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Argon and mixtures of argon with carbon dioxide in the range of 1–50% have been used as moderator gases for negative ion production in an electron impact ion source of a VG ZAB-2F mass spectrometer. The enhancement of quasi-molecular anion ([M – H]?) currents of oxygen-containing samples has been studied. It is a function of the composition of moderator gas mixture, moderator gas pressure, and sample pressure in the ion source. Most intensive quasi-molecular anion currents have been observed at a pressure in the ion source of c. 2.5 × 10?5 Torr (measured by the ion gauge remote from the ion source of the ZAB-2F) using a moderator gas mixture of 10% CO2 in argon. Fragmentation of the samples may be increased by increasing the concentration of CO2 in the moderator gas. 相似文献
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Mycelium Products in Higher Fungi. I. Phenoxazine Derivatives in Calocybe gambosa. Phenoxazone and α-Amino-phenoxazone have been detected in cultured mycelium of Calocybe gambosa (FR .) DONK . 相似文献
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Martin J. Farncombe Keith R. Jennings Rod S. Mason Urs P. Schlunegger 《Journal of mass spectrometry : JMS》1983,18(12):612-616
The amino acid sequence of three simple peptides has been determined by the technique of metastable mapping. The products of decompositions in the first field free region of a forward geometry double focussing mass spectrometer are studied by decreasing the electric sector field between scans of the magnetic field. 相似文献
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Hansjrg Walther Urs Peter Schlunegger Felix Friedli 《Journal of mass spectrometry : JMS》1983,18(12):572-575
The B2E = constant linked scan is shown to be an excellent tool for quantifications with reversed geometry mass spectrometers. Deuterium-labelled analogues may be used as internal standards, thus providing very simple clean-up procedures. The principle is demonstrated with the example of chloro-substituted benzoic acid methyl esters. Possible interferences arising from isotope peaks are discussed. The method is applied to the quantification of caffeine in beverages. 相似文献
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A fully automated computer-controlled system was used to generate series of different linked scans at constant B2E and constant neutral loss in the second field-free region. This system has been shown to be suitable for deriving the amino acid sequence of oligopeptides. 相似文献
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H Reinhard R Lauber U P Schlunegger 《Rapid communications in mass spectrometry : RCM》1989,3(4):95-99
The positive electron ionization and negative chemical ionization mass spectra of 15 different derivatives of the tripeptide Phe-Ala-Leu have been compared. Total ion currents and ion currents of sequence-characterizing ions have been measured and compared. The negative-ion spectra, using 10% carbon dioxide in argon as moderator gas, proved to be simpler and contained more abundant sequence ions than the positive electron ionization spectra. 相似文献
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Urs Peter Schlunegger 《Angewandte Chemie (International ed. in English)》1975,14(10):679-688
“Direct Analysis of Daughter Ions” (DADI) can be carried out with commercial mass spectrometers embodying the Nier-Johnson inverse geometry. DADI measurements permit experimental detection of the consecutive formation of molecule fragments (fragment genesis). Knowledge of fragment genesis enables the chemist to clarify the fragmentation processes of molecule-ions and provides information on the structure of fragments formed in the mass spectrometer. In combination with classical mass spectrometry such information makes it easier to determine the structure of compounds, to analyze mixtures, to determine the sequence in periodically constructed molecules, for example oligopeptides, and to study rearrangement reactions occurring in the mass spectrometer. 相似文献
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Urs Peter Schlunegger Samuel Leutwyler Felix Friedli Rolf Scheffold 《Helvetica chimica acta》1975,58(1):65-73
The structure of the fragment-ion m/e 178 of the title compound was elucidated by the analysis of its formation and its subsequent fragmentation, using DADI, defocussing, peak matching, and deuterium labeling. 相似文献