Ionization and Mass Analyzers

1
Ionization and Mass Analyzers

• Ionizations
• Electron Ionization - hard
• Chemical Ionization - soft
• MALDI - desorption
• FAB - desorption
• Laser Post Ionization - increase signal!
• Ion Bombardment (SIMS) - soft or hard
• Depends on ion fluence
• Mass Analyzers
• Analyze all mass/charge
• Time-of-flight
• Pre- Select Ions
• Quadropole
• Magnetic or Electric Sectors

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Electron Ionization

• Molecule e-
  molecule 2e-
• Four electromagnetic poles
• Rapidly oscillating field
• If mass of ion and frequency of oscillation are
  comparable then the ion will oscillate towards
  the detector and be measured
• A certain mass range can be selected depending on
  the pole diameter

Quadropole Mass Analyzer
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Electrostatic and Magnetic Sectors
B strength of magnetic field V ion
accelerating voltage r radius of ion
curvature m mass of ion z charge of ion
M 1-50 (change by changing B)
http//www.cea.com/cai/simsinst/m_anal.htm
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Secondary Ion Mass Spectrometry Ionization
Ga
Static SIMS lt 1 x 1013 ions/cm2
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Time-of-Flight Analyzer
e charge on an electron 1.6 x 10-19 C t time
for ion to reach detector m mass v velocity
V stage voltage d length of field free
region V voltage of detector
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TOF-SIMS Instrument
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Laser Postionization (LPI)
Laser Beam
Postionization parameters 800 nm,
150 fs laser pulses, 8.5 x 1012 W/cm2
power density
8
TOF-SIMS Molecule-Specific Imaging
Si
Cu
copper grid affixed to silicon substrate with
silver paste
9
TOF-SIMS Identification of Plasma Membrane Lipids
DPPE dipalmitoylphosphatidylethanolamine
m/z 682 (MH)
10
Are there Lipid Domains in the Inner Leaflet of
the Membrane?
Total Ion DPPE/Cholesterol
250 µm x 250 µm
Intensity
Au
-
A. G. Sostarecz C. M. McQuaw et. al. J. Am.
Chem. Soc. 2004.
C. M. McQuaw A. G. Sostarecz et. al. Langmuir
2005.
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Multi-Isotope Imaging Mass Spectrometry
Atomic Mass Images
14N
nucleus
lamellipodia
endothelial cell
Image from Claude Lechene Harvard Medical School
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MIMS is a Secondary Ion Mass Spectrometry
Technique
B strength of magnetic field V ion
accelerating voltage r radius of ion
curvature m mass of ion z charge of ion
M 1-50 (change by changing B)
http//www.cea.com/cai/simsinst/m_anal.htm
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MIMS uses an Electrostatic and Magnetic Sector
Mass Analyzer
mass separate
focus
14N
ion 1
84
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Image from Claude Lechene
MIMS analysis is performed as a collaborative
project with Dr. Claude Lechene at the
National Resource for Imaging Mass Spectrometry
at Harvard Medical School