Low Ionic Strength Solutions Research Articles

Compatibility of activity coefficients estimated experimentally and by Pitzer equations for the assessment of seawater pH

Calibration of pH meters is usually performed with reference pH buffer solutions of low ionic strength, I ≤ 0.1 mol kg−1. For seawater pH measurements (I ≈ 0.7 mol kg−1), calibration buffers in high ionic strength matrix are required. The Harned cell, in association with the Nernst equation and a model for estimating the chloride ion activity coefficient, \(\gamma_{{{\text{Cl}}^{ - } }} ,\) is the basis of the primary method for pH assignment to reference pH buffers. The semi-empirical Pitzer model is, in principle, adequate to estimate \(\gamma_{{{\text{Cl}}^{ - } }}\) of complex solutions, namely seawater. Nevertheless, no assessment of the validity of the model for this matrix is known to the authors. This work aims at estimating the adequacy of the Pitzer model by assessing the metrological compatibility of mean activity coefficients, in this case \(\gamma_{ \pm } = \sqrt {\gamma_{{{\text{H}}^{ + } }} \gamma_{{{\text{Cl}}^{ - } }} }\) estimated experimentally with the Harned cell, \(\gamma_{ \pm }^{\text{Exp}} ,\) and using the Pitzer model, \(\gamma_{ \pm }^{\text{Ptz}}\). The measurement uncertainty considered in the compatibility test was estimated using the bottom-up approach, where components were combined by the numerical Kragten method after checking its adequacy. The compatibility of the estimated \(\gamma_{ \pm }\) was assessed for solutions with increasing complexity and an ionic strength of 0.67 mol kg–1. \(\gamma_{ \pm }^{\text{Exp}}\) and \(\gamma_{ \pm }^{Ptz}\) are metrologically compatible for a confidence level of 95 % where the relative standard uncertainty of their difference ranged from 1.1 % to 3.1 % in all chloride solutions to approximately 6.3 % when sodium sulfate was also present. This led to assume the validity of the Pitzer model equations to estimate \(\gamma_{{{\text{Cl}}^{ - } }} ,\) required to define reference pH values of buffer solutions with high ionic strength.

Fast flow microfluidics and single-molecule fluorescence for the rapid characterization of α-synuclein oligomers.

α-Synuclein oligomers can be toxic to cells and may be responsible for cell death in Parkinson's disease. Their typically low abundance and highly heterogeneous nature, however, make such species challenging to study using traditional biochemical techniques. By combining fast-flow microfluidics with single-molecule fluorescence, we are able to rapidly follow the process by which oligomers of αS are formed and to characterize the species themselves. We have used the technique to show that populations of oligomers with different FRET efficiencies have varying stabilities when diluted into low ionic strength solutions. Interestingly, we have found that oligomers formed early in the aggregation pathway have electrostatic repulsions that are shielded in the high ionic strength buffer and therefore dissociate when diluted into lower ionic strength solutions. This property can be used to isolate different structural groups of αS oligomers and can help to rationalize some aspects of αS amyloid fibril formation.

Phosphatidylglycerol Flip-Flop Suppression due to Headgroup Charge Repulsion.

The kinetics and thermodynamics of 1,2-distearoyl-sn-glycero-3-[phospho(1'-rac-glycerol)] (DSPG) flip-flop in 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) membranes were examined by sum-frequency vibrational spectroscopy (SFVS). The effect of DSPG concentration in the membrane and the influence of electrolyte concentration were examined in an attempt to decipher the role the anionic PG headgroup plays in dictating the dynamics of PG flip-flop for this biologically important lipid species. DSPG flip-flop dynamics and the activation barrier to exchange were found to be directly dependent on the amount of DSPG present in the bilayer. Analysis of the activation free energy for DSPG flip-flop in mixed DSPG + DSPC bilayers reveals that charge repulsion between neighboring PG headgroups modulates the free energy barrier and subsequently, the rate of translocation. Specifically, when DSPG comprises a small portion of the bilayer, the electrostatic potential of neighboring PG lipids are effectively shielded from each other under high ionic strength conditions and little to no charge repulsion occurs. When DSPG lipids are close enough to experience charge repulsion from neighboring PG lipids, as in bilayers containing a large fraction of DSPG, or for bilayers in low ionic strength solutions, the influence of charge repulsion on the energetics of lipid flip-flop are measurable. For biological membranes, where the concentration of PG is relatively low, the neighboring PG lipids are spaced far enough apart that their anionic charges are effectively shielded, such that under physiological conditions the charged nature of the headgroup does little to modulate its lipid flip-flop energetics and corresponding rate of translocation.

