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  • 1
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Two kerogen samples from shales of different geological age, selected from each of Types I, II and III, have been characterized by matrix-assisted laser desorption ionization mass spectroscopy (MALDI-MS). A Kratos Kompact MALDI III time-of-flight mass spectrometer equipped with a nitrogen laser operated at 337 nm was used on samples mounted in a matrix of sinapinic acid. The spectrometer was used in linear mode with a mass range up to 270 000 u and an ion extraction voltage of 20 kV. Individual spectra from 50 laser shots at low laser fluence were summed for each spectrum. The present study is a first attempt at characterizing kerogens by MALDI-MS. At low mass (200-500 u) families of peaks consisting of overlapping homologous series of apparently polar compounds have been observed: these peaks appear to be distinct from those due to the matrix material. In higher mass regions of the spectra, continua of masses extending from 1000 u up to around 10 000 u were observed; ions at higher masses were separated to baseline up to masses of 50 000 u. Evidence was found for a relationship between the minimum laser power sufficient for activating the MALDI-ionization process and the geological age of the kerogens; the laser power decreased as the geological age increased. In the case of one kerogen, a high laser fluence was used to generate molecular ions up to the detection limit of the mass spectrometer, in excess of 260 000 u. This paper presents results from a preliminary study of kerogens which requires an in-depth examination of the desorption process in complex mixtures.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Steviol (ent-13-hydroxykaur-16-en-19-oic acid), the aglycone of various plant-derived glycoside sweeteners consumed by human populations, is known to be mutagenic toward Salmonella typhimurium strain TM677 when metabolically activated using a 9000 × g supernatant fraction derived from the liver of Aroclor 1254-pretreated rats. Mass spectral analysis of this diterpenoid and some analogs revealed characteristic patterns reflecting differential stereochemistry at the C/D rings and variations in the nature of the substituents present. Such information has been used to help identify several in vitro metabolites of steviol in conditions known to produce a mutagenic response, when analyzed by human populations, is known to be mutagenic toward Salmonella typhimurium strain TM677 when metabolically be allylic oxidation and epoxidation. 15-Oxosteviol, a product of oxidation of the major steviol metabolite, 15α-hydroxysteviol, was found to be a direct-acting mutagen.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 235-238 
    ISSN: 0935-6304
    Keywords: Cryogenic modulation ; LMCS ; GC×GC ; multidimensional GC ; comprehensive gas chromatography ; petroleum analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 2 (1975), S. 126-130 
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is described for the micro-identification of both mono- and diesters of 12-deoxyphorbol based upon a combination of thin-layer chromatography and mass spectrometry. The technique may be used on as little as 5 ml of fresh plant latex. Nine thin-layer systems are described, six of which are adsorption systems based on silica gel or alumina as adsorbent, and three are partition systems using diethyleneglycol as stationary phase. The migration by means of thin-layer chromatography is dependent upon the chain length of the C-13 esterifying acid and on the presence or absence of a free primary hydroxyl group at C-20. By means of mass spectrometry it was possible to confirm the identity of the esterifying moiety at both the C-13 and C-20 positions of 12-deoxy-4βOH-phorbol.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 4 (1977), S. 331-336 
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mass spectra of grayanotoxin III and some of its mono-, di-, and tri-ester derivatives are discussed. Some of the physiological reponses of this compound class are also presented. The extraction of this material from a natural source is discussed as well as the schemes for ester derivatization and spectral characterization of all compounds studied. High resolution mass spectral analysis and comparison of the mass spectra of similar compounds were used to define possible fragmentation mechanisms.
    Additional Material: 8 Ill.
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  • 6
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use the naturally occurring ent-kaurene diterpene glycoside, stevioside, as a sucrose substitute in several countries has resulted in the need for improved methods to analyze its potential metabolites. Altogether 21 diterpenes related in structure to steviol, the aglycone of stevioside, have been subjected to desorption chemical ionization mass spectrometry using methane, ammonia and dimethyl ether as reagent gases. Both methane and ammonia provided the molecular weights of these derivatives, but failed to produce any adduct ions of particular diagnositc value for differentiating compounds in the steviol series. On the other hand, dimethyl ether produced positive ion chemical ionization spectra that differed according to the nature of the functional groups represented among the steviol derivatives examined. Prominent adduct ions observed using dimethyl ether were [M + 1 - 18]+, [M + 1]+, [M + 45 - 32]+, [M + 45]+ and [M + 47]+. Mechanisms have been proposed for the formation of these adducts.
    Additional Material: 6 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 19 (1996), S. 403-408 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Cryogenic trapping ; Capillary ; Focusing ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cryogenic trapping of solutes leads to narrowing of the chromatographic band. By placing the trap at the end of a capillary column, it is possible to study the effectiveness of the trap in terms of producing a sharpened elution profile. The trap may be heated by supplementary heating, but here convective heating from the GC oven is employed simply by turning off the cryogenic coolant. It is estimated that it takes about 50 s for the trap to heat up sufficiently to allow trapped solute to be remobilized, although this depends upon the oven temperature and thermal mass of the trap. It can also be shown that the more volatile solutes mobilize faster from the trap in this particular mode of operation. The recovery of trapped components shows that there is essentially quantitative trapping, and the solutes are trapped just at the leading edge of the trap.
    Additional Material: 4 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 19 (1996), S. 622-626 
    ISSN: 0935-6304
    Keywords: Multidimensional capillary chromatography ; Polychlorinated biphenyls ; PCBs ; Congener ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Multidimensional chromatography was used to resolve the specific chlorobiphenyl (CB) congeners 28, 52, 101, 118, 138, 153, and 180 in technical aroclor standards. Single column analysis of polychlorinated biphenyls (PCBs) results in co-elution of key congeners with other components in the mixture; therefore using two columns of different selectivity was necessary to enhance the resolution achievable on just one column. The HT8 column (8% phenylpolycarborane-siloxane phase) has been reported to have specific selectivity characteristics for improved PCB separation. When coupled with a BPX5 column (5% phenylpolysiloxane-silphenylene phase), it has been shown here to provide unambiguous identification of 7 marker compounds which are used to monitor PCB occurrence and distribution. All seven marker CBs are present in aroclor 1254, and by adjusting the size of the heartcut window, it was possible to obtain resolution of the marker congeners from other congeners. Single column analysis is unable to achieve this result. This offers an alternative to GC-MS analysis.
    Additional Material: 3 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 620-622 
    ISSN: 0935-6304
    Keywords: Multidimensional gas chromatography ; comprehensive two-dimensional gas chromatography ; kerosene analysis ; cryogenic modulation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 245-252 
    ISSN: 0935-6304
    Keywords: LMCS ; cryogenic modulation ; comprehensive gas chromatography ; GC×GC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Comprehensive gas chromatography is the realization of true continuous multidimensional (dual column) gas chromatography. The key requirement in the comprehensive GC experiment is that the second dimension analysis is completed in a rapid time-frame compared to the elution of components in the first dimension, and that the two coupled dimensions represent ‘orthogonal’ analyses towards the analytes to be separated. The former normally necessitates pulsing of contiguous segments of each chromatographic band from the first to the second dimensions. The two dimensions should be in fluid communication. The comprehensive GC×GC experiment passes all the column flow from the first column to the second column, leading to no sample loss, but this also requires a suitable method for time- or zone-compression of the band to be pulsed to the second column. The final pulse should be narrow, and should be delivered to the second column quickly. A simple procedure can achieve this using the cryogenic modulator that has been recently described by this group. The system uses a cryogenic trap which can be moved away from the cooled zone of the column faster than 10 ms. A fast-acting pneumatic ram achieves this performance. The cooled column heats up to the prevailing oven temperature within 10-15 ms. Molecules as volatile as C5 alkanes or small aromatics will be fully retained by the trap within the period of modulation used for GC×GC. The technique is simple to implement and requires no special column connections. Using a gas chromatograph which allows control of external events and can acquire from a detector at 50 Hz or faster, and a timing controller for modulation, the comprehensive result can easily and effectively be achieved.
    Additional Material: 7 Ill.
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