Mass spectroscopy is a technique that determines the molecular mass of compounds by ionizing molecules and measuring their mass-to-charge ratios. It works by first volatilizing and ionizing molecules via electron bombardment, which produces molecular ions. The molecular ions are then accelerated and separated based on their mass-to-charge ratios using electric and magnetic fields. Finally, the ions are detected, and a mass spectrum is produced by plotting the relative abundances of each ion versus the mass-to-charge ratio. Key terms include molecular ion peak, daughter ion peaks, base peak, and metastable ions. Mass spectroscopy is widely used in science to determine molecular structures and isotopic abundances.

1. Mass Spectroscopy
By
Dr. P. R. Padole
Associate Professor
Department of Chemistry
Shri Shivaji Science College, Amravati.

2. SpectroscopySpectroscopy
Contents
 Introduction
 Defination
 Basic principle / Theory
 Brief outline of instrumentation.
 Ion formation and types
 Fragmentation processes
 Fragmentation patterns
 Fragmentation characteristics in relation to
parent structure and functional groups
2

3. What is a Mass Spectroscopy?
A Mass Spectroscopy is a machine that
weighs molecules !
0 units

4. What is a Mass Spectroscopy?
A Mass Spectroscopy is a machine that
weighs molecules !
12 units
8 9 10 11 12 13 14 15 16
C

5. What is a Mass Spectroscopy?
A Mass Spectroscopy is a machine that
weighs molecules !
16 units
8 9 10 11 12 13 14 15 16
C N O
H = 1

6. Basic Chemistry
• Everything is made of Atoms
– Atoms are made of protons, neutrons, and
electrons
– Many atoms together make up molecules
U
ATOM

7. Oxygen
Nitrogen

8. 8

9. 9

10. 10

11. Carbon

12. Do you know?
Mass Spectroscopy

13. Introduction:
M. S. is
used to
Determine the relative atomic mass
of elements
Molecular mass of compounds
Structure of compounds
Mass spectroscopy is used widely in science.

14. Mass Spectroscopy?
 Mass spectroscopy is an
instrumental technique in which
sample is converted rapidly into
positive ions by electron
bombardment and charged particles
are separated according to their
masses (m/z or m/e values).
14
A mass spectrometer is a device that
measures the mass-to-charge (m/z) ratio snoi fo.

15. pramodpadole@gmail.com
Application of Mass spectroscopy:
Determining Molecular mass
Finding out structure of
unknown compounds
“Verifying the identity and
purity of a known substance”
Application of
Organic
Chemistry
Providing data
on isotopic
abundance

16. Question

17. Q.1) Write / Explain in brief principle of mass spectroscopy.
(S-10, W-13, S-14 & S-19, 2-4 Mark)
Q.2) Explain the principle of mass spectroscopy.
(W-12, 2 Mark)
Q.3) Describe in short the principle of mass spectroscopy.
(W-15, 4 Mark)
Q.4) Describe the principle of mass spectroscopy.
Q.5) Which of the following spectroscopy would determine molecular
weight of a compound? (S-18, ½ Mark)
(a) UV-Visible (b) NMR (c) IR (d) Mass spectroscopy
17

18. Theory or Principle:
The basic principle is quite simple.
 A compound whose mass spectrum is to be
determined is first converted into a vapour form.
Liquid samples are volatilized under vacuum
in the heated reservoir and the vapour is leaked
into ionization chamber where the pressure is
kept very low (10-5 mm).
18Only the cation is detected by mass spectroscopy.

19. 19
A mass spectrometer is a device that measures the mass-to-charge (m/z) ratio snoi fo.

