Ionic Volume Research Articles

Investigation of fragrance stability used in the formulation of cosmetic and hygienic products using headspace solid-phase microextraction by nanostructured materials followed by gas chromatography with mass spectrometry.

A new composite coating of polypyrrole and sodium lauryl ether sulfate was electrochemically prepared on a stainless-steel wire using cyclic voltammetry. The application and performance of the fiber was evaluated for the headspace solid-phase microextraction of a fragrance in aqueous bleach samples followed by gas chromatography combined with mass spectrometry to assess the fragrance stability in this kind of household cleaning product. To obtain a stable and efficient composite coating, parameters related to the coating process such as scan rate and numbers of cycles were optimized using a central composite design. In addition, the effects of various parameters on the extraction efficiency of the headspace solid-phase microextraction process such as extraction temperature and time, ionic strength, sample volume, and stirring rate were investigated by experimental design methods using Plackett-Burman and Doehlert designs. The optimum values of 53°C and 28 min for sample temperature and time, respectively, were found through response surface methodology. Results show that the combination of polypyrrole and sodium lauryl ether sulfate in a composite form presents desirable opportunities to produce new materials to study fragrance stability by headspace solid-phase microextraction.

Development of a dispersive liquid-liquid microextraction technique for the analysis of aryloxyphenoxy-propionate herbicides in soy-based foods

In this work, an ionic liquid–dispersive liquid-liquid microextraction (IL-DLLME) method combined with liquid chromatography and diode-array detection (DAD) was used for the determination of four aryloxyphenoxy-propionate herbicides (fenoxaprop-p-ethyl, quizalofop-p-tefuryl, propaquizafop and haloxyfop-p-methyl) in two soy-based foods (soy milk and soy sauce) was used. For this purpose, the phosphonium-based room temperature ionic liquid (trihexyl(tetradecyl)phosphonium bistriflamide) was used as the extractant. The effect of the experimental parameters on extraction efficiency such as type of disperser solvent, disperser solvent/ ionic liquid volumes ratio, pH, nature and concentration of salt in the aqueous phase, sample volume, and centrifugation and extraction times were investigated and optimized. Since matrix effects were detected, the standard addition method was used for quantification. Under the optimized conditions, the proposed sample preparation method coupled to high performance liquid chromatography-diode array detection (HPLC-DAD) had a satisfactory performance to determine the four herbicides in soy sauce and soy milk. The enrichment factors ranged from 18 to 43 and recovery factors from 25 to 66%. Although the recoveries were not high because of the presence of organic solvent in the sample preparation step, the inter-day reproducibility was 8.4% or less, depending on the analyte, the limits of detection (S/N=3) were obtained in the range of 0.12–0.34mgL−1, the limits of quantification (S/N=10) between 0.36 and 1.04mgL−1, and linear ranges from LOQs to 9.26mgL−1. Finally, the IL-DLLME methodology is inexpensive, simple, fast, and environmentally friendly for the determination of the studied herbicides in soy sauce and soy milk. This study constitutes the first application of an IL-DLLME methodology to aryloxyphenoxy-propionate herbicides analysis in commercial soy-derived foods.

Crystal Structure and Thermochemical properties of Rubidium Pyruvate CH3COCOORb

One important compound rubidium pyruvate C3H3O3Rb(s) was synthesized and characterized by chemical analysis, elemental analysis and X–ray crystallography. X–ray single crystal structural analysis revealed that the compound is composed of one anion CH3COCOO− and one cation Rb+. An obvious feature of the crystal structure of the compound is the formation of a five-membered chelate ring, which is good for the stability of the compound. The lattice potential energy and ionic volume of the common anion were obtained from crystallographic data. The lattice potential energy $$ U_\text{POT}^{{}} $$ [C3H3O3Rb(s)] is 570.0 kJ·mol−1 and the volume of the anion CH3COCOO− is 0.1139 nm3. Molar enthalpies of dissolution of the compound at various molalities in the doubly distilled water were determined by use of an isoperibol solution-reaction calorimeter at 298.15 K. According to Pitzer’s model, the molar enthalpy of dissolution of C3H3O3Rb(s) at infinite dilution was derived to be 50.0 kJ·mol−1. Finally, the molar enthalpy of hydration of CH3COCOO−(g) was calculated to be −232.0 kJ·mol−1 from a thermochemical cycle.

