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  • 1
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The ion detection process in a discrete-dynode electron multiplier can result in significant mass resolution losses in time-of-flight mass spectrometry (TOF-MS) for higher mass-to-charge (m/z) ion species. This resolution loss is attributed to propagation time delays and signal broadening in the ion detector. This is presumed tobe due to the generation o a distribution of secondary ion species produced initially upon impact of a primary ion with the first ynoe surface of the ion detector. Comparisons are made between the signals produced by a standard discrete dynode ion detector (which amplified the negatively chqrged species produced by impact of a primry ion) and a detector modified to respond to only the positively charged secondary ion species produced by a primary ion impact. Ion signals for higher m/z ions with the standard detector geometry are see to be due to a narrow signal component, most likely due to the generation o secondary electrons and/or very low mass secondary ions (H-), and a broad signal component, apparently due to secondary ions which take signifiant amounts of time to traverse the low potential fields between the first and second detector dynode. This results in ion signal tailing for higher m/z ion species. Numerical subtraction of the ion signal obtained with the standard and modified detector geometries (singly protonated molecular ion species of equine myoglobin) results in an improvement in mass resolution, such that a new adduct ion species (from trifluoroacetic acid) can be resolved.
    Additional Material: 7 Ill.
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  • 2
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Results are oresented for various instrumental configurations employed for matrix-assisted laser desorption mass spectrometry. Mass resolution is determined for a linear time-of-flight mass spectrometer for various lengths of the field-free region. A wire ion guide is utilized and is shown to improve ion transport efficiencies for longer field-free regions. It is also determined experimentally that a modest mass resolution increase is often obtained in configurations employing the wire ion guide when compared to the mass resolution obtained with the same geometr without the wire ion guide. Optimal applied potentials are determined for the wire ion guide. No mass dependence on the opitmal applied potential (-100 V) for the wire ion guide is observed for samples of equine myoglobin (MW 16 951.5 Da) and a bacterial protease (MW 27 228.4 Da). The optimal applied voltage was also found to b identical (-100 V) for the singly through quadruply charged molecular ion species of rabbit gamma globulin (MW ≍ 150 000 Da). It is shown that a 2 m flight tube with a wire ion guide provides better signal-to-noise mass spectra than a 1 m flight tube without the wire ion guide and can more than double the mass resolution obtainable. Utilization obtainable. Utilization of a 4 m flight tube gives minimal mass resolution enhancement at the expense of signal-to-noise.
    Additional Material: 5 Ill.
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  • 3
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Resonance effects on measured isotope ratios in lead using three-photon one-colour resonance ionization mass spectrometry are discussed. The shape of the ionization signal is considered for the case of a non-monochromatic laser field. The intensity of the laser radiation is adjusted to be low enough not to cause saturation of the transitions. The variation of the measured isotope ratio as a function of laser frequency is considered. It is shown that the deviation of the measured from the expected isotope ratio, for a Lorentzian laser lineshape equals the ratio of the isotope shift to the laser bandwidth. Unfortunately, the background noise in the experiments makes verification of this behaviour difficult for the isotopes of low abundance.
    Additional Material: 3 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 17 (1986), S. 351-354 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 15NH4ReO4 was synthesized and the Raman spectrum recorded at various temperatures between 10 and 300 K. 15N isotopic shifts of both internal and external modes of the ammonium ion relative to 14NH4ReO4 were observed. The temperature dependence of the external modes was studied. The librational lattice mode associated with the ammonium ion disappeared above about 180 K. At this temperature anomalies were observed in the temperature dependence of the perrhenate ion lattice modes.
    Additional Material: 7 Ill.