20. Electron Impact
M
e-
e-
e-
M:(g) + e-  M.+
(g) + 2e-
This reaction creates the molecular ion so is very
useful.
However, the excess energy from the electron can
cause the molecular ion to fall apart: Fragments

21. 21
2

22. Electron Impact
A+M
e-
e-
e-
M:(g) + e-  M.+
(g) + 2e-
M.+
(g)  A+
Fragment 1 (g) + B.
Fragment 2 (g)
• Electron energy is chosen by compromise.
• Fragment Information is useful. It can help structural determination.
However, many ions produce only fragments with no molecular ion
remaining. Molecular ion often very unstable.
• 70 eV “Classical Spectra” to be used for comparisons
BB

23. Calculation of m/z (m/e) values:
• For a calculation of m/z (or m/e) value the
masses of atoms are reported in amu.
23
12
C=12 13
C=13 H=1 D=2
14
N=14 16
O=16 19
F=19 35
Cl=35
37
Cl=37 79
Br=79 81
Br=81 S=32
I=127 etc

24. 24
lone pair (n) < conjugated π (>C=C-C=C<) < non conjugated π (>C=C-C-C=C<) < σ electrons

25. A mass spectrometer

26. It consists of
Inlet system
Ion source
Mass analyzer
Detector

27. Working in the Instrument:
27
Only the cation is detected by
mass spectroscopy.

28. SpectroscopySpectroscopy
Some ions with their m/e values:
28
(i) CH3
+
= 15 mass units
(ii) C2
H5
+
= 29
(iii) C3
H7
+ = 43
(iv) C4
H9
+
= 57
(v) C5
H11
+ = 71
(vi) C6
H5
+
= 77
(vii) CO + = 28
(viii) C2
H4
+ = 28
(ix) CH3
-C
H
O
H
: .+
= 45

29. 29

30. Electron Impact
A+M
e-
e-
e-
M:(g) + e-  M.+
(g) + 2e-
M.+
(g)  A+
Fragment 1 (g) + B.
Fragment 2 (g)
• Electron energy is chosen by compromise.
• Fragment Information is useful. It can help structural determination.
However, many ions produce only fragments with no molecular ion
remaining. Molecular ion often very unstable.
• 70 eV “Classical Spectra” to be used for comparisons
BB

31. MASS ANALYZER
 The positively charged ions produced in the ion chamber are
accelerated by applying an acceleration potential of 10 KV.
 These ions then enter the mass analyzer where there
differentiate on basic of their mass to charge (mz) ratio.

32. ION DETECTOR:
 ELECTRICAL METHOD:
 In this method the detector is usually electron multiplier
which produce electrical signal proportional to number
of ions, sticking the detector.These signals are
amplified by a series of dynodes.The result of these
amplified signals is presented in the form of graph.
 The amplified signals
from electron multiplier is
usually recorded by
 A chart recorder
 A computer

33. SpectroscopySpectroscopy
Deflection of cations:
33

34. 34

35. Question

36. SpectroscopySpectroscopy
Q.1) Explain the terms: Mass spectrum.
(W-09, 2 Mark)
Q.2) A plot of mass to charge (m/z) ratio values along abscissa
and their relative abundance along the ordinate is called mass
spectrum.
(S-15, ½ Mark)
36 Mass

37. SpectroscopySpectroscopy
MASS SPECTRUM:
A plot of mass to charge (m/z) ratio values
along abscissa (X-axis) and their relative
abundance along the ordinate (Y-axis)
is called mass spectrum.
The m/z (or m/e) value of the parent ion (molecular ion) is equal to the
molecular (molar) mass of the compound.
m/z (or m/e)
Relativeabundance
10 20 30 40 50
Base peak (100 % intensity)
Molecular ion peak
M+
Daughter ion peaks
0 %
100%
(M+1)
(M+2)
Isotopic abundance
2

38. SpectroscopySpectroscopy
Q.1) Define term: Molecular ion peak.
(S-10, W-11, W-13, S-14, W-14, S-15 & W-16, 2 Mark)
Q.2) Define term: Parent ion. (S-11 & W-14, 2 Mark)
Q.3) Explain the terms: Molecular ion. (S-16, S-17 & W-17, 2 Mark)
Q.4) The last peak in the mass spectrum is called as molecular
ion peak. (W-16, ½ Mark)
Q.5) Explain the terms: Molecular ion peak with an example.
(W-19, 2 Mark)
Mass

39. Molecular ion or Parent ion:

40. SpectroscopySpectroscopy
Molecular ion or parent ion:
 Defination:
The peak at highest m/e (or m/z) value is
called as molecular ion or parent ion or
radical cation peak.
M: + e-
[ M ] + 2 e-
Neutral
Molecule
Molecular Ion
or Parent ion
10 -70 eV +.

