This document provides an overview of mass spectroscopy including its instrumentation and applications. It describes how mass spectroscopy works by bombarding compounds with electrons to produce ions or fragments that are then separated by mass and detected. The key components of a mass spectrometer are described as the sample inlet, ion source, mass analyzer, detector, and vacuum system. Common types of mass analyzers like magnetic sector, quadrupole, and time-of-flight are explained. Applications of mass spectroscopy include identification of unknown compounds, clinical research, and determination of molecular formulas and fragmentation patterns.

1. NAVEEN K L
1st M.Pharm
Dept. of Pharmacology
Srinivas College of Pharmacy
Instrumentation and Application
of Mass Spectroscopy

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Contents:
Introduction
Instrumentation
Applications
References

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Mass Spectroscopy
Mass spectroscopy is a method in which the
compound under investigation is bombarded
with a beam of electrons which produce an
ionic molecule or fragments of the original
species.
The resulting charged particle is separated
according to their masses. The spectrum is
produced, known as mass spectrum.

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Instrumentation of Mass Spectrometer
1. Sample inlet system (sample handling system).
2. Ion source (Ionization chamber).
3. Electrostatic accelerating chamber.
4. Mass analyzers – Electrostatic and Magnetic analyzers.
5. Collectors – Detectors.
6. Vacuum system.
7. Data handling (amplifiers and recorders).

5. INSTRUMENTATION OF MASS
SPECTROMETER:
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SIGNAL
PROCESSOR
READOUT
ION SOURCE
MASS
ANALYSER
DETECTOR
Vacuum
system

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Mass spectrometer

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1. Sample inlet systems
Permits introduction of sample in to the ion source.
Mass spectrometer should have a vapour sample and
it should enter the ionisation chamber at constant rate.
The sample is converted into gaseous state in the
inlet system.

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The rate at which sample is introduced into ionization
chamber must remain constant so that to achieve relative
abundance of different species in mass spectrum can be
determined.
A sample size of about 1μ is required.
Only about 0.1% is ionized in the chamber.
Gas samples:
Transfer of sample from small containers like glass bulb, of
known volume( about 3ml) coupled to a mercury manometer.

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Liquid samples:
Hypodermic needle injection through a silicone
rubber dam.
The low pressure in reservoir draws in the liquid and
vaporizes it instantly.
Solids or Non-volatile liquids:
 Directly introduced on silica or platinum probe and
then volatilized by gentle heating .

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2. Ion Sources:
Chemical ionization:
In this method ionization results from ion molecule chemical
interaction.
The interaction process involves large amount of reagent gas
and a small amount of sample.
The reagent ion and sample molecule may react via any of the
several modes like proton exchange.
Reagent gas : Argon, helium and nitrogen show fragmentation
patterns with increased sensitivity.

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3. Mass analyzers and ion separator:
After passing through the electrostatic slits, ions enter in to the
analyzers.
Separate the ions according to their mass by charge ratio.
Different types of mass analyzers are:
1.Magnetic deflection or sector mass analyzer .
2.Double focus mass analyzer .
3.Quadrupole mass analyzer .
4.Time of flight mass analyzer.

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1. Magnetic deflection or sector mass analyzer:
 In this type, the homogeneous beam of ions from the slit can
be focus by a magnetic field in a shape of a sector.
 Gas phase molecules are ionized by a beam of high energy
electrons.
 Electrons may be ejected from molecules (ionization) or
bonds in molecules may rapture (fragmentation)
 Ions are then accelerated in a field (sector) at a voltage V.
 Basis of separation by m/z

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2. Double focus mass analyzer :
 Here the ions are analyzed according to their
momentum and translational energies.
 There is an electrostatic deflection field between the
ion source and the mass analyzer.
 As the ions are passed through the electrostatic
sector, they are deflected according to their
translational energy.
 Finally the magnetic sector disperses the ions
according to their momentum.

