共查询到20条相似文献,搜索用时 15 毫秒
1.
Many nonvolatile organic compounds, e.g., polyaromatic hydrocarbons (PAHs), are readily stripped during aerobic biodegradation.
This is because of the high infinite dilution activity coefficient resulting from forces generated by the water-organic interactions
at the molecular level. Several models have been proposed for air-stripping based on the Henry’s law constant. By definition,
the Henry’s law constant is the infinite dilution activity coefficient multiplied by the pure component vapor pressure. In
this article, a gas saturation technique was used to measure the very low vapor pressures exhibited by these nonvolatile compounds.
Literature values of other PAHs have been tabulated and are presented. For determining infinite dilution activity coefficients,
a differential ebulliometery apparatus has been constructed. In this technique, the boiling point difference between pure
water and a water-organic solution is measured very precisely. Thermodynamics is then used to calculate the infinite dilution
activity coefficient. The method’s accuracy has been tested using the phenol-water system. 相似文献
2.
《The Journal of chemical thermodynamics》2001,33(7):755-764
We present a simple method for measuring Henry’s constant kHof ethanol using photoacoustic spectroscopy. At T = 298.1 K the measured value forkH is (0.877 ± 0.039)kPa · kg · mol − 1. Our data show that Henry’s law is valid at ethanol molalities between 0.1mol · kg − 1 and 1.4 mol · kg − 1. The temperature dependence of Henry’s constant was carefully examined by measuring the ethanol vapour pressure of six different aqueous solutions between T = 273.1 K and T = 298.1 K. By analysing the gas phase concentration and applying Henry’s law, an ethanol molality of 0.864 mol · kg − 1in the liquid phase can be measured with an error of ± 0.038mol · kg − 1. The detection limit of the photoacoustic sensor is a gaseous ethanol pressure of 10 − 3kPa. Ethanol molality changes as low as 1.10 − 3mol · kg − 1can be measured. 相似文献
3.
This study evaluates Jolly’s method to estimate the difference in homolytic bond dissociation energy between two isoelectronic molecules by the use of atomic and ionic electronegativities. The use of intermediate species as an energetic “stepping stone” between the two diatomic species in question is discussed, particularly within the context of Hess’ law. We also show a sample calculation for a pair of diatomic species that is fully consistent with data from atomic physics. 相似文献
4.
Isabelle C?té Piotr Robouch Benjamin Robouch David Bisson Philippe Gamache Alain LeBlanc Pierre Dumas Mika?l Pedneault 《Accreditation and quality assurance》2012,17(4):389-393
The ??uncertainty function?? introduced by Thompson et al. estimates the reproducibility standard deviation as a function of concentration or mass fraction. This model was successfully applied to data derived from three proficiency testing schemes aiming at the quantification of cadmium, lead and mercury in blood and urine. This model allows the estimation of standard deviation for the performance assessment for proficiency testing rounds. 相似文献
5.
Antonin Chapoy Hooman Haghighi Bahman Tohidi 《The Journal of chemical thermodynamics》2008,40(6):1030-1037
In this communication, we report new experimental data on n-pentane, i-pentane, cyclopentane, n-hexane, and toluene solubility in water at low temperature (below 298.15 K) and atmospheric pressure conditions. The new experimental data together with those reported in the literature have been used in developing a new equation for Henry’s constants of normal alkanes (methane to decane), BETEX compounds, and acid gases in aqueous phase over a wide range of temperature (typically from 273.15 K to 373.15 K). The new equation is based on a thermodynamic model, which uses the Peng–Robinson equation of state combined with the classical quadratic mixing rules for modelling non-aqueous phases, while the NRTL model is used to calculate the water activity.The predictions of the developed thermodynamic model are compared to the experimental data and the results of a thermodynamic approach, which uses the Valderrama modification of the Patel–Teja equation of state and non-density dependent mixing rules for modelling all fluid phases. Good agreement is observed between the experimental data and the model predictions. 相似文献
6.
