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排序方式: 共有163条查询结果,搜索用时 140 毫秒
61.
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63.
Friedrich Oehme 《Fresenius' Journal of Analytical Chemistry》1962,186(1):215-230
Ohne Zusammenfassung 相似文献
64.
65.
P. Oehme 《Fresenius' Journal of Analytical Chemistry》1956,150(2):93-99
Zusammenfassung Es wurde gezeigt, daß die von Hashimoto und Mori angegebene subjektive Methode der Hochfrequenzpapierchromatographie zu einem Registrierverfahren ausgebaut werden kann. Die im Chromatogramm vorhandenen elektrolythaltigen Zonen bewirken Ableitungsverluste des Meßkondensators und werden durch Gitterstrommessungen eines Quarzoscillators nachgewiesen. Mit einer Kompensationsschaltung unter Anwendung eines Gleichstromverstärkers können Registrierkurven eines Schleifenoscillographen ausgewertet werden. Halbquantitative Auswertungen sind möglich, wenn durch eine bestimmte Präparationstechnik der Chromatogramme definierte Feuchtigkeitsmengen auf den Streifen festgelegt werden können. Entgegen den Angaben der japanischen Autoren konnte die Methode mit Erfolg nur zum Nachweis stärkerer Elektrolyte herangezogen werden. 相似文献
66.
An analytical technique is described which allows the determination of C2? C6 hydrocarbons in the ppt-range from up to 21 air samples after removal of air humidity. Preconcentration is carried out on a two stage cryotrap system. The compounds are separ ated on a temperature-programmed capillary coated with Al2 O3. Detection limits (S/N 2:1) of 1.5 to 5 ppt were obtained for air samples from the Arctic. The reproducibility of the method was about 3% at the 50–100 ppt level. Practical problems are discussed in detail. 相似文献
67.
LUDVÍK BENEŠ KLÁRA MELÁNOVÁ JAN SVOBODA VÍTĚZSLAV ZIMA 《Journal of inclusion phenomena and macrocyclic chemistry》2006,55(3-4):289-293
Intercalates of o-, m-, and p-toluidine into α-Zr(HPO4)2 · H2O were prepared and characterized by powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. As follows from IR, toludine molecules are protonated in the interlayer space. Toluidine molecules are arranged in a bimolecular way in the intercalates containing more than 1.5 toluidine molecules per Zr atom. On the other hand, a monolayer of the toluidine molecules is supposed in the intercalates with less than one toluidine molecule per Zr atom. 相似文献
68.
Michael Oehme Roland Kallenborn Karin Wiberg Christoffer Rappe 《Journal of separation science》1994,17(8):583-588
Two capillary columns, one coated with 90 % biscyanopropyl 10 % phenylcyanopropylpolysiloxane (RTx 2330) the other with dimethyl-t-butyl-silylated β-cyclodextrin dissolved in 85 % methyl 15 % phenyl polysiloxane (PS-086), have, when employed in tandem, enabled the enantioselective separation of all the chiral chlordanes present in the fish oil reference material SRM 1588, without any overlap between enantiomers of different isomers. This capillary column combination is, furthermore, able to separate the enantiomers of other chiral polychlorinated pesticides such as o,p′–DDT, oxy-chlordane, a chiral nonachlor, and heptachlor exo-epoxide. It can be used to determine the enantiomer ratio of these compounds present in the low pg/g range in extracts of marine biota and ambient air. 相似文献
69.
Differentiation of isomeric flavone/isoflavone aglycones by MS2 ion trap mass spectrometry and a double neutral loss of CO 总被引:1,自引:0,他引:1
Kuhn F Oehme M Romero F Abou-Mansour E Tabacchi R 《Rapid communications in mass spectrometry : RCM》2003,17(17):1941-1949
The fragmentation behaviour of seven pairs of isomeric flavone/isoflavone aglycones (solely hydroxylated and/or methoxylated) was studied using ion trap mass spectrometry with atmospheric pressure ionisation (API, both electrospray and APCI) in the positive and negative ion modes. A major difference was found in the neutral loss of 56 u, which was a common feature of all isoflavones in API(+). It was identified as a double loss of CO by accurate mass tandem mass spectrometric (MS/MS) measurements using a hybrid quadrupole time-of-flight (Q-TOF) instrument. Fragmentation of daidzein with (13)C-isotope labelling of the carbon C2 showed that this double loss occurred from the central ring of the molecule. A mechanism for this selective fragmentation is given. Further isoflavone-specific fragmentations were used to develop a guideline for the identification of isoflavone structures. A software-based neutral loss scan of 56 u in the API(+)-MS(2) mode was applied to extracts of leaves of Lupinus albus and to soy flour. The structure elucidation guideline allowed identification of hydroxy and/or methoxy isoflavones. Structures could be confirmed for those available as reference compounds. 相似文献
70.
Frank Luderer Helmut Reinke Hartmut Oehme 《Journal of organometallic chemistry》1996,510(1-2):181-188
Treatment of 2,4,6-triisopropylbenzaldehyde with tris(trimethylsilyl)silylmagnesium bromide (2) gives 2,4,6-triisopropylphenyl-tris(trimethylsilyl)silyl-methanol (3) in approximately 70% yield and E-3,4-bis(2,4,6-triisopropylphenyl)-1,1,2,2-tetrakis(trimethylsilyl)-1,2-disilacyclobutane (5) (15%). 5 is the [2 + 2] head-to-head cyclodimer of the transient 1,1-bis(trimethylsilyl)-2-(2,4,6-triisopropylphenyl)silene (4), formed by trimethylsilanolate elimination according to a Peterson mechanism from the magnesium alkoxide, derived from the alcohol 3. Deprotonation of 3 with McLi at low temperature in ether produces a complex mixture of products, the main constituents being the silene dimer 5 (10%) and bis(trimethylsilyl)-2,4,6-triisopropylbenzyl-trimethylsiloxysilane (10) (60%), which is formed by readdition of the eliminated lithiumtrimethylsilanolate at the Si=C bond of 4. The deprotonation of 3 with McMgBr or PhMgBr (activated by LiBr) in THF at room temperature results in the formation of the polysilane (Me3Si)3SiSi(SiMe3)2CH2(2,4,6-C6H2iPr3) (13). Its generation indicates that there exists an equilibrium between the magnesium alkoxide derived from the alcohol 3 on one side, and the magnesium silanide 2 and 2,4,6-triisopropylbenzaldehyde on the other side. Possible pathways of the formation of the compounds mentioned, as well as of further by-products, are discussed. The 1,2-disilacyclobutane 5 is characterized by an X-ray crystal structure analysis. 相似文献