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

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

Electrostatic and Magnetic Sectors

http://www.cea.com/cai/simsinst/m_anal.htm

22

2r

V

B

z

m

B = strength of magnetic field

V = ion accelerating voltage

r = radius of ion curvature

m = mass of ion

z = charge of ion

focusmass

separate

M = 1-50 (change by changing B)

Secondary Ion Mass Spectrometry“Ionization”

Static SIMS = < 1 x 1013 ions/cm2

Ga+

-+e-

10 ion

20 particles

Time-of-Flight Analyzer

2

2

2

2

2

2

1

2

1

d

teV

z

m

t

dmzeV

mvzeVd

Field Free Region

+V

M+

MCPdetector

-V

V = stage voltaged = length of field free regionV = voltage of detector

e = charge on an electron1.6 x 10-19 C

t = time for ion to reach detectorm = massv = velocity

Sam

ple

Sam

ple

TOF-SIMS InstrumentTOF-SIMS Instrument

Laser Postionization (LPI)Laser Postionization (LPI)

Postionization parametersPostionization parameters: 800 nm, 150 fs laser pulses, 8.5 x 1012 W/cm2 power density

Laser Beam

TOF-SIMS Molecule-Specific Imaging

molecule-specific image

Si+

Si+

Cu+

Cu+

Ag+

Ag+

m/z, +ions

total ion image

0 12 24 36 48 60 72 84 96 108 1200

1000

2000

3000

4000

5000

570 µm x 570 µm

Inte

nsity

copper grid affixed to silicon substrate with silver paste

Ion Gun

x

y

TOF-SIMS Identification of Plasma Membrane Lipids

m/z 369

OH

cholesterolm/z 385 (M-H)+

DPPE – dipalmitoylphosphatidylethanolamine

m/z 552m/z 142+2H** **

m/z 682 (M+H)+

O

O O

H

O

O

P

O

O

H3N

O

+ --

C. M. McQuaw; A. G. Sostarecz et. al. Langmuir 2005.

250

µm

x 2

50 µ

m

Are there Lipid Domains in the Inner Leaflet of the Membrane?

Total Ion DPPE/CholesterolTotal Ion DPPE/Cholesterol

-

O

O O

H

O

O

P

O

O

H3N

O

+552552

Cholesterol

cholesterolcholesterol

DPPE

DPPEDPPE

Inte

nsity

Inte

nsity

A. G. Sostarecz; C. M. McQuaw et. al. J. Am. Chem. Soc. 2004.

Au

Multi-Isotope Imaging Mass Spectrometry

endothelial cell

Image from Claude LecheneImage from Claude LecheneHarvard Medical SchoolHarvard Medical School

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nucleusnucleus lamellipodialamellipodia

Atomic Mass ImagesAtomic Mass Images

MIMS is a Secondary Ion Mass Spectrometry Technique

http://www.cea.com/cai/simsinst/m_anal.htm

22

2r

V

B

z

m

B = strength of magnetic field

V = ion accelerating voltage

r = radius of ion curvature

m = mass of ion

z = charge of ion

focusmass

separate

M = 1-50 (change by changing B)

-+e-

10 ion

20 particles

MIMS uses an Electrostatic and Magnetic Sector Mass Analyzer

*** MIMS analysis is performed as a collaborative project with Dr. Claude Lechene at the National Resource for Imaging Mass Spectrometry at Harvard Medical School

focusfocus mass separatemass separate

ion 1ion 1

Image from Claude Lechene

84 %84 %

16 %16 %

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