This document provides an overview of the key components and operating principles of mass spectrometry. It discusses the inlet system, ion sources, mass analyzers, detectors, and vacuum system. Common types of ion sources like electron impact and chemical ionization are described. Popular mass analyzers such as quadrupole, time-of-flight, ion trap, and double focusing are explained. The document also covers the theory behind how mass spectrometry separates ions based on their mass-to-charge ratio and discusses the need for high vacuum levels in mass spectrometers.

1. Instrumentation of
mass spectrometry
REPORTED BY
MANALI PARAB
M.PHARMACY FIRST YEAR
PHARMACEUTICS (SEM II)
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2. Mass spectrometers
 Instrument that produces ions and separate them according to their mass to
charge ratios, m/z.
 Following are components of mass spectrometer
 1) inlet system
 2) ion sources
 3) mass analysers
 4) detectors
 5) vacuum system
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3. Sample
Inlet system
Ion sources Mass analyzer
Detector
Signal
processor
Read out
Block diagram of Components of Mass Spectrometer 3

4. Description of instrument components
Inlet system
•To introduce very small
amount of sample (a micro
mole or less) into the mass
spectrometer
•Components are converted
to gaseous ions.
•Volatilizing solid or liquid
samples
Ion sources
•Convert the components of
a sample into ions
•Output is a stream of
positive or negative ions
(more commonly positive)
that are then accelerated
into the mass analyzer.
Mass analyzer
•Ions are dispersed based on
the mass-to-charge ratios of
the analyte ions.
Transducer
•That converts the beam of
ions into an electrical signal
that can then be processed,
stored in the memory of a
computer, and displayed or
recorded
Vacuum system
•Requirement of an
elaborate vacuum system to
create low pressures (10-4 to
10-8 torr) in all of the
instrument components
except the signal processor
and readout.
•Conditions lead to
infrequent collisions with
atmospheric components
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5. Ion sources
Basic type Name of ion source Ionizing agents
Gas phase Electron Impact (EI) Energetic electrons
Chemical Ionization (CI) Reagent gaseous ions
Field Ionization (FI) High potential electrode
Desorption Field Desorption (FD) High potential electrode
Matrix Assisted Laser
Desorption Ionization (MALDI)
Laser beam
Fast Atom Bombardment
(FAB)
Energetic atomic beam
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7. Theory behind mass spectrometry
 Sample to introduce into the ion source of the mass spectrometer in the vapour
form what is bombarded by electrons of about 70 eV
 The positive ions formed in the Ion source are accelerated by using the plates
which are kept at the potential difference of about 3000 to 6000 volts the
accelerated ions enter the magnetic field which is applied perpendicular to the
direction of motion of ions this produces a force which is perpendicular both to the
motion of the electrons and also to the direction of the applied magnetic field this
force causes the deflection of Ions based on there mass to charge ratio
 Then the ions passed through and exits slit or collectors list and impinge upon a
collector the signal received is then amplified in the form of peaks in the mass
spectrum
 The ions of a different mass to charge values follow the path of different curvature
 In the analyser in electric field all the ions acquired the same kinetic energy. The
kinetic energy of the ions is expressed as m is the mass of ion and v is velocity.
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8.  The velocity of the heavier ions is lesser as compared to the light ions. Because of
the higher mass heavier ion resists that changed in the direction of the motion also
they are accelerated do a lesser extent as a compared to the light ions. Therefore
they follow the path of the greater curvature because of them smaller mass.
 The light ions get deflected easily also they are accelerated more compared to the
heavy ions Therefore they follow the path of a smaller curvature and reach the
detector faster than the heavier ions
 By changing either the accelerating voltage(V) or the magnetic field(H), the radius
(r) of the ion path can be changed which allows the ions of different mass to charge
ratios to impinge upon the collector at the same point.
