Mass spectrometry is a technique used for structural elucidation, molecular mass determination, and compound identification. It works by ionizing molecule fragments and separating the ions based on their mass-to-charge ratios. The key components are the ion source, mass analyzer, and ion detector. Common ionization methods include electron impact, chemical ionization, electrospray, and matrix-assisted laser desorption ionization. Popular mass analyzers are quadrupoles, time-of-flight, and ion traps. Mass spectrometry has wide applications in fields like pharmaceuticals, petrochemicals, polymers, and biomedicine.
1. Mass Spectrometry
Presented by,
Ms.Smita P.Shelke,
Assistant Professor
Gokhale Education Society’s
Sir Dr M.S. Gosavi College Of Pharmaceutical Education & Research
Prin.T.A.Kulkarni Vidyanagar, Nashik-422005
India (Maharashtra). Ph No. 0253 2232799.
2. Mass Spectrometry
Used by Three Ways:-
For structural elucidation of ionic
fragments
Measurement of relative molecular
mass: molecular formula
Comparison and identification of
known compounds
3. Theory of MS
MS separates individual atoms because of differences
in their masses
consider M is a molecule focused with beam of e-
M + e- M+ + 2e-
ions accelerated with voltage V,
now energy of each particle = kinetic energy
½ mv2 =eV………………………..(1)
• v= Velocity of particle
• m= Mass of particle
• e= Charge on electron
• V= Voltage
4. Now charge particles enter a magnetic field H, field
attracts the particle and they move in a circle around
it with a force Hev
• However particles have centrifugal force mv2 /r
• When these two forces are equal :molecule start
moving: i.e.
mv2 /r = Hev………………..(2)
• v= Velocity of particle
• m= Mass of particle
• r= Radius of circle
• H= magnetic field
• e= Charge on electron
5. m/e = H2 r2 / 2V…………..(3)
• m/e= mass to charge ratio is depends on H, V and r
As e, V and H are constant
• m= mass is depends on r
11. Basic Components of MS Instrument
Sample Inlet System
Ion Source / Ionization Chamber
Electrostatic Accelerating System
Ion Seperator / Analyser
Magnetic Field
Ion Collector
Vacuum System
12. Sample Inlet Systems in MS
Sample must be in vapour phase
Less volatile heated before injection in
ampoule.
Smples with less vapour pressure are with
Probe
13. IONIZATION METHODS
1. Gas Phase
Electron Impact
Chemical Ionization
Field Ionization
2. Desorption Phase
Field desorption
Electro spray Ionization
MALDI
FAB
Thermo spray Ionization
14. Electron Impact (EI)
A high energy electron beam dislodges an
electron from a
sample molecule to produce a positive ion
M + e → M+. + 2e
M= analyte molecule, M+.= Radical ion
16. Benefits
o well-understood
o can be applied to virtually all volatile
compounds
o reproducible mass spectra
o fragmentation provides structural
information
o libraries of mass spectra can be searched
for EI mass spectral "fingerprint"
17. Chemical Ionization (CI)
Gaseous atoms of the sample are
bambarded with reagent gas.
Reagent gas- methane gas
All of the primary ions of methane
react rapidly with methane (at virtually
every collision) to give product ions
18. Mechanism of Methane gas
Collison of methane to produce ions
CH4
+ + CH4 --> CH5
+ + CH3
CH3
+ + CH4 --> C2H5
+ + H2
Interaction of ions with molecule M
MH + C2H5
+ --> MH2
+ + C2H4
MH + C2H5
+ --> M+ + C2H6
19. Field Ionization (FI) Soft Ionization
Emitters of Tungsten wire used on which
microscopic dendrites / emmitters are
formed (by Pyrolysis)
The mechanism of ionisation - when a
molecule is subjected to a very high
electric field, ( > 10*9 volts/metre), a
valence electron tunnels through the
potential barrier and is removed from the
molecule. The resulting ion is therefore a
radical, M+.
20. carbon emitters and silicon emitters.
Silicon emitters are robust, relatively
inexpensive, and they can handle a higher
current for field desorption.
Carbon emitters are more expensive, but
they can provide about an order of
magnitude better sensitivity than silicon
emitters.
22. Desorption Field Ionization
Field desorption ionization are soft
ionization methods that tend to
produce mass spectra with little or no
fragment-ion content.
Benefits
simple mass spectra, typically one
molecular or molecular-like ionic
species per compound.
23. little or no chemical background
works well for small organic molecules,
many organometallics, low molecules -
polymers and some petrochemical
fractions
Limitations
sensitive to alkali metal contamination and
sample overloading
emitter is relatively fragile
relatively slow analysis as the emit
the sample must be thermally volatile
24. Electrospray Ionization
The sample solution is sprayed across a
high potential difference (a few kilovolts)
from a needle into an orifice in the
interface. Heat and gas flows are used to
desolvate the ions existing in the sample
solution.