Differences Among Rice Cultivars in their Adaptation to Low Ionic Strength Solution with Toxic Level of Aluminum that Mimics Tropical Acid Soil Conditions

Nutrient deficiencies are often an additional growth-limiting factor in tropical acid soils. Considering the potential interactions between Al stress and low-nutrient stress, differences among rice cultivars for Al tolerance, low-nutrient tolerance, and combined stress tolerance were investigated. The main objective of this study was to identify the predominant growth-limiting factor in tropical acid soils. Tolerance to low nutrient stress and combined stress did not show any relationship with aluminum (Al) tolerance indicating that these stress factors act independently. Al-tolerant cv. Rikuu-132 was tolerant to combined stress. Conversely, highly Al-sensitive cv. BR34 was most tolerant to combined and low nutrient stress. Combined stress tolerance of shoot was positively correlated with calcium (Ca) content of shoot. The results indicate that Al tolerance alone is not adequate for superior performance on most acid soils. Tolerance to combined stress factors would be needed to improve productivity of rice on low fertility acid soils.

44. Considerations for electromagnetic warming of vitrified biomaterials

During vitrification, nucleation of ice crystals occurs most rapidly at low temperatures during later stages of cooling, while actual growth of ice crystals is most rapid at warmer temperatures near the solution melting point. Warming rates required to avoid significant ice growth during recovery from vitrification are therefore larger than the cooling rates required during vitrification, when the sample is relatively un-nucleated. Large samples vitrified by external conduction cooling therefore require more rapid warming by internal means if damaging ice growth and cryoprotectant toxicity are to be avoided. Oscillating electric fields coupling to polar molecules (dielectric heating) and mobile ions (ohmic heating) can achieve this. For uniform warming, the oscillation frequency must be low enough to deposit energy inefficiently into the sample (skin depth > > sample size). However the inefficiency cannot be so low that the electric field strength necessary for a desired warming rate causes dielectric breakdown of the sample or surrounding air (arcing). The wavelength inside and outside the sample must also be much larger than the sample to avoid field nodes and antinodes. For vitrified samples of tens or hundreds of grams (human organs), the skin depth and wavelength constraints are met by frequencies of tens of megahertz. Dielectric absorption as a function of frequency is maximal at the Debye relaxation frequency of dipoles. This frequency increases as viscosity decreases, and is therefore temperature-dependent. It’s desirable to choose a frequency with maximal absorption at the temperature at which the ice growth rate is maximal so that the warming rate is fastest when ice growth is fastest. This also promotes temperature uniformity by slowing warming in sample regions that warm past the temperature of maximal energy absorption. In the vitrification solution M22, the target temperature for maximum warming is approximately −60°. The corresponding frequency appears to be on the order of 30 MHz, which fortuitously also meets the aforementioned skin depth and wavelength constraints. Unlike dielectric heating that has a characteristic temperature of maximum absorption for a given frequency, ohmic heating only increases as temperatures increases, leading to “thermal runaway.” It’s therefore desirable to use a cryoprotectant carrier solution of low ionic strength, such as lactose/mannitol-based LM5. Boundary conditions of electric fields at dielectric interfaces also make sample geometry important for achieving a uniform internal field. Previous work in our laboratory with a 27 MHz 200-watt RF source demonstrated peak warming rates of 160 °C during warming a vitrified 20-mL cylindrical volume of M22 in LM5, and half that rate in a vitrified rabbit kidney in the same volume, with 3 °C and 15 °C maximum internal temperature differences respectively. Greater temperature non-uniformity within the organ vs. plain solution reflects decreased dielectric absorption within the non-polar lipid-rich renal pelvis. The maximum warming rate achievable within organs will likely be determined by such differential energy absorption, and the maximum tolerable temperature non-uniformities that result. Future study requires higher power, larger samples, variable frequency, and detailed measurements of cryoprotected tissue electrical properties as a function of frequency to permit accurate modeling.