 The variation in the magnetic field provides a wide range of ions to be covered in a
single sweep but the voltage sweep makes the scanning very rapid
 The relation between the magnetic field and accelerating voltage the radius of the
ions path and the m/z value of an ion can be obtained as follows in an electric field
the potential energy of ion is a converted to its kinetic energy in magnetic field as
follows
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9. • In the electrical field, the potential energy(P.E.) of an ions converted to kinetic
energy(K.E.)
P.E. = K.E.
Zv=1/2 mv2
• In the magnetic field the ions follws the semi-circular path and hence centripetal
force is a balanced by the centrifugal force
CPF=CFF
Or Hzv=mv2/r
Or v= Hzr/m
• by putting the value of v from equation the m/z of an ion can be obtained
Zv=1/2 m(Hzr/m)2
½ H2z2r2/m
V=1/2 H2zr2/m
Hence m/z= H2r2/2V
• Above equation shows the radius of the ion paths various for the ions having the
different mass to charge ratio if the values of H and V are kept constant. If all the
ions of a different m/z values to be collected at the same point on a detector the
value of a radius should be kept constant
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10. • This makes the fabrication of the mass spectrometer much
simpler and allows the collection of a different ions at one point
without the need for a change in a position of a collector's slit.
This can be achieved by changing the other magnetic of a
electric field at the magnetic field or both
• In some mass spectrometer the magnetic field is kept constant
and the accelerating potential is gradually increased
• If H and r kept constant on the right hand side of this equation,
then the value of the inversely proportional to the V that is
heavier ions can be collected by applying a small and
accelerating potential and vice versa
• If V and r are kept constant then the value of m/z is directly
proportional to H. In this case at a lower have values of H, ions
with the smaller values would be collected, and as we increase
the value of H ions of higher m/z values would get recorded
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11. Double focusing spectrometry
 The term double focusing is applied to mass spectrometers in which the directional
aberrations and the energy aberrations of a population of ions are simultaneously
minimized.
 Careful selection of combinations of electrostatic and magnetic fields.
 Ion beam is first passed through an electrostatic analyser (ESA) consisting of two
smooth curved metallic plates across which a dc voltage is applied.
 Effect of limiting the kinetic energy of the ions reaching the magnetic sector to a
closely defined range.
 Ions with energies greater than average strike the upper side of the ESA slit and are
lost to ground. Ions with energies less than average strike the lower side of the ESA
slit and are thus removed.
 The most sophisticated of these are capable of resolution in the 105 range.
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12. Analysis of ions
 The curvature in the ion path is obtained by applying the magnetic field in
the direction perpendicular to the direction of motion of ions
 The ions with higher m/z values follow the path of larger radius and the
ions with lower m/z values follows the path of smaller radius
 Hence time taken by the particles of smaller m/z value to reach the
collector is shorter as compared to the required by the higher m/z value
ions
 Thus in magnetic field, the ions are separated based on their m/z ratio.
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14. Quadrapole mass ANALYZER
 They are generally considerably more compact than magnetic sector instruments
and are commonly found in commercial bench top mass spectrometers.
 The heart of a quadrupole instrument is the four parallel cylindrical (originally
hyperbolic) rods that serve as electrodes.
 Opposite rods are connected electrically, one pair being attached to the positive
side of a variable dc source and the other pair to the negative terminal. Variable
radio-frequency ac voltages, which are 1800 out of phase, are applied to each pair
of rods.
 To obtain a mass spectrum with this device ions are accelerated into the space
between the rod; by a potential difference of 5 to 10 V
 Meanwhile, the ac and dc voltages on the rods are increased simultaneously while
maintaining their ratio constant. At any given moment, all of the ions except those
having a certain mlz value strike the rods and are converted to neutral molecules.
Thus, only ions having a limited range of mlz values reach the transducer.
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16. Time of flight mass analyser
 The ions produced are then accelerated by an electric field pulse of 103 to 104 V.
The accelerated particles pass into a field-free drift tube about a meter long.
 All ions entering the tube ideally have the same kinetic energy, their velocities in
the tube must vary inversely with their masses, with the lighter particles arriving at
the detector earlier than the heavier ones.
