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  • Analytical Chemistry and Spectroscopy  (126)
  • 2000-2004
  • 1990-1994  (126)
  • 1980-1984
  • 1945-1949
  • 1940-1944
  • 1992  (126)
Collection
Keywords
Publisher
Years
  • 2000-2004
  • 1990-1994  (126)
  • 1980-1984
  • 1945-1949
  • 1940-1944
Year
  • 1
    Electronic Resource
    Electronic Resource
    Structural characterization of sulfonated azo dyes using liquid secondary ion mass spectrometry/tandem mass spectrometry (1992)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 27 (1992), S. 289-299 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Eight monosulfonated and disulfonated azo dyes were analyzed using liquid secondary ion mass spectrometry/tandem mass spectrometry, in the negative ion mode, under low-energy collision conditions (110-150 eV). Many structurally characteristic fragment ions were obtained, several of which have not been reported previously using other mass spectrometric techniques. Among the structurally important ions observed were those due to loss of SO2, SO3 and various aromatic substituents, such as NO2 and NHCOCH3. Losses of N2 were also proposed. In addition, product ions due to cleavage at the azo linkage were observed, and also SO3- and HSO3- ions. Several of the azo cleavage product ions detected did not contain sulfonate groups. Possible pathways for the formation of product ions are proposed. The structural information obtained should help to better characterize and identify sulfonated azo dyes in the future.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210270322
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  • 2
    Electronic Resource
    Electronic Resource
    Gas chromatographic/mass spectrometric characteristics of 16-androstenes, saturated analogues and their derivatives (1992)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 21 (1992), S. 160-164 
    Details
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper we have presented gas chromatographic retention times and characteristic mass spectrometric fragmentation patterns for the 16-androstenes, 5α- and 5β-androst-16-en-3α- and 3β-ols, 5,16-androstadien-3β-ol, 5α-and 5β-androst-16-en-3-one and 4,16-androstadien-3-one, and their isomeric saturated analogues. The behaviour of these underivatized steroids has also been compared with the trimethylsilyl ethers, tert-butyldimethylsilyl ethers and acetyl esters of the alcohols, together with the methoximes and pentafluorobenzyloximes of the ketones. A number of gas chromatographic elution patterns have emerged from this study: (i) the retention times of the underivatized saturated compounds were generally longer than those of the corresponding 16-androstenes; (ii) retention times of androstanones were generally longer than those of corresponding 16-unsaturated steroids; (iii) resolution of the 5,16-androstadien-3β-ol from 16-androsten-3β-ol was extremely difficult; (iv) the syn- and anti- forms of pentafluorobenzyloximes of all ketones studied were resolved but this was not so for all of the methoximes. From a study of the fragmentation patterns of the various steroidal alcohols, ketones and their derivatives, two or three ions are suggested which are suitable for selected ion monitoring (SIM). For quantification of 16-androstenones O-methoximes, choice of M+, [M - 15]+ or [M - 60]+ is available for SIM, the exact fragmentation being characteristic of the steroid concerned. These derivatives did not give such intense mass ions as the underivatized ketones or pentafluorobenzyloximes. The latter oximes again showed marked differences in fragmentation patterns between steroids.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200210308
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  • 3
    Electronic Resource
    Electronic Resource
    Matrix-assisted laser desorption with ultra-short laser pulses (1992)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 6 (1992), S. 187-191 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: An excimer pumped dye laser generating ultra-short (560 fs full width at half maximum, FWHM) pulses in the ultraviolet (UV, 248 nm) and visible (496 nm) spectral ranges is used to desorb protein ions from different matrices. The effects of laser-light energy and power density on secondary-ion yields from insulin are reported. These data are compared to data obtained by employing a nitrogen laser (337 nm, 3 ns FWHM). The existence of a threshold energy density for the matrix-asisted laser desorbtion (MALD) of insulin ions by the ultra-short pulses is established. This threshold energy is of the same order of magnitude for the two laser systems employed and does not depend on the laser pulse length (the energy deposition time). Thus we demonstrate that the amount of laser energy deposited into the sample, rather than the laser power, is the important parameter in the MALD process.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290060307
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  • 4
    Electronic Resource
    Electronic Resource
    Thermally assisted electrospray interface for liquid chromatography/mass spectrometry (1992)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 6 (1992), S. 727-733 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: An electrospray interface for liquid chromatography/mass spectrometry (LC/MS) is described that combines the direct heating of High-performance liquid chromatography (HPLC) effluent that is characteristic of thermoooospray-type interfaces. This interface is called the thermally assisted electrospray interface for LC/MS. The device can accept the total effluent from a liquid chromatograph at flow rates ranging up to 500 μL/min. The HPLC effluent is nebulized into charged droplets by a combination of heat and an applied electric field. Ions emitted from charged droplets are mass-analyzed by a triple quadraupole mass spectrometer equipped with an atmospheric pressure ion sampling orifice. Singly or multiply charged ions, indicating the molecular weight of a sample, are observed with minimal fragmentation. The extent of multiple charging observed in electrospray and ion spray mass spectrometry is decreased somewhat in thermally assisted electrospray. Labile compounds which undergo thermal decomposition by conventional thermospray show no decomposition with thermally assisted electrospray.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290061204
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  • 5
    Electronic Resource
    Electronic Resource
    Electrospray mass spectrometry of Malayan pit viper (Calloselasma rhodostoma) venom (1992)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 6 (1992), S. 724-726 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A high-performance liquid chromatography protocol has been developed for the analysis of snake venoms. This system has been used to isolate eight fractions from Malayan pit viper (Calloselasma rhodostoma) venon. The fractions have been analysed using electrospray mass spectrometry. A number of major components were found with masses ranging from 13670 to 22750 Da.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290061203
