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Mass spectral interpretation is the systematic analysis of mass spectra for molecule identification. It is most often used for the identification of organic compounds from electron ionization mass spectrometry.〔''Spectrometric identification of organic compounds'' Silverstein, Bassler, Morrill 4th Ed.〕〔''Organic spectroscopy'' William Kemp 2nd Ed. ISBN 0-333-42171-X〕 Organic chemists obtain mass spectra of chemical compounds as part of structure elucidation and the analysis is part of many organic chemistry curricula. ==Electron ionization== Electron ionization (EI) is a type of mass spectrometer ion source in which a beam of electrons interacts with a gas phase molecule M to form an ion according to : with a molecular ion . The superscript "+" indicates the ion charge and the superscript "•" indicates an unpaired electron of the radical ion. The energy of the electron beam is typically 70 electronvolts and the ionization process typically produces extensive fragmentation of the chemical bonds of the molecule. The peak in the mass spectrum with the greatest intensity is called the base peak. The molecular ion is often, but not always, the base peak. Identification of the molecular ion can be difficult. Examining organic compounds, the relative intensity of the molecular ion peak diminishes with branching and with increasing mass in a homologous series. In the spectrum for toluene for example, the molecular ion peak is located at 92 m/z corresponding to its molecular mass. Molecular ion peaks are also often preceded by a M-1 or M-2 peak resulting from loss of a hydrogen radical or dihydrogen. More peaks may be visible with ''m/z'' larger than the molecular ion peak due to isotope distributions, called isotope peaks. The value of 92 in the toluene example corresponds to the monoisotopic mass of a molecule of toluene entirely composed of the most abundant isotopes (1H and 12C). The so-called M+1 peak corresponds to a fraction of the molecules with one higher isotope incorporated (2H or 13C) and the M+2 peak has two higher isotopes. The natural abundance of the higher isotopes is low for frequently encountered elements such as hydrogen, carbon and nitrogen and the intensity of isotope peaks subsequently low. In halogens on the other hand, higher isotopes have a large abundance which results in a specific mass signature in the mass spectrum of halogen containing compounds. Peaks with mass less than the molecular ion are the result of fragmentation of the molecule. Many reaction pathways exist for fragmentation, but only newly formed cations will show up in the mass spectrum, not radical fragments or neutral fragments. Metastable peaks are broad peaks with low intensity at non-integer mass values. These peaks result from ions with lifetimes shorter than the time needed to traverse the distance between ionization chamber and the detector. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mass spectral interpretation」の詳細全文を読む スポンサード リンク
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