Transcription of 13.24: Mass Spectrometry - College of Arts and Science
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13.24: Mass Spectrometry - College of Arts and Science
1 Chapter 13: Spectroscopy Methods of structure determination Nuclear Magnetic Resonances (NMR) Spectroscopy (Sections ) Infrared (IR) Spectroscopy (Sections ) Ultraviolet-visible (UV-Vis) Spectroscopy (Section ) Mass (MS) Spectrometry (not really spectroscopy) (Section ) Molecular Spectroscopy: the interaction of electromagnetic radiation (light) with matter (organic compounds). This interaction gives specific structural information. 2 : Mass Spectrometry : molecular weight of the sample formula The mass spectrometer gives the mass to charge ratio (m/z), therefore the sample (analyte) must be an ion. Mass Spectrometry is a gas phase technique- the sample must be vaporized. Electron-impact ionization Sample Inlet10-7 - 10-8 torrR-Helectr on beam 70 eV (6 700 KJ/mol)e_R-H+massanalyze rm/zioniza tion chamber(M+)proton u neutron u electron u 13 mass m charge z ==B2 r2 2V B= magnetic field strength r = radius of the analyzer tube V= voltage (accelerator plate) The Mass Spectrometer Io niz atio nchamberIo ns of selectedmas s/charge rat ioare detect edIo ns o f n on-selectedmass/char ge r at ioar e not detect edMagnetic Field, Bo 4 Exact Masses of Common Natural Isotopes Isotope mass natural abundance 1H 2H 12C 13C ( ) 14N 15N ( ) 16O 1
10-7 3 γ Rays X-Rays Ultraviolet 10-11 10-9 10-5 14 13.2: Principles of Molecular Spectroscopy: Quantized Energy Levels molecules have discrete energy levels (no continuum between levels) A molecule absorbs electromagnetic radiation when the energy of photon corresponds to the difference in energy between two states 7
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