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  • 6
    Electronic Resource
    Electronic Resource
    Unimolecular reactions of ionized methyl allyl ether (1992)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 27 (1992), S. 905-915 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fragmentation of CH2=CHCH2OCH3+· cation-radicals has been investigated by means of 2H- and 13C-labelling experiments and by analysis of collision-induced dissociation spectra. Metastable C4H8O+· species decompose via one of three main channels which involve loss of (a) a hydrogen atom, (b) a methyl radical or (c) a formaldehyde molecule. Extensive, but not complete, exchange of the hydrogen and deuterium atoms in specifically labelled C4H8-nDnO+· analogues precedes each of the three fragmentation pathways. The role of distonic ions in the rearrangement steps which bring about hydrogen exchange is discussed. The influence of isotope effects on the relative rates of the major reactions and the associated kinetic energy releases is examined. Only loss of a hydrogen atom is subject to a substantial isotope effect. Elimination of a methyl radical releases a large amount of kinetic energy, as is shown by the broad and dish-topped appearance of the corresponding metastable peak (T1/2 ≈ 42 kJ mol-1). The carbon atom of the original methoxy group is specifically expelled in this process. Both the large T1/2 value and the unusual site selectivity are atypical of methyl and other alkyl radical losses from ionized alkenyl methyl ethers. The carbon atom of the methoxy group also participates specifically in formaldehyde elimination, but the two hydrogen atoms are not always selected from the three contained in the initial methoxy group. The implications of these labelling results for the synchronicity of concert of formaldehyde loss, which can be formu lated as a pericyclic process, is analysed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210270812
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  • 7
    Electronic Resource
    Electronic Resource
    Fragmentations and rearrangements of metastable [C2H5OS]+ ions (1992)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 27 (1992), S. 1131-1133 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several [C2H5OS]+ ions with different structures were generated from the appropriate precursors and their metastable ion spectra were determined. Deuterium labelled analogues of some of the [C2H5OS]+ ions were used to elucidate the nature of the observed fragmentations and their mechanisms. [C2H5OS]+ ions with different C—O—S skeletons were found to give different fragmentation reactions. There are no indications for fast isomerization reactions leading to common intermediates before fragmentation. Most of the observed fragmentations can occur directly from the initial structures.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210271025
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  • 8
    Electronic Resource
    Electronic Resource
    Internal energy deposition in doubly charged tungsten hexacarbonyl on charge exchange at high energy with atomic and molecular targets (1992)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 27 (1992), S. 769-776 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Charge exchange of W(CO)62+ in the course of 7 keV collisions with various targets results in singly charged ions which are highly internally excited. The distribution of internal energies estimated by the degree to which consecutive fragmentations by CO loss occur is broad and includes very high energies (up to 15 eV). This result is inconsistent with exclusive operation of long-range electron transfer e.g. by either a curve crossing or Demkov mechanism; rather it suggests that direct excitation to a high-energy repulsive state of the products also occurs perhaps by an electronic excitation mechanism. The nature of the internal energy distribution suggests mechanistic analogies with simple collisional activation. Different target gases give rise to different average internal energy depositions monatomics and diatomics yielding higher energy depositions than do polyatomic targets. There is an approximate correlation between energy deposition and target ionization energy which is consistent with the proposed excitation mechanism considering the shapes of the potential energy surfaces. When the detailed internal energy distributions are compared characteristic differences are seen for individual targets. The efficiencies of the various targets at producing charge exchange were also compared. Large differences were found with the polyatomic targets having the greatest efficiencies. In addition a rough correlation was observed between the extent of charge exchange and target ionization energy and this is interpreted in terms of greater contributions from the long-range electron transfer process for targets of lower ionization energy. All the results are also consistent with contributons from more violent collisions which involve electron transfer at relatively small internuclear distances where the shapes of the potential surfaces are strongly dependent on distance.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210270702
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  • 9
    Electronic Resource
    Electronic Resource
    Formation and decay of doubly charged ions in n-alkanes from methane to triacontane (1992)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 27 (1992), S. 855-863 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Coincidence techniques were used to study dissociative double ionization of selected n-alkanes from methane to triacontane (C30H62) and of the hexane isomers. Following photoionization at 40.8 eV, both covalent and coulombic dissociations of the molecular dications take place. The main decay route of doubly charged alkanes larger than butane is fast charge separation followed by secondary dissociation of energetic singly charged primary ions. A simulation based on quasi-equilibrium theory and the spectra of the isomers confirm this breakdown mechanism for hexane.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210270803
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  • 10
    Electronic Resource
    Electronic Resource
    Decompositions of ammonium adducts of some isomeric sesquiterpene alcohols under collisional activationCDRI Communication No. 4589. (1992)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 27 (1992), S. 1134-1138 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The decompositions of the ammonium adducts of some sesquiterpene alcohols have been studied using collisional activation mass spectrometry. Losses of ammonia and water are the two primary fragmentation pathways of these adduct ions. Some of the isomeric pairs show differences in the abundances of the fragment ions, whereas others give similar ion abundances in the two isomers.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210271026
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