So far the majority of the measurements of mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH) were obtained from on-line high performance liquid chromatography–gas chromatography–flame ionization detection (on-line HPLC–GC–FID). Since this technique is not available in many laboratories, an alternative method with more easily available tools has been developed. Preseparation on a small conventional liquid chromatographic column was optimized to achieve robust separation between the MOSH and the MOAH, but also to keep out the wax esters from the MOAH fraction. This was achieved by mixing a small portion of silica gel with silver nitrate into highly activated silica gel and by adding toluene into the eluent for the MOAH. Toluene was also added to the MOSH fraction to facilitate reconcentration and to serve as a keeper preventing loss of volatiles during solvent evaporation. A 50 μl volume was injected on-column into GC–FID to achieve a detection limit for MOSH and MOAH below 1 mg/kg in most foods. 相似文献
We compare extensive experimental results for the
gravity-driven steady drainage of oil-in-water emulsions with two
theoretical predictions, both based on the assumption of Poiseuille flow.
The first is from standard foam drainage theory,
applicable at low aqueous volume fractions, for which a
correction is derived to account for the effects
of the confinement of the emulsion. The second arises
from considering the permeability of a model porous
medium consisting of solid sphere packings, applicable
at higher aqueous volume fractions. We find quantitative
agreement between experiment and the foam drainage theory at low
aqueous volume fractions. At higher aqueous volume
fractions, the reduced flow rate calculated from the
permeability theory approaches the master curve
of the experimental data. Our experimental data
demonstrates the analogy between the problem of electrical flow and liquid
flow through foams and emulsions. 相似文献
Here we developed a highly sensitive, fast and reliable liquid chromatography tandem mass spectrometry (LC-MS/MS) method for the detection and analysis of 16 different polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs that have been identified as carcinogens and classified according to their biological potency. Comparison to standard analysis procedures based on gas chromatography-mass spectrometry (GC-MS) instrumentation demonstrated an improved easiness of sample preparation and sensitivity of detection achieved with the new LC-MS/MS method employing an atmospheric pressure photoionization (APPI) source attached to an API 4000 mass spectrometer (LC-APPI-MS/MS). The favorable outcome could be confirmed by analyzing complex mixtures such as certain Standard Reference Materials (SRMs) obtained from the National Institute of Standards & Technology (NIST), i.e., SRM 1975 and SRM 2975, and several diesel exhaust soots provided by the German automobile industry. Certified concentrations of individual analytes provided by NIST not only could be confirmed, but additional extremely potent carcinogens such as several isomeric hexacyclic dibenzopyrenes (DBPs), 5-methylchrysene (5-MC), and others have been detected in these crude samples in a concentration range down to below 1 ng g(-1) raw material. 相似文献
OIT's oxidation condition is very harsh for pure and irradiated polymers, particularly PP. PP undergoes pronounced molecular weight degradation in the course of processing and is prone to very fast oxidation and consequently very fast degradation, especially on samples submitted to previous aging and irradiation.
We developed a more useful method applicable by a much broader set of resins. Our group has recently introduced a new procedure to determine OIT, in non-stabilized and stabilized, irradiated and non-irradiated polypropylene. The new procedure was based on two main features: (1) starting the oxidation on melted samples at temperatures as low as possible; (2) oxidation under slow heating conditions. So each sample has a set of two values of time and temperature, as the new method is not isothermal any longer, so we better call it “Temperature dependent oxidative induction-time”. The new method showed itself as reproducible, sensitive to small changes in additive compositions and simple and inexpensive. 相似文献
We formulate and apply a continuum model that incorporates elasticity, yield stress, plasticity, and viscous drag. It is motivated by the two-dimensional foam rheology experiments of Debregeas et al. [Phys. Rev. Lett. 87, 178305 (2001)10.1103/PhysRevLett.87.178305] and Wang et al. [Phys. Rev. E 73, 031401 (2006)10.1103/PhysRevE.73.031401], and is successful in exhibiting their principal features, which are an exponentially decaying velocity profile and strain localization. Transient effects are also identified. 相似文献
Close examination of wealth distributions reveal the existence of two distinct power law regimes. The Pareto exponents of the super-rich, identified, for example in rich lists such as provided by Forbes, are smaller than the Pareto exponents obtained for top earners in income data sets. Our extension of the Slanina model of wealth is able to reproduce these double power law features. 相似文献
The Morse–Witten theory provides a formulation for the inter-bubble forces and corresponding deformations in a liquid foam, accurate in the limit of high liquid fraction. Here we show how the theory may be applied in practice, including allowing for polydispersity in the bubble sizes. The resulting equilibrated 2D structures are consistent with direct calculations, within the limitations of the theory. The path to developing a 3D model is outlined for future work. 相似文献