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https://www.readbyqxmd.com/read/29907413/development-and-optimization-of-a-solid-phase-microextraction-gas-chromatography-tandem-mass-spectrometry-methodology-to-analyse-ultraviolet-filters-in-beach-sand
#1
Marlene Vila, Maria Llompart, Carmen Garcia-Jares, Vera Homem, Thierry Dagnac
A methodology based on solid-phase microextraction (SPME) followed by gas chromatography-tandem mass spectrometry (GC-MS/MS) has been developed for the simultaneous analysis of eleven multiclass ultraviolet (UV) filters in beach sand. To the best of our knowledge, this is the first time that this extraction technique is applied to the analysis of UV filters in sand samples, and in other kind of environmental solid samples. Main extraction parameters such as the fibre coating, the amount of sample, the addition of salt, the volume of water added to the sand, and the temperature were optimized...
June 6, 2018: Journal of Chromatography. A
https://www.readbyqxmd.com/read/29907288/colorimetric-ionophore-based-coextraction-titrimetry-of-potassium-ions
#2
Kajorngai Thajee, Lu Wang, Kate Grudpan, Eric Bakker
Potassium ion concentration can be successfully determined volumetrically by moving the titration from a homogeneous phase to a two phase solvent system. This is because potassium can be readily complexed in a selective and thermodynamically stable manner by ionophores such as valinomycin. Previous work demonstrated the successful titration of potassium by ion-exchange into an organic phase containing valinomycin, but the sample itself served as titrant, which is not sufficiently practical for routine applications...
October 31, 2018: Analytica Chimica Acta
https://www.readbyqxmd.com/read/29907287/low-cost-scholl-coupling-microporous-polymer-as-an-efficient-solid-phase-microextraction-coating-for-the-detection-of-light-aromatic-compounds
#3
Xintong Xie, Junhui Wang, Juan Zheng, Junlong Huang, Chuyi Ni, Jie Cheng, Zhengping Hao, Gangfeng Ouyang
A cost-effective microporous polymer was synthesized using cheap monomer and catalyst via one-step Scholl-coupling reaction, and its chemical, morphological characteristics and pore structure were investigated. The as-synthesized polymer with large surface area and narrow pore distribution (centered in 1.2 nm) was prepared as a fiber coating for solid-phase microextraction (SPME). Headspace SPME was used for the extraction of the light aromatic compounds, e.g. benzene, toluene, ethylbenzene, m-xylene, naphthalene and acenaphthene...
October 31, 2018: Analytica Chimica Acta
https://www.readbyqxmd.com/read/29907071/the-influence-of-polarizability-and-charge-transfer-on-specific-ion-effects-in-the-dynamics-of-aqueous-salt-solutions
#4
Mary Nguyen, Steven W Rick
The diffusion rates for water molecules in salt solutions depend on the identity of the ions, as well as their concentration. Among the alkali metal ions, cesium and potassium increase and sodium strongly decreases the diffusion constant of water. The origin of the difference can be understood by examining the simulation results using different potential models. In this work, aqueous solutions of salts are simulated with a variety of models. Commonly used non-polarizable models, which otherwise reproduce many experimental properties, do not capture the trend in the diffusion constant, while models which include polarization and/or charge transfer interactions do...
June 14, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29907070/effective-charges-and-zeta-potentials-of-oil-in-water-microemulsions-in-the-presence-of-hofmeister-salts
#5
Alexandre P Dos Santos, Yan Levin
We present a theory which allows us to calculate the effective charge and zeta potential of oil droplets in microemulsions containing Hofmeister salts. A modified Poisson-Boltzmann equation is used to account for the surface and ion polarizations and hydrophobic and dispersion interactions. The ions are classified as kosmotropes and chaotropes according to their Jones-Dole viscosity B coefficient. Kosmotropes stay hydrated and do not enter into the oil phase, while chaotropes can adsorb to the oil-water interface...