41. SpectroscopySpectroscopy
Q.1) Explain the term: Peak area. (W-09 & S-18, 2 Mark)
Q.2) Define the term: Base peak.
(S-10, W-11, W-13, S-14, W-14, S-15 & W-16, 2 Mark)
Q.3) Explain the term Base peak with suitable example.
(S-13, W-17 & W-19, 2 Mark)
Q.4) A peak in mass spectrum whose intensity is assumed to be
100% is known as Base peak. (S-13, ½ Mark)
Q.5) In mass spectrum the peak given by most abundant ion and
whose intensity is assumed to be 100% is known as
Base peak. (W-15, ½ Mark)
Q.6) The peak corresponding to the most abundant ion in the mass spectrum
of a compound is called Base peak. (W-17, ½ Mark)
Q.7) What is base peak? (W-18, 1 Mark)
m/z (or m/e)
Relativeabundance
10 20 30 40 50
Base peak (largest peak or 100 % intensity)
Molecular ion peak
M+
Daughter ion peaks
0 %
100%
(M+1)
(M+2)

42. SpectroscopySpectroscopy
Base Peak or Peak Area:
Mass

43. SpectroscopySpectroscopy
Base peak:
 Defination:
The peak at highest intensity is called as
base peak.
(Relative intensity or relative abundance of
base peak is taken as 100%).

44. SpectroscopySpectroscopy
Q.1) Define the term: Daughter ion.
(S-11, 2 Mark)

45. SpectroscopySpectroscopy
Daughter ion or Fragment ion peak:
Defination:
When an energy is given further more upto 70 eV, molecular
ion fragments into daughter ions or fragments ions, it have lower
mass number than that of the parent ion.
 Therefore, daughter ion peaks are produced (obtained) at lower
m/e (m/z) values as compared to parent ion.

46. LOGO
Metastable ion (m*) or peaks:
(m2)2
m1
= m* (metastable ion)
Q.1) Explain the term: Metastable peak.(W-18 & W-2019, 2 Mark)

47. Metastable ion (m*) or peaks:
 Metastable peaks can be easily determined in a mass spectrum.
 Some important characteristics of these peaks are:
 They do not necessarily occurs at the integral m/e values
 These are much broader than the normal peaks and
 These are of relatively low abundance (intensity).
m1 m2 + neutral fragment
+ + m*
m2
m1
m/e
However, it is often possible for some of the m1 ions to decompose during
flight rather than in the ion chamber.
This diffused daughter ion formed in the flight is called metastable ion (m*).
Whereas, m1 & m2 are observed at unit m/e values, m* may appear at a functional m/e value.
It is denoted by m*.
(m2)2
m1
= m* (metastable ion)

48. SpectroscopySpectroscopy
Metastable ion (m*) or peaks:
Metastable ion (m*):
Molecularion
peak
Daughter
ion peaks
m1 m2 + neutral fragment
+ + m*
m2
m1
m/e
M + e m1 + 2 e
+10-15eV
70eV
Board

49. SpectroscopySpectroscopy Metastable ion (m*) or peaks:
However, it is often possible for some of the m1 ions to decompose during
flight rather than in the ion chamber.
This diffused daughter ion formed in the flight is called metastable ion
(m*).
Whereas, m1 & m2 are observed at unit m/e values,
m* may appear at a functional m/e value.
It is denoted by m*.
A mathematical relationship exists, during the interdependence of m1, m2 &
m*:
(m2)2
m1
= m* (metastable ion)
Molecular ion
peak
Daughter
ion peaks
m1 m2 + neutral fragment
+ + m*
m2
m1
m/e
M + e m1 + 2 e
+10-15 eV
70 eV

