Argon and water

Computer simulation of liquid argon and water has shown that the structural inhomogeneity pattern visualized by coloring their instantaneous structures according to the volumes of the Voronoi polyhedra is the same for both liquids. The dynamics of argon atoms in the cavity of a clathrate hydrate and in liquid water is considered. The argon atoms included in the network of hydrogen bonds in liquid water are involved in concerted motion. As a result of this concerted motion, the distance between two argon atoms can fluctuate around some value for a fairly long time. The environment of argon atoms in a liquid aqueous solution differs significantly from their environment in clathrate hydrates.     

Determination of dissolved hexavalent chromium in river water, sea water and waste water

Summary A simple and reliable method for the determination of dissolved hexavalent chromium in aquatic systems is described. Chromium(VI) is quantitatively coprecipitated with lead sulfate from weakly acidic (pH 3.5) sample solutions. It is determined by graphite furnace atomic absorption spectroscopy at 357.9 nm. The detection limit of the method is 0.3 g/l at a 95% confidence level. Relatively high concentrations of chromium(III) do not interfere in the determination of hexavalent chromium. High chloride (> 6 g/l) or sulfate (> 800 mg/l) concentrations cause a significant decrease in the Cr(VI) recoveries. These interferences are mutually influenced.The sulfate interference is reduced, but not eliminated in the presence of high chloride concentrations, while chloride interferences are eliminated in the presence of a sufficient sulfate concentration in the original sample. Chromium(VI) is recovered quantitatively from river water and effluent samples, but its recovery from sea water is incomplete (83%), due to interferences by sulfate during the coprecipitation procedure.

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Bestimmung von gelöstem Chrom(VI) in Fluß-, Meer- und Abwasser

Zusammenfassung Eine einfache und zuverlässige Methode zur Chrom(VI)-bestimmung in wäßrigen Systemen wurde ausgearbeitet. Dabei wird Chrom(VI) aus schwach saurer Lösung (pH 3,5) mit Bleisulfat mitgefällt und mit Hilfe der Graphitofen-AAS bei 357,9 nm bestimmt. Die Nachweisgrenze liegt bei 0,3 g/l bei 95% Vertrauensbereich. Relativ hohe Konzentrationen an Chrom(III) stören nicht. Hohe Gehalte an Chlorid (> 6 g/l) oder Sulfat (> 800 mg/l) können zu beträchtlichen Minderbefunden an Cr(VI) führen. Diese Störungen beeinflussen sich gegenseitig. So wird die Störung durch Sulfat in Gegenwart großer Chloridmengen herabgesetzt, aber nicht ganz eliminiert, während die Chloridstörung durch genügend Sulfat beseitigt wird. Chrom(VI) konnte aus Fluß- und Abwasser quantitativ wiedergefunden werden, aus Meerwasser nur zu 83% (wegen der Störung durch Sulfat bei der Mitfällung).

     

The permittivity of water and water vapor in saturation states

The applicability of several well-known equations describing the dependences of the relative permittivities of liquid water and water vapor on their densities and temperature is analyzed. An original semiempirical equation was suggested to relate the permittivity of equilibrium vapor to that of the liquid phase. The temperature intervals within which the equations under consideration described experimental data most accurately were established. The results were used to tabulate the calculated permittivities of water and water vapor in saturation states.     

Strategy for pesticide control in ground water and drinking water

Summary The analysis of pesticides is quite difficult and expensive. It is shown in this paper which analytical methods and systems have to be used for pesticide-monitoring in ground water and drinking water. Clear identification, control of positive results, quantitative determination, accuracy and precision are very important points for pesticide analysis.     

