Mass Spectroscopy seminar prepared by Shantanu Nimbalkar M Pharm 1st year IPER, Wardha

1. Mass Spectroscopy
.
08-10-2018IPER, Wardha 1

2. CONTENTS:-
 Principle.
 Theory.
 Instrumentation.
 Meta stable Ion.
 Isotopic Peaks.
08-10-
2018
IPER, Wardha 2

3. 08-10-2018IPER, Wardha 3

4. it is a total number of protons
and neutrons present in the atomic nucleus.
egS: C-12, O-16, N-14, F-17.
08-10-2018IPER, Wardha 4
No. of
Protons
(Z)
No. of
Neutrons
(N)
Mass
number
(A)

5. What is Mass spectroscopy??
 It is a modern analytical technique which is very
applicable in identification of unknown compound in the
sample, and also for structure elucidation.
 It is most reliable technique now days.
 Its process involves conversion of sample into its gaseous
ions due to bombardment of high energy beam of
electron with or without fragmentation, which are then
detected by detector according to there Mass to Charge
(M/Z) ratio and relative abundance.
08-10-2018IPER, Wardha 5

6. Principle of Mass Spectroscopy:-
 The main principle behind Mass spectroscopy is that, molecules in
the sample are bombarded with high energy beam of electron.
 The molecules are ionised and broken up into many fragments,
some of which are positive ions.
 And these fragmented ions are not only separated by their mass(M)
but also charge(Z).
 Each kind of ion has a particular mass to charge ratio(M/Z).
 But for most of the ions the charge is one(1) so the M/Z value for
those molecules is their molecular mass/ mass number.
 The intensity of each signal represent the relative abundance and
the most abundant signal is called as peak having relative intensity
100.
08-10-2018IPER, Wardha 6

7. 08-10-2018IPER, Wardha 7
Relative
Intensity 100 15.738.541.5
Fragmentation
(C5H12) M/Z= 72
NEOPENTANE
- e

8. 08-10-2018IPER, Wardha 8
29
15.7
41.5
57
72
m/e peak or parent
peak
mass of original
molecule
fragments peaks
100% intensity peak
called the base peak

9. 08-10-2018IPER, Wardha 9
M
e-
15
eV
+
+
++Parent/
Molecular
Ion M+
D
e
t
e
c
t
o
r
e-
70
eV
Fragmented ions
(Cations, Radicals,
neutral molecules,
radical cation etc.)

10. WORKING OF MASS SPECTROMETRY
08-10-2018IPER, Wardha 10

11. INSTRUMENTATION OF MASS SPECTROMENTRY
The parts in the mass spectrometric analyzer consist of
1) SAMPLE INLET SYSTEM .
2) ION SOURCE .
3) MASS ANALYSER .
4) ION DETECTOR .

12. SAMPLE INLET SYSTEM
 The selection of a sample inlet depends upon the sample state.
 Mainly the gaseous state molecules are used in inlet system.
 But solid and liquid sample also used by inlet system.
 The rate at which the sample introduced into an ionization chamber must
remain constant so that the relative abundances of different species in mass
spectra can be determined.
 In mass spectrometry very small amount of sample i.e. 1µ mole is required.
 Solid samples directly inserted into ionization chamber and volatization is
controlled by heating the probe.
 Liquid sample are handled by hypodermic needles injection through a
silicon rubber dam.
 Gaseous samples are leaked directly into ionization chamber by the help
of mercury monometer.
08-10-2018IPER, Wardha 12

13. Methods of sample ionization
 Many ionization methods are available, ionization method to be used
should depend on the type of sample under investigation and the mass
spectrometer available.
 Ionization methods include the following:
 Electron Impact (EI)
 Chemical Ionization (CI)
 Field Desorption / Field Ionization (FD/FI)
 Atmospheric Pressure Chemical Ionization (APCI)
 Electrospray Ionization (ESI)
 Fast Atom Bombardment (FAB)
 Matrix Assisted Laser Desorption Ionization (MALDI)
 Thermospray Ionization (TSP)
08-10-2018IPER, Wardha 13

