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  • Artikel  (15)
  • Analytical Chemistry and Spectroscopy  (15)
  • 1980-1984  (15)
  • 1
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 12 (1983), S. 2-7 
    ISSN: 0049-8246
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: Two common methods of applying dead-time corrections in EDS systems, both of which are carried out internally in the electronics, are examined. The Barnhart method shows serious discrepancies when making dead-time corrections and in certain cases no correction is made at all. The problem is associated with the reliance on the fast amplifier to count all x-rays collected by the detector. In practice, however, the fast amplifier does not always succeed in carrying out this function since x-rays with energies 〈 1500 eV may fall below its threshold level. The problems become worse when a formvar window is substituted for beryllium since a greater proportion of low energy x-rays can now reach the detector. The magnitude of the discrepancy is shown also to be a function of specimen and electron accelerating voltage. Similar experiments with an EDS system using the Covell method show that no such discrepancies arise.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 13 (1984), S. 69-77 
    ISSN: 0049-8246
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: A study of the low-energy region (below 1. 5 keV) of energy dispersive x-ray spectra has been carried out. Firstly, because some counting systems do not provide a reliable dead time correction, a new method of dealing with the problem is given. Next, the effects of different positioning of the energy discriminator within the analyser circuitry are discussed with reference to the consequences for light element analysis. Electronic noise counts can present a problem for analysis of x-rays of less than 300 eV and a straightforward method for noise removal is described. Finally, an unexpected artifact in the spectrum below 500 eV is identified; its size is related to the total number of counts in the spectrum and a practical method of dealing with it is demonstrated. Once the above factors have been taken into account a low energy spectrum is produced, consisting solely of characteristic x-ray lines and a true continuum background.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 176-179 
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Chemical ionization mass spectrometry and mass analyzed ion kinetic energy spectrometry in conjunction with collision induced dissociation are used to study the fragmentation behavior of a series of α,ω-hydroxyalkylamines. The difference between the ionic population present at equilibrium in the source, and that which is sampled under nonequilibrium conditions, is revealed in the striking differences observed in product distributions in the chemical ionization mass spectra and the mass analyzed ion kinetic energy spectra. The major fragmentations in the mass analyzed ion kinetic energy spectra, loss of NH3 and H2O, show large variations in intensity as a function of the chain length between the hydroxy and amino functionalities. These results are rationalized through analysis of the relevant thermochemical data.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 18 (1983), S. 418-422 
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: It has been noticed that the major part of the loss of ṠH from the molecular ion of most of the o-methoxythioamides results from an ortho effect of the methoxy group. Comparison of the MIKE spectra of the [M—SH]+ of 1-(2-methoxyphenylthioxomethyl)piperidine and 1-(2-methoxyphenylthioxomethyl)pyrrolidine with the MIKE spectra of [M—SH]+ of the corresponding unsubstituted compounds, reported earlier, indicated two parallel pathways for the formation of [M—SH]+ in the o-methoxy compounds. In the first pathway, as has been noticed in thioamides in general, the loss of ṠH involves the migration of either the α-hydrogen in the amine moiety or the hydrogen attached to nitrogen. In the second pathway, the migration of a hydrogen from the o-methoxy group to the sulphur atom followed by ejection of SH from the molecular ion leads to a stable cyclized ion. Interesting secondary fragmentations as a consequence of this ortho effect have also been noticed.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 19 (1984), S. 457-458 
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 13 (1980), S. 143-147 
    ISSN: 0030-4921
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Two resonance lines were observed in 2,6-dichlorobenzamide, both in liquid nitrogen and at room temperatures, using a self quenched super-regenerative NQR spectrometer. Analysis of the Zeeman effect on the two lines using an uncut crystal grown from solution reveals: (1) the crystal belongs to the orthorhombic system; (2) there are two crystallographically equivalent but physically non-equivalent directions for the principal field gradient making an angle of 71° for the low frequency line, and four such directions for the high frequency line; (3) the directions of the crystalline axes a, b and c are tentatively fixed as (90°, 90°), (90°, 90°) and (0°, - ); (4) from morphological studies a: b: c are estimated as 0.959 ± 0.005: 1:1,402 ± 0.005 and, from the estimated density (1.440 gms/cc) of the crystal, the absolute values a, b, c are calculated, on the basis of four molecules per unit cell, as a = 8.33 Å, b = 8.68 Å and c = 12.18 Å; (5) there are a mininium of four molecules per unit cell; the four molecules lie in four different planes which are, however, connected by symmetry operations. There is an inplane bending by 6.5° between the two C—Cl bonds away from one another and (6) the ionic, single bond and double bond characters for both chlorines are almost equal and are in the ratio 25:72:3.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 15 (1980), S. 220-220 
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 17 (1982), S. 409-415 
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Interesting skeletal rearrangements, resulting in the formation of unexpected fragments, have been noticed in the mass spectra of aromatic thioamides of cyclic amines such as piperidine, morpholine and pyrrolidine. Suitable mechanisms, based on mass analysed ion kinetic energy spectra, high voltage scan spectra and high resolution data, have been proposed for the formation of [M—SH]+ ions and the fragment at m/z (103+R) in the mass spectra of these compounds. The mass spectra of the thioamides of non-cyclic amines and the thioamides of aliphatic acids contain peaks corresponding to a four-centred skeletal rearrangement followed by the elimination of either the thioalkoxy or the thiophenoxy radical from the molecular ions.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 18 (1983), S. 162-167 
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Interesting competitive oxygen migrations from the nitro group to the nitrogen and to the sulfur have been noticed during the mass spectral decomposition of ortho nitro aromatic thioamides on electron impact. The migration of the oxygen to the nitrogen of the thioamide function results in the formation of stable o-nitrosothiobenzoyl cation. The other novel ortho effect noticed in the ortho isomers is the transfer of an oxygen from the nitro group to the sulfur followed by the ejection of SO from the molecular ions. A mechanism involving the initial oxygen migration to the sulfur through a favourable 6-membered transition state followed by cyclization with the concomitant expulsion of SO is proposed for this process. Other interesting decomposition processes occurring as a consequence of this ortho effect have also been noticed. The proposed mechanisms for these processes are supported by mass analysed ion kinetic energy spectra and high voltage scans.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 499-501 
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Simultaneous hydrogen transfers - one from the methoxy group and the other from the alkyl group - to both the oxygen atoms of the ester function result in the formation of a common ion at m/z 152 in the alkyl o-methoxybenzoates on electron impact. Expulsion of the formyl radical from this ion leads to a fragment resembling the protonated benzoic acid. Another novel feature in these compounds is the loss of H2O from the [M—R]+ ion which arises through an ortho effect during a secondary fragmentation process.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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