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51.
Addition of a small amount of polar solvent (i.e., modifier) to CO2 in packed column supercritical fluid chromatography (SFC) has shown major improvements in both polar analyte solubility and interaction of the polar analyte with the stationary phase. Recently, the addition of an ionic component (i.e., additive) to the primary modifier by one of us has been shown to extend even further the application of SFC to polar analytes. In this work, the effect of various ionic additives on the elution of ionic compounds, such as sodium 4-dodecylbenzene sulfonate and sodium 4-octylbenene sulfonate, has been studied. The additives were lithium acetate, ammonium acetate, tetramethylammonium acetate, tetrabutylammonium acetate, and ammonium chloride dissolved in methanol. Three stationary phases with different degrees of deactivation were considered: conventional cyanopropyl, deltabond cyanopropyl, and bare silica. The effect of additive concentration and additive functionality on analyte retention was investigated. Sodium 4-dodecylbenzene sulfonate was successfully eluted using all the additives with good peak shape under isocratic/isobaric/isothermal conditions. Different additives, however, yielded different retention times and in some cases different peak shapes. 相似文献
52.
53.
The crystal structure of a second high-pressure copper vanadate phase, CuVO3(II), has been determined and refined by full-matrix least-squares procedures using automatic diffractometer data to a residual R = 0.042 (Rw = 0.051). The space group is rhombohedral, , with hexagonal unit cell a = 4.966(2) and c = 14.084(5) Å [aR = 5.501(2) Å and α = 53.66(3)°]. The structure is the fully ordered ilmenite-type and, on the basis of published magnetic data and the interatomic distances, the valence distribution Cu+V5+O3 is proposed. This represents a unique example of Cu+ in an octahedral environment. 相似文献
54.
The apparent molal volumes and compressibilities of NaCl, KCl, and CsCl in mixtures of 18-Crown-6 and water have been calculated from density and speed-of-sound measurements at 25°C. The partial molal volumes and compressibilities of the salts when all cations have formed complexes with 18-Crown-6 molecules have been evaluated. The sign and magnitude of the volume and compressibility changes of complex formation strongly suggest that the charge of the cation becomes very effectively screened by the crown ether. 相似文献
55.
Ohne Zusammenfassung
Gas-chromatographie determination of ethylene glycol, diethylene glycol and triethylene glycol in water相似文献
56.
Summary The semi-empirical theory on the retention volume in gas chromatography recently developed by some experiments, was found to require partial correction. It was newly refined and summarized. Overall experimental checking was performed by the use of Cl2, Br2, and I2.
Gas-Chromatographie von Halogenen
Zusammenfassung Die halbempirische Theorie über das Retentionsvolumen in der Gas-Chromatographie, die kürzlich an Hand einiger Versuche entwickelt wurde, erforderte eine teilweise Korrektur. Sie wurde verbessert und zusammenfassend dargestellt. Kontrollversuche wurden mit Hilfe von Chlor, Brom und Jod durchgeführt.相似文献
57.
L.A. Leites A.V. Zabula S.S. Bukalov A.A. Korlyukov P.S. Koroteev O.S. Maslennikova M.P. Egorov O.M. Nefedov 《Journal of Molecular Structure》2005,750(1-3):116-122
Vibrational (Raman and IR) spectra of the 1:1 complexes of dihalogermylene and dihalostannylene with 1,4-dioxane and PPh3 have been reported, the structures of the complexes Cl2Ge·C4H8O2 and Cl2Ge·PPh3 updated using high-resolution X-ray method. Quantum-chemistry calculations of the geometry and normal mode frequencies and eigenvectors were carried out for some of the complexes. The results show that in the structure of the polymeric solid complexes of X2M with 1,4-dioxane, intermolecular coordination XM plays a prominent role, whereas the corresponding complexes with PPh3 are monomeric. In the vibrational spectra of all the complexes, an inversion of symmetric and antisymmetric stretching νXM (X=Cl, Br; M=Ge, Sn) frequencies, found for ‘free’ X2MII particles, still persists, suggesting that the X2M moieties preserve their specifity as carbene analogues also in the complexes. 相似文献
58.
