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81.
82.
83.
Two-dimensional on-line detection of brominated and iodinated volatile organic compounds by ECD and ICP-MS after GC separation 总被引:1,自引:0,他引:1
Inductively coupled plasma-mass spectrometry (ICP-MS) was coupled to a gas chromatographic (GC) system with electron capture detector (ECD), which enables relatively easy characterization and quantification of brominated and iodinated (halogenated) volatile organic compounds (HVOCs) in aquatic and air samples. The GC-ECD system is connected in series with an ICP-MS by a directly heated transfer line and an outlet port-hole for elimination of the ECD make-up gas during ignition of the plasma. The hyphenated GC-ECD/ICP-MS system provides high selectivity and sensitivity for monitoring individual HVOCs under fast chromatographic conditions. The ECD is most sensitive for the detection of chlorinated and brominated but the ICP-MS for iodinated compounds. The greatest advantage of the use of an ICP-MS is its element-specific detection, which allows clear identification of compounds in most cases. The absolute detection limits for ICP-MS are 0.5 pg for iodinated, 10 pg for brominated, and 50 pg for chlorinated HVOCs with the additional advantage that calibration is almost independent on different compounds of the same halogen. In contrast to that detection limits for ECD vary for the different halogenated compounds and lie in the range of 0.03-11 pg. The two-dimensional GC-ECD/ICP-MS instrumentation is compared with electron impact mass spectrometry (EI-MS) and microwave induced plasma atomic emission detection (MIP-AED). Even if EI-MS has additional power in identifying unknown peaks by its scan mode, the detection limits are much higher compared with GC-ECD/ICP-MS, whereas the selective ion monitoring mode (SIM) reaches similar detection limits. The MIP-AED detection limits are at the same level as EI-MS in the scan mode. 相似文献
84.
Regulation of polar cap formation in the life cycle of Escherichia coli 总被引:48,自引:0,他引:48
85.
Helmut Schwarz Chrysostomos Wesdemiotis Ferdinand Bohlmann 《Journal of mass spectrometry : JMS》1974,9(12):1223-1225
The electron-impact-induced elimination of piperidine from the title compound could be established by investigation of the unsymmetrically 2H-labelled compound. The mechanism of a 1,1-elimination can be excluded be unequivocally. 相似文献
86.
87.
Nils Siegbahn Mats-Olle Maånsson Klaus Mosbach 《Applied biochemistry and biotechnology》1987,12(2):91-105
A soluble, bifunctional enzyme complex has been prepared by crosslinking lactate dehydrogenase and alcohol dehydrogenase with
glutaraldehyde. The crosslinking was performed on a solid phase while the active sites of alcohol dehydrogenase and lactate
dehydrogenase were held adjacent to one another with the aid of a bis-NAD analog. Subsequently, the enzyme complex was released
from the solid phase. The soluble enzyme complex was then purified by using NAD-Sepharose as an affinity adsorbent. Based
on gel filtration experiments, the complex was estimated to consist of one of each dehydrogenase.
By using a third enzyme, lipoamide dehydrogenase, which competes with lactate dehydrogenase for NADH produced by alcohol dehydrogenase,
the effect of site-to-site orientation was studied. It was found that about 83% of the NADH produced by alcohol dehydrogenase
was oxidized by site-to-site oriented lactate dehydrogenase compared to a figure of only about 61% obtained in an identical
system of separate enzymes. This indicates that given two alternative routes, the preference for the one to lactate dehydrogenase
over the one to lipoamide dehydrogenase is enhanced when lactate dehydrogenase and alcohol dehydrogenase are site-to-site
oriented. 相似文献
88.
89.
Synthesis of the Stannatetraphospholanes (tBuP)4SnR2 (R = tBu, nBu, C6H5) and (tBuP)4Sn(Cl)nBu Molecular and Crystal Structure of (tBuP)4Sn(tBu)2 The reaction of the diphosphide K2[tBuP-(tBuP)2-PtBu] 4 with the halogenostannanes (tBu)2SnCl2, (nBu)2SnCl2, (C6H5)2SnCl2 or nBuSnCl3 in a molar ratio of 1 : 1 leads via a [4 + 1]-cyclocondensation reaction to the stannatetraphospholanes (tBuP)4SnR2 3 b–3 d and (tBuP)4Sn(Cl)nBu 3 e , respectively, with the binary 5-membered P4Sn ring system. 3 b was characterized by a single crystal structure analysis; the 5-membered ring exists in a planar conformation. The compounds 3 b–3 e were identified by NMR and also by mass spectroscopy; the 31P{1H}-NMR spectra of 3 b–3 d showed an AA′MM′ (AA′MM′X), 3 e on the other hand an ABCD (ABCDX) spin system. 相似文献
90.
Sigmar Spauszus Claus Schwarz und Hans -Jürgen Weigel 《Fresenius' Journal of Analytical Chemistry》1961,182(3):184-192
Zusammenfassung Einige der üblichen Methoden zur Phosphorbestimmung in wolframlegierten Stählen werden unter Anwendung von 185W und 32P einer Nachprüfung unterzogen. Dabei erweisen sich die Phosphorverluste durch Adsorption an dem Wolframsäureniederschlag als gering, so daß sie bei weniger anspruchsvollen Bestimmungen unberücksichtigt bleiben können. Erheblich größer sind dagegen die Fehler, die durch Mitfällung von Wolframsäure mit dem Ammoniummolybdatophosphatniederschlag entstehen können. Es werden zwei Methoden angegeben, nach denen eine quantitative Abtrennung des Wolframs und damit eine sichere Bestimmung des Phosphors möglich ist.Herr Prof. Dr.-Ing. K. Schwabe ermöglichte es uns freundlicherweise, die Untersuchungen mit radioaktivem Wolfram und Phosphor im Zentralinstitut für Kernphysik Rossendorf, Bereich Radiochemie, durchzuführen. Ihm sei auch an dieser Stelle herzlichst gedankt. 相似文献