14. 08-10-2018IPER, Wardha 14

15. 08-10-2018IPER, Wardha 15

16. ION SOURCE
 The first and important step to obtained mass spectrum is to ionize the sample
under investigation.
 The minimum energy require to ionize an atom or a molecule is called ionization
potential.
 The common technique used for formation of ions is by bombardment of high
energy beam of electron.
 The bombardment of electron is produced from an electrically heated tungsten
filament.
 Molecular ions are formed only when the energy of electron beam reaches to 10- 15
eV.
 Because the energy require for removing one electron from the neutral parent
molecule is usually 10 eV.
 And fragmentation of ions is only happen when energy of beam reaches to
70 eV.
Because if energy is high around 70eV, then additional energy is consumed in
fragmenting the parent or molecular ion. This result into fragmented ions or daughter
ion 08-10-2018IPER, Wardha 16

17. ANALYZERS USED IN MASS SPECTROMETRY
 All mass analyzers use static or dynamic electric and magnetic fields that can be alone or combined.
 Once the gas-phase ions have been produced, they need to be separated according to their masses, which must be determined.
 The physical property of ions that is measured by a mass analyzer is their mass-to-charge ratio (m/z) rather than their mass alone.
 Each mass analyzer has its advantages and limitations.
Types of analyzers used in mass spectrometry.
Type of analyzer Symbol Principle of separation
 Electric sector E or ESA Kinetic energy
 Magnetic sector B Momentum
 Quadrupole Q m/z (trajectory stability)
 Ion trap IT m/z (resonance frequency)
 Time-of-flight TOF Velocity (flight time)
 Fourier transform ion cyclotron resonance FTICR m/z (resonance frequency)
 Fourier transform orbitrap FT-OT m/z (resonance frequency)
08-10-2018IPER, Wardha 17

18. QUADRUPOLE ANALYZERS
 The quadrupole analyser is a device which uses the stability of the trajectories in
oscillating electric fields to separate ions according to their m/z ratios.
 A quadrupole mass filter consists of four parallel metal rods. The rods must be
perfectly parallel
 Two opposite rods have an applied potential of (U+Vcos(wt)) and the other two rods
have a potential of -(U+Vcos(wt)), where U is a dc voltage and Vcos(wt) is an ac
voltage.
 A positive ion entering the space between the rods will be drawn towards a negative
rod. If the potential changes sign before it discharges itself on this rod, the ion will
change direction.
 For given dc and ac voltages, only ions of a certain mass-to-charge ratio pass through
the quadrupole filter and all other ions are thrown out of their original path.
 A mass spectrum is obtained by monitoring the ions passing through the quadrupole
filter as the voltages on the rods are varied.
08-10-2018IPER, Wardha 18

19. 08-10-2018IPER, Wardha 19

20. Time of Flight (TOF) MASS ANALYZER
 It is a non-magnetic separation
 The time-of-flight (TOF) mass analyzer is based on the simple idea that the
velocities of two ions, created at the same instant with the same kinetic
energy, will vary depending on the mass of the ions—the lighter ion will have
a higher velocity. If these ions are traveling toward the mass spectrometer’s
detector, the faster (lighter) ion will strike the detector first.
08-10-2018IPER, Wardha 20

21. DETECTORS USED IN MASS SPECTROMETRY
 The ions pass through the mass analyser and are then
detected and transformed into a usable signal by a detector.
 Detectors are able to generate from the incident ions an
electric current that is proportional to their abundance.
 Three types of ion detectors are used:
 Faraday cup detector (electron current from well protected
electrode)
 Electron multiplier detector (galvanometers with sensitized
paper strip chart recorder)
 Photographic plate detector (photographic results in double-
focus)
08-10-2018IPER, Wardha 21
 The ions pass through the mass analyser and are then
detected and transformed into a usable signal by a detector.
 Detectors are able to generate from the incident ions an
electric current that is proportional to their abundance.
 Three types of ion detectors are used:
 Faraday cup detector (electron current from well protected
electrode)
 Electron multiplier detector (galvanometers with sensitized
paper strip chart recorder)
 Photographic plate detector (photographic results in double-
focus)
 The ions pass through the mass analyser and are then
detected and transformed into a usable signal by a detector.
 Detectors are able to generate from the incident ions an
electric current that is proportional to their abundance.
 Three types of ion detectors are used:
 Faraday cup detector (electron current from well protected
electrode)
 Electron multiplier detector (galvanometers with sensitized
paper strip chart recorder)
 Photographic plate detector (photographic results in double-
focus)

