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181.
W. Borchard 《Colloid and polymer science》1993,271(1):1-10
A thermodynamic theory has been developed to define the swelling pressure equilibrium between a homogeneous gel and a pure solvent, where phase transitions of the solvent, such as evaporation and crystallization can occur. It is shown that the equilibrium curve, which describes the temperature dependence of the composition in the gel phase under the condition of a constant swelling pressure, has distinct bends at the transition temperatures. These bends are related to the enthalpies of transition of the pure solvent at the transition temperatures. As a consequence of the phase transition of the solvent the swelling pressure-temperature curve at constant composition of the gel shows a discontinuous behavior at the transition point. Numerical calculations with a modified Flory-Huggins expression, based on results of swelling and deswelling measurements of the system crosslinked PEG/water, are presented.The discussion includes natural systems, which are in the gel state, where water may crystallize in the extracellular space. 相似文献
182.
A novel method using liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry in the
negative selected ion monitoring mode has been developed and validated for rapid simultaneous determination of triptolide
and tripdiolide in the extract of Tripterygium wilfordii Hook. f. The molecular ions m/z [M–H]− 359 and 375 were selected for the quantification in selected ion monitoring mode for triptolide and tripdiolide. Standard
calibration curve was linear over the concentration range of 0.12–24 and 0.15–30 μg mL−1 for triptolide and tripdiolide. The relative standard deviations of intra- and inter-day were in the range of 4.7–9.9 and
8.9–12.6%. The average recoveries were between 96.4 and 104.6%. The limits of quantitation were 2.0 × 10−3 and 2.5 × 10−3 μg mL−1 for triptolide and tripdiolide. 相似文献
183.
Manuel Temprado 《Thermochimica Acta》2005,435(1):49-56
The vaporization enthalpies and vapor pressures of acetoin, ethyl 3-hydroxybutyrate and ethyl 3-hydroxyhexanoate, found in a variety of foods and flavors, are evaluated at T = 298.15 K using correlation-gas chromatography; values of (48.7 ± 0.4), (55.9 ± 0.6) and (61.9 ± 0.6) kJ mol−1, respectively, were obtained. These values are in good agreement with estimated values. Vapor pressures of the standards as a function of temperature were also used to calculate vapor pressures of the target compounds and all resulting data were fit to second order polynomials. These polynomials were then used to predict boiling temperatures of both standards and target substances. Agreement with experimental boiling temperatures was generally within 10 K suggesting that vapor pressures are accurate to within a factor of two. Acetoin exists as an equilibrium mixture of monomer and dimer. This report provides an example of the utility of using correlation-gas chromatography to obtain thermochemical data on an impure material. 相似文献
184.
This study examines the reagent gas pressure and ion source temperature dependence for dimethyl ether chemical ionization (DME CI) mass spectra recorded with an external source ion trap mass spectrometer (ITMS). Information for better controls of the reagent gas pressure in order to obtain fair CI spectra is provided. The origin of M+? ions observed in DME CIMS is discussed in detail. Furthermore, the ion source temperature effect on the DME CI is also investigated. 相似文献
185.
Summary Organic acids, such as lactic, malic and citric acids, are involved in primary metabolism of all living organisms. Their presence in food products contributes to the flavour and their equilibrium with inorganic cations defines to a large extent the acidity of the food preparations. A resin cation-exchanger device, normally used for separating amino-acids, can be adapted for characterizing 10 organic acids: formic, propionic, fumaric, succinic, lactic, malic tartaric, citric, and oxalic. Two monitoring systems were used, one of them based on specific iron III salt coloration with hydroxy-acids. 相似文献
186.
气相渗透法中的溶质吸附效应 总被引:1,自引:0,他引:1
在气相渗透仪上,用四个低分子量有机化合物和五个已知平均分子量的窄分布聚苯乙烯低聚体,对VPO方法中的溶质吸附效应作了研究,提出了一种对吸附效应作改正的方法.所得结果表明,在扣除溶质吸附效应后,仪器常数K无分子量依赖性,提高了测定低分子量聚合物数均分子量的准确性. 相似文献
187.
Aleš Podgornik 《Journal of separation science》2022,45(12):1984-1996
Modern convection-based supports differ substantially in pore size, porosity, and microstructure topology. Due to such variability, it is challenging to evaluate the contribution of a particular microstructure topology on flow resistance. We demonstrated that the flow resistance parameter ( ) introduced decades ago can be used as a criterion to evaluate the effect of microstructure topology on a pressure drop when the pore size is used as a characteristic support dimension. Furthermore, the value of simple cubic packing was calculated over the entire range of open porosity and compared to the values determined for pressure drop models derived for particular convection-based supports and experimental values of various convection-based supports from the literature. It was shown that different convection-based supports become clustered into distinct groups when plotted according to their and open porosity values, allowing their discrimination. 相似文献
188.
S. Sawamura M. Tsuchiya T. Ishigami Y. Taniguchi K. Suzuki 《Journal of solution chemistry》1993,22(8):727-732
Solubility of naphthalene in water was measured at 25°C and pressures up to 200 MPa. The solubility decreased with increasing pressure. From the pressure coefficient of the solubility, the volume change V accompanying the dissolution was estimated as 13.8±0.4 cm
3
-mol
–1
. Further we estimated the volume change V
CH
accompanying hydrophobic hydration as –0.1±0.6 cm
3
-mol
–1
using the V value, the molar volume of crystalline naphthalene, and the partial molar volume of naphthalene in n-heptane. This V
CH
is much larger (i.e., less negative) than that for hydrophobic hydration of alkyl-chain compounds and suggests that the hydration structure of naphthalene differs from that of alkyl-chain compounds. 相似文献
189.
Valérie Bernat Catherine Ringard-Lefebvre Geneviève Le Bas Sylviane Lesieur 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):113-119
Interactions of α-cyclodextrin (α-CD) with dimyristoylphosphatidylcholine (DMPC) and Egg phosphatidylcholine (Egg-PC) were studied (i) by analyzing surface
pressure-area isotherms and surface tension of phospholipid monolayers formed at the interface between air and α-CD aqueous solutions and (ii) by X-ray diffraction performed on fully hydrated α-CD/phospholipid binary mixtures. The cyclodextrin molecules strongly interact with the two-dimension phospholipid assembly.
Their addition into the aqueous sub-phase leads to the removal of part of the phospholipids from the air-water interface:
the higher the α-CD concentration, the higher the phospholipid depletion. This should preferentially involve interactions between cyclodextrin
and the phosphatidylcholine head group as α-CD is water-soluble and not surface-active. At the three-dimension level, the bilayer packing of the phospholipid lamellar
phase appears not affected by the presence of cyclodextrin as shown by X-ray scattering at small angles whereas wide-angle
diffraction patterns reveal the formation of a crystalline phase organized in a pseudo-hexagonal lattice usually characteristic
of α-CD dimers. These results point out that α-CD should interact with bilayer-forming phospholipid molecules but likely according to a process that would preserve intact
at least a part of the multilamellar assembly. 相似文献
190.
对聚对苯二甲酸乙二醇酯(PET)在特定的结晶条件下是否生成伸直链晶体进行了论证,系统总结了伸直链晶体形成的证据,并讨论了PET伸直链晶体形成的机理。 相似文献