Presentation on mass spectroscopy

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.

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

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

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

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

Flow of Ions in Mass Spectroscope

INSTRUMENTATION
OF
MASS SPECTROSCOPY

Basic Components of MS Instrument
 Sample Inlet System
Ion Source / Ionization Chamber
Electrostatic Accelerating System
Ion Seperator / Analyser
Magnetic Field
Ion Collector
Vacuum System

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

IONIZATION METHODS
1. Gas Phase
 Electron Impact
 Chemical Ionization
 Field Ionization
2. Desorption Phase
 Field desorption
 Electro spray Ionization
 MALDI
 FAB
 Thermo spray Ionization

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

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"

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

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

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+.

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.

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.

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

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.

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

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.

Ionization (MALDI)
The matrix absorbs the energy from the
laser pulse and produces a plasma that
results in vaporization and ionization of the
analyte.

Ionization (MALDI)

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

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.

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.

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)

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.

1.1 Single Focusing Sector Analyser

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.

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.

Quadrupole analyser : Mass filter

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.

Quadrupole analyser : Ion Trap

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.

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).

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

FT-Ion Cyclotron resonance (FT-ICR)

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.

Tandem Mass Spectroscopy MS-MS

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.

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.

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

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

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.

Presentation on mass spectroscopy

QUADRUPOLE
and 27.9949 Daltons, respectively2.

Types of Ion in MS / Interpertation
Mass Spectrum

Applications of Mass Spectroscopy

Presentation on mass spectroscopy

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