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3.Quadrupole mass analyzer:
The Quadrupole consists of four parallel rods. The opposing
rods have the same polarity while adjacent rods have opposite
polarity.
Each rod is applied with a DC and RF (Oscillating radio
frequency) voltage.Ions are scanned by varying the DC/RF
quadrupole voltages.
Only ions with the selected mass to charge ratio will have the
correct oscillatory pathway in the RF field.

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Quadrupole mass analyzer:

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4. Time of flight mass analyzer:
As the name indicates the mass spectrum is obtained depending upon
the time it took for the ion to reach the detector from accelerating
chamber.
The ions are accelerated and accelerated particles entering the tube have
same kinetic energies .
 The lighter particles arrives at the collector earlier than heavier
particles.
t = L/v ------- time of flight equation.
t - time taken for the ion to pass through a drift tube.
v - velocity of the charged particle.
L - length of the tube.

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Time of flight mass analyzer
Ion source reflector
flight tube
detector
same m/z, but higher
initial kinetic energy than
20 kV 23 kV
t (m/z)
Good resolution !
Mass accuracy ± 10-50 ppm
Sensitivity (low femto-mole)
I

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4. Detectors:
Ions are amplified and recorded.
Measure one m/z value at a time (single channel
detectors)
 Multiple detectors are used for multiple ion
detection
High resolution magnetic sector instruments use
multiple detectors (called Multicollectors)

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Various detectors used are-
I. Faraday cup collector.
II. Electron multiplier.
III.Ion sensitive photographic plates.
IV.Array detector.

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I. Faraday cup collector:
Simple and effective means of monitoring ion current.
When sufficient amount of sample is available, the
measurement can be done by collecting them in single Faraday
cup and scanning for different mass by charge values.
•Advantages:
Current as low as 10-5A may be detected.
•Disadvantage:
It needs high impedance amplifier , which limits the speed at
which spectrum can be scanned.

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Faraday cup collector

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II. Electron multiplier:
 When the amount of sample available is small, the ion current
produced is such a low current, which cannot be measured
directly with a Faraday cup and further amplification is carried
out by the secondary electron multiplier.
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III. Ion sensitive photographic plates:
Here the ions directly exposed to a photographic film.
This type of detectors used in mass analyzers. Which disperse
ions according to their mass to charge ratio.
The ion sensitive photographic plate integrate the ions and
record them.
This detector provides greater resolution and highest
sensitivity.

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IV. Array Detectors:
Used in Time of Flight Mass instruments
Employs a focal plane camera (FPC) consisting of an array of
31 Faraday Cup
Up to 15 m/z values can be measured simultaneously
 Exhibits improved precision compared with single channel
detectors.

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5. The vacuum system:
Whole instrument is kept under high vacuum conditions
10-6 to 10-7 torr.
Types of pump systems are used -
1. Oil diffusion pumps
2. Mercury diffusion pump

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6. Data handling:
Data are digitalized and collected on magnetic tape or stored in
a memory of computer.
7. Recorders:
Multichannel ultraviolet recorder.
Pens, tape recorders, oscillators other data collecting systems
are used as recording devices.

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Applications:
It is used in environmental analysis.
Identification of unknown compounds.
Used in forensic analysis.
Also used in clinical research.
In generation of Physico-chemical data.
To measure the relative molecular masses (Molecular
weight) with very high accuracy; from this can be
deduced exact molecular formula.

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Cont…
It is also used to find out the places within molecule
at which it prefers to fragment.
Mass spectrometry is being used to identify the
mixtures of complicated samples such as urine,
lymph, blood, and it is used with high sensitivity
methods to measure low doses and long time point
data.
Determination of isotopic composition of different
elements.

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References:
1. YR Sharma, S Chand. Elementary Organic Spectroscopy
Principle and Chemical application; P.No:292-95.
2. Gurudeep R. Chatwal, Sham K. Anand, ‘Instrumental methods
of chemical analysis; P.No: 2.278-2.283.
3. Skoog Holler, Crouch. Instrumemal Analysis. Ind six ed;
P.No:606-08.
4. Douglas A Skoog, Donald M West, F James Holler, Stanley R
Crouch. Fundamentals of Analytical Chemistry. Ninth ed;
P.No:806-16