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排序方式: 共有136条查询结果,搜索用时 15 毫秒
21.
Dr. Gerold Adam 《Colloid and polymer science》1964,195(1):1-8
Zusammenfassung In der vom Verfasser vorgeschlagenen molekular-kinetischen Theorie der Nachwirkungserscheinungen organischer Gl?ser im Einfrierbereich
wird die Beziehung zwischen Enthalpie- und Volumenrelaxation untersucht.
Die theoretischen Beziehungen werden mit den Experimenten der Volumen- und Enthalpienachwirkung an Polystyrol, Polyvinylacetat
und Glucose verglichen.
Die Theorie stimmt quantitativ mit den Experimenten überein, wenn der Ausgangszustand vor der Nach-wirkung beibehalten wird.
Dabei werden Enthalpie- und Volumenrelaxation im Rahmen der Me?- und Auswertegenauigkeit durch die gleichen molekularen Parameter
beschrieben.
?ndert man den Ausgangszustand vor der Nachwirkung, so bleibt die Theorie nur qualitativ richtig. Zur quantitativen Beschreibung
dieses Effektes hat man eine ?nderung des Parameters, der die Nichtlinearit?t der Nachwirkung beschreibt, mit dem Ausgangszustand
in Rechnung zu ziehen. Diese kann von der Theorie in der bisherigen Form noch nicht erkl?rt werden.
Hernn Prof. Dr.F. H. Müller danke ich herzlich für die M?glichkeit, die Arbeit in seinem Institut durchführen zu k?nnen und für anregende Diskussion.
Der Deutschen Forschungsgemeinschaft bin ich dankbar, da? sie mir die Untersuchungen durch ein Forschungsstipendium erm?glicht
hat. 相似文献
22.
23.
Thermospray (TSP) ionization was evaluated with respect to its suitability in the LC-MS determination of a broad range of pesticides. The sensitivity and the selectivity of this method for the determination of 128 pesticides having a wide range of structures and polarities were investigated. An LC separation in combination with postcolumn addition of a volatile salt solution was developed, which permits the analysis of 95 pesticides with a single LC-MS method using reversed-phase gradient caution. The retention data and TSP mass spectra of these compounds are presented. The advantages of TSP postcolumn techniques in comparison with conventional systems are discussed. The application of this method to the analysis of an environmental sample (river water) spiked with eight phenylureas is demonstrated. lie method was evaluated with respect to detection limit, linearity and reproducibility. In addition, a simple method for enhancing the structural information from TSP spectra is reported, which makes use of specific instabilities found with many pesticides. As an example, possibilities for the confirmatory analysis of carbamates are described. 相似文献
24.
Fernanda das Neves Costa Ricardo Moreira Borges Gilda Guimares Leito Gerold Jerz 《Journal of separation science》2019,42(8):1528-1541
Salicornia species have just been introduced to the European market as a vegetable named ‘samphire’, ‘green asparagus’, or ‘sea asparagus’. Due to its increasing attention, and associated value, minor compounds of Salicornia gaudichaudiana Moq were investigated. The use of countercurrent chromatography and mass spectrometry enabled the search for known, as well as potentially novel natural products. Their identification was achieved based on molecular weights and mass‐spectrometric fragmentation data. Low detection limits enabled the visualization of all compounds with their identification in almost real time close to the preparative countercurrent chromatography experiment. A list of known natural products from Salicornia genus guided the identification process of compounds occurring in Salicornia gaudichaudiana Moq by tandem mass spectrometry fragment comparison. The natural product classes were divided into four groups: chlorogenic acid derivatives; flavonoid derivatives; pentacyclic triterpenoid saponins; and other compounds. 相似文献
25.
A lignan, sisymbrifolin (1) found in the fruits of Solanum sisymbriflolium has been isolated from the bark extract of Salix alba (Salicaceae). Its structure was elucidated by its direct spectrum data of ESI-MS and one- and two-dimensional NMR spectroscopy for the first time. 相似文献
26.