June 14, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29907067/relative-permittivity-in-the-electrical-double-layer-from-nonlinear-optics
#6
Mavis D Boamah, Paul E Ohno, Franz M Geiger, Kenneth B Eisenthal
Second harmonic generation (SHG) spectroscopy has been applied to probe the fused silica/water interface at pH 7 and the uncharged 11¯02 sapphire/water interface at pH 5.2 in contact with aqueous solutions of NaCl, NaBr, NaI, KCl, RbCl, and CsCl as low as several 10 μM. For ionic strengths up to about 0.1 mM, the SHG responses were observed to increase, reversibly for all salts surveyed, when compared to the condition of zero salt added. Further increases in the salt concentration led to monotonic decreases in the SHG response...
June 14, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29907065/does-an-electronic-continuum-correction-improve-effective-short-range-ion-ion-interactions-in-aqueous-solution
#7
Ellen E Bruce, Nico F A van der Vegt
Non-polarizable force fields for hydrated ions not always accurately describe short-range ion-ion interactions, frequently leading to artificial ion clustering in bulk aqueous solutions. This can be avoided by adjusting the nonbonded anion-cation or cation-water Lennard-Jones parameters. This approach has been successfully applied to different systems, but the parameterization is demanding owing to the necessity of separate investigations of each ion pair. Alternatively, polarization effects may effectively be accounted for using the electronic continuum correction (ECC) of Leontyev et al...
June 14, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29907058/chemical-potentials-of-alkaline-earth-metal-halide-aqueous-electrolytes-and-solubility-of-their-hydrates-by-molecular-simulation-application-to-cacl-2-antarcticite-and-sinjarite
#8
Filip Moučka, Jiří Kolafa, Martin Lísal, William R Smith
We present a molecular-level simulation study of CaCl2 in water and crystalline hydrates formed by CaCl2 at ambient (298.15 K, 1 bar) conditions and at a high-temperature high-pressure state (365 K, 275 bars) typical of hydraulic fracturing conditions in natural-gas extraction, at which experimental properties are poorly characterized. We focus on simulations of chemical potentials in both solution and crystalline phases and on the salt solubility, the first time to our knowledge that such properties have been investigated by molecular simulation for divalent aqueous electrolytes...
June 14, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29907048/concentration-dependent-and-configuration-dependent-interactions-of-monovalent-ions-with-an-rna-tetraloop
#9
Jacob Carlson Miner, Angel Enrique García
Monovalent salt solutions have strongly coupled interactions with biopolymers, from large polyelectrolytes to small RNA oligomers. High salt concentrations have been known to induce transitions in the structure of RNA, producing non-canonical configurations and even driving RNA to precipitate out of solution. Using all-atom molecular dynamics simulations, we model a monovalent salt species (KCL) at high concentrations (0.1-3m) and calculate the equilibrium distributions of water and ions around a small tetraloop-forming RNA oligomer in a variety of structural arrangements: folded A-RNA (canonical) and Z-RNA (non-canonical) tetraloops and unfolded configurations...
June 14, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29907046/high-density-liquid-structure-enhancement-in-glass-forming-aqueous-solution-of-licl
#10
G Camisasca, M De Marzio, M Rovere, P Gallo
We investigate using molecular dynamics simulations the dynamical and structural properties of LiCl:6H2 O aqueous solution upon supercooling. This ionic solution is a glass forming liquid of relevant interest in connection with the study of the anomalies of supercooled water. The LiCl:6H2 O solution is easily supercooled and the liquid state can be maintained over a large decreasing temperature range. We performed simulations from ambient to 200 K in order to investigate how the presence of the salt modifies the behavior of supercooled water...