Microwave-assisted ionic liquid homogeneous liquid–liquid microextraction coupled with high performance liquid chromatography for the determination of anthraquinones in Rheum palmatum L.

The microwave-assisted ionic liquid homogeneous liquid–liquid microextraction (MA-IL-HLLME) coupled with high performance liquid chromatography with diode array detection (HPLC-DAD) was developed for the determination of anthraquinones, including aloe-emodin, emodin, chrysophanol and physcion in root of Rheum palmatum L. Several experimental parameters influencing the extraction efficiency, including amount of sample, type and volume of ionic liquid, volume and pH value of extraction medium, microwave power and extraction time, concentration of NH4PF6 as well as centrifugal condition were optimized. When 140μL of ionic liquid ([C8MIM][BF4]) was used as an extraction solvent, target analytes can be extracted from sample matrix in one minute with the help of microwave irradiation. The MA-IL-HLLME is simple and quick. The calibration curves exhibited good linear relationship (r>0.9984). The limits of detection and quantification were in the range of 0.015–0.026 and 0.051–0.088μgmL−1, respectively. The spiked recovery for each analyte was in the range of 81.13–93.07% with relative standard deviations lower than 6.89%. The present method is free of volatile organic solvents, and represents lower expenditures of sample, extraction time and solvent, compared with ultrasonic and heat reflux extraction. The results indicated that the present method can be successfully applied to the determination of anthraquinones in medicinal plant.

HPLC-SEC: a new approach to characterise complex wastewater effluents

ABSTRACTThis work investigates the use of HPLC-SEC to characterise dissolved organic matter (DOM) of complex wastewater effluents. A silica-based column, sodium acetate eluent and multiple detections were employed: UV-254 absorbance for humictype, and tryptophan-like (Ex/Em = 270/355) and tyrosine-like (Ex/Em = 270/310) fluorescence for protein type compounds. Effects of eluent pH, eluent ionic strength and injection volume on separation efficiency were tested. Humic-type and protein-type fractions were clearly differentiated and eluted within and out of calibration range. Eluent ionic strength had the greatest influence on global resolution; the lowest eluent concentration of 0.01 M produced the best separation for all wastewater effluents tested at any detection. UV-254 absorbance was higher at neutral and basic eluent pH while tryptophan-like fluorescence depended on the sample composition rather than on the eluent pH or ionic strength. Tyrosine-like fluorescence decreased significantly with the increase of eluent ionic strength. Accurate molecular weight measurements could not be done, the separation being influenced by secondary interactions, but could be approximated using separate calibrations with sodium salts of polystyrene-sulfonates and protein standards. The results show that this method is suitable for determining DOM in wastewater at low eluent concentrations (up to 0.03 M), at neutral or slightly basic pH.

Ionic Liquids as Electrolytes for Electrochemical Double-Layer Capacitors: Structures that Optimize Specific Energy.