D. Wollenweber Silke Stra?burg Gerold Wünsch 《Fresenius' Journal of Analytical Chemistry》1999,364(5):433-437
Some important analytes in ICP-MS are interfered by plasma argon or argon species, such as ArO+ and 56Fe, 40Ar and K or Ca. One approach to overcome this interference is the use of reduced forward power and a metal shield inserted
between torch and load coil. These so called cold plasma conditions reduce the background caused by argon species and the
formerly interfered analytes can be easily detected in the ng/g-range. Other elements in the lower mass region also profit
from these conditions even when they are not interfered in normal plasma mode. The limits of detection are improved due to
reduced background noise level and enhanced ion transmission. On the other hand, the reduced power fed to the plasma lowers
the analytical performance and makes it susceptible to matrix effects. Elements of higher mass generally show higher detection
limits compared to normal plasma mode.
Received: 30 November 1998 / Revised: 4 February 1999 / Accepted: 8 February 1999 相似文献
27.
28.
Iron Precursor Decomposition in the Magnesium Combustion Flame: A New Approach for the Synthesis of Particulate Metal Oxide Nanocomposites
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Amir R. Gheisi Matthias Niedermaier Gerold Tippelt Werner Lottermoser Johannes Bernardi Oliver Diwald 《Particle & Particle Systems Characterization》2017,34(10)
Powders of Fe–Mg–O nanocomposite particles have been grown using a novel chemical vapor synthesis approach that employs the decomposition of a metalorganic precursor inside the metal combustion flame. After annealing in controlled gas atmospheres composition distribution functions, structure and phase stability of the obtained magnesiowüstite nanoparticles are measured with a combination of techniques such as inductively coupled plasma‐optical emission spectroscopy, energy dispersive X‐ray spectroscopy, X‐ray diffraction, and scanning and transmission electron microscopy. Complementary Mössbauer spectroscopy measurements reveal that depending on Fe loading and temperature of annealing either metastable and superparamagnetic solid solutions of Fe3+ ions in periclase (MgO) or phase separated mixtures of MgO and ferrimagnetic magnesioferrite (MgFe2O4) nanoparticles can be obtained. The described combustion technique represents a novel concept for the production of mixed metal oxide nanoparticles. Adressing the impact of selected annealing protocols, this study underlines the great potential of vapor phase grown non‐equilibrium solids, where thermal processing provides means to trigger phase separation and, concomitantly, the emergence of new magnetic properties. 相似文献
29.
Johannes Wellmann Beate Hartmann Esther-Corinna Schwarze Silke Hillebrand Stephan I. Brueckner Jakob Ley Gerold Jerz Peter Winterhalter 《Molecules (Basel, Switzerland)》2022,27(11)
Previously, different Hydrangea macrophylla ssp. serrata cultivars were investigated by untargeted LC-MS analysis. From this, a list of tentatively identified and unknown compounds that differ significantly between these cultivars was obtained. Due to the lack of reference compounds, especially for dihydro-isocoumarins, we aimed to isolate and structurally characterise these compounds from the cultivar ‘Yae-no-amacha’ using NMR and LC-MS methods. For purification and isolation, counter-current chromatography was used in combination with reversed-phase preparative HPLC as an orthogonal and enhanced purification workflow. Thirteen dihydro-isocoumarins in combination with other metabolites could be isolated and structurally identified. Particularly interesting was the clarification of dihydrostilbenoid glycosides, which were described for the first time in H. macrophylla ssp. serrata. These results will help us in further studies on the biological interpretation of our data. 相似文献
30.
If sample pretreatment, nebulization and method of calibration are suitably adapted to each other the performance of inductively coupled plasma - mass spectrometry ICP-MS can be greatly increased. High accuracy is obtained by high precision and low bias. For a given concentration higher sensitivity means higher count rates and therefore higher precision. Systematic errors are minimized by employing a definitive method of calibration. Increased sensitivity is obtained by introducing higher amounts of sample into the measurement system via high efficiency nebulizers (ultrasonic nebulizer, hydraulic-high pressure nebulizer according to Berndt and concentric high efficiency nebulizer according to Meinhard). Because this means also higher matrix effects a combination of ion chromatographic (IC-TMS) and thermal trace-matrix-separation by aerosol desolvation (T-TMS) is introduced. Isotope dilution (ID) proves to be the calibration most suitable to achieve the highest accuracy. First applications on the analysis of refractory metals (e.g. Ti, V, Nb, Ta) and non-metals (e.g. P, S, As, Se) showed recoveries of 60-105%, an imprecision of the recoveries of 2-50%, but an overall inaccuracy of only 0.1 to 4%. 相似文献