Mass Spectroscopy

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Chapter 22

• Mass Spectroscopy
• Quantitative Chemical Analysis
• Harris, 6th Edition

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What is Mass Spec

• Generation and Separation of Charged Molecules
  based on a mass to charge ratio.
• Applications from Geochemistry to Biotechnology

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Mass Definitions

• Atomic Mass Mass from periodic table based
  isotope abundance
• Molecular Mass Mass for the sums of the atomic
  masses (Water 21.0079 15.9994 18.0152
  Da)
• Nominal Mass - Sum of integer masses of most
  abundant isotopes. (Water 18 Da)

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Typical Mass Spectrometer

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

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Ionization Process

• M e- (70 eV) ? M. e- (55 eV)
  e- ( 0.1 eV)
• Typical ionization energies are 9 to 10 eV

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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

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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

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Small portion of Methyl Stearate
(CH3(CH2)16CO2CH3
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Isotope patterns tell us much.
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For interpretation
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Quadrupole Ion Separators
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Time of Flight
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Quadrupole Ion Trap
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Quadrupole Ion Trap
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LC MSPneumatically Assisted Electrospray
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Gas Phase Ion Formation
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Outlet Photograph
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CZE MS Interface
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Atmospheric Pressure Chemical IonizationAPCI
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Selected Ion Monitoring
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Triple Quad Instruments
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MALDI Matrix Assisted Desorption / Ionization
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MALDI Example
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Electrospray of Proteins (Multiple Charges)
Acidified bovine cytochrome c
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