Key parameters that influence the specific energy of electrochemical double-layer capacitors (EDLCs) are the double-layer capacitance and the operating potential of the cell. The operating potential of the cell is generally limited by the electrochemical window of the electrolyte solution, that is, the range of applied voltages within which the electrolyte or solvent is not reduced or oxidized. Ionic liquids are of interest as electrolytes for EDLCs because they offer relatively wide potential windows. Here, we provide a systematic study of the influence of the physical properties of ionic liquid electrolytes on the electrochemical stability and electrochemical performance (double-layer capacitance, specific energy) of EDLCs that employ a mesoporous carbon model electrode with uniform, highly interconnected mesopores (3DOm carbon). Several ionic liquids with structurally diverse anions (tetrafluoroborate, trifluoromethanesulfonate, trifluoromethanesulfonimide) and cations (imidazolium, ammonium, pyridinium, piperidinium, and pyrrolidinium) were investigated. We show that the cation size has a significant effect on the electrolyte viscosity and conductivity, as well as the capacitance of EDLCs. Imidazolium- and pyridinium-based ionic liquids provide the highest cell capacitance, and ammonium-based ionic liquids offer potential windows much larger than imidazolium and pyridinium ionic liquids. Increasing the chain length of the alkyl substituents in 1-alkyl-3-methylimidazolium trifluoromethanesulfonimide does not widen the potential window of the ionic liquid. We identified the ionic liquids that maximize the specific energies of EDLCs through the combined effects of their potential windows and the double-layer capacitance. The highest specific energies are obtained with ionic liquid electrolytes that possess moderate electrochemical stability, small ionic volumes, low viscosity, and hence high conductivity, the best performing ionic liquid tested being 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

Fabrication of ferrocene functionalised ionic liquid/carbon nanotube nanocomposite modified carbon-ceramic electrode: application to the determination of hydrazine

ABSTRACTA novel ionic liquid, 1-(ferrocenyl butyl)-3-methylimidazolium tetrafluoroborate (Fc-IL), was synthesised. The nanocomposite of Fc-IL and multi-walled carbon nanotubes (MWCNTs) was constructed and used for surface modification of carbon-ceramic electrode. The modified electrode was applied to the determination of hydrazine. Operational parameters such as pH of the solution, ionic liquid volume and amount of carbon nanotubes, which affect the analytical performance of the modified electrode, were optimised. The linear range of the modified electrode toward hydrazine concentration was 0.96–106.10 μg L–1 with a detection limit of 0.64 μg L–1 (S/N = 3). The modified electrode displayed high repeatability, reproducibility, long-term life time and low response time (<3 s). The applicability of this method was further tested by analysing the hydrazine content in boiler-feed water samples containing different concentrations of hydrazine and the results were in good agreement with the spectrophotometry method.

Controlling the ion release from mixed alkali bioactive glasses by varying modifier ionic radii and molar volume

Partially substituting one alkali oxide for another reduces the crystallisation tendency and improves the processing of bioactive glasses. Here, we investigate how we can use alkali ions of varying ionic radii to control glass degradation and ion release from Bioglass 45S5. Partially replacing sodium by lithium reduced ion release in static and dynamic dissolution studies in Tris buffer, while ion release increased with increasing potassium for sodium substitution. While the mixed alkali effect is known to reduce ion release from conventional silicate glasses (compared to compositions containing one alkali oxide only), in the glasses studied here ion release was controlled by the packing of the silicate network, described by glass molar volume and oxygen density. Incorporating an alkali ion of smaller ionic radius (Li for Na or Na for K) resulted in a more compact network of higher oxygen density, which reduced ion release. On the other hand, an alkali ion of larger ionic radius (K for Na or Na for Li) expanded the silicate network, allowing for faster ion release. This can be explained by water molecules penetrating an expanded silicate network more easily than a more compact one, thereby directly influencing the ion exchange between modifier ions and protons from the dissolution medium. This shows that the use of modifier ions of varying ionic radii allows for tailoring bioactive glass ion release and degradation while maintaining silicate network polymerisation and network connectivity. And, indeed, recent literature suggests that this concept can be extended to other modifiers besides alkali metal ions, making it possible to design bioactive glasses of tailored solubility.

The non-dominance of counterions in charge-asymmetric electrolytes: non-monotonic precedence of electrostatic screening and local inversion of the electric field by multivalent coions.