James A. Green Sheeba Jem Irudayam Richard H. Henchman 《The Journal of chemical thermodynamics》2011,43(6):868-872
The entropy of vaporization at a liquid’s boiling point is well approximated by Trouton’s rule and even more accurately by Hildebrand’s rule. A cell method is used here to calculate the entropy of vaporization for a range of liquids by subtracting the entropy of the gas from that of the liquid. The liquid’s entropy is calculated from the force magnitudes measured in a molecular dynamics simulation based on the harmonic approximation. The change in rotational entropy is not accounted for except in the case of liquid water. The predicted entropies of vaporization agree well with experiment and Trouton’s and Hildebrand’s rules for most liquids and for water except other liquids with hydrogen bonds. This supports the idea that molecular rotation is close to ideal at a liquid’s boiling point if hydrogen bonds are absent; if they are present, then the rotational entropy gain must be included. The method provides a molecular interpretation of those rules by providing an equation in terms of a molecule’s free volume in a liquid which depends on the force magnitudes. Free volumes at each liquid’s boiling point are calculated to be ~1 Å3 for liquids lacking hydrogen bonds, lower at ~0.3 Å3 for those with hydrogen bonds, and they decrease weakly with increasing molecular size. 相似文献
7.
Chromatographia - The relationship between Hashimoto's thyroiditis and vitamin D concentration was already presented in many studies. The aim of this study was to analyze the differences in the... 相似文献
8.
B. Maupas S. Letellier F. Guyon 《Journal of inclusion phenomena and macrocyclic chemistry》1995,23(4):259-267
Inclusion of anticoagulant drugs within the cavity of methyl--cyclodextrin in aqueous solution was studied by ultraviolet absorption, fluorimetry and reversed-phase liquid chromatography. Formation constants were obtained for complex formation of methyl--cyclodextrin with warfarin and 8-chlorowarfarin. 相似文献
9.
The method of Barker is a popular scheme for determination of activity coefficients from total pressure measurements. A comprehensive review of this method is presented in this study. While discussing this technique various aspects of (vapor + liquid) equilibrium (VLE) data reduction process including types of algorithms applied, roles of saturated vapor pressures and equilibrium vapor compositions data, and types of objective functions used are analyzed. Activity coefficient or liquid state models frequently used in VLE data reduction are shown and their comparisons are investigated. More so, advantages and limitations of Barker’s method are demonstrated. 相似文献
10.
Jiansheng Li Jidan Wang Liuyang Zhang Xiaojing Sang 《Journal of Coordination Chemistry》2017,70(17):2950-2957
The anion form of a cobalt-substituted mono-lacunary Keggin-type polyoxometalate (POM) complex in aqueous solution was identified as [Co(H2O)(H3PW11O39)]2? and its stability constant was determined to be 5.19 × 104 by spectrophotometry. Additionally, the electrocatalytic performances toward water oxidation of different concentrations of [Co(H2O)(H3PW11O39)]2? were investigated in the neutral phosphate buffer solution, and it was found that [Co(H2O)(H3PW11O39)]2? anion itself has little activity; the activity of [Co(H2O)(H3PW11O39)]2? solution actually results from dissociated [Co(H2O)6]2+. This work provides a simple way to understand the origin of catalytic water oxidation activity of a POM-based complex. 相似文献
11.
B. R. Saifutdinov A. A. Pimerzin N. S. Emel’yanova S. V. Kurbatova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2012,86(2):289-297
Adsorption in Henry’s range of structurally related aryl- and hetaryl-substituted 1,3,4-oxadiazoles from n-hexane-dichloromethane and water-acetonitrile solutions on the surface of porous graphitic carbon (PGC) under the conditions
close to equilibrium is studied by high-performance liquid chromatography. The characteristics of sorption of 1,3,4-oxadiazoles
from solutions on the surface of this adsorbent, octadecyl silica gel, and on hypercrosslinked polystyrene are compared. It
is shown that the structure of the molecules and their Van der Waals surface area and polarity affect adsorption on a PGC
surface. A variant of the mechanism of adsorption of the polar molecules on the PGC surface, explaining the anomalously high
values of their Henry constants of adsorption and based on the planar location of the 1,3,4-oxadiazoles molecules with respect
to the adsorbent surface and the specific adsorbate-adsorbent intermolecular interaction in addition to the background dispersion
interactions, is proposed. It is established that the linear the Gibbs energy relationship upon the adsorption of the studied
compounds from n-hexane-dichloromethane and water-acetonitrile solutions on the PGC surface holds. 相似文献
12.
《Fluid Phase Equilibria》2003,211(2):241-256
In this work, Henry’s Law constants of nonpolar solutes in four polymers were obtained by extrapolation of finite concentration vapor–liquid equilibrium (VLE) data using the UNIQUAC equation to infinite dilution condition. The consistency of the results was confirmed by comparing them with infinite dilution data through the linear relationship between logarithm of Henry’s Law constants and inverse of temperatures. This verification provided good method for crosschecking a reliability of finite concentration VLE data with infinite dilution data. Henry’s Law constants were correlated based on both types of data as a function of temperature using the classical van’t Hoff equation. Generalized correlations of the Henry’s Law constants of solutes were proposed for polyisoprene (PI), polyisobutylene (PIB) and poly(n-butyl methacrylate) (PBMA). 相似文献
13.