Role of Heavy Meromyosin in Heat-Induced Gelation in Low Ionic Strength Solution Containing L-Histidine.

The gelation of myosin has a very important role in meat products. We have already shown that myosin in low ionic strength solution containing L-histidine forms a transparent gel after heating. To clarify the mechanism of this unique gelation, we investigated the changes in the nature of myosin subfragments during heating in solutions with low and high ionic strengths with and without L-histidine. The hydrophobicity of myosin and heavy meromyosin (HMM) in low ionic strength solution containing L-histidine was lower than in high ionic strength solution. The SH contents of myosin and HMM in low ionic strength solution containing l-histidine did not change during the heating process, whereas in high ionic strength solution they decreased slightly. The heat-induced globular masses of HMM in low ionic strength solution containing L-histidine were smaller than those in high ionic strength solution. These findings suggested that the polymerization of HMM molecules by heating was suppressed in low ionic strength solution containing L-histidine, resulting in formation of the unique gel.

Visualization of Micro-Particle Retention on a Heterogeneous Surface Using Micro-models: Influence of Nanoscale Surface Roughness

Nanoscale surface roughness and charge heterogeneity have been widely recognized to influence particle retention in porous media under unfavourable chemical conditions such as solutions of low ionic strength (IS) or high pH. However, previous researches have not appreciated the influence of nanoscale surface roughness on particle retention under favourable chemical conditions (e.g. high solution IS). This information is needed to better understand and predict particle transport and retention in such natural environments, such as enhanced oil recovery in a high-salinity reservoir. A glass-etched micro-model was employed to directly visualize retention of micro-sized particles and their spatial distribution on the glass surface under various chemical conditions. The extended DLVO calculations accounting for the effect of nanoscale surface roughness on the interaction energies were employed to quantitatively evaluate the experimental results. It was shown that nanoscale roughness on solid surfaces significantly reduced the strength of primary minimum attachment when the solution IS was high. In particular, increasing the density of roughness on the solid surface increased the strength of primary minimum, whereas increasing the roughness height decreased the strength of primary minimum interaction. Consequently, retained particles in the primary minimum are expected to be susceptible to detachment via hydrodynamic drag forces and movement of air–water interfaces during transient in water saturation (e.g. drainage or imbibition). Indeed, results obtained from the micro-model experiments demonstrated that only a fraction of solid surface was available for particle retention even at a very high IS of 0.6 M.

Solubilisation of muscle proteins from chicken breast muscle by ultrasonic radiations in physiological ionic medium

AbstractSolubilisation of myofibrillar proteins in physiological or low ionic strength solutions is essential for their utilisation as supplementary protein food. In order to achieve low ionic strength solubility, ultrasonication as a physical force has been introduced as an effective method to shift the solubility range of myofibrillar proteins from high to low ionic medium. In this study, change in the solubility behaviour of extracted actomyosin by ultrasonication in tris-maleate (with/without 0.1 M NaCl) and water is studied. Our results demonstrate that ultrasonication solubilises actomyosin in all the three investigated systems i.e. tris-maleate (with 0.1 M NaCl), tris-maleate only (without 0.1 M NaCl) and water. A decreasing trend in the investigated biochemical parameters such as ATPases (Ca2+, Mg2+) and turbidity was observed as a result of ultrasonic exposure. Analysis of SDS-PAGE profiles showed least solubility of myosin heavy chain in water compared to tris-maleate (with/without 0.1 M NaCl), ...