50. SpectroscopySpectroscopy
 Mass spectrum of ethane:
In alkanes, ionisation of C-C σ bonds is easier than that of C-H bonds due to
its stability of molecular ion.
But as we are bombarding molecular ion with 70 eV energy, this much energy
causes ejection of any electrons from molecule.
C C C C+
C C e-
Molecule
Molecular ion
Fragement
Cation Radical
Hemi-heterolysis+ 10 - 70 eV
C C C C+
C C e-
Molecule
Molecular ion
Fragement
Cation Radical
Hemi-heterolysis+ 10 - 70 eV
OR

51. SpectroscopySpectroscopy
Mass spectrum of n-propane:
CH3
-CH2
-CH3 + e CH3
-CH2
.+CH3
+ 2 e
__
(m/e = 44) 70 eV m/e = 44
Molecular ion
or parent ion

52. SpectroscopySpectroscopy
Types of Fission:
Homolytic Fission or Homolysis:
Homolysis – cleavage of a two electron sigma bond, one
electron staying with each fragement,
Heterolytic Fission or Heterolysis:
 Heterolysis – cleavage of a two electron sigma bond, both
electrons staying with one or other fragment, i.e., generates
the cations and anions

53. SpectroscopySpectroscopy
Types of Fission:
Hemi-Heterolytic Fission:
Definition: It is a cleavage of an ionized sigma bond; to
form cation and free radical.
 There is only one electron in the bonding sigma orbital,
hence the use of a single headed arrow.
 Note that: All molecular ions [cation-radicals] are written
inside square brackets.
 Hemi-Heterolysis: This special type of breaking of
ionized sigma covalent bond and
is possible in saturated hydrocarbons.
C C C C+
C C e-
Molecule
Molecular ion
Fragement
Cation Radical
Hemi-heterolysis+ 10 - 70 eV
C C C C+
C C e-
Molecule
Molecular ion
Fragement
Cation Radical
Hemi-heterolysis+ 10 - 70 eV
OR
A B
Hemi-Heterolysis
A B
A B
Hemi-Heterolysis
A B. + .
+

54. SpectroscopySpectroscopy
Some ions with their m/e values:
(i) CH3
+
= 15 mass units
(ii) C2
H5
+
= 29
(iii) C3
H7
+ = 43
(iv) C4
H9
+
= 57
(v) C5
H11
+ = 71
(vi) C6
H5
+
= 77
(vii) CO + = 28
(viii) C2
H4
+ = 28
(ix) CH3
-C
H
O
H
: .+
= 45
12
C=12 13
C=13 H=1 D=2
14
N=14 16
O=16 19
F=19 35
Cl=35
37
Cl=37 79
Br=79 81
Br=81 S=32
I=127 etc

55. SpectroscopySpectroscopy
Mass spectrum of n-propane:
CH3
-CH2
-CH3 + e CH3
-CH2
.+CH3
+ 2 e
__
(m/e = 44) 70 eV m/e = 44
Molecular ion
or parent ion

56. SpectroscopySpectroscopy
Neopentane
on the basis of mass spectrometry:
Q.1) Calculate m/z values for the molecular ions for each of the
Neopentane compounds. (W-11, 2 Mark)
Q.2)Describe mass spectrum of neopentane. (W-18, 4 Mark)

57. SpectroscopySpectroscopy
Neopentane
on the basis of mass spectrometry:
3o > 2o > 1o
H3C C CH3
CH3
CH3
H3C C
CH3
CH3
+ CH3
m/z = 72
H3C C CH3
CH3
CH3
e
_
Molecule of
Neopentane
10 - 70 eV
m/z = 57
H3C C CH3
CH3
CH3
m/z = 72
+
Hemi-Heterolysis