Monitoring of water content and water distribution in ischemic hearts

We determined water content and water distribution by fitting dielectric spectra of ischemic canine hearts between 5 MHz and 3 GHz with a newly developed model which describes heart cells and subcellular organelles as rotational ellipsoids filled with electrolyte enclosed by an isolating membrane. The fraction of dry material is modelled by spherical particles with a small dielectric permittivity. Free model parameters were water content, cell volume fraction, and the conductivity of the electrolytes. Resulting model parameters were compared to data from tissue desiccation and to conductivity changes produced by protons and lactate ions. We investigated hearts in two states: during ischemia after interruption of blood flow (pure ischemia, PI, n=5) and during ischemia after resuscitation with Tyrode's solution (IAR, n=14).The difference between water content determined by tissue desiccation and by dielectric spectroscopy was less than 0.5%. During 360 min of ischemia, water content in IAR decreased from 85+/-1.6% to 83+/-2.2% and in PI from 80+/-0.8% to 78+/-1.5%. Cellular volume fraction in IAR increased from 0.47+/-0.045 to 0.63+/-0.031 and in PI from 0.62+/-0.014 to 0.73+/-0.013, which is consistent with published morphometric data. After 180 min of ischemia, the increase of the cytosolic conductivity was 0.14+/-0.02 S/m as calculated from the dielectric spectrum and was similar to the conductivity increase which was roughly estimated on the basis of tissue lactate concentration.In conclusion, dielectric spectroscopy combined with our model analysis facilitates the monitoring of water content and distribution by means of nondestructive surface probes.     

Separation of trace elements from natural water and waste water

Summary Methods of discrimination between different chemical forms of trace elements in natural waters and for their separation are discussed and results given for their application to Rhine water. Various methods of trace element separation are presented: separation from sea-water by adsorption on activated carbon in presence of complexing agents, separation from mineral waters by use of the chelating cellulose exchanger Hyphan, separation of actinide elements by co-precipitation with barium sulphate, co-precipitation from waste water with hydrous ferric oxide and with ferric phosphate.

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Trennung von Spurenelementen aus natürlichem Wasser und Abwässern

Zusammenfassung Methoden der Unterscheidung verschiedener chemischer Formen der Spurenelemente in natürlichen Wässern und ihre Trennung werden diskutiert und für Rheinwasser angewendet. Folgende Ergebnisse von Spurenelement-Trennungen werden beschrieben: Abtrennung aus Meerwasser durch Adsorption an Aktivkohle in Gegenwart von Komplexbildnern, Abtrennung aus Mineralwässern unter Verwendung des chelatbildenden Zelluloseaustauschers Hyphan, Abtrennung der Actinidenelemente M^IV durch Mitfällung mit Bariumsulfat, Mitfällung mit Eisenhydroxid und Eisenphosphat aus Abwasser.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

β-Aluminas and water

TG, DSC and X-ray measurements were made to characterize the water absorption process by Li (50%) — Na (50%)β-alumina. The equilibrium water content, dehydration enthalpies and lattice parameter values have been determined and compared with those previously obtained for pure Li and Naβ-aluminas. The mixedβ-alumina is shown to be very similar to Liβ-alumina as concerns the dehydration enthalpy and the temperature range in which the dehydration occurs, while it seems to be very similar to Naβ-alumina with respect to the equilibrium water content andc-axis values.     

Computational studies of liquid water and diluted water in carbon tetrachloride

Molecular dynamics simulations were carried out to study solvent effects on the energetic and dynamical properties of water molecules in liquid water and in carbon tetrachloride (CCl4). In these studies, the free-energy profiles or potentials of mean force (PMF) for water dimers in both solvents were computed. The computed PMF results showed a stable minimum near 3 A for the O-O separation, with a minimum free energy of about -2.8 kcal/mol in CCl4, as compared to a value of -0.5 kcal/mol in liquid water. The difference in free energy in water as compared to that in CCl4 was expected and is the result of competition from surrounding water molecules that are capable of forming hydrogen bonds in the liquid water. This capability is absent in the diluted water found in CCl4. We found that the rotational motions of H2O/D2O were nonisotropic, with the out-of-plane vector correlation times in H2O/D2O varying from 5.6/5.8 ps at 250 K to 0.57/0.56 ps at 350 K and the corresponding OH/OD bond vectors varying from 6.5/7.7 ps to 0.75/0.75 ps. The results compare reasonably well to the available NMR experimental and computer simulation data on the same system (Farrar; Skinner; et al. J. Am. Chem. Soc. 2001, 123, 8047). For diluted water in CCl4, we found the computed rotational correlation times also were nonisotropic and much longer than the corresponding NMR experimental values at the same concentration (Farrar; et al. J. Phys. Chem. A 2007, 111, 6146). Upon analyzing the water hydrogen-bonding patterns as a function of water concentration, we conclude that the differences in the rotational correlation times mainly result from the formation of water hydrogen-bonding networks as the water concentration is increased in liquid CCl4. In addition, we found the rotational correlation times to be substantially faster in liquid CCl4 than in liquid water.     