26. Advantages of ESI
• good for charged, polar or basic
compounds
• permits the detection of high-mass
compounds at mass-to-charge ratios that
are easily
• best method for analyzing multiply
charged compound
• very low chemical background leads to
excellent detection limits
• compatible with MS/MS methods
27. Matrix Assisted Laser Desorption
Ionization (MALDI)
The analyte is dissolved in a solution
containing an excess of a matrix such as
sinapinic acid or dihydroxybenzoic acid
that has a chromophore that absorbs at
the laser wavelength.
28. Matrix Assisted Laser Desorption
Ionization (MALDI)
The matrix absorbs the energy from the
laser pulse and produces a plasma that
results in vaporization and ionization of the
analyte.
30. Advantages of MALDI
rapid and convenient molecular weight
determination
Limitations of MALDI
MS/MS difficult
requires a mass analyzer that is
compatible with pulsed ionization
techniques
not easily compatible with LC/MS
31. Fast Atom Bombardment (FAB)
The analyte is dissolved in a liquid matrix
such as glycerol, thioglycerol, m-
nitrobenzyl alcohol, or diethanolamine and
a small amount (about 1 microliter) is
placed on a target.
32. Fast Atom Bombardment (FAB)
The target is bombarded with a fast atom
beam (for example, 6 keV xenon atoms)
that desorb molecular-like ions and
fragments from the analyte.
Cluster ions from the liquid matrix are also
desorbed and produce a chemical
background that varies with the matrix
used.
35. Mass analyzers / Seperators
1.Sector analysers
Single focusing
Double focusing
2. Quadrupole analyser
Mass filter
Ion trap/ Ion storage
3. Time of Flight (TOF)
4. FT-Ion Cyclotron Resonance (FT-ICR)
36. Mass analyzers / Seperators
1. Sector analysers:
uses an electric and/or magnetic field to affect
the path and/or velocity of the charged particles .
bend the trajectories of the ions as they pass
through the mass analyzer, according to their
mass-to-charge ratios.
deflecting the more charged and faster-moving,
lighter ions more.
38. 1.2 Double Focusing
Mass spectrometer that incorporates a
magnetic sector and an electric sector
connected in series in such a way that
ions with the same m/z but with
distributions in both the direction.
40. 2.1 Quadrupole analyser : Mass filter
A quadrupole mass filter consists of four
parallel metal rods
Two opposite rods have an applied
potential
The applied voltages affect the trajectory
of ions traveling between the four rods.
only ions of a certain mass-to-charge ratio
pass through the quadrupole filter.
42. Quadrupole analyser : Ion Trap
an ion trap uses constant DC and radio
frequency (RF) oscillating AC electric
fields to trap ions.
It is commonly used as a component of
a mass spectrometer.
44. 3. Time Of Flight (TOF)
an ion's mass-to-charge ratio is
determined via a time measurement.
Ions are accelerated by an electric field of
known strength.
This acceleration results in an ion having
the same kinetic energy.
The velocity of the ion depends on the
mass-to-charge ratio.
The time that it takes for the particle to
reach a detector at a known distance is
measured.
46. 3. FT-Ion Cyclotron resonance (FT-ICR)
the mass-to-charge ratio (m/z) of ions
based on the cyclotron frequency of the
ions in a fixed magnetic field.
The ions are trapped in a Penning trap (a
magnetic field with electric trapping plates)
where they are excited by rf
After the excitation field is removed, the
ions are rotating at their cyclotron
frequency in phase (as a "packet" of ions).
47. FT-Ion Cyclotron resonance (FT-ICR)
These ions induce a charge on a pair of
electrodes as the packets of ions pass
close to them.
The resulting signal is called a free
induction decay (FID), transient or
interferogram that consists of a
superposition of sine waves.
The useful signal is extracted from this
data by performing a Fourier transform
50. Tandem Mass Spectroscopy MS-MS
Multiple stages of mass analysis separation
can be accomplished with individual mass
spectrometer.
Elements separated in space or using a
single mass spectrometer with the MS
steps separator.
52. Methods of Ion Detection / Ion
detectiors
Mass analysis - i.e. the separation of
bunches or streams of ions according to
their individual mass-to-charge (m/z) ratio.
The most common types of ion detector
used in modern instruments:
1. The Faraday Cup or Cylinder
2. The Electron Multiplier
3. The Photomultiplier or
Scintillation Counter.
53. 1. The Faraday Cup or Cylinder
The basic principle is that the incident ion
strikes the dynode surface, which emits
electrons and induces a current which is
amplified and recorded.
The dynode electrode is made of a
secondary emitting material like CsSb,
GaP or BeO.
The Faraday cup is very robust.
55. 2. The Electron Multiplier
A Faraday cup uses one dynode, it has
series of dynodes maintained at increasing
potentials resulting in a series of
amplifications.
Their are two types of electron multiplier
57. 3. The Photomultiplier or
Scintillation Counter.
The ions initially strike a dynode which
results in electron emission.
These electrons then strike a phosphorous
screen which in turn releases a burst of
photons.
The photons then pass into the multiplier
where amplification occurs in a cascade
59. Interpretation of MS Spectrum
The mass spectrum produced will usually
be presented as a vertical bar graph, in
which each bar represents an ion having a
specific mass-to-charge ratio (m/z) and the
length of the bar indicates the relative
abundance of the ion.