Phase equilibria in polymer/solvent systems. Part V: Thermodynamic theory of the swelling pressure equilibrium of a crosslinked substance with a solvent in various phases

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.     

Simultaneous Determination of Triptolide and Tripdiolide in Extract of Tripterygium wilfordii Hook. f. by LC–APCI-MS

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.     

Application of correlation-gas chromatography to evaluate the vaporization enthalpy of a component in an equilibrium mixture

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.     

Action of α-cyclodextrin on phospholipid assemblies

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.     

Crystallite Nanosize Effect on the Structural Transitions of WO3 Studied by Raman Spectroscopy

Nanocrystallites of tungsten oxide samples of 2, 4, 16, 35 and 60 nm of diameter were prepared by cryosol and pyrosol techniques. The pressure- and temperature-induced phase transitions of these samples were monitored by Raman spectrometry from 0.1 MPa to 34 GPa and from 77 to 1200 K. The tetragonal (α)-orthorhombic (β)-monoclinic (γ) transitions in these nanometric samples are strongly downshifted in temperature by comparison with the bulk WO₃. For instance, the tetragonal phase which exists above 1171 K for the bulk tungsten oxide can be stabilized at 700 K for the 35 nm sample. In the same way, the monoclinic P2₁/n-monoclinic P2₁/c high-pressure-induced transition is slightly shifted from 0.1 GPa to a higher pressure (1.5 GPa). The discussion of these transition-line shifts is based on thermodynamic considerations in which the surface energy of crystallites plays an important role.     

千克级窄分子质量分布聚苯乙烯的制备与表征

以正丁基锂为引发剂，以经过处理的工业级环己烷为溶剂、四氢呋喃为促进剂，用阴离子聚合的方法，在常压和惰性气体保护条件下，制得一系列千克级窄分子质量分布的聚苯乙烯，利用IR、^1H-NMR、GPC等技术对聚苯乙烯产物进行了表征，分析了影响聚苯乙烯的分子质量及分子质量分布的因素。     

Effects of pressure pulsation on oxygen transfer rate measured by sulfite method

Pressure pulsation (PP) was investigated for its effects on oxygen transfer rate (OTR) measured by sulfite oxidation. By manipulating airflow rate, 0.41–1.2 vvm, and a control valve in a 4-L bioreactor, the frequency of PP was varied at different gas pressures3–15 psig. A mathematical model of OTR was built and compared to experimental data. OTR was also examined at constant gas pressure, 4.5–15.0 psig. The results indicate a good agreement between measurement and model prediction. OTR above 9 psig during PP showed significant enhancement at 25°C. This proves that PP not only affects the elevation of DO level, but also increases the interfacial area and mass transfer coefficient.     

Topical Problems in Elemental Analysis of Advanced Ceramic Materials

Selected prominent problems in the analysis of advanced ceramic materials are surveyed. The importance of reliability of results is discussed in the field of elemental trace- and microanalysis in view of its interaction with economy, power of detection, local resolution and speciation selectivity. Particular problems in the analysis of major constituents, trace components and microlocal distributions are based on the striking propertics of ceramics; they are exemplified. Analytical assistance must start from the beginning of the production processing, in the preparation of the powdered base materials. Determination of the stoichiometry requires high accuracy and differentiation of chemical species in bulk and surface analysis of ceramic base powders. Element trace determination by direct instrumental methods requires standard reference materials for calibration; these are currently inavailable in a sufficient variety. For optimum reliability and power of detection, element traces must be prepared in isolated form in a small excitation volume for analysis. A review on the state-of-the-art of wet-chemical combined procedures is presented. Decomposition position procedures are emphasized, due to their risk of contributing severe systematic error. Combustion in elementary fluorine is presented for decomposition of refractory materials. The performance of some direct procedures is discussed. Very efficient methods are available for element trace determinations in ceramic materials, offering high detection power. Several approaches for high-resolution local microanalysis in non-conductive ceramic materials are identified as the most promising development in the analysis of sintered compact ceramic products and devices.     

Liquid chromatography/atmospheric pressure ionization-mass spectrometry in drug metabolism studies

The study of the metabolic fate of drugs is an essential and important part of the drug development process. The analysis of metabolites is a challenging task and several different analytical methods have been used in these studies. However, after the introduction of the atmospheric pressure ionization (API) technique, electrospray and atmospheric pressure chemical ionization, liquid chromatography/mass spectrometry (LC/MS) has become an important and widely used method in the analysis of metabolites owing to its superior specificity, sensitivity and efficiency. In this paper the feasibility of LC/API-MS techniques in the identification, structure characterization and quantitation of drug metabolites is reviewed. Sample preparation, LC techniques, isotope labeling, suitability of different MS techniques, such as tandem mass spectrometry, and high-resolution MS in drug metabolite analysis, are summarized and discussed. Automation of data acquisition and interpretation, special techniques and possible future trends are also the topics of the review.     

Methane Decomposition in a Barium Titanate Packed-Bed Nonthermal Plasma Reactor

The behavior of lattice oxygen species of the ferroelectric material during methane oxidation was investigated using a nonthermal plasma reactor packed with BaTiO ₃ pellets. Lattice oxygen species in BaTiO ₃ play an important role in the formation of N ₂ O and the oxidation of CH ₄ . The oxidation products such as CO and CO ₂ were formed from independent reaction pathways. Lattice oxygen species were able to preferentially oxidize the carbon species deposited on the pellet surface into CO. Also, N ₂ O and NO _x were independently formed in the N ₂–O ₂ reaction, suggesting that different oxygen species give N ₂ O and NO _x. N ₂ O was produced by the oxidation of molecular nitrogen with lattice oxygen species.