The asymptotic convergence of the thermodynamic and structural properties of unequally-sized charge-symmetric ions in strong electric fields was postulated more than thirty years ago by Valleau and Torrie as the dominance of counterions via the non-linear Poisson-Boltzmann theory [Valleau and Torrie, J. Chem. Phys., 1982, 76, 4623]. According to this mean field prescription, the properties of the electrical double layer near a highly charged electrode immersed in a size-asymmetric binary electrolyte converge to those of a size-symmetric electrolyte if the properties of counterions are the same in both instances. On the other hand, some of the present authors have shown that, in fact, counterions do not dominate the electrical properties of a spherical macroion in the presence of unequally-sized ions, symmetric in valence, if ion correlations and ionic excluded volume effects are taken into account consistently. These ingredients are neglected in the classical Poisson-Boltzmann picture. In the present work, we show the occurrence of the non-dominance of counterions in the opposite scenario, that is, when ions are equally-sized but asymmetric in valence. This is performed in the presence of highly charged colloidal surfaces of spherical and planar geometries for different ionic volume fractions. In addition to the phenomenon of non-dominance of counterions, our simulations and theoretical data also exhibit a non-monotonic order or precedence in the mean electrostatic potential, or electrostatic screening, at the Helmholtz plane of a charged colloid. This interesting behaviour is analyzed as a function of the coion's valence, the ionic volume fraction, and the charge and size of the colloidal particle. All these phenomena are explained in terms of the decay of the electric field near the colloidal surface, and by the appearance of a local inversion of both the electric field and the integrated surface charge density of the colloidal particle in the presence of monovalent counterions and multivalent coions.

The Effect of Complex Anions on the Structure of Water

The microscopic ionic volumes, v A, of complex inorganic anions, obtained from crystal unit cell volumes, as well as their standard molar volumes, $$ V_{\text{A}}^{\infty } $$ , in aqueous solutions serve to establish whether these anions are water-structure-breakers or -makers. This is done via correlations with well known criteria for such effects, namely the ionic viscosity B-coefficients and the structural entropies. Complex anions with charges z A are structure-breakers if v A > 0.1|z A| nm3·ion−1 or $$ V_{\text{A}}^{\infty } $$ > 35|z A|4/3 cm3·mol−1 and structure-makers if otherwise.

Enhancement of methane–water volumetric mass transfer coefficient by inhibiting bubble coalescence with electrolyte

The effect of electrolyte on methane–water volumetric mass transfer coefficient (kLa) was investigated in this study. Various electrolytes including MgSO4, K2SO4, Na2SO4, MgCl2, KCl, NaCl, MgBr2, NaBr, KBr, Mg(NO3)2, KNO3, and NaNO3 were employed and enhancement of kLa from 103h−1 (in pure water) to 711h−1 was observed, depending on electrolyte type and concentration. This is the highest methane–water kLa value measured at ambient condition. For all electrolytes, ions with large charge density (charge valency per ionic volume) exhibited larger enhancement in methane–water kLa values. Furthermore, anions exhibited larger influence than cations on the enhancement of kLa. Enhancement of methane–water kLa by electrolytes was due to the inhibition of methane bubble coalescence.

Modeling gas solubilities in imidazolium based ionic liquids with the [Tf2N] anion using the GC-EoS

The group contribution equation of state (GC-EoS) is extended to model gas solubilities in the homologous 1-alkyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl) imide family. The gases considered in this work are CO2, CO, H2, CH4, and C2H6. The model parameters were estimated on the basis of 1400 experimental data points in the temperature range of 278–460 K and pressures up to 160 bars. A correlation is also presented to calculate the critical diameter, a characteristic parameter of the GC-EoS repulsive term, as a function of the ionic liquid molar volume. Density data is most often available for ionic liquids; hence, the correlation provides a predictive method for ionic liquids not included in the parameterization process. The new parameters were then used to predict the phase behavior of binary mixtures containing different solutes (including C3H8, C4H10, and C6H14) and ionic liquids with different chain lengths than those used in the parameterization process.

