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  • Analytical Chemistry and Spectroscopy  (15)
  • Earth model, also for more shallow analyses !  (5)
  • 1980-1984  (20)
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  • 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
    Organic Magnetic Resonance 16 (1981), S. 123-125 
    ISSN: 0030-4921
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Two NQR lines were observed for 35Cl in 2,5-dichloro-4-nitroaniline at room temperature, using a self-quenched super-regenerative spectrometer. Analysis of the Zeeman effect on the two lines using a cylindrical single crystal reveals that the crystal belongs to the monoclinic system. The principal field gradient Z axes enclose an angle of 35° and 28° in the cases of the low and high frequency resonance lines, respectively. The b axis is parallel to 81°, 280°. The unit cell contains either two or a multiple of two molecules. The molecules in the crystal can be arranged into two sets, with the molecular planes in each set being parallel among each other. The angle subtended between the two planes is 159° and each of the planes is inclined to the b axis at an angle of 79.5°. There is an in-plane bending of the two C—Cl bonds by 5.5°. The ionic, single bond and double bond characters of the C—Cl bonds for both chlorines are almost equal, and are in the ratio 24:73:3.
    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 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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  • 5
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 17 (1982), S. 465-469 
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The mass spectrum of o-picolinotoluidide gives rise to three major fragments at m/z 184, m/z 169 and m/z 168, corresponding to the loss of CO from the molecular ion followed by the loss of ṄH2 and ĊH3 by independent pathways. It has been shown that the ortho methyl group and the nitrogen of the pyridine ring in the 2-position are involved in the formation of these three major fragments observed in the mass spectrum of o-picolinotoluidide. The mass spectrum of 2-(o-toluidino) pyridine, the molecular ion of which can resemble the [M—CO]+ ion in o-picolinotoluidide, also shows loss of CH3 and NH2 radicals from the molecular ions. Based on these observations coupled with the high resolution data, the mass analysed ion kinetic energy spectrometry and high voltage scans of these fragments in both the compounds, two mechanistic pathways have been proposed for the formation of these ions in o-picolinotoluidide.
    Zusätzliches Material: 4 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 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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  • 8
    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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  • 9
    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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  • 10
    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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