Interpretation of Mass Spectra

Abstract

The chapter includes an introduction to the main ionisation techniques in mass spectrometry and the way the resulting fragments can be analysed. First, the fundamental notions of mass spectrometry are explained, so that the reader can easily cover this chapter (graphs, main pick, molecular ion, illogical pick, nitrogen rule, etc.). Isotopic percentage and nominal mass calculation are also explained along with fragmentation mechanism. A paragraph emphasises the ionisation energy issues, the basics of ionisation voltage, the developing potential and the energy balance. A frame time of the main theoretical milestones in both theory and experimental mass spectrometry is highlighted here. In the second part of the chapter, the molecular fragmentation for alkanes, iso-alkanes, cycloalkanes, halogen, alcohols, phenols, ethers, carbonyl compounds, carboxylic acids and functional derivatives, nitrogen compounds (amines, nitro compounds), sulphur compounds, heterocycles and biomolecules (amino acids, steroids, triglycerides) is explained. Fragmentation schemes are followed by the simplified spectra, which help the understanding of such complex phenomena. At the end of the chapter, acquisition of mass spectrum is discussed. The chapter presented here is an introduction to mass spectrometry, which, we think, helps the understanding of the mechanism of fragmentation corroborating spectral data and molecular structures.The scientific term spectrograph starts being part of the scientific vocabulary (1884) [1,3] E. Goldstein studied 'canal rays' composed of positive ions. His work opened the gate to mass spectrometry (1886) [1,3] Wilhelm Wien showed that the mass-to-charge ratio of the positive ions (canal rays) has opposite polarity that of the electron (1898) [1,3]