This document provides an outline and overview of mass spectrometry. It discusses the basic components and process of mass spectrometry including ionization, separation in an analyzer, and detection. It describes different types of ionizers, analyzers, and detectors. The document also covers isotopes and how they are observed in mass spectra through M+1, M+2, and other peaks. It discusses classification of isotopes and representation of isotopic abundance. Examples of mass spectra are provided to illustrate these concepts.

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Presented by:
oan.sahito@gmail.com

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OUTLINES
 INTRODUCTION
 BASIS OF SEPARARION
 IONIZER, ANALYZER AND DETECTOR TYPES
 ISOTOPES AND OBSERVATION OF ISOTOPES
 CLASSIFICATION OF ISOTOPES
 SPECTRAS
 ISOTOPIC ABUNDANCE
 CONCLUSION
 REFERENCES
 ACKNOWLEDGEMENTS

4. 
It subjects vaporized molecules to bombardment by a
stream of high-energy electrons, converting these
molecules to ions
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INTRODUCTION

5. 
These ions are then accelerated in an electric field
The accelerated ions are then separated according to
their mass-to-charge ratio in a magnetic or electric
field
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BASIS OF SEPARATION

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INSTRUMENTAL DIAGRAM

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Ionizer
Sample introduction/ionization method:
Ionization
method
Typical
Analytes
Sample
Introduction
Mass
Range
Method
Highlights
Electron Impact
(EI)
Relatively small
volatile
GC or liquid/solid
probe
to
1,000
Daltons
Hard method versatile
provides structure
info
Chemical
Ionization (CI)
Relatively small
volatile
GC or
liquid/solid
probe
to
1,000
Daltons
Soft method
molecular ion peak
[M+H]+
Electrospray (ESI)
Peptides
Proteins
non-volatile
Liquid
Chromatography
or syringe
to
200,000
Daltons
Soft method ions
often multiply charged
Fast Atom
Bombardment
(FAB)
Carbohydrates
Organometallics
Peptides nonvolatile
Sample mixed
in viscous
matrix
to
6,000
Daltons
Soft method but
harder than ESI or
MALDI
Matrix Assisted
Laser Desorption
(MALDI)
Peptides
Proteins
Nucleotides
Sample mixed
in solid
matrix
to
500,000
Daltons
Soft method
very high
mass

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Ion Analyzer
Analyzer System Highlights
Quadrupole
Unit mass resolution, fast scan, low
cost
Sector (Magnetic and/or
Electrostatic)
High resolution, exact mass
Time-of-Flight (TOF)
Theoretically, no limitation for m/z
maximum, high throughput
Ion Cyclotron Resonance (ICR)
Very high resolution, exact mass,
perform ion chemistry
Tandem Mass Spectrometry
(MS/MS)
Molecular structure determination

9. Detector, Vacuum
Detector
Convert the beam of ions in an electrical signal that can
be processed, stored, displayed and recorded in many
ways.
Vacuum
System
MS require the high vacuum is maintained in all
spectrometer components (except signal processing)
Electron Multiplier (most commonly used)
Faraday cup
Photographic plates
Scintillation type
Other:

10. 
 Mass spectrometers analyze gas-phase ions, not neutral
molecules
 Neutrals don’t respond to electric and magnetic
fields
 If a molecule cannot ionize, MS cannot help
 MS is not a “magic bullet” technique
 MS can describe atomic composition of an ion
 Connectivity of the atoms is much more challenging
 Although MS requires a vacuum, it cannot be
performed in a vacuum of information
 Deriving useful information from MS data often
requires some knowledge of the system under
investigation8/28/2014 10
IMPORTANT POINTS TO REMEMBER

11. Francis William Aston
"For his discovery, by means of his mass spectrograph, of isotopes,
in a large number of non-radioactive elements, and for his
enunciation of the whole-number rule8/28/2014 11
1922 Nobel Prize

12. 
Isotopes can be classified as
Mono-isotope
Di-isotope
Poly-isotope
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Isotopic Classification of the Elements

13. 
Monoisotopic Elements
.
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Among 82 naturally occurring stable elements,
20 elements do exist in the form of only one
single naturally occurring stable isotope.
Among the monoisotopic elements,
Fluorine (19F), Sodium (23Na), Phosphorus
(31P), and Iodine (127I)
belong to the more prominent examples in
organic mass spectrometry.

15. Methyl Floride
15

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Nonetheless,
there are many more such as
9Be, 27Al, 55Mn, 59Co, 75As, 93Nb,
103Rh, 133Cs, and 197Au

17. 
The monoisotopic elements are also referred to as
M, A or X elements.
If radioactive isotopes were also taken into
account, not a single monoisotopic element would
remain.
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Di-isotopic Elements

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Several elements exist naturally in two isotopes.
These elements can even be sub-classified into
those having
ONE isotope that is 1 u heavier than the most
abundant isotope.
The first group has been termed M+1 elements.
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Prominent examples of M+1 elements are
Hydrogen (1H, 2H = D),
Carbon (12C, 13C),
and
Nitrogen (14N, 15N).

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Those having one isotope that is 2 u heavier than
the most abundant isotope
They have been termed M+2 elements,
respectively

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Elements such as chlorine, bromine,
oxygen, sulfur, and silicon, can be dealt
with as X+2 elements

23. Silicon
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Among the X+2 elements,
Chlorine (35Cl, 37Cl),
Bromine (79Br, 81Br) are relatively common but
Copper (63Cu, 65Cu),
Gallium (69Ga, 71Ga),
Silver (107Ag, 109Ag),
Indium (113In, 115In),
and antimony (121Sb, 123Sb) also belong to this
group.

25. 84-49=35 49-14=35
A+2 peak with fragment of 35 indicates
Cl presence.
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26. Chlorine
35Cl (P= .75)
37Cl (P= .25)
Ratio 3:1
Probability : [M+] / [M + 2] = 0.75 / 0.25 = 3 / 1
100 : 33
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Methyl Bromide: An example of A+2 isotopes
The ratio of peaks containing 79Br and its isotope 81Br
(100/98) confirms the presence of bromine in the compound.

28. 
A-1 Peak
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If we do not restrict our view to the elements, one
should add the class of A–1 elements with one
minor isotope of 1 u lower mass than the most
abundant one

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The elements
Lithium (6Li, 7Li),
Boron (10B, 11B),
and Vanadium (50V, 51V)
come along with a lighter isotope of lower
abundance than the heavier one and thus, they
can be grouped together as X–1 elements.

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31. 
BORON
31

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Poly-isotopic Elements

33. 
The majority of elements are grouped as poly-
isotopic elements because they consist
of three or more isotopes showing a wide variety
of isotopic distributions.
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35. Tungsten
Index MS-fragmentation
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36. 
Isotopic abundances are listed either as their sum
being 100% or with the abundance of the most
abundant isotope normalized to 100%. The custom
of reporting mass spectra normalized to the base
peak.
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Representation of Isotopic Abundance

37. Isotopic abundances for Carbon containing compounds
Relative ratio: [M+1]+ / [M+ ] = n(0.989)n-1 (0.011) / (0.989)n
= n (0.011) / (0.989)
= n (0.0111)
In percentage: n x 1.1 %
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38. Isotopic abundances for other common nuclei
For 15N: [M+1]+ / [M]+ => n x 0.36%
For 33S: [M+1]+