Mass spectroscopy is a technique used to identify molecules based on their mass. It works by ionizing molecules and then separating the resulting ions based on their mass-to-charge ratio. The document discusses the basic principles and instrumentation of mass spectroscopy. It explains how molecules are ionized by bombarding them with electrons, then the ions are accelerated and deflected based on their mass-to-charge ratios before being detected. Key aspects like molecular ion peaks, fragmentation patterns, and isotopic peaks are described to help interpret mass spectra.

1. Mass Spectroscopy
By
Mr. G. P. Sadawarte
Asst. Professor and Head ,
Dept. of Chemistry
B. P. Arts, S.M.A. Sci. and K.K.C. Comm. College chalisgaon
Email: gautamsadawarte@gmail.com
B.P. Arts, S.M.A. Science And K.K.C.
Commerce College, Chalisgaon,

2. Introduction
Molecular mass and elements detection
Principle of MASS
• Substance in gaseous state or vapor state high voltage
electric current to loss electron to gives cation.
• Cation accelerated and passes to electric and
magnetic field deflected
• deflection depend upon mass to charge ratio
• 70 e. V. energy

3. • Mass spectra is used in two general ways:
1) To prove the identity of two compounds.
2) To establish the structure of a new a compound.
• The mass spectrum of a compound helps to establish
the structure of a new compound in several different
ways:
1) It can give the exact molecular mass.
2) It can give a molecular formula or it can reveal the
presence of certain structural units in a molecule.
Introduction

4. • Mass spectroscopy deals with the examination of the characteristics
fragments(ions) arising from the breakdown of organic molecules.
• A mass spectrum is the plot of relative abundance of ions against
their mass/charge ratio.
• The basic aspect of organic mass spectrometry consist of
bombarding the vapour of an organic compound with a beam of
energetic electron accelerated from a filament to an energy of 70
eV to form positively charged ions (molecular ions)
• The additional energy of the elecrons is dissipated in breaking the
bonds in the molecular ion, which undergoes fragmentation to yield
several neutral or positively charged species.
• This fragmentation may result in the formation of an even- electron
ion and radical.
Basic Theory

5. • The various positive ions, thus formed, can be accelerated and
deflected by magnetic or electric fields.
• The deflection of ions, however, depends on its mass, charge and
velocity.
• a given charge, velocity and deflecting force, the deflection is less
for a heavy particle as compared to that of a light one.
• Thus, a number of beams each containing ions with the same m/z
values are obtained.
• These beams are then made to strike against a photographic plate
where not only they appear as separate lines but the intensity of
each peak is also recorded.
• The clear visual presentation of a mass spectum is usually obtain
by plotting m/z value against relative abundance, assigning the
most abundant ion (base peak)in the spectrum as100 per cent.
Basic Theory

6. Fragmentation in mass
M + e 50 -70 eV
M
Moleculer ion peak
+ 2 e
M M1 M2
+
M M1 M2
+
OR

7. Instrumentation

8. Instrumentation
• A beam of high-energy electrons is emitted from a filament
that is heated to several thousand degrees Celsius.
• These high-energy electrons strike the stream of molecules
that has been admitted from the sample inlet system.
• The electron–molecule collision strips an electron from the
molecule creating a cation.
• Most organic compounds have ionization potentials ranging
between 8 -15 electron volts (eV).
• Beam of electrons does not create ions with high efficiency
until it strikes the stream of molecules with a potential of
50 to 70 eV
• Standard 70-eV electron beam is used.
Ionization Chamber

9. Instrumentation
• Acceleration and Deflection
• once the sample has been ionized, the beam of ions is
accelerated by an electric field or magnetic field so
they have same KE and then passes into the mass
analyzer.
• Mass analyzer-the region of the mass spectrometer
where the ions are separated according to their mass-
to-charge (m/z) ratios.
• Just like there are many different ionization methods
for different applications.
• there are also several types of mass analyzers.
• Magnetic Sector Mass Analyzer, Double-Focusing Mass Analyzers ,
Quaterpole Mass Analyzers, Time of flight mass analyzer

10. Instrumentation
• Detector
• Some ions move towards detector
• Mass to charge ratio analyzed by detector
• The beam of ions passing through the machine is
detected electrically
• Detector of a typical mass spectrometer consists of a
counter that produces a current that is proportional to
the number of ions that strike it.
In a case like this, an ion of any given m/z value makes it through the
analyzer only 1 time out of 300. Clearly, each peak in the mass spectrum
represents a very small electrical signal, and the detector must be able to
amplify this tiny current.

11. Nature of spectrum
• The signal from the detector is fed to a recorder, which
produces the mass spectrum. In modern instruments, the
output of the detector is fed through an interface to a
computer.
• The x-axis of the mass spectrum is the m/z ratio, and the y-
axis is ion abundance
A portion of a typical
mass spectrum—that of
dopamine,a substance
that acts as a
neurotransmitter
in the central
nervous system

12. • When a molecule is bombarded with electrons in high vacuum
in Mass spectrometer, it is converted into positive ions by loss
of an electron. These ions are called as Molecular or Parent
ions.
M + e → M +° + 2e —
Where, M – represents the Molecule;
M+° – represents the Molecular or Parent ion
• Height of molecular ion peak is greater
• Aromatic is more intense than aliphatic
• It is represented by M+°
Molecular ion or Parent ion
σ electrons > non-conjugated п >
conjugated п > non bonding or
lone pair of electrons.
The order of energy required
to remove electron