22. FARADAY CUP DETECTOR
 The basic principle involves that the incident ion strike the dynode
surface which emits electron and induces a current which is amplified
and recorded.
 A Faraday cup is made of a metal cup or cylinder with a small orifice.
 Ions reach the inside of the cylinder and are neutralized by either
accepting or donating electrons as they strike the walls. This leads to
a current through the resistor. The discharge current is then amplified
and detected. It provides a measure of ion abundance.
 The dynode electrode ids made of secondary emitting material like
CsSb, GaP, BeO.
08-10-2018IPER, Wardha 22

23. ELECTRON MULTIPLIER
 Electron multiplier are the most commonely used
detector in MS. Specially when positive and negative
ions needs to be detected on the same instrument
 Dynodes made up of copper-beryllium which
transduces the initial ion current, and electron emitted
by first dynode are focused magnetically from dynode
to the nest
 Final current is amplifies more than millions times.
08-10-2018IPER, Wardha 23

24. 08-10-2018IPER, Wardha 24

25. Metastable ion
This is one type of the ionization which done in the analyser
region rather than source region.
Molecular or parent ion did not fragmented inside the source
region due to some what stability they get, and then they
travels into the analyser region and their they get fragmented
into smaller ion and because of they have travelled long path
that’s why they are called Metastable ion.
Metastable ions are easily recognized in the mass spectrum
due to its characteristics of peak like,
1) They show broad peaks than normal ions.
2) They show relatively low abundance.
08-10-2018IPER, Wardha 25

26. FORMATION OF METASTABLE
ION
 Consider M* as an molecular or parent ion m*1 as an daughter ion, if
M* converted to m*1 in the source region then m*1 has to travel all the
analyzer and to be detected as m*1 in detector,
 But if the conversion of M* to m*1 is done in the analyzer region
because of stability of parent ion(M*) and before the collector region
then m*1 is called metastable ion.
 Mass of metastable ion is depends upon the mass of metastable ion(M*)
itself and the mass of parent or molecular ion (Mp) too.
 Mass of metastable ion
M= M*/Mp
08-10-2018IPER, Wardha 26

27. FORMATION OF METASTABLE ION
08-10-2018IPER, Wardha 27
Sample
inlet M*
m*1
m*2
Analyzer
Ion
source
Detector
e- gun
Metastable ion

28. ISOTOPIC ION
Most elements are mixture of two or more
stable isotopes differing by one or 2 masses
Eg; Cl2 and Br2 have 2 isotopes as Cl35 : Cl37
and Br29: Br31 in ratio of 3:1 & 1:1 resp.
Presence can be recognized by isotopic
abundance observed in spectrum.
08-10-2018IPER, Wardha 28

29. 08-10-2018IPER, Wardha 29

30. Refrences:
 Sharma Y. R., book of elementary organic spectroscopy, published by
S. Chand publisher, page number 280.
 Chatwal R. G., Instrumental methods of chemical analysis, published
by Himalaya publishing house. Page no.55
 H Edmond, S Vincent, Book of mass spectromentry 3rd edition.
 Pavia, Lampman. introduction to spectroscopy, 4th edition.
 www.Wikipedia/massspectroscopy.com
 https://www.slideshare.net/solairajananant/mass-spectrometry-
38534267
08-10-2018IPER, Wardha 30

31. 08-10-2018IPER, Wardha 31