Multiple response optimization of sequential speciation of chromium in water samples by in situ solvent formation dispersive liquid–liquid microextraction prior to electrothermal atomic absorption spectrometry determination

A sensitive and selective in situ solvent formation dispersive liquid–liquid microextraction (in situ DLLME) method followed by electrothermal atomic absorption spectrophotometry for sequential extraction and determination of trace level of chromium (Cr) species was developed. The preconcentration and extraction of Cr species were carried out using ammonium pyrrolidine dithiocarbamate as a chelating agent, and a water-immiscible ionic liquid based on in situ solvent formation as an extraction solvent. Various operating variables such as sample pH, the KPF6 amount and the ionic liquid volume on the extraction efficiency responses (EE%) of Cr(III) and Cr(VI) ions were investigated. Response surface methodology using central composite design was employed for modeling of the responses. Multi-response optimization with desirability function (DF) approach has been used to maximize EE% one Cr species in the presence of another species. After this step, DF was employed to optimize the variables to define the best extraction conditions for Cr speciation. Under the optimal extraction conditions, the calibration curves were linear in the concentration ranges of 20–200 ng L−1 for Cr(III) and 70–250 ng L−1 for Cr(VI) with the limit of detections of 3.7 ng L−1 for Cr(III) and 2.13 ng L−1 for Cr(VI). The relative standard deviations of five microextractions of 100 ng L−1 Cr(III) and Cr(VI) were 9.07 % and 2.39 %, respectively. Finally, the developed method was applied to the determination of Cr(III) and Cr(VI) ions in real water samples.

Steric effects on electrokinetic flow of non-linear biofluids

Abstract Some of electrokinetic-based biomicrofluidic devices work at zeta potentials that are sufficiently high for ionic size (steric) effects to show up. In the present effort, consideration is given to the steric effects on the hydrodynamics of electroosmotic flow in a rectangular microchannel. The distinction between this research and the previous ones is that we account for non-linear rheology of the fluids encountered in biomicrofluidic systems by means of the power-law viscosity model. The method of analysis consists of a finite-difference-based numerical procedure for a non-uniform distribution of grid points, which is applied to the dimensionless form of the governing equations including the modified Poisson-Boltzmann equation. Our findings show that, unlike the electroosmotic flow of Newtonian fluids, the inclusion of the ionic size may enhance the velocity of the power-law fluids. We demonstrate that this phenomenon is due to the reduction of the fluid effective viscosity which is another consequence of the steric effects, besides the already explored feature of lowering the electroosmotic body force. Consequently, the ultimate influence of the ionic finite volumes on the electroosmotic flow of the power-law fluids is determined by the relative importance of the above-mentioned phenomena. Generally, the reduction of the body force is dominant; nevertheless, the opposite is true for shear-thickening fluids of very high flow behavior index, resulting in higher fluid velocities in the presence of the steric effects.

A multidomain model for ionic electrodiffusion and osmosis with an application to cortical spreading depression

Ionic electrodiffusion and osmotic water flow are central processes in many physiological systems. We formulate a system of partial differential equations that governs ion movement and water flow in biological tissue. A salient feature of this model is that it satisfies a free energy identity, ensuring the thermodynamic consistency of the model. A numerical scheme is developed for the model in one spatial dimension and is applied to a model of cortical spreading depression, a propagating breakdown of ionic and cell volume homeostasis in the brain.