58. SpectroscopySpectroscopy
Methanol
on the basis of mass spectroscopy:
 Formation of Molecular ion & Daughter ions:
CH3
OH
H2C OH
H
+ HH2C OH
H3C OH CH3 + OH
m/z = 31
m/z = 32
m/z = 15m/z = 32
2)
(I) [ [
Q.1) Calculate m/z values for the molecular ions for each of the
Methanol compounds. (W-11, 2 Mark)
Q.2) Write the molecular ions of the following compound and
calculate the m/z values. (S-13, 2 Mark)
CH3OH

59. SpectroscopySpectroscopy
Mass spectrum of Ethanol:
 Q.1) Discuss /Explain the mass spectrum of ethanol.
(W-09 & W-14, 2-4 Mark)
 Q.2) Calculate m/z values for the molecular ions for each of
the Ethanol compounds. (S-13 & S-14, 2 Mark)
 Q.3) Calculate m/z values for the molecular ions for each of
the Methanol compounds. (W-15, 2 Mark)
CH3-CH2-OH
 Q.4) Calculate m/z values for the following molecular ion:
(W-16, S-17 & S-19, 2 Mark)
 Q.5) Give the structure of a compound C2H6O, whose mass spectrum
shows m/z values of 15, 29, 31 and 46.
(S-18, 4 Mark)
[CH3CH2OH]

60. SpectroscopySpectroscopy
Mass spectrum of Ethanol:
CH3
-CH2
-O-H
Base peak
CH3CH2OH e CH3CH2OH
M
(m/z=46)
CH2 OHCH3
m/z=31
Homolysis
CH3
m/z=15
Heterolysis
CH3CH2 OH
m/z=29
Heterolysis
CH3CH2 OH
CH3 CH2 OH
+
10 - 70 eV
CH3 CH2 OH CH2 OH
.

61. SpectroscopySpectroscopy
Mass spectrum of Acetone:
 Q.1) Discuss /Explain the mass spectrum of acetone.
 Q.2) Calculate m/e values for the molecular ions for each of
the Acetone compounds. (S-11, S-12 & S-14, 2 Mark)
 Q.3) Write the molecular ions of the following compound and
calculate the m/e values. (S-12, S-14 & W-14, 2 Mark)
CH3COCH3
 Q.4) Calculate m/z values for the molecular ions of the
Acetone compound. (W-11, 2 Mark)
 Q.5) Calculate m/z values for the following molecular ion:
[CH3COCH3]+. (S-17 & W-17, 2 mark)
 Q.6) Discuss the fragmentation of Acetone. (S-18, 4 Mark)
CH3C O
+.
..

62. SpectroscopySpectroscopy
Mass spectrum of Acetone:
H3C C
O
CH3 e H3C C
O
CH3
2 e
This is molecular ion
appeared at m/z = 58
+
10 - 70 eV
H3C C
O
CH3
Homolysis
H3C C O CH3
Acylium ion which is resonance
stabilized appeared at
m/z = 43
H3C C
O
CH3
Heterolysis CH3
m/z = 15
:
:
H3C C O+
m/z = 58
m/z = 58

63. SpectroscopySpectroscopy
Mass spectrum of Benzaldehyde:
 Q.1) Calculate m/z values for each of the following:
(S-16, 2 Mark)
 Q.2) Calculate m/z values for each of the following:
(S-16 & W-17, 2 Mark)
O +
C-H
.
m/e = 106
[C6H5-C-H]
O
+
.
m/z = 106

64. SpectroscopySpectroscopy
Mass spectrum of Benzaldehyde:
+H
O
H
O
M+
: m/z = 106
Homolysis
+ H
O
m/z = 105
Heterolysis
m/z = 77
:
e-
Molecule
:
H
O
M+
: m/z = 106
:
H
O
M+
: m/z = 106
:
H C O+
10 - 70 eV
Molecular ion

65. Problems

66. SpectroscopySpectroscopy
Some Important example on
Mass Spectroscopy:
Q.1) Write the molecular ions of the following
compounds and calculate the m/e values: (S-
12, S-14 & W-14, 2 Mark)
CH3-NH2
Ans: Fragments of m/e = 31, 30 & 28
+.CH3NH2 + e
- 10 - 70 eV
[ CH3NH2 ]
m/e = 31OR
+.
CH3 NH2 + e
- 10 - 70 eV
[ CH3 NH2 ]
m/e = 31
..