June 14, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29907044/concentrated-aqueous-sodium-chloride-solution-in-clays-at-thermodynamic-conditions-of-hydraulic-fracturing-insight-from-molecular-dynamics-simulations
#11
Martin Svoboda, Martin Lísal
To address a high salinity of flow-back water during hydraulic fracturing, we use molecular dynamics (MD) simulations and study the thermodynamics, structure, and diffusion of concentrated aqueous salt solution in clay nanopores. The concentrated solution results from the dissolution of a cubic NaCl nanocrystal, immersed in an aqueous NaCl solution of varying salt concentration and confined in clay pores of a width comparable to the crystal size. The size of the nanocrystal equals to about 18 Å which is above a critical nucleus size...
June 14, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29907042/a-simulation-study-of-homogeneous-ice-nucleation-in-supercooled-salty-water
#12
Guiomar D Soria, Jorge R Espinosa, Jorge Ramirez, Chantal Valeriani, Carlos Vega, Eduardo Sanz
We use computer simulations to investigate the effect of salt on homogeneous ice nucleation. The melting point of the employed solution model was obtained both by direct coexistence simulations and by thermodynamic integration from previous calculations of the water chemical potential. Using a seeding approach, in which we simulate ice seeds embedded in a supercooled aqueous solution, we compute the nucleation rate as a function of temperature for a 1.85 NaCl mol per water kilogram solution at 1 bar. To improve the accuracy and reliability of our calculations, we combine seeding with the direct computation of the ice-solution interfacial free energy at coexistence using the Mold Integration method...
June 14, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29907030/understanding-the-scale-of-the-single-ion-free-energy-a-critical-test-of-the-tetra-phenyl-arsonium-and-tetra-phenyl-borate-assumption
#13
Timothy T Duignan, Marcel D Baer, Christopher J Mundy
The tetra-phenyl arsonium and tetra-phenyl borate (TATB) assumption is a commonly used extra-thermodynamic assumption that allows single ion free energies to be split into cationic and anionic contributions. The assumption is that the values for the TATB salt can be divided equally. This is justified by arguing that these large hydrophobic ions will cause a symmetric response in water. Experimental and classical simulation work has raised potential flaws with this assumption, indicating that hydrogen bonding with the phenyl ring may favor the solvation of the TB- anion...
June 14, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29907024/diffusion-of-aqueous-solutions-of-ionic-zwitterionic-and-polar-solutes
#14
Xiaojing Teng, Qi Huang, Chamila Chathuranga Dharmawardhana, Toshiko Ichiye
The properties of aqueous solutions of ionic, zwitterionic, and polar solutes are of interest to many fields. For instance, one of the many anomalous properties of aqueous solutions is the behavior of water diffusion in different monovalent salt solutions. In addition, solutes can affect the stabilities of macromolecules such as proteins in aqueous solution. Here, the diffusivities of aqueous solutions of sodium chloride, potassium chloride, tri-methylamine oxide (TMAO), urea, and TMAO-urea are examined in molecular dynamics simulations...
June 14, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29907021/a-kirkwood-buff-derived-force-field-for-alkaline-earth-halide-salts
#15
Nawavi Naleem, Nikolaos Bentenitis, Paul E Smith
The activity and function of many macromolecules in cellular environments are coupled with the binding of divalent ions such as calcium or magnesium. In principle, computer simulations can be used to understand the molecular level aspects of how many important macromolecules interact with ions. However, most of the force fields currently available often fail to accurately reproduce the properties of divalent ions in aqueous environments. Here we develop classical non-polarizable force fields for the aqueous alkaline earth metal halides (MX2 ), where M = Mg2+ , Ca2+ , Sr2+ , Ba2+ and X = Cl- , Br- , I- , which can be used in bimolecular simulations and which are compatible with the Simple Point Charge/Extended (SPC/E) water model...
June 14, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29907016/salt-effects-in-surfactant-free-microemulsions
#16
Sebastian Schöttl, Dominik Horinek
The weakly associated micellar aggregates found in the so-called "pre-ouzo region" of the surfactant-free microemulsion water/ethanol/1-octanol are sensitive to changes in the system composition and also to the presence of additives like salt. In this work, we study the influence of two salts, sodium iodide and lithium chloride, on aggregates in water/ethanol/1-octanol by molecular dynamics simulations. In both cases, ethanol concentration in the nonpolar phase and at the interface is increased due to a salting out effect on ethanol in the aqueous pseudo-phase...