13. Base Peak
• The most intense peak (tallest)in mass spectrum because
of ion with the greatest abundance called as base peak
• base peaks are not always molecular ions, and molecular
ions are not always base peaks.
The clear visual presentation of a mass
spectrum is usually obtain by plotting
m/z value against relative abundance,
assigning the most abundant ion in the
spectrum as 100 per cent

14. Mass of methenol
• In the spectrum of methanol
peak shows at m/z ratio =31
is more intense peak called as
base peak due to loss of H.
• While molecular ion peak
appear at m/z ratio = 32

15. Metastable peak
• Fragment of a parent ion will give rise to a new ion (daughter)
plus either a neutral molecule or a radical.
• An intermediate situation is possible; M1+ may decompose to M
2+ while being accelerated.
• The resultant daughter ion M2+ will not be recorded at either M1
or M2, but at a position M * as a rather broad, poorly focused
peak. Such an ion is called a metastable ion
• Metastable ions have lower kinetic energy than normal ions and
metastable peaks are smaller than the M1 and M2 peaks and also
broader.
• These metastable ions arise from fragmentation that takes place
during the flight down through ion rather than in the ionization
chamber.

16. Metastable peak
Molecular ions formed in the ionization chamber do one of
the following things:
1. Either they decompose completely and very rapidly in
the ion source and never reach the collector (as in case
of highly branched molecular ions with life times less
than 10 -5 seconds).
2. Or else they survive long enough to reach the collector and
be recorded there (life times longer than 10 -5).
Metastable ions are useful in helping to establish fragments routes.
Metastable ion peak can also be used to distinguish between
fragmentation Processes, which occur in few microseconds

17. Isotopic peak
• In mass spectrum of halogen multiple peak occur due to
different isotope of halogen are called as isotopic peak
https://www.google.com/search?q=isotopic+peak+of+HCl+in+mass&sxsrf=ALeKk01Eh6Hzib7y7vLsSucxaW3J47E1qw:1621056085359&s
ource=lnms&tbm=isch&sa=X&ved=2ahUKEwjUtYPBMrwAhUX7HMBHQpCBEoQ_AUoAXoECAEQAw&biw=1366&bih=657#imgrc=aSRDzrVtB
PyaeM
A compound with 1 chlorine
atom gives a M+2 peak, which is
one third the intensity of the
molecular ion peak(M+) due to
the presence of Molecular ion
containing Cl 37 isotope.{Cl has
two isotope Cl 35 & Cl 37 (3:1) }
Aliphatic chlorine compounds
fragment mainly by the loss of
HCl to give peaks at M-36 and
M-38. HCl peaks can also be seen
at m/z 36, 38

18. Isotopic peak
• In a mono bromo derivative the M+2 peak is almost of
equal intensity to the molecular ion and is due to the
presence of molecular ion containing Br 81 isotope. {Br
has two isotope Br 79 & Br 81 (1:1) }
Fluorine and Iodine
being mono isotopic
do not give these
patterns.(F-19 and I- 127
only)
https://www.google.com/search?q=isotopic+peak+of+CH3Br+in+mass&tbm=isch&ved=2ahUKEwirypjC-MrwAhX5xnMBHUbXDqEQ2-
cCegQIABAA&oq=isotopic+peak+of+CH3Br+in+mass&gs_lcp=CgNpbWcQA1DDuQpYxtwKYJXeCmgAcAB4AIAB0QaIAeILkgEHMC40LjYtMZgBAK
ABAaoBC2d3cy13aXotaW1nwAEB&sclient=img&ei=V1qfYOvCMPmNz7sPxq67iAo&bih=657&biw=1366#imgrc=oloXREhz6e8VgM

19. • organic compounds containing exclusively hydrogen,
carbon, nitrogen, oxygen, silicon, phosphorus,
sulfur, and the halogens either have
• if a molecular ion has an odd mass it must have an
odd number of nitrogen(s) and that a molecular ion
with an even mass must either lack nitrogen atoms
or contain an even number of them
• NH3 M/Z= 17
• C2H5NH2 M/Z= 45
• C5H5 N2 M/Z= 94
• CH4 M/Z= 16,
• CH3OH M/Z=32
• CH3CN M/Z=41
Nitrogen Rule

20. The ―Rule of Thirteen‖ can be used to identify possible
molecular formulas for an unknown hydrocarbon, CnHm.
{C+H=12+1=13}
Step 1: n = M+ /13 (integer only, use remainder in step 2)
Step 2: m = n + remainder from step 1
• Example: The formula for a hydrocarbon with M+ =106
can be found:
–Step 1: n = 106/13 = 8 (R = 2)
– Step 2: m = 8 + 2 = 10
– Formula: C8H10
Rule of Thirteen

21. Example: The formula for a hydrocarbon with M+ =94 can
be found:
–Step 1: n = 94/13 = 7 (R = 3)
–Step 2: m = 7 + 3= 10
– Formula: C7H10
If a heteroatom is present, – Subtract the mass of each
heteroatom from the MW – Calculate the formula for the
corresponding hydrocarbon – Add the heteroatoms to the
formula
Rule of Thirteen

22. • Introduction to Spectroscopy, Donald L. Pavia Gary M.
Lampman George S. Kriz James R. Vyvyan..
• Sharma Y.R. Elementary organic spectroscopy principles and
chemical applications. 1 ed. S. Chand and Company ltd; New
Delhi :2008 by Y.R. Sharma.
• Spectrometric Identification of Organic Compounds, R. M.
Silverstein and F. X. Webster , John Wiley and Sons.
• Nirali Publication & prashant publication textbook
KBCNMUjalgaon.
References

23. Any ?