Mass Spectrometry

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Mass Spectrometry
1.Introduction to Mass Spectrometry Chapter 11
2. Molecular Mass Spectrometry Chapter 20
Homework Chapter 11 11-1 Chapter 20 20-1,
20-3, 20-5, 20-7, 20-10
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Uses of Mass Spec

• forms ions, usually positive, study charge/mass
  ratio
• very characteristic fragmentation pattern in
  charge/mass ratio
• data easier to interpret than IR and/or NMR
• provides accurate MW of sample
• used to determine isotopic abundances

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• Basic concepts
• Atomic or molecular weights (amu, or Da)
• Mass-to-Charge ratio m/z (12C1H4, m/z16.035/1)

Ethyl Benzene
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Types of atomic mass spectrometry
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Components of Mass Spec
Sample

Inlet System
Ion Source
Mass Analyzer
Detector
10-5 - 10-8 torr
Signal Processor
Vacuum System
Readout
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Detectors Electron multipliers and Faraday Cup
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Mass analyzers
1. Quadrupole mass analyzer
ICPMS
2. Time-of-flight mass analyzers
3. Double Focus Mass analyzers
4. Single Focus Mass analyzers
5. Ion Trap Analyzer (FT Mass spectrometry)
Molecular Mass spectrometers
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Quadrupole Mass Spectrometer
Like a band-pass filter
-- 4 short parallel metal rods -- Opposite rods
same charge on dc source, AC rf applied
ontop
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Pass high-M
AC

Pass low-M
F Eze (E electric field intensity)
F am (a acceleration, m mass)
Like a band-pass filter
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Time of Flight Analyzers

• non-magnetic separation
• detector - electron multiplier tube
• instantaneous display of results

Example (a) calculate the kinetic energy that a
singly charged ion (z1) Will Acquired if it is
accelerated through a potential of 103 V in an
electron-Impact source. (b) Does the kinetic
energy is depend upon its mass? (c) Does the
velocity of the ion depend upon its mass?
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Schematic of a time-of-flight mass analyzer
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Mass analyzers
1. Quadrupole mass analyzer
ICPMS
2. Time-of-flight mass analyzers
3. Double Focus Mass analyzers
4. Single Focus Mass analyzers
5. Ion Trap Analyzer (FT Mass spectrometry)
Molecular Mass spectrometers
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Single-Focusing Analyzerswith Magnetic Deflection

• Fig. 20-12
• pg. 515
• "Schematic of a
• magnetic sector
• spectrometer."

Monochromator
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Magnetic Centripetal Force

• Fm Bzev
• where Fm gt magnetic centripetal force
• B gt magnetic field strength
• v gt velocity of particle
• z gt charge on particle
• e gt charge of electron

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Centrifugal Force

• Fc mv2/r
• where Fc gt balancing centrifugal force
• r gt radius of curvature of magnetic
  sector
• m gt mass of particle

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Mass to Charge Ratio, m/z

• Fm Fc
• thus
• Bzev mv2/r
• where v Bzr/m
• m/z (B2r2e)/2V

Only the ions with certain m/z can pass
through the exist slit at certain B, V, r.
Example 20-4
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Kinetic Energy

• KE zeV 1/2mv2
• where KE gt kinetic energy
• V gt accelerating potential

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Mass Analyzer

• Double-Focusing Analyzers
• higher resolution, need higher amplification
• 2 magnets or 1 magnet 1 electrostatic field

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Mattacuh-Herzog type double-focusing mass
spectrometer.
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Double FocusMass Spectrometer
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Mass analyzers
1. Quadrupole mass analyzer
ICPMS
2. Time-of-flight mass analyzers
3. Double Focus Mass analyzers
4. Single Focus Mass analyzers
5. Ion Trap Analyzer (FT Mass spectrometry)
Molecular Mass spectrometers
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Ion Trap Analyzer

• Variable radio frequency voltage applied to the
  ring electrode
• ions of appropriate m/z circulate in stable orbit
• scan rf, heavier particles stable, lighter
  particles collide with ring electrode
• ejected ions detected by transducer as an ion
  current

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Fig. 20-15, pg. 518Ion Trap Mass Spectrometer
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Mass Analyzers ION TRAPS  

• Three-dimensional quadrupole field
• Wolfgang Paul Nobel Prize1989
• MSn capability.