As an extension of previous reports, the barium carbonate procedure has been optimized in detail for the preparation of apolar columns. The aim was to produce optimum overall column characteristics, and to maintain them unchanged under the prolonged influence of the highest possible temperature. The main parameters under optimization were glass variety, leaching of glass surface with aqueous HCl, and amount of barium carbonate deposited, while deactivation and coating were kept constant. The basic column characteristics were adsorption properties and thermostability of deactivation, acid/base behaviour and separation efficiency. They were determined by a new, quantitative testing procedure. Intense leaching was able to eliminate almost totally the differences between glass varieties and to create a well-defined glass surface. While untreated glass, leached glass, and barium carbonate treated glass showed specific weak points in the respective column quality, the combination of leaching and barium carbonate treatment yielded the highest and most stable quality. Some technical modifications of the preparation procedure are described, including deactivation in the gas phase, and use of pentane as a solvent for static coating. 相似文献
59.
Summary A micro carbon rod atomizer has been employed for specific and quantitative bromine determinations. This Br-specific gas-chromatographic detector works by help of InBr-bands and measurement at 372.7 nm. The performance of this flame band emission detector (FBD) is demonstrated by calibration curves and the detection limits of 2 examples (ethyl bromide, ethylene dibromide), the latter being 5 and 36 ng of bromine, respectively. The reproducibility has been found to be 4.3%. An example of this detector in comparison with a thermoconductivity detector (TCD) is presented.
Verwendung einer Mikro-Graphitküvette als Br-spezifischer Detektor für die Gas-Chromatographie
Zusammenfassung Eine Mikro-Graphit-Küvette wird für spezifische quantitative Brombestimmungen nach der Indium-Methode bei 372,7 nm benützt und in Verbindung mit einem Gas-Chromatographen als Br-spezifischer Detektor eingesetzt. Die Leistungsfähigkeit dieses Detektors wird an 2 Beispielen (Äthylbromid, Dibromäthan) mit Hilfe von Eichkurven, Bestimmung von Nachweisgrenzen u. ä. demonstriert. Die Nachweisgrenzen liegen bei 5 bzw. 36 ng Brom für die 2 genannten Substanzen. Die Reproduzierbarkeit der Messungen liegt bei 4,3%. Ein Beispiel für die Registrierung eines Gemisches verschiedener Substanzen, gemessen mit dem GC + Flammen-Banden-emissions-Detektor (FBD) und zum Vergleich mit einem Wärmeleitfähigkeitsdetektor (TCD), wird dargestellt.
This research work was supported by financial help of the Bundesminister für Forschung und Technologie in Bonn (GFR). 相似文献
60.
V. Slavinska Dz. Sile G. Rozenthal G. Maurops J. Popelis M. Katkevich V. Stonkus E. Lukevics 《Chemistry of Heterocyclic Compounds》2006,42(5):570-573
The hydrogenation of ethyl 4-R-2,4-dioxobutyrates (R = phenyl, 2-furyl) at 5% Pt/Al2O3 catalyst, modified with cinchonidine, and at palladium black was investigated. The former had low activity under the conditions
we tested. The main products during the hydrogenation of these compounds at palladium black are ethyl 4-R-2-hydroxy-4-oxobutyrates.
The yield of the phenyl derivative amounts to 68.5%, while the yield of the corresponding 2-furyl derivative amounts to 97%.
In the last case ethyl 2-hydroxy-4-oxo-4-(2-tetrahydrofuryl)butyrate was detected as impurity. The optimum conditions for
the formation of ethyl 2-hydroxy-4-phenylbutyrate (yield 88.2%) were determined.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 655–659, May, 2006. 相似文献