Amino-acid and water molecules adsorbed on water clusters in a beam

Water clusters (H2On and (D2On (n相似文献   

Ion association of persulphates in water and water+acetone mixtures

Conductometric studies have been made for the persulphates of sodium, potassium, and ammonium in water and water+acetone (X_acetone=0.016, 0.033, 0.072, 0.117 and 0.171) mixtures at 298.15, 303.15, 308.15 and 313.15 K, using Shedlovsky and Fuoss–Kraus extrapolation techniques. The limiting molar conductance (Λ_o), association constant (K_A), Walden product (Λ_oη_o) and the thermodynamic functions for the process of ion-pair formation have been evaluated and discussed.     

Nucleation rates of water and heavy water using equations of state

The original formula of Gibbs for the reversible work of critical nucleus formation is evaluated in three approximate ways for ordinary and heavy water. The least approximate way employs an equation of state to evaluate the pressure difference between the new and old phases. This form of the theory yields a temperature dependence for the nucleation rate close to that observed experimentally. This is a substantial improvement over the most commonly used (and most approximate) form of classical theory.     

Studies on water retention and water release from some protein systems

The hydrogen-bond properties (WBI index), water retention and water release from the protein-water systems gluten-water, soya protein- water and casein-water, have been investigated using differential scanning calorimetry in the temperature range 223–423 K. The proteins were characterized by their isoelectric point, contents of carboxyl groups and sulfur-containing groups, and readiness of undergo chloromethylation. It was concluded that the marked difference in water-release behaviour is chiefly explained by conformational differences and charge effects.

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Zusammenfassung Wasserstoffbrückenbindugseigenschaften (WBI-Index), Wasserretention und Wasserabgabe von Protein-Masser-Systemen — Gluten-Wasser, Sojaprotein-Wasser und Casein-Wasser — wurden im Temperaturbereich von 233–423 K mit einem Scanning-Kalorimeter untersucht. Die Proteine wurden durch ihren isoelektrischen Punkt, den Gehalt an Carbonylgruppen und Schwefel enthaltenden Gruppen und durch ihre Reaktivität in der Chlormethylierung charakterisiert. Es wurde gefolgert, dass der ausgesprochene Unterschied im Wasserabgabeverhalten in erster Linie auf strukturelle Unterschiede und Ladungseffekte zurückzuführen ist.

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223–423 K , , — , — — . , , . , .

     

Enthalpies of alkyl sulfonates in water,heavy water,and water-alcohol mixtures and the interaction of water with methylene groups

The heats of solution of the sodium n-alkyl sulfonates from methyl to octyl have been measured at 25°C in water, D₂O, and three alcohol-rich mixtures with water, all at solute concentrations low enough so that solute-solute interaction is negligible. Methylene-group contributions to the enthalpies of transfer are readily identified. Collation with the results of earlier studies of enthalpies of transfer leads to the conclusion that methylene-group enthalpies of transfer can be identified as follows: 0.87 kcal-mole^–1 for transfers to the gas phase from water and –0.035 kcal-mole^–1 for transfers to D₂O from H₂O, independent of the solute type provided only that methylene-group contributions can be identified in the data. Compared to other solvents, water is about as lipophilic as dimethylsulfoxide or a mixture of 27 moles of water with 73 moles of methanol. However, the range of the interactions between different groups on a given solute molecule seems to be much greater in water than in any of the other solvents studied, making it more difficult to identify group contributions to solvation in water. Another example of the complexity of the solvation of alkyl groups in water is encountered when one compares the solvation enthalpy of hexane in various solvents with some of the above results.     