June 14, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29906730/fate-of-methoprene-in-temperate-salt-marsh-ditches-following-aerial-applications
#17
David J Tonjes, Anne E McElroy, Robin K Barnes-Pohjonen, Dominick V Ninivaggi, Walter Dawydiak, Gregory T Greene, Bruce J Brownawell
Aerial applications of liquid methoprene are used in salt marshes to control mosquitoes by preventing adult emergence. Despite concern about toxicity to non-target organisms, little is known about environmental concentrations after applications, nor methoprene's persistence in salt marsh environments. Aqueous and sediment samples were collected from two marshes receiving weekly applications. Aqueous samples were collected as early as 30 min after applications and as long as nine days afterwards; sediment samples were taken within hours of application and as long as 19 days post-application...
June 12, 2018: Science of the Total Environment
https://www.readbyqxmd.com/read/29906726/evaluation-of-fouling-in-nanofiltration-for-desalination-using-a-resistance-in-series-model-and-optical-coherence-tomography
#18
Jongkwan Park, Sungyun Lee, Jeongyeop You, Sanghun Park, Yujin Ahn, Woonggyu Jung, Kyung Hwa Cho
Resistance-in-series models have been applied to investigate fouling behavior. However, it is difficult to model the influence of morphology on fouling behavior because resistance is indirectly calculated from the water flux and transmembrane pressure. In this study, optical coherence tomography (OCT) was applied to evaluate the resistance of the fouling layer based on fouling morphology. Sodium alginate, humic acid, and bovine serum albumin (BSA) with high salts concentrations (conductivity: 23 mS/cm) were used as model foulants...
June 12, 2018: Science of the Total Environment
https://www.readbyqxmd.com/read/29906624/features-of-chicken-egg-yolk-immunoglobulin-igy-against-the-infection-of-red-spotted-grouper-nervous-necrosis-virus
#19
Lizhu Yi, Zhendong Qin, Hanzuo Lin, Yang Zhou, Jiabo Li, Zhen Xu, Sarath Babu V, Li Lin
Red-spotted grouper nervous necrosis virus (RGNNV) is one of the most important viruses which mainly infects the larva of marine and freshwater fish with high mortality and affects the fishery industry worldwide. Currently, there are no effective vaccines available for the fish larva infected with NNV. Immunoglobulin yolk (IgY) origin of oviparous animals is passed from the blood serum and concentrated in the egg yolk. With the advantages of high yield, cost-effectiveness, and high stability, IgY can be widely used in passive immunization, especially in young animals in which adaptive immunity is not fully developed...
June 12, 2018: Fish & Shellfish Immunology
https://www.readbyqxmd.com/read/29906243/the-chemerin-knockout-rat-reveals-chemerin-dependence-in-female-but-not-male-experimental-hypertension
#20
Stephanie W Watts, Emma S Darios, Adam E Mullick, Hannah Garver, Thomas L Saunders, Elizabeth D Hughes, Wanda E Filipiak, Michael G Zeidler, Nichole McMullen, Christopher J Sinal, Ramya K Kumar, David J Ferland, Gregory D Fink
Measures of the adipokine chemerin are elevated in multiple cardiovascular diseases, including hypertension, but little mechanistic work has been done to implicate chemerin as being causative in such diseases. The chemerin knockout (KO) rat was created to test the hypothesis that removal of chemerin would reduce pressure in the normal and hypertensive state. Western analyses confirmed loss of chemerin in the plasma and tissues of the KO vs. wild-type (WT) rats. Chemerin concentration in plasma and tissues was lower in WT females than in WT males, as determined by Western analysis...
June 15, 2018: FASEB Journal: Official Publication of the Federation of American Societies for Experimental Biology
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