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991.
Judefeind A Jansen van Rensburg P Langelaar S Wiechers JW du Plessis J 《Journal of chromatographic science》2008,46(6):544-550
A gas chromatographic (GC) method with mass spectrometric (MS) detection is developed and validated for the accurate and precise determination of octadecenedioic acid (C18:1 DIOIC) in human skin samples and transdermal perfusates. C18:1 DIOIC is extracted using methanol. The saturated analogue 1,18-octadecanedioic acid (C18:0 DIOIC) is added as internal standard. Prior to analysis, both compounds are converted to their trimethylsilylated derivatives using N,O-bis(trimethylsilyl)trifluoroacetamide with 15% trimethylchlorosilane. Quantitation is performed in selected ion monitoring mode with a limit of quantitation of 250 ng/mL. Linearity with a correlation coefficient of 0.998 is obtained over a concentration range of 250-2000 ng/mL. Values for within-day accuracy range from 94.5% to 102.4%, and from 97.5% to 105.8% for between-day accuracy. Within- and between-day precision values are better than 5% and 7%, respectively. The recovery values from the various matrices vary from 92.6% to 104.0%. The GC-MS method is employed for the determination of C18:1 DIOIC after application of an emulsion containing the active ingredient onto human skin in vitro. The results demonstrate that the method is suitable for the determination of C18:1 DIOIC in human skin samples and transdermal perfusates. 相似文献
992.
Nagl J Auböck G Hauser AW Allard O Callegari C Ernst WE 《The Journal of chemical physics》2008,128(15):154320
Electronic excitation spectra of homo- (K(3),Rb(3)) and heteronuclear (K(2)Rb,KRb(2)) alkali trimers in the high-spin quartet state have been investigated in a broad spectral range (10,600-17,400 cm(-1)). Ten new bands showing laser induced fluorescence (LIF) were measured. Due to the pickup statistics, overlapping spectra of all possible oligomers are present at once, complicating the unraveling and assignment of individual spectra. To circumvent the problem, two variations of beam depletion spectroscopy were employed in addition to the conventional analysis of the relation between signal and pickup pressure: A two-laser V-type double resonance scheme combining beam depletion with LIF, and a mass selective beam depletion scheme. In principle, these allow accurate separation of an arbitrary number of overlapping spectra. The benefits and drawbacks of each method are discussed. Assignment to electronic states is achieved by comparison with ab initio complete active space self-consistent field calculations of the excited electronic level structure of the molecules. 相似文献
993.
Izak J. van der Walt Johann T. Nel Philippus L. Crouse 《Journal of fluorine chemistry》2008,129(4):314-318
Despite the fact that the thermal decomposition of polytetrafluoroethylene has been extensively studied over the past six decades, some inconsistencies regarding the kinetic parameters, e.g. the order of the reaction, remain. Representative kinetic data are essential for practical purposes such as reactor design and scaling. In general the literature data refer to homogeneous bulk heating, whereas the case of the non-homogeneous heating of a single particle has not received attention. Data (reaction rate and pre-exponential factor) applicable to this latter case were experimentally determined from isothermal thermogravimetric analyses of the depolymerisation reaction of PTFE. The kinetic data obtained on coarse granules (800-1000 μm) are reported here. The rate law is consistent with a shrinking particle kinetic model, with chemical kinetics controlling phase-boundary movement. The mass loss rate is directly proportional to surface area. A rate law applicable to this case, and useable for geometries of arbitrary shape, is derived. 相似文献
994.
Serpa C Schabauer J Piedade AP Monteiro CJ Pereira MM Douglas P Burrows HD Arnaut LG 《Journal of the American Chemical Society》2008,130(28):8876-8877
Time-resolved photoacoustic calorimetry is used to measure the energy released upon injection of an electron from an electronically excited dye adsorbed to nanocrystalline TiO2 into the conduction band of this material. More energy is released when the environment of the dye is made less polar, because the energy of the dye-oxidized state has a more pronounced solvent dependence than the edge of the conduction band of the TiO2 semiconductor. Such energy dependences should be considered in the design of more efficient dye-sensitized solar cells. 相似文献
995.
Summary In this paper Green's functions for the reduced wave equation (Helmholtz equation) in a circular annular domain with the Dirichlet, the radiation, and Neumann boundary conditions are derived. The convergence of the series representing Green's functions is then established. Finally it is shown that these functions reduce to Green's function for the exterior of a circle as given by Franz and Etiènne when the outer radius is moved towards infinity. 相似文献
996.
Natalie J. Waleska Dr. Fabian Düll Dr. Philipp Bachmann Felix Hemauer Johann Steinhauer Dr. Christian Papp 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(68):17087-17093
The reactivity of iron nanocluster arrays on h-BN/Rh(111) was studied using in situ high-resolution X-ray photoelectron spectroscopy. The morphology and reactivity of the iron nanoclusters (Fe-NCs) were investigated by CO adsorption. On-top and hollow/edge sites were determined to be the available adsorption sites on the as-prepared Fe-NCs and CO dissociation was observed at 300 K. C- and O-precovered Fe-NCs showed no catalytic activity towards CO dissociation because the hollow/edge sites were blocked by the C and O atoms. Therefore, these adsorption sites were identified to be the most active sites of the Fe-NCs. 相似文献
997.
Chromatographia - The development and applications of asymmetric flow field-flow fractionation (AF4) are outlined in comparison with the older and better-known size exclusion chromatography. Recent... 相似文献
998.
The maximum achievable temperature (energy density) and minimum kinetic energy required for the formation of a baryon-rich quark-gluon plasma formed at central rapidity in small impact parameter nuclear collisions is estimated. A possible mechanism leading to the pile-up of matter is introduced. Plasma formation is expected to appear at about 15 GeV/Nucleon uranium beam energy on a stationary target or 2.7 GeV/Nucleon in colliding beams. 相似文献
999.
1000.
Johann Mulzer 《Monatshefte für Chemie / Chemical Monthly》2000,22(12):205-238
Microtubule stabilizing natural products, as exemplified by paclitaxel (taxol?), are being considered as novel drugs against malignant therapy resistent solid tumors. Among these compounds, epothilone B and some of its derivatives have emerged as particularly promising candidates for industrial development. The total and partial syntheses of these compounds are described in detail, and some of the most important recent results on their biological activity are discussed. 相似文献