Surfactant-free oil/water and bicontinuous microemulsion composed of benzene, ethanol and water

<正>Generally,a microemulsion consists of oil,water,surfactant and sometimes cosurfactant.Herein,we report a novel suffactant-free microemulsion(denoted as SFME) composed of benzene,water and ethanol without the amphiphilic molecular structure of traditional surfactant.The phase behavior of the ternary system was investigated,finding that there were a single-phase region and a two-phase region in ternary phase diagram.The electrical conductivity measurement was employed to investigate the microregion of the single-phase region,and a bicontinuous microregion and a benzene-in-water(O/W) microemulsion microregion were identified,which was confirmed by freeze-fracture transmission electron microscopy(FF-TEM) observations.The sizes of the microemulsion droplets are in the range of 20-50 nm.     

Hydraulic and osmotic permeabilities of water and water/sucrose solutions through cellophane membranes

Measurements were made of different transport phenomena in cellophane membranes, using a specially designed device. The aqueous, hydraulic permeability was studied over a range of temperatures between 30 and 50°C. The hydraulic permeability/temperature relationship was found to be linear. The use of sucrose solutions of equal concentration in the two phases on either side of the membrane produced a considerable variation in the hydraulic permeability when the solution concentrations were greater than 0.1 M. Osmotic flow experiments were carried out for sucrose/water solutions, and the coefficient of osmotic permeability was found to be independent of the solution concentrations separated by the membrane within the range of concentrations studied (up to 0.2 M). The equivalent pore radius was calculated for the membranes used; these values are higher than that of the molecular diameter of water. The reflection coefficient was calculated for one of the membranes used and a value of 0.077 was obtained.     

Steam chromatography with water—salt and water—acid inorganic phases

Th peculiarities of steam chromatography with water-salt and water-acid stationary liquid phases have been studied. The effects of the nature of the salt, its concentration in the stationary liquid phase, and the temperature of the column on retention values have been studied using C₁-C₈ primary nonbranched alcohols as an example. The advantages and disadvantages of steam chromatography with aqueous electrolyte phases arid challenges for the development of' this method are discussedTranslated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1733–1739, July, 1996.     

Strong slowing down of water reorientation in mixtures of water and tetramethylurea

We use mid-infrared pump-probe spectroscopy to study the ultrafast dynamics of HDO molecules in mixtures of tetramethylurea (TMU) and water. The composition of the studied solutions ranges from pure water to an equimolar mixture of water and TMU. We find that the vibrational relaxation of the OD-stretching vibration of HDO proceeds via an intermediate level in which the molecule is more strongly hydrogen bonded than in the ground state. As the TMU concentration is increased, the lifetime of the excited state and of the intermediate increase from 1.8 to 5.2 ps and from 0.7 to 2.2 ps, respectively. The orientational relaxation data indicate that the solutions contain two types of water molecules: bulk-like molecules that have the same reorientation time constant as in the pure liquid (taurot = 2.5 ps) and molecules that are strongly immobilized (taurot > 10 ps). The immobilized water molecules turn out to be involved in the solvation of the methyl groups of the tetramethylurea molecule. The fraction of immobilized water molecules grows with increasing TMU concentration, reaching a limiting value of 60% at very high concentrations.     

大气、水等环境样品的分析

本文是《分析试验室》定期评述中“大气、水等环境样品的分析”的开篇 ,主要评述 2 0 0 2年 6月到 2 0 0 4年 6月两年内我国大气、水等环境样品的分析情况 ,引用文献 5 5 9篇