DNA Diffusion is Dependent on Ionic Strength

Capillary electrophoresis can be employed to measure the translational diffusion of ionic molecules using very small volumes of very dilute solutions. Diffusion is observed by increases in peak width when the analyte remains in the capillary for variable periods of time in the absence of an electric field. We have made this technique more efficient by repeatedly reversing the direction of the electric field, thus allowing the ionic molecules to pass the detection window multiple times after a single injection.We have applied this technique to measure the translational diffusion coefficients of double-stranded DNA molecules ranging in size from 71 to 960 base pairs, injected into buffers of different ionic strengths. Surprisingly, we find that the diffusion coefficients decrease with increasing ionic strength; i.e., the DNAs diffuse faster in low ionic strength solutions. The decrease in the diffusion coefficients correlates with the decrease in the Debye length with increasing ionic strength. We therefore suggest that the diffusing unit in these measurements is the DNA molecule together with the surrounding Debye layer. The decrease in the Debye length with increasing ionic strength would increase the aspect ratio of the DNAs, increasing solvent friction and decreasing the diffusion coefficients.

A study on Rh incompatibility and frequency of weak D among blood donors and patients at a tertiary care referral teaching hospital in Tirupati, Andhra Pradesh

Background: Rh D antigen is the next most important after ABO antigens in the field of transfusion medicine. Weak D refers to reduced expression of D antigen on the red blood cell that requires an extended testing with indirect antiglobulin test (IAT) to get detected. Clinical importance of weak D arises when labelling the donor and patient, as the donor is labelled as D positive, patient as D negative. Methods: In our center all blood donor and patient samples are tested for ABO and Rh D by conventional tube technique using two anti-D reagents; anti-D immunoglobulin M (IgM) monoclonal and a blend of anti-D IgM and immunoglobulin G (IgG). The blood samples which were negative for agglutination by immediate spin method were further tested for weak-D using IgG anti-D in the IAT phase with low ionic strength solution (LISS)/Coombs’gel card. Results: A total of 46,654 blood samples were tested (22,326 donors and 24,328 patients) during the period January 2012 to August 2014. Among these 43,771 (93.82%) were Rh D positive and remaining 2,883 (6.18%) were Rh-D negative. A total of 30 individuals (16 donors and 14 patients) were weak D positive constituting 1.04% of Rh-D negatives and 0.06% of total individuals screened. Conclusions: This study shows the prevalence of weak D antigen in our population who are representative of Rayalaseema region of Andhra Pradesh. It also stresses the need to identify individuals with variant D (rather than weak or partial D) and to inform them about their status as donor and recipient of blood/organ.

Specific ion and buffer effects on protein-protein interactions of a monoclonal antibody.

Better predictive ability of salt and buffer effects on protein-protein interactions requires separating out contributions due to ionic screening, protein charge neutralization by ion binding, and salting-in(out) behavior. We have carried out a systematic study by measuring protein-protein interactions for a monoclonal antibody over an ionic strength range of 25 to 525 mM at 4 pH values (5, 6.5, 8, and 9) in solutions containing sodium chloride, calcium chloride, sodium sulfate, or sodium thiocyante. The salt ions are chosen so as to represent a range of affinities for protein charged and noncharged groups. The results are compared to effects of various buffers including acetate, citrate, phosphate, histidine, succinate, or tris. In low ionic strength solutions, anion binding affinity is reflected by the ability to reduce protein-protein repulsion, which follows the order thiocyanate > sulfate > chloride. The sulfate specific effect is screened at the same ionic strength required to screen the pH dependence of protein-protein interactions indicating sulfate binding only neutralizes protein charged groups. Thiocyanate specific effects occur over a larger ionic strength range reflecting adsorption to charged and noncharged regions of the protein. The latter leads to salting-in behavior and, at low pH, a nonmonotonic interaction profile with respect to sodium thiocyanate concentration. The effects of thiocyanate can not be rationalized in terms of only neutralizing double layer forces indicating the presence of an additional short-ranged protein-protein attraction at moderate ionic strength. Conversely, buffer specific effects can be explained through a charge neutralization mechanism, where buffers with greater valency are more effective at reducing double layer forces at low pH. Citrate binding at pH 6.5 leads to protein charge inversion and the formation of attractive electrostatic interactions. Throughout the report, we highlight similarities in the measured protein-protein interaction profiles with previous studies of globular proteins and of antibodies providing evidence that the behavior will be common to other protein systems.

