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Chapter 22

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  1. Chapter 22 Mass Spectroscopy Quantitative Chemical Analysis Harris, 6th Edition

  2. What is Mass Spec • Generation and Separation of Charged Molecules based on a mass to charge ratio. • Applications from Geochemistry to Biotechnology

  3. Mass Definitions • Atomic Mass – Mass from periodic table based isotope abundance • Molecular Mass – Mass for the sums of the atomic masses (Water = 2*1.0079 + 15.9994 = 18.0152 Da) • Nominal Mass - Sum of integer masses of most abundant isotopes. (Water = 18 Da)

  4. Typical Mass Spectrometer • Ion source - electron beam • Ion separation - magnet • Ion detection - Electron multiplier • A high vacuum method (avoid collisions that will effect ions)

  5. Ionization Process • M + e- (70 eV)→ M+. + e- (~55 eV)+e- ( 0.1 eV) • Typical ionization energies are 9 to 10 eV

  6. Chemical Ionization • Add a gas such as methane in greater amount. The methane in ionized and then the energy is transferred to the analyte on collision. • Much less energy passed to analyte

  7. Resolution • Most application require the ability to resolve integer difference in the working range. • Some high resolution instruments are available and these can give exact molecular formula

  8. Small portion of Methyl Stearate (CH3(CH2)16CO2CH3

  9. Isotope patterns tell us much.

  10. For interpretation

  11. Quadrupole Ion Separators

  12. Time of Flight

  13. Quadrupole Ion Trap

  14. Quadrupole Ion Trap

  15. LC – MSPneumatically Assisted Electrospray

  16. Gas Phase Ion Formation

  17. Outlet Photograph

  18. CZE – MS Interface

  19. Atmospheric Pressure Chemical IonizationAPCI

  20. Selected Ion Monitoring

  21. Triple Quad Instruments

  22. MALDI – Matrix Assisted Desorption / Ionization

  23. MALDI Example

  24. Electrospray of Proteins (Multiple Charges) Acidified bovine cytochrome c