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31.
Rudolf Wagner 《Fresenius' Journal of Analytical Chemistry》1976,282(4):315-321
Summary Problems, techniques and means of water sampling are reviewed. Applicability and performance are discussed with regard to individual and composite samples, and also to automatic sampling. Storage and preservation of samples are dealt with.
Probenahme und Behandlung von ProbenWasser
Zusammenfassung Probleme, Verfahren und Hilfsmittel bei der Probenahme von Wasser werden behandelt. Ausführung und Anwendbarkeit von Einzel und Mischproben sowie der automatischen Probenahme werden diskutiert, ebenso die Aufbewahrung und Konservierung von Proben.
Start of discussion held at the 6th Annual Symposium on Recent Advances in the Analytical Chemistry of Pollutants, April 21–23, 1976; Vienna, Austria. 相似文献
32.
Andreas Hofer Eva Brosche und Rudolf Heidinger 《Fresenius' Journal of Analytical Chemistry》1971,253(2):117-119
Zusammenfassung Eine rasche und selektive Methode zur Bestimmung von wasserlöslichem Bor in Mischdüngern wird beschrieben. Bor wird aus der Probelösung, die etwa 0,1 N an Salzsäure sein soll, durch zweimaliges Schütteln mit 20%iger Lösung von 2-Äthyl-1,3-hexandiol in Methylisobutylketon isoliert. Anschließend wird es mit 0,5 N Natronlauge in die wäßrige Phase zurückgeschüttelt und mit, Azomethin H spektralphotometrisch bei 415 nm bestimmt.
Der Direktion der Österreichischen Stickstoffwerke A.G. danken wir für die Erlaubnis zur Veröffentlichung. 相似文献
Spectrophotometric determination of water-soluble boron in complex fertilizers using azomethine h following a separation by extraction with 2-ethyl-1,3-hexanediol
A rapid and selective method for the determination of water-soluble boron in complex fertilizers is described. Boron is separated from the sample solution, which should be approximately 0.1 N in hydrochloric acid, by shaking twice with 20% solution of 2-ethyl-1,3-hexanediol in hexone. Following this extraction boron is back-extracted into the aqueous phase with 0.5 N sodium hydroxide. It is finally determined spectrophotometrically at 415 nm using azomethine H as reagent.
Der Direktion der Österreichischen Stickstoffwerke A.G. danken wir für die Erlaubnis zur Veröffentlichung. 相似文献
33.
The biosynthesis of several sesquiterpenes has been proposed to proceed via germacrene A. However, to date, the production of germacrene A has not been proven directly for any of the sesquiterpene synthases for which it was postulated as an intermediate. We demonstrate here for the first time that significant amounts of germacrene A (7.5% of the total amount of products) are indeed released from wild-type aristolochene synthase (AS) from Penicillium roqueforti. Germacrene A was identified through direct GC-MS comparison to an authentic sample and through production of beta-elemene in a thermal Cope rearrangement. AS also produced a small amount of valencene through deprotonation of C6 rather than C8 in the final step of the reaction. On the basis of the X-ray structure of AS, Tyr 92 was postulated to be the active-site acid responsible for protonation of germacrene A (Caruthers, J. M.; Kang, I.; Rynkiewicz, M. J.; Cane, D. E.; Christianson, D. W. J. Biol. Chem. 2000, 275, 25533-25539). The CD spectra of a mutant protein, ASY92F, in which Tyr 92 was replaced by Phe, and of AS were very similar. ASY92F was approximately 0.1% as active as nonmutated recombinant AS. The steady-state kinetic parameters were measured as 0.138 min(-1) and 0.189 mM for k(cat) and K(M), respectively. Similar to a mutant protein of 5-epi-aristolochene (Rising, K. A.; Starks, C. M.; Noel, J. P.; Chappell, J. J. Am. Chem. Soc. 2000, 122, 1861-1866), the mutant released significant amounts of germacrene A (approximately 29%). ASY92F also produced various amounts of a further five hydrocarbons of molecular weight 204, valencene, beta-(E)-farnesene, alpha- and beta-selinene, and selina-4,11-diene. 相似文献
34.
Zellner M Winkler W Hayden H Diestinger M Eliasen M Gesslbauer B Miller I Chang M Kungl A Roth E Oehler R 《Electrophoresis》2005,26(12):2481-2489
For the preparation of proteins for proteome analysis, precipitation is frequently used to concentrate proteins and to remove interfering compounds. Various methods for protein precipitation are applied, which rely on different chemical principles. This study compares the changes in the protein composition of human blood platelet extracts after precipitation with ethanol (EtOH) or trichloroacetic acid (TCA). Both methods yielded the same amount of proteins from the platelet preparations. However, the EtOH-precipitated samples had to be dialyzed because of the considerable salt content. To characterize single platelet proteins, samples were analyzed by two-dimensional fluorescence differential gel electrophoresis. More than 90% of all the spots were equally present in the EtOH- and TCA-precipitated samples. However, both precipitation methods showed a smaller correlation with nonprecipitated samples (EtOH 74.9%, TCA 79.2%). Several proteins were either reduced or relatively enriched in the precipitated samples. The proteins varied randomly in molecular weight and isoelectric point. This study shows that protein precipitation leads to specific changes in the protein composition of proteomics samples. This depends more on the specific structure of the protein than on the precipitating agent used in the experiment. 相似文献
35.