The determination of pH in hypersaline lakes with a conventional combination glass electrode

pH in natural waters is commonly measured with a pH glass combination electrode. This method, however, yields accurate results only in low ionic strength solutions whereas its application to high ionic strength solutions "suffers" from bias introduced mainly by liquid junction potential. The determination of pH in high ionic strength solutions was conducted with dual ion selective electrodes systems that are liquid‐junction‐free. In the present work, we provide a method for determining the pH over a very wide range of ionic strengths using a conventional glass pH electrode. The method is based on calibrating the signal of the conventional combination glass electrode against the signal of a liquid‐junction‐free H+|Cl‐ electrode pair. The calibration was conducted on the Dead Sea brine and its dilutions with deionized water. It yielded a pH correction function of ionic strength, ΔpH(I), that allows evaluating the pH of Dead Sea brines and other brines of similar compositions using a regular glass combination pH electrode, over an ionic strength range of ~1‐10 m. A pH measurement of the Dead Sea brine with a conventional combination glass electrode yielded a value of 6.26 ± 0.04 after applying the ΔpH(I) correction function, identical to the 6.27 ± 0.03 value obtained by the liquid‐junction‐free H+|Cl‐ electrode pair.

Recovery of small dye molecules from aqueous solutions using charged ultrafiltration membranes

Recovery of reactive dyes from effluent streams is a growing environmental challenge. In this study, various charged regenerated cellulose (RC) ultrafiltration (UF) membranes were prepared and tested for removal of three model reactive dyes (reactive red ED-2B, reactive brilliant yellow K-6G, and reactive brilliant blue KN-R). Data were obtained with charged UF membranes having different spacer arm lengths between the base cellulose and the charge functionality. The effects of charge density of the dye molecules, ionic strength of the feed solution, spacer arm length of charged membranes and filtrate flux were studied. Results indicated that dye retention was greatest with the most negatively charged dye molecule. Higher rejection was also observed in low ionic strength solutions. Results were consistent with model calculations based on the partitioning of a charged sphere into a charged cylindrical pore. The membranes with longer spacer arm length had higher rejection coefficients, consistent with the greater negative charge on these membranes. This study confirms that charged UF membranes can effectively recover small reactive dye molecules at low pressures (below 100kPa) under appropriate solution conditions due to the strong electrostatic repulsion from the membrane pores.

Comparison of the Aggregation Behavior of TiO2 Nanoparticles Exposed to Fulvic Acid and Bacillus subtilis Exudates

The objective of this study was to compare the relative impact of humic and non-humic natural organic matter (NOM) on the aggregation behaviors of engineered TiO2 nanoparticles (nano-TiO2). After exposure of nano-TiO2 to varying concentrations of Suwannee River fulvic acid (SRFA) and Bacillus subtilis exudate in high and low ionic strength (IS) solutions at pH 3 to pH 7.5, aggregation behaviors were evaluated via dynamic light scattering (DLS) measurements and sedimentation studies. Although pH, IS, and NOM concentration exerted strong controls on nano-TiO2 aggregation behaviors, suspensions exposed to either SRFA or bacterial exudate at normalized dissolved organic carbon (DOC) concentrations exhibited remarkably similar behaviors. In high IS systems, nano-TiO2 exposed to either SRFA or bacterial exudate sedimented rapidly, except in the presence of high NOM concentrations at pH 6 and 7.5. Low IS treatments exhibited a larger range of effects. In fact, relative to NOM-free controls, nano-TiO2 aggregates in SRFA and bacterial exudate exposures sedimented up to 14 times faster at pH 3 and up to 13 times slower at pH 7.5. Adsorption of organic molecules onto nano-TiO2 can enhance aggregation via colloidal bridging and/or charge neutralization, or with more complete surface coverage, can diminish aggregation via electrostatic repulsion and/or steric hindrance. Collectively, these data suggest that solution pH, IS, and NOM concentration, and to a lesser extent NOM origin, can control the fate and mobility of nano-TiO2 in geologic systems.

Quantitative characterization by asymmetrical flow field-flow fractionation of IgG thermal aggregation with and without polymer protective agents.