Electrical and structural studies of ionic liquid-based poly(vinyl alcohol) proton conductors

Ionic liquid-based proton conducting polymer electrolytes containing poly(vinyl alcohol) (PVA), ammonium acetate (CH3COONH4) and 1-butyl-3-methylimidazolium bromide (BmImBr) are prepared and investigated in this present work. The ionic conductivity of polymer electrolytes increases with temperature as shown in temperature dependent-ionic conductivity study. All the polymer electrolytes follow Vogel–Tamman–Fulcher (VTF) relationship. This principle infers the coupling effect of ionic hopping mechanism and free volume theory. The pseudo-activation energy of all the polymer electrolytes is also determined by fitting the plots with VTF empirical equation. The complexation between PVA, CH3COONH4 and BmImBr is verified in Attenuated Total Reflectance–Fourier Transform Infrared (ATR–FTIR) study. Addition of ionic liquid reduces the crystallinity of polymer electrolytes as proven in x-ray diffraction (XRD) by calculating the degree of crystallinity of polymer electrolytes. The crystallite sizes of polymer electrolytes are also determined using XRD. Proton nuclear magnetic resonance (H-NMR) spectrum reveals the rapid conduction mechanism in the polymer electrolyte by determining the ion diffusion coefficient.

Ionic and molar volumes of room temperature ionic liquids

A large set of ionic volumes of the constituent ions of a variety of (non-protic) RTILs is used for the estimation of their molar volumes, hence their densities, at various temperatures by means of two fitting parameters only. The difference between the sum of the ionic volumes of the cation and the anion per mole and the actual molar volume is ascribed to the expansion of the RTIL on melting.

Development of a SOFC Performance Model to Analyze the Powder to Power Performance of Electrode Microstructures

A computational model that evaluates the triple phase boundary length, normalized effective transport coefficients, and charge production within solid oxide fuel cell electrode microstructures is described. Local charge production, within the electrode, is predicted by coupling the species transport equations with an expression for the electrochemical reaction rate. A particle placement model, employing the drop-and-roll algorithm, is used to generate the electrodes studied in this work. Parametric studies with the computational model are then preformed to investigate the influence of the anode porosity and solid volume fraction on charge production. It was found that charge production is jointly influenced by the reaction site (triple phase boundary) density, and ionic transport within the electrode structures. High current densities are observed in electrodes with low porosities and ionic volume fractions greater than 50%, for equal sized particles.

Effect of Temperature, Anion, and Alkyl Chain Length on the Density and Refractive Index of 1-Alkyl-3-methylimidazolium-Based Ionic Liquids

The density and refractive index of 15 room temperature ionic liquids (ILs) grouped according to whether they had the same cation or anion have been measured at atmospheric pressure in a temperature range from 293.15 K to 343.15 K. Changes in the physical properties have been quantified as a function of temperature and alkyl chain length for each cation or anion family. It has been observed that ionic liquid density increases when the alkyl length of the cation decreases but not with the molecular weight of the anion. We have proposed a new method to assign the ionic volume of each component in an IL that explains the trend, followed by all experimental data in this work, and allows us to predict the molecular volume and density of many ILs prior to synthesis. It was also seen that the refractive index increases as alkyl chain length of the cation increases. The temperature-dependent correlation between density and refraction index for the ILs studied has been quantified.

Excess volumes and excess heat capacities of {1,2-alkanediol + methanol} mixtures and ionic volumes in these systems

Densities of {1,2-propanediol+MeOH}, {1,2-butanediol+MeOH} and {1,2-pentanediol+MeOH} mixtures and densities of dilute solutions of three electrolytes (NaI, NaBPh4 and Ph4PI) in mentioned mixtures with exception the system containing 1,2-pentanediol were measured at T=298.15K. Isobaric specific heat capacities for {1,2-propanediol+MeOH} and {1,2-pentanediol+MeOH} mixtures were measured using a differential scanning calorimeter over the temperature range from (293 to 324) K. The excess molar volumes and excess molar isobaric heat capacities of binary systems were calculated and fitted by the Redlich–Kister polynomials. For ternary systems apparent molar volumes of electrolytes were determined at an electrolyte concentration of 0.025molkg−1 over the entire mixed solvent composition range. Single ionic apparent molar volumes of transfer, ΔtVφ (ion) were calculated using the tetraphenylphosphonium tetraphenylborate (TPTB) assumption. The influence of the carbon–chain length over the obtained functions was studied. The results were analyzed in terms of intermolecular association.