A SPME-HPLC-post-column fluorescent derivatization method for the direct determination of saxitoxin (STX), the most potent paralytic shellfish poisoning (PSP) toxin, in water has been developed. Commercially available SPME devices with 50 microm Carbowax templated resin (CW/TPR) coating was found to be able to pre-concentrate STX from aqueous media. A special pre-conditioning treatment of soaking the SPME coating in 0.1 M NaOH solution significantly improved the extraction efficiency. The optimal pH for the SPME process is 8.1 and the equilibration time is 40 min. The partition coefficient, K, of the distribution of STX between the SPME coating and the aqueous media was measured to be 2.99 +/- 0.04 x 10(3). Extracted toxin on the SPME stationary phase was difficult to be desorbed by the HPLC mobile phase under dynamic desorption mode. A static ion-pairing desorption technique using a desorption solvent mixture of 20 mM sodium 1-heptanesulfonate in 30% aqueous acetonitrile acidified with 50 mM sulfuric acid was developed to overcome this problem. The method detection limit and repeatability achieved by this SPME-HPLC method were 0.11 ng ml(-1) and 3.7%, respectively, with a sample volume of just 5 ml of water. This analytical method is adequate for the monitoring of the PSP toxin in fresh/drinking waters. However, serious interference was observed when this technique was applied to saline water samples. This is probably due to competition of sodium ions with the cationic STX for absorption into the SPME stationary phase. 相似文献
36.
Ursula E. Spichiger Rudolf Eugster E. Haase G. Rumpf Peter Gehrig Angela Schmid Bruno Rusterholz Wilhelm Simon 《Fresenius' Journal of Analytical Chemistry》1991,341(12):727-731
Summary The selectivity of a new magnesium ionophore (ETH 7025) induced in membranes of different compositions is experimentally studied in view of the ion activities in human serum. The required selectivity coefficient against calcium for the application of an ion-selective magnesium electrode to human serum is calculated for the worst case. Other critical parameters for the application of a liquid PVC-based ion-selective membrane to undiluted human serum discussed are: the sensor lifetime which is related to the lipophilicity of the carrier as well as the ruggedness of the membrane against interactions with components of the relatively lipophilic sample. 相似文献
37.
Proton-active substances react with certain electron-rich olefins with cleavage of the central C?C double bond to give compounds that can be formally regarded as insertion products of nucleophilic carbenes. If they satisfy certain structural conditions, they isomerize with β elimination to give open-chain compounds. Both CH-acidic compounds and compounds containing NH or OH groups can undergo this reaction. The mechanisms are discussed, and the importance of the intermediate products to biochemistry (thiamine, tetrahydrofolic acid) is indicated. 相似文献
38.
39.
Edwin Haselbach Urs Klemm Rudolf Gschwind Thomas Bally Laurant Chassot Stephan Nitsche 《Helvetica chimica acta》1982,65(8):2464-2471
The radical cations of indeno [2, 1-a]indene ( 1 ), stilbene ( 2 ) and 3, 5, 3', 5'-tetramethylstilbene ( 3 ) were prepared by γ-irradiation of the neutral precursors in an electron-scavenging matrix at 77 K . Their electronic spectra were recorded and compared to the photoelectron spectra ( PE .) of the neutral precursors. The results show that either the fourth or the fifth excited doublet state of the cations is of «Non-Koopmans» type, with specific doublet energy (D) D (2Bg)=2.74 eV ( 1 +), =2.59 eV ( 2 +), =2.49 eV ( 3 +). Remarkably, 1 + possesses two electronic states in the 2.7-2.8 eV energy range: 2Au («Koopmans»-type) and 2Bg («Non -Koopmans»-type). The «SDT»-equation \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm D} = \sqrt {{\rm S} \cdot {\rm T}} $\end{document} approximately connecting excited singlet (S) and triplet (T) states of a neutral alternant system with the excited doublet (D) states of its radical cation - provided e-promotion occurs For all three excited states between the same (paired) orbitals-is satisfyingly exemplified by 1 : S1 = 3.92 eV and T1= 2.06 eV for 1 , D4 or 5=2.74 eV for 1 +. 相似文献
40.
Jarmila Štetinová Rudolf Kada Miloslava Dandárová Marcela Krublová Ján Leśko 《Chemistry of Heterocyclic Compounds》1995,31(10):1231-1233
Substituted ]-(6-methoxy-2-benzothiazolyt)-2-pyridones were prepared from 2-amino-6-methoxybenzathiazate through N-(6-methoxy-2-benzothiazotyl) cyanvorearmileaznd-3-aryl-N-(6-methoxy-2-benzothiazolyt)-2-cyano-2-propenamides. The cyclization of the latter with malonodinitrile in the presence of piperidine gave the corresponding pyridones. The structures of the synthesized compounds were confirmed by1H NMR and mass spectral data.Department of Organic Chemistry, Mass Spectrometry Laboratory, Slovak Technical University, 812 37 Bratislava, Slovakia. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1402–1404, October, 1995. Original article submitted August 24, 1995. 相似文献