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FT Mass Analyzers ICR-MS the sound of ions  Ion
cyclotron Resonance (ICR)
Centripetal
Frequency
Centrifugal
Angular velocity
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ICR Let the magic begin! 
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Mass Analyzers ICR  
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Resolution of Mass spectrometer
R m/Dm
Dm the mass difference
Example 20-3 What reolution is needed to separate
the ions C2H4 (28.0313) CH2N (28.0187)
R m/Dm (28.031328.0187)/2/(28.0187-28.0313)
2.22 x 103
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Components of Mass Spec
Sample

Inlet System
Ion Source
Mass Analyzer
Detector
10-5 - 10-8 torr
Signal Processor
Vacuum System
Readout
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Ion Sources for Molecular Mass Spectroscopy
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Electron Impact Source

• bombardment of sample with beam of electrons

An electron impact source."
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Typical Reactions during Electron Impact
Example 20-2 Calculate the energy (in J/mol) that
electrons Acquire as a result pf being
accelerated through a potential of 70 kV
Energy 70eV ? 6700 kJ/mol Typical bond
energies ? 200 to 600 kJ/mol ? EXTENSIVE
FRAGMENTATION
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Electron Impact Spectra

• Different molecules behave differently
• Good molecular ion ? little fragmentation
• No molecular ion ? extensive fragmentation
• Isotopes are extremely important!
• Molecular ion isotopic cluster

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Chemical Ionization Source
CI REAGENT GAS
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Chemical Ionization MS Sources
CH4
High Energy electrons ?
CH4 CH4 CH3 CH2
Molecule Ions ?
Sample Molecule MH ?
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EI vs. CI
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Mass spectra for glutamic acid

• (a) electron impact ionization,
• (b) field ionization, and
• (c) field desorption

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Field Ionization /Field Desorption Sources

• Apply large electric fields to carbon dendrites
  on a tungsten wire
• Field Ionization gas is passed over ionization
  source
• Field Desorption dipped in solution containing
  sample and placed back in spectrometer

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Ionization vs. Desorption?
FIELD IONIZATION FIELD DESORPTION
E
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Field Ionization and Field Desorption
FIELD IONIZATION
E V/(kr)      K shape factor (Sphere 1,
others ,1) if V 5000V, r 1m ?
F500,000,000V/m!!!                       
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Field Ionization Sources
Apply large electric fields to carbon dendrites
on a tungsten wire
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Matrix Assisted Laser Desorption/Ionization
(MALDI)

• MWs of polar biopolymers ranging from a few
  thousand to several hundred thousand daltons
• Solution of analyte is mixed with a large amount
  of radiation absorbing matrix material
• The solid material was placed on a metallic probe
  and inserted into a Time-of-Flight MS
• Mixtures exposed to a pulsed laser beam
• Complete MS measured between each pulse

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MALDI
Koichi Tanaka
Nobel Prize, 2002

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Solid Matrix Materials for MALDI
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MALDI-TOF
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MALDI Spectrum from Nicotinic Acid Matrix of
Monoclonal Antibody (IgG)
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FAB Ionization Fast Atom Bombardment

SECONDARY ION MASS SPECTROMETRY ?SIMS
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FAB Ionization
Primary Ion Beam
Xe
Atom Gun
Xe0
Secondary ion Beam to MS
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MS Instrument Components
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Determination ofMolecular FormulaEI Mass-spec

• distinguish between compounds of same MW
• C5H10O4 or C10H14

(M1)/M ratio of isotopes is different
for different element
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Determination ofMolecular Formula

• distinguish between compounds of same MW
• C5H10O4
• 13C 5 1.08 5.40
• 2H 10 0.016 0.16
• 17O 4 0.04 0.16
• -------
• 135peak/134peak 5.72

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Determination ofMolecular Formula

• distinguish between compounds of same MW
• C10H14
• 13C 10 1.08 10.8
• 2H 14 0.016 0.22
• -------
• 135peak/134peak 11.0

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Determination ofMolecular Formula

• Table 20-6, pg. 526
• "Isotopic Abundance Percentages and Molecular
  Weights for Various Combinations of Carbon,
  Hydrogen, Oxygen, and Nitrogen."

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Example 20-5

• Calculate the ratios of the (M1) to M peak
  heights for the following compounds
  dinitrogenbenzene and an olefin,

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Table 20-6, pg. 526
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Mass Spectrometry
1.Introduction to Mass Spectrometry Chapter 11
2. Molecular Mass Spectrometry Chapter 20
Homework Chapter 11 11-1 Chapter 20 20-1,
20-3, 20-5, 20-7, 20-10