 Typical flight times are in the microsecond range for a 1m flight tube
 The transducer in a TOF mass spectrometer is usually an electron multiplier whose
output is displayed on the vertical deflection plates of an oscilloscope and the
horizontal sweep is synchronized with the accelerator pulses; an essentially
instantaneous display of the mass spectrum appears on the oscilloscope screen.
 Because typical flight times are in the microsecond range, digital data acquisition
requires extremely fast electronics.
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18. Disadvantages of TOF
 In resolution and reproducibility, instruments equipped with TOF mass
analysers are not as satisfactory as those with magnetic or quadrupole
analysers.
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19. Ion trap analysers
 An ion trap is a device in which gaseous anions or cations can be formed and
confined for extended periods by electric and magnetic fields.
 Components of ion trap analysers:
 1) It consists of a central doughnut-shape ring electrode and a pair of end cap
electrodes.
 2) A variable radio-frequency voltage is applied to the ring electrode while the two
end-cap electrodes are grounded.
 3) Ions with an appropriate mlz value circulate in a stable orbit within the cavity
surrounded by the ring.
 4) As the radio-frequency voltage is increased, the orbits of heavier ions become
stabilized and those for lighter ions become destabilized, causing them to collide
with the wall of the ring electrode.
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20. Operation of ion trap analysers
Ion are admitted through a grid in the upper end cap.
The ions over a large mass range of interest are trapped simultaneously.
The ion trap can store ions for relatively long times, up to 15 minutes for
some stable ions.
A technique called mass-selective ejection is then used to sequentially
eject the trapped ions in order of mass by increasing the radiofrequency
voltage applied to the ring electrode
As trapped ions become destabilized, they leave the ring electrode cavity
via openings in the lower end cap. The emitted ions then pass into a
transducer such as the electron multiplier
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23. Vacuum system
 Diffusion and turbomolecular pumps often used to achieve the high vacuum
necessary for operating many mass spectrometers.
 These pumps are used with a rough pump (or forepump) to move gas molecules
from inside a vacuum chamber (a mass spectrometer) to outside the system.
 Although the pressures achieved by these two pumping systems are similar, the
cost of equipment, the operating costs, and the procedures and speed of pump
down and vent cycles are quite different.
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24. Necessity of vacuum pump
 At any pressure, gas molecules move in random directions, changing directions of
motion only through collision. The mean free path — the average distance between
collisions — of gas molecules can be calculated, and this parameter serves to
define the conditions of viscous and molecular flow
 When the mean free path of the gas molecules exceeds the dimensions of the
vacuum container, the system is under molecular flow conditions.
 Under such conditions, the residual gas molecules move without colliding with
other gas molecules, instead ultimately colliding with the surfaces and devices
within the vacuum chamber.
 Pumping is accomplished when a net (non random) direction to the movement of
residual gas molecules in the vacuum chamber is attained.
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25. Types of pumps
Diffusion pump
• In a diffusion pump, a net direction
is achieved by collision of the
residual gas molecules with a
directed and confined stream of gas-
phase molecules of the pump’s
working fluid
Turbomolecular pump
• In a turbomolecular pump, the
residual gas molecule collide with
the angled spinning rotors on a
turbine shaft.
In both cases, the net direction imparted to the residual gas molecules is into a region
of higher pressure and toward the exhaust of the high vacuum pump.
The exhaust of the high vacuum pump is connected through the foreline to a rough
pump that accomplishes the transport of the residual gas molecules to the final exhaust
at atmospheric pressure
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27. Reference
 Principles of Instrumental Analysis, by Douglas A. Skoog (Stanford
University), F James Holler(University of KentuckJ‘), Stanley R. Crouch
(Michigan State University), 8th edition, published by Thomson Brooks/Cole
 Instrumental methods of analysis, by Dr. Supriya Mahajan, Published
by CBS Publishers & Distributors Pvt. Ltd, 2010
 High vacuum pumps in Mass spectrometry, by Kenneth L Busch, Published
by Mass Spectrometry Forum, May 2001, www.spectroscopyonline.com
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