Mass spectrum distorted

Both Q and SF mass spectrometers are scanning (sequential) analyzers and multiisotope analysis can be achieved at the expense of the measurement sensitivity and precision. The sequential measurement of m/z at different points within a time-dependent concentration proble of a transient signal can result in peak distortions and quantisation errors commonly referred to as spectral skew. The alternative is TOF-MS which features the ability to produce a complete atomic mass spectrum in less than 50 xs and thus allows very brief transient signals to be recorded with high bdelity. This is especially useful in the on-line isotope ratio determination. However, a 10-fold loss in sensitivity of a TOF-ICP-MS instrument in comparison with the latest Q instruments often creates an obstacle for the wider application of TOF-ICP-MS as a detector in the CE of metallobiomolecules in biological samples. 

Mass spectral quality is an important consideration in performing a successful GC-MS analysis. The quality of the mass spectra depends on (1) the concentration of the constituents in the sample solution, (2) the GC operating conditions used to resolve the peaks, and (3) excessive pressure fluctuation in the MS unit of the GC-MS system leading to distortion of the mass spectrum, especially an El mass spectrum, as reflected in the relative abundance of the ion peaks. The implication of (3) is that distortions of this type could lead to misinterpretation of the spectrum even though a library search is performed. 

In contrast to the mass spectrum of a compound obtained by direct probe measurement, the spectrum of the same compound obtained by GC-MS analysis does not contain meta-stable ions. The absence of these ions makes the interpretation of mass spectra obtained by GC-MS analysis more difficult than those obtained by direct probe measurement. In addition, during editing of mass spectral data (see Sect. 9.1.3.4), the ratio of the relative intensity of an ion fragment at m/z p to its naturally occurring 13C isotope ion peak at m/z (p + 1) may be distorted. 

Figure 2.30 Selective ejection of an intense peak at a single ra/z reduces the space charge distortion of the mass spectrum. Here, the high m/z selectivity of such resonant excitation is shown for in the presence of Sr+ and Zr+. If is not ejected prior to mass analysis (upper trace), the spectrum is space charge distorted. By ejecting the m/z 89 peak prior to mass analysis, an undistorted spectrum is obtained (lower trace virtually identical to the spectrum of a solution containing only Sr and Zr). Comparison of the spectra shown with spectra of Sr and Zr solutions without Y shows that ejection of Y+ is 50000 times more efficient than ejection of either Sr+ or Zr ...

Vibrational properties can also be computed using the total energy formalism. Here, the atomic mass is required as input and the crystal is distorted to mimic a frozen-in lattice vibration. The total energy and forces on the atoms can be computed for the distorted configuration, and, through a comparison between the distorted and undistorted crystal, the lattice vibrational (or phonon) spectrum can be computed. Again, the agreement between theory and experiment is excellent. [22]... 

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