67. Q.2) Calculate the m/z (m/e) values for the
following ion in mass spectroscopy:
(S-15 &S-19, 2 Mark)
• Ans: m/e = 31
Q.3) Calculate the m/z (m/e) values for each of the
particles. (S-11, S-13 & S-14, 2 -4 Mark)
+.
[ CH3NH2 ]
(i) CH2=NH2 & (ii) CH3C O
+ .+ .

68. Q.4) Calculate the m/z (m/e) values for the molecular
ions of the following compounds: (W-15, 2 Mark)
CH3CH2NH2
Q.5) Calculate the m/z (m/e) values for the molecular
ions of the following compound: (W-11, 2 Mark)
(i) Ethyl chloride, CH3CH2Cl
Q.6) Write the molecular ions of the following
compound and calculate the m/z (m/e) values.
(S-13, 2 Mark)
CH3CHO
68

69. Q.7) Calculate the m/z (m/e) values for the
following ion in mass spectroscopy:
[(CH3)2CH]+ (S-15 & S-19, 2 Mark)
Q.8) Calculate the m/z (m/e) values for the
following ion in mass spectroscopy:
(S-16, 2 Mark)
69
+
CH3
CH3
CH-NH2
[ [

70. Q.9) Calculate the m/z (m/e) values for the
following molecular ion in mass spectroscopy:
(W-16 & S-19, 2 Mark)
70
[C6H5-CH3]

71. Q.10) Calculate the m/z (m/e) values for the
following ions: (W-18, 4 Mark)
71
[C6H5](i)
(ii) [CH3COOH]

72. Last Problem:
72
.
CH3CH2OH
[CH3CH2OH]
2e
2e
O
C
H3C CH3
O
H3C CH3
2e
e.g.-1)
e.g.-2)
e.g.-3)
m/e=78
m/e=46
m/e=58
+ e-
+ e-
+ e- 10 - 70 eV
10 - 70 eV
10 - 70 eV

73. SpectroscopySpectroscopy
Retro-Diels Alder fragmentation:
 Compounds containing six member cyclic alkene, like structures show
Retro-Diels Alder fragmentation in which two alpha-beta (α, β) bonds are
simultaneously broken.
Q.1) Draw the radical cation formed by ionization of cyclohexene. Suggest two
mechanisms which will account for a fragmentation in which C (4) and C (5)
are extruded as neutral ethylene.
e
Retro-Diels Alder fragmentation
m/z = 54
4
5
CH2
CH2
Ethylene



+
10 - 70 eV
CH2
CH2
Ethylene
Retro-Diels Alder fragmentation
4
5
e




+
10 - 70 eV
m/z = 54
OR

74. SpectroscopySpectroscopy
Mc-Lafferty fragmentation:
 Mc-Lafferty fragmentation which involves migration of γ -hydrogen to the
carbonyl oxygen atom. It is an intra-molecular elimination. This process
involves cleavage of the allylic bond and transfer of the γ –hydrogen to the
ionized bond. The radical cation charge stays within one or other of the
fragments.
 Compounds like alkenes, alkynes, carbonyl compounds containing gamma (γ)
hydrogen atom which flexible enough to form six member cyclic rings shows
Mc-Lafferty fragmentation.
 In this fragmentation process migration of gamma (γ) hydrogen and breaking of
alpha-beta (α, β) bond takes place simultaneously, via six member cyclic state.
O
C
C
H2
H3C
CH2
CH3
e
O
C
C
H2
H3C
CH2
CH2
H
Mc-Laferty
fragmentation.
OH
C
CH2
H3C CH2
m/z=58
CH2
 
 



Ethylene

75. 75

76. THE END!