Hayat T. Ahmed Bilal Abbasi F. M. Alsaedi A. 《Journal of Thermal Analysis and Calorimetry》2022,147(1):409-419
Journal of Thermal Analysis and Calorimetry - Nanomaterials are quite significant in the physiological and engineering processes. Such materials have motivated the recent scientists in view of... 相似文献
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Based on the linear rheological constitutive model that is used to describe viscoelastic-plastic behavior of viscoelastic materials, a formula of the Poisson’s ratio was deduced according to the relationship between the shear creep compliance and tensile compliance. Instrumented indentation under various loading conditions and universal creep tests were performed on polyamide 12 samples to obtain the relevant rheological parameters. Results show that the Poisson’s ratio for a step load indentation can obtain a constant but overrated value. However, the Poisson’s ratio approaches an asymptotic value and an accurate value can be gained at a certain loading rate. 相似文献
17.
Determination of total selenium and selenium distribution in the milk phases in commercial cow’s milk by HG-AAS 总被引:3,自引:0,他引:3
Muñiz-Naveiro O Domínguez-González R Bermejo-Barrera A Cocho JA Fraga JM Bermejo-Barrera P 《Analytical and bioanalytical chemistry》2005,381(6):1145-1151
A procedure has been developed for determining the selenium in cows milk using hydride generation–atomic absorption spectrometry (HG-AAS) following microwave-assisted acid digestion. The selenium distributions in milk whey, fat and micellar casein phases were studied after separating the different phases by ultracentrifugation and determining the selenium in all of them. The detection limits obtained by HG-AAS for the whole milk, milk whey and micellar casein were 0.074, 0.065 and 0.075 g l–1, respectively. The accuracy for the whole milk was checked by using a Certified Reference Material CRM 8435 whole milk powder from NIST, and the analytical recoveries for the milk whey and casein micelles were 100.9 and 96.9%, respectively. A mass balance study of the determination of selenium in the different milk phases was carried out, obtaining values of 95.5–100.8%. The total content of selenium was determined in 37 milk samples from 15 different manufacturers, 19 whole milk samples and 18 skimmed milk samples. The selenium levels found were within the 8.5–21 g l–1 range. The selenium distributions in the different milk phases were studied in 14 whole milk samples, and the highest selenium levels were found in milk whey (47.2–73.6%), while the lowest level was found for the fat phase (4.8–16.2%). A strong correlation was found between the selenium levels in whole milk and the selenium levels in the milk components. 相似文献
18.
Two simple and sensitive spectrophotometric methods for the determination of cefetamet in either pure form or in its pharmaceutical formulations were described. The method Ⅰ is based on the interaction of 3-methylbenzo[d]- thiazolin-2-one hydrazone (MBTH) with cefetamet in the presence of freshly prepared ferric chloride in a neutral medium. The resulting blue colored product has λmax at 628 nm. The method Ⅱ describes the reduction of ferric ion by the drug to ferrous ion followed by a complex formation reaction with 1,10-phenanthroline (1,10-phen) to form an orange red colored chromogen exhibiting 2max at 510 nm. The products are stable for more than 5 and 8 h respectively. Common excipients used as additives in pharmaceutical preparations do not interfere in the proposed methods. Both methods are highly reproducible and have been applied to a wide variety of pharmaceutical preparations and the results are comparable with those of official methods. 相似文献
19.
A new chemiluminescence amplification reaction has been developed, which is on the coupling of the oxidation of Eosin by hydrogen peroxide under the catalysis of HRP at pH 3. 5 to the chemiluminescent reaction of luminol and hydrogen peroxide catalyzed by HRP at pH 10 to measure the activity of HRP and labelled-HRP. The detection limit of HRP is 10-10 g/mL. The lowest dilution ratio of HBsAb-HRP is 1 : 1. 8×102 and 1 : 106 for the direct method and coupled method respectively. 相似文献
20.
《Analytical letters》2012,45(14):2797-2803
Abstract A rapid, simple and sensitive fluorimetric method has been developed for the determination of cyanide with fluorescein as fluorogenic reagent (λex = 494 nm, λem = 514 nm) at pH 6.0–7.0. A linear calibration curve was obtained in the range 0.004–2.0 μg CN?/25 ml. The detection limit is 0.004 μg CN-/25 ml. The method was successfully applied to the determination of cyanide in waste water. 相似文献