Complexes formed between poly(acrylates) and polyclonal immunoglobulin G (IgG) in its native conformation and after heat stress were characterized using asymmetric flow field-flow fractionation (AF4) coupled with on-line UV-Vis spectroscopy and multi-angle light-scattering detection (MALS). Mixtures of IgG and poly(acrylates) of increasing structural complexity, sodium poly(acrylate) (PAA), a sodium poly(acrylate) bearing at random 3 mol % n-octadecyl groups, and a random copolymer of sodium acrylate (35 mol%), N-n-octylacrylamide (25 mol%) and N-isopropylacrylamide (40 mol%), were fractionated in a sodium phosphate buffer (0.02 M, pH 6.8) in the presence, or not, of 0.1 M NaCl. The AF4 protocol developed allowed the fractionation of solutions containing free poly(acrylates), native IgG monomer and dimer, poly(acrylates)/IgG complexes made up of one IgG molecule and a few polymer chains, and/or larger poly(acrylates)/IgG aggregates. The molar mass and recovery of the soluble analytes were obtained for mixed solutions of poly(acrylates) and native IgG and for the same solutions incubated at 65 °C for 10 min. From the combined AF4 results, we concluded that in solutions of low ionic strength, the presence of PAA increased the recovery ratio of IgG after thermal stress because of the formation of electrostatically-driven PAA/IgG complexes, but PAA had no protective effect in the presence of 0.1 M NaCl. Poly(acrylates) bearing hydrophobic groups significantly increased IgG recovery after stress, independently of NaCl concentration, because of the synergistic effect of hydrophobic and electrostatic interactions. The AF4 results corroborate conclusions drawn from a previous study combining four analytical techniques. This study demonstrates that AF4 is an efficient tool for the analysis of protein formulations subjected to stress, an important achievement given the anticipated important role of proteins in near-future human therapies.

Interaction of Molybdenum(VI) Oxyanions with +2 Metal Cations

The association of molybdenum(VI) oxyanions with metal cations was investigated in solutions of low ionic strength, such as those prevailing in most natural waters. Potentiometric titrations were carried out for the systems containing molybdenum(VI) anions and divalent metal cations (M = Mg, Ca, Sr, Ba, Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg and Pb). This selection includes the major cations and some other cations of high environmental relevance. The interaction of iron(III) with Mo(VI) anions was also studied. At neutral and basic pH values and for those systems where the solubility of the molybdate salt is high enough, ionic species pairs such as [M(MoO4)] predominate. At acidic pH values, [M(HMoO4)]+ and [M(Mo7O24)]4– are formed, the latter species are only relevant for total molybdenum concentrations higher than 1 mmol·L−1. These results provide the basis for molybdenum speciation in natural aquatic systems, on which the environmental fate, bioavailability and toxicity of the element depend.

The solubility and conformational characteristics of porcine myosin as affected by the presence of l-lysine and l-histidine

The influence of l-lys and l-his on the solubility, surface hydrophobicity, sulphydryl content and conformational characteristics of porcine myosin solubilised in high (0.6M), physiological (0.15M) and low (1mM) ionic strength solutions were explored. The solubility of myosin was increased in the presence of l-his and/or l-lys in all ionic strength solutions used. The presence of l-his and l-lys caused increases in the surface hydrophobicity and reactive sulphydryl content (p<0.05). Circular dichroism revealed a significant decrease of α-helical content with an increase of random coils, β-turns and β-sheets in the presence of l-his and/or l-lys. These results demonstrate that the introduction of l-lys and l-his causes the unfolding of myosin, resulting in loss of α-helical structure, which is followed by increases in random coils, β-turns and β-sheets, which exposes buried hydrophobic and sulphydryl groups to the myosin surface, ultimately increasing the solubility of porcine myosin.

Layer-by-layer assembly of graphene oxide membranes via electrostatic interaction

