dissolved PoPD were measured in DMSO solutions containing halogenide ions and two reversible redox peak currents were evident. The redox potential shifted with the concentration of the dissolved halogenide ion. The relationship between the potential shift and the concentration determined the relative association constant of PoPD for four halogenide ions: 104 mol⁻¹ dm⁻³ for F⁻; 32 mol⁻¹ dm⁻³ for Cl⁻; 29 mol⁻¹ dm⁻³ for Br⁻ and 9 mol⁻¹ dm⁻³ for I⁻.     

Intradiffusion coefficients for perchlorate ions in zinc perchlorate and zinc chloride solutions at 25°C: Comparing transport properties of zinc chloride and zinc perchlorate systems

Intradiffusion coefficients for³⁶ClO ₄ ^– have been measured in solutions of zinc perchlorate of concentration 0.1 to 3 mol dm^–3 at 25°C by the diaphragm cell technique. In addition, intradiffusion coefficients for perchlorate ions in zinc chloride solutions have been measured over a concentration range at 25°C. The results confirm previous work on the effect of complexation on diffusion in zinc chloride solutions above a salt concentration of 0.1M. The present data, together with literature data for diffusion coefficients of the other species present in the zinc perchlorate electrolyte system, have enabled a simple analysis of the hydration around the zinc ions to be carried out. This indicates that the water diffusion data are consistent with the zinc ions having an effective hydration sphere of 11 (±2) water molecules. This is in keeping with values obtained for other simple divalent electrolytes using the same model. The model is extended here to allow analysis of water diffusion in zinc chloride solutions taking into account the presence of complexed chloro-zinc species. The experimental data are consistent with the effective hydration of the chloro-zinc complexes being independent of the number of chloride ligands and equal to 18±3 over a concentration range of 0 tol mol-dm^–3. This postulate is discussed in terms of its consequences on the water ligand dynamics for the complex equilibria.     

Determination of As(III) and As(V) ions by chemiluminescence method

A new chemiluminescence (CL) method for the selective determination of As(III) and As(V) ions in aqueous solution has been studied using a FIA system. The method is based on the increased CL intensity with the addition of As(V) ion into a solution of lucigenin and hydrogen peroxide. The addition of As(III) ion into the solution did not change the CL intensity. Total concentration of As ions was determined after pre-oxidation of As(III) to As(V) with hydrogen peroxide in basic solution. The As(III) content was estimated by subtracting the content of As(V) ion from total As concentration. The effects of concentrations of KOH and H₂O₂, and flow rates of reagents on CL intensity have been investigated. The calibration curve for As(V) ion was linear over the range from 1.0×10^-2 to 10 μg/g, the coefficient of correlation was 0.997 and the detection limit was 5.0×10^-3 μg/g under the optimal experimental conditions.     

Intensitätsverhalten von Molekülanionen organischer Substanzen unter verschiedenen Versuchsbedingungen

A modified commercial mass spectrometer was used to perform quantitative measurements on negative ions of selected organic compounds at about 10^?4 Torr source pressure. The pressure dependency of the molecular ion intensity on pure compounds and binary mixtures shows up two different sources of slow secondary electrons. At low total source pressures a log-log plot of the ion intensity against the sample amount is linear and slow electrons are produced predominantly by wall effects, whereas at high pressures plasma effects arise with a non-linear pressure dependency.     

Electron kinetics in a collision-dominated SiH4 rf plasma including self-consistent rf field strength calculation

The electron kinetics of a collision-dominated rf plasma in silane has been studied by solving the nonstationary electron Boltzmann equation. Ionization and attachment processes and the spatially averaged electron loss to the plasma wall by ambipolar diffusion have been included in the kinetic approach. This makes it possible to calculate, in addition to the time-resolved energy distribution, the self-consistent rf field amplitude which is necessary for the maintenance of the steady-state rf discharge. The impact of the rf field frequency, of the density ratio of negative ions to electrons, and of superelastic (second kind) collisions with excited silane molecules was studied. In particular, large, rf field amplitudes of about 100 V cm^–1 Torr^–1 result, connected with large modulations of the energy distribution for field frequencies in the megahertz region.