jiwaji university gwalior Msc.pharmaceutical chemistry

1. SEMINAR REPRESENTATION
TOPIC – MASS SPECTROSCOPY
Represented by
Khushi Sharma (M.SC 2nd Semester )
School of studies in environmental chemistry
Represented to
Dr Nimisha Jadon
[ Assistant Professor]

2. CONTENT
• Introduction to mass spectrometry
• Basic principle
• Instrumentation
• Ionization techniques
• Type of ions
• Fragmentation rules
• McLafferty rearrangement
• Applications of mass spectroscopy

3. INTRODUCTION TO MASS SPECTROMETRY
• Mass spectrometry (MS) is an analytical chemistry technique that
helps identify the amount and type of chemicals present in a sample
by measuring the mass to charge ratio and abundance of gas-phase
ions. A mass spectrum is a plot of the ion signal as a function of the
mass to charge ratio.

4. BASIC PRINCIPLE
• In this technique , molecules are bombarded with a beam of
energetic electrons.
• The molecules are ionized and broken up into many fragments ,some
of which are positive ions.
• Each kind of ion has a particular ratio of mass to charge, m/e ratio.
For most ions, the charge is one and thus, m/e ratio is simply the
molecular mass of the ions
• The ions passes through magnetic field and electric field to reach
detector where they are detected and signals are recorded to give
mass spectra.

5. INSTRUMENTATION

6. INSTRUMENATION
• Sample inlet: Sample stored in large reservoir from which molecules
reaches ionization chamber at low pressure in steady stream by a
pinhole called molecular leak
• Ionization: Atoms ionized by knocking one or more electrons off to
give positive ions by bombardment with a stream of electrons. Most
of the positive ions formed will carry charge +1.
• Acceleration: Ions accelerated so that they all have same kinetic
energy. +VE ions pass through 3 slits with voltage in decreasing order.
Middle slit carries intermediate and finals at zero volts.

7. INSTRUMENTATION
• Deflection – Ions are deflected by a magnetic field due to difference
in their masses . The lighter mass , more they are deflected . It also
depends upon the number of +VE charge an ion is carrying.
• Detector – The beam of ions passing through the mass analyzer are
detected by detector on the basis of m/z ratio. When an ion hit the
metal box. Change is neutralized by an electron jumping from metal
on to the ion.

8. IONIZATION TECHNIQUES
• Electron Ionization (EI-MS)
• Chemical Ionization (CI-MS)
• Desorption Technique (FAB)

9. ELECTRON IONIZATION(EI –MS)
• Beam of high energy electrons (~70eV) is emitted from filament
which is pre heated to several thousand degrees.
• High energy electrons strike stream of molecules to strip and electron
from molecule and form a cation.

10. CHEMICAL IONIZATION
• It is a soft ionization technique.
• Samples molecule are combined with ionized reagent gas which
is present in excess than the sample.
• Due to collision , various molecules are ionized by different
mechanism like proton transfer, electron transfer, adduct
formation.
• Any readily available gas or highly volatile liquid can be used as
CS-MS ionized reagent gas. For ex- Methane, Ammonia,
Isobutane and Methanol.
• In case of methane ,proton transfer takes place .

11. DESORPTION TECHNIQUE
• Allows analysis of large molecular weighted molecules.
• Included FAB-Fast atom bombardment method.
• Sample to be analyzed is dispersed in the matrix and placed in the
path of high energy neutral atoms.
• Xenon and Argon neutral atoms are used in this technique.
• Collision of neutral atoms takes place with molecule of sample to
form ions and are forwarded to accelerating plates and finally to mass
analyzer.
• Inn FAB, it uses neutral atoms to ionize sample which means both +VE
and –VE ions are formed could be analyzed.
• These molecules basically include polypeptides, nucleotides ,
oligonucleotides etc .

12. TYPES OF IONS
• Molecular ion/ Parent ion
• Fragment ion
• Rearrangement ion
• Multi charged ions
• Negative ions
• Meta stable ions

13. IONS PEAK ON SPECTRA

14. TYPES OF MASS ANALYZER
• Magnetic sector mass analyzer
• Double focusing mass analyzer
• Quadra pole mass analyzer

15. FRAGMENTATION RULES
• The relative height of the molecular ion peak is greatest for the
straight chain compound and decreases as the degree of branching
increases.
• The relative height of the molecular ion peak usually decreases with
increasing molecular weight in a homologous series.
• Cleavage is favoured to alkyl substituted carbon atoms ;the more
substituted ,the more likely is cleavage. This is consequence of the
increased stability of a tertiary carbon atom over a secondary ,which
in turn is more stable than a primary.

16. In alkyl substituted aromatic compounds ,cleavage is very probable at
the bond betta to the ring , giving the resonance stabilized benzyl ion
or more likely ,the tropylium ion.
EX : mass spectra of n-butyl benzene

17. McLafferty Rearrangement
• It involves the migration of gamma hydrogen atom followed by the
cleavage of betta bond.
• The rearrangement leads to the elimination of neutral molecules from
aldehydes , ketones , amines , unsaturated compounds , substituted
aromatic compounds.
• The rearrangement proceeds through a sterically hindered six
membered transition state.
• The molecular formula of the unknown compound can be determined
from the various fragment ions and also the parent ion of the mass
spectrum.

18. McLafferty Rearrangement

19. APPLICATIONS
• Environmental monitoring and analysis ( soil, water and air pollutants
,water quality.)
• Geochemistry – age determination, soil and rock composition ,oil and
gas surveying.
• Chemical and petrochemical industry – Quality control
• Identify structures of biomolecules ,such as carbohydrates ,nucleic
acids.
• Sequence biopolymers such as proteins and oligosaccharides.

20. REFERENCE
• Sharma Y.R. Elementary organic spectroscopy principles and chemical
applications . 1st ed. S. Chand and Company ltd
• Chatwal G.R, Anand S.K. Instrumental methods of chemical analysis .
1st ed. Himalaya Publishing house
• Skoog DA, West DM. principle of instrumental analysis . 2nd edition