We fabricated a novel type of water purification membrane by layer-by-layer assembling negatively charged graphene oxide (GO) nanosheets on a porous poly(acrylonitrile) support and interconnecting them with positively charged poly(allylamine hydrochloride) (PAH) via electrostatic interaction. A series of characterization techniques were used to confirm the successful assembly of multiple GO–PAH bilayers, quantify their composition and thickness, and understand the structure of the GO membrane. Quartz crystal microbalance-dissipation (QCM-D) results showed that each GO–PAH bilayer in the membrane is around 16.5nm thick and dominated by GO (mass of GO is 2–5 times higher than that of PAH), indicating multiple layers of GO nanosheets exist in each bilayer. This is most likely because the mass-to-charge ratio of GO is much higher than that of PAH. Transport of water and selected solutes in the GO membrane was investigated in a pressurized system and also in a forward osmosis (FO) and pressure retarded osmosis (PRO) system. Water permeability of the GO membrane was found to be about one order of magnitude higher than that of a commercial FO membrane. The solute flux of the GO membrane for sucrose (as a representative uncharged species) was much lower than that for an ionic species, although the hydrated radius of the ions is comparable to that of sucrose. This is most likely because the GO–PAH bilayers tend to swell in ionic solutions. In solutions of low ionic strength, the GO membrane retained a tight structure and exhibited high rejection to sucrose (~99%), indicating an MWCO of around 342 or an equivalent pore size of around 1nm. Therefore, at the present stage, the GO membrane can be well suited for applications such as FO-based emergency water purification using sugary draw solutions and water treatment not requiring high ionic strength.

Size distribution analysis of colloid generated from compacted bentonite in low ionic strength aqueous solutions

An experimental methodology is presented, with the objective of investigating erosion and colloid generation from compacted bentonite, to evaluate its possible effects on radionuclide migration in a deep geological repository (DGR) in crystalline rock.Bentonite erosion studies were performed using a natural bentonite and considering two possible scenarios existing in a DGR in crystalline rock: the first one, where the water hydrating the bentonite is stagnant (static scenario) and the second one where the water can flow at the bentonite surface, simulating the existence of a water conducting fracture (dynamic scenario).In particular, the size of the generated colloids was analysed, as it is a very important parameter for transport and retention/filtration processes in crystalline rock and, ultimately, for colloid-driven radionuclide transport. The analysis of the size distribution of colloids, detected in erosion experiments, was carried out by the very sensitive single particle counting (SPC) technique.As bentonite colloids are particularly stable and mobile in low ionic strength (I) solutions, these chemical conditions were considered of particular interest.Results showed that the quantity of colloids generated from compacted bentonite depends on the chemistry of the water, and that the presence of calcium in the electrolyte inhibits the maximum generation of colloidal particles. The maximum concentration of bentonite colloid in solution corresponds to particles with a size around 50–100nm.The size distribution of bentonite colloids was similar in all the analysed cases, but the concentration of particles of smaller size (50–100nm) was always higher in the absence of calcium, indicating the clear effect of this element on their aggregation.Results also evidenced the importance of water/clay interactions: these can be of extreme importance for the evaluation of erosion and stability of colloids in a DGR at a long term.

Oxygen isotope systematics in the aragonite–CO2–H2O–NaCl system up to 0.7 mol/kg ionic strength at 25 °C

To investigate the oxygen isotope systematics in the aragonite–CO2–H2O–NaCl system, witherite (BaCO3) was precipitated quasi-instantaneously and quantitatively from Na–Cl–Ba–CO2 solutions of seawater-like ionic strength (I=0.7mol/kg) at two pH values (∼7.9 and ∼10.6) at 25°C. The oxygen isotope composition of the witherite and the dissolved inorganic carbon speciation in the starting solution were used to estimate the oxygen isotope fractionations between HCO3− and H2O as well as between CO32− and H2O. Given the analytical error on the oxygen isotope composition of the witherite and uncertainties of the parent solution pH and speciation, oxygen isotope fractionation between NaHCO3° and HCO3−, as well as between NaCO3− and CO32−, is negligible under the experimental conditions investigated.The influence of dissolved NaCl concentration on the oxygen isotope fractionation in the aragonite–CO2–H2O–NaCl system was also investigated at 25°C. Aragonite was precipitated from Na–Cl–Ca–Mg–(B)–CO2 solutions of seawater-like ionic strength using passive CO2 degassing or constant addition methods. Based upon our new experimental observations and published experimental data from lower ionic strength solutions by Kim et al. (2007b), the equilibrium aragonite–water oxygen isotope fractionation factor is independent of the ionic strength of the parent solution up to 0.7mol/kg. Hence, our study also suggests that the aragonite precipitation mechanism is not affected by the presence of sodium and chloride ions in the parent solution over the range of concentrations investigated.