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  • 5
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The temperature dependence of the Raman spectrum of potassium perrhenate is reported. Some new detailed results on the temperature dependence of the low frequency Raman bands of ammonium perrhenate are also presented. The frequency versus temperature plots for both internal and external modes of the ReO4- ion in KReO4 appear to be linear over the temperature range from 20 to 300 K. This is in contrast to the non-linear behaviour of the external modes of the ReO4- ion in NH4ReO4. A crossing of the frequencies of the Ag and Eg librational modes of the ReO4- ion in NH4ReO4 occurs near 200 K, the temperature at which anomolies have been observed in the temperature dependence of several physical properties of this salt. The apparent discontinuities near 200 K in the slopes of the wavenumber versus temperature curves reported earlier1 are now shown to be shoulders on smooth curves. Extrapolation of the frequency versus temperature plots of the Eg and Bg translational modes of the ReO4- ion in KReO4 indicates that a crossing of the curves would occur at about 500 K, while for NH4ReO4 the crossing of the frequencies of these modes is observed near 200 K. The significance of these observations with respect to the structure and a possible higher order phase transition in the NH4ReO4 crystal is discussed.
    Additional Material: 5 Ill.
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  • 6
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A Kratos MS-25RFA medium resolution mass spectrometer and a Concept IS high resolution mass spectrometer were used to analyse a range of highly substituted aromatic alcohols for kinetic studies.
    Additional Material: 2 Ill.
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  • 7
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new inorganic mass spectrometric technique is described which allows sensitive, rapid and economic determination of trace element concentrations and isotope ratios in aqueous samples. This paper illustrates the potential of the technique in one particular application area, namely the measurement of strontium isotope ratios in human blood and urine following ingestion of an enriched stable strontium isotope. The data from a human volunteer experiment illustrate the viability of the analytical method, with measurement precisions of ± 0.2% (1σ) achieved for the isotope ratio in urine samples, which contained approximately 300 ng 86Sr in the volume required for analysis. Measurement precision is limited by counting statistics.
    Additional Material: 4 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 13 (1982), S. 53-55 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The pressure dependences at room temperature of the translational lattice modes and of the ν2 and ν4 internal bending modes of the ReO4- ion in solid NH4ReO4 are reported. There is no evidence of any phase transition up to a pressure of 15 kilobar. The pressure coefficients of the translational modes are 2.0 cm-1 GPa-1 and 3.0 cm-1 GPa-1 for the Bg and Eg modes respectively. The pressure coefficients of the bending modes are 1.0 cm-1 GPa-1 and 5.4 cm-1 GPa-1 for the Bg and Ag components of ν2, and 4.1 cm-1 for the overlapped Bg and Eg components of ν4.The symmetry assignments of the low frequency lines in the spectrum were checked by means of polarized Raman spectra of a single crystal. The previous assignments are correct.
    Additional Material: 4 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 9 (1980), S. 28-32 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Raman spectra of NH4IO4 and ND4IO4 have been recorded at several temperatures between 83 K and 371 K. As the temperature is increased, several bands due to both internal and external modes of the periodate ion are shifted to lower wavenumbers. There is a crossing of the Ag and Eg librational modes of the IO4-ion near 200 K. The bands due to the ammonium ion vibrations are broadened as the temperature is increased and the librational lattice mode is no longer observable above about 200 K. The present results are correlated with observations from NQR, NMR and X-ray diffraction studies.
    Additional Material: 6 Ill.
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  • 10
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Raman spectra of polycrystalline normal and three 15N isotopic ammonium nitrates (15NH4NO3, NH4 15NO3 and 15NH4 15NO3) were recorded at various temperatures between 10 and 300 K. Isotopic shifts of both internal and external modes of the ammonium ion relative to isotopic normal NH4NO3 were observed. Various components of the hetero-ionic coupled internal mode (ν3 of the nitrate ion with ν4′ of the ammonium ion) were assigned with more certainty on the basis of the 15N isotopic shifts. Detailed studies of the temperature dependence of one internal mode (ν1) of the NO3 - ion and several external modes were made. The frequency and half band width versus temperature plots for both the internal mode and the external modes of 15NH4NO3 indicate only one crystal structure (phase V) between 10 and 257 K. Comparison of the frequency shifts between various isotopic compounds in the external mode region permitted a more precise assignment of the lattice modes associated with the NH4+ and NO3- ions to be made.
    Additional Material: 11 Ill.
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