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  • 1
    ISSN: 1432-0517
    Keywords: Key words Trace elements ; Water ; Intercomparison ; Comparability ; Traceability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract  The sixth round of the International Measurement Evaluation Programme (IMEP) is presented. The programme offers reference values, established by primary methods of measurement, against which participating laboratories can evaluate their performance. The degree of comparability is thus established against the most objective references available at present. In IMEP-6, reference values for total concentrations of 14 trace elements in a synthetic and a natural water were established mainly by isotope dilution mass spectrometry (IDMS). For the majority of the measurands, results traceable to the international system of units (SI) and having expanded uncertainties, U (k=2), of 2% could be established. Measurements results from 165 field laboratories in 29 countries are evaluated and presented as descriptive (regional, national and intercontinental) pictures of the participants' self-declared degree of experience, status of accreditation, performance (including target values for uncertainty set by authorities) and instrumental methods used. The participants' use of certified reference materials and calibrants has been documented, and some comments on this matter are raised. The results and characteristics for IMEP-6 are compared with those of IMEP-3 (1991–1993) and discussed in view of the forthcoming IMEP-9 (1998).
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5001
    Keywords: AIDS ; DYANA ; HIV-1 ; NMR structure ; ribonuclease H ; RNA-DNA hybrid ; torsion angle dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract A high-quality NMR solution structure of the chimeric hybrid duplex r(gcaguggc)⋅r(gcca)d(CTGC) was determined using the program DYANA with its recently implemented new module FOUND, which performs exhaustive conformational grid searches for dinucleotides. To ensure conservative data interpretation, the use of 1H-1H lower distance limit constraints was avoided. The duplex comprises the tRNA–DNA junction formed during the initiation of HIV-1 reverse transcription. It forms an A-type double helix that exhibits distinct structural deviations from a standard A-conformation. In particular, the minor groove is remarkably narrow, and its width decreases from about 7.5 Å in the RNA/RNA stem to about 4.5 Å in the RNA/DNA segment. This is unexpected, since minor groove widths for A-RNA and RNA/DNA hybrid duplexes of ∼11 Å and ∼8.5 Å, respectively, were previously reported. The present, new structure supports that reverse transcriptase-associated RNaseH specificity is related primarily to conformational adaptability of the nucleic acid in 'induced-fit'-type interactions, rather than the minor groove width of a predominantly static nucleic acid duplex.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Fast-atom bombardment, thermal ionization and inductively coupled plasma mass spectrometry are contrasted in comparative measurements of 64Zn/67Zn isotope ratios on samples isolated in the course of a human mineral-nutrition experiment. The data are evaluated with reference to the precision normally required in enriched stable-isotope mineral-nutrition studies, and the convenience of the mass spectrometric techniques is also compared.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Mass Spectrometry Reviews 11 (1992), S. 41-67 
    ISSN: 0277-7037
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 6 (1972), S. 1207-1215 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Mass spectra of eleven bridged aza bicyclic derivatives have been recorded. In all cases, the fragmentation is clean and characteristic. A clearcut stereochemical effect on fragmentation is observed on two pairs of epimers.
    Notes: Les spectres de masse d'une série de dérivés aza-bicycliques pontés sont examinés Dans la totalité des cas, la fragmentation est à la fois simple et caractéristique. De plus, sur deux couples d'épimères, on observe un effet stéréochimique, se traduisant par des fragmentations nettement différenciées.
    Additional Material: 2 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 12 (1985), S. 477-488 
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The main ionization methods in a mass spectrometer for isotope ratio determinations of the elements are discussed in this review. These methods are thermal ionization, spark source, electron impact, inductively coupled plasma and field desorption. As concerns thermal ionization, electron impact and field desorption, a survey of the possibilities of isotope analyses in the periodic table of the elements is given. Besides kinetic studies, trace element determination by isotope dilution technique is the main application for isotope ratio measurements of the elements. The definitive method, isotope dilution mass spectrometry, is discussed as a potential tool for achieving accurate and precise trace analyses. Using field desorption mass spectrometry, one example of calcium kinetics in man and one example of thallium trace determination in an animal tissue are given. Other metal trace analyses with the isotope dilution technique are presented for biological and medical samples using positive thermal ionization mass spectrometry. Negative thermal ions are formed for the mass spectrometric analysis of non-metals and non-metal compounds in food samples, e.g. for iodine and nitrate in milk powder. Preliminary results with the isotope dilution technique are presented for a new quadrupole thermal ionization mass spectrometer which is a low-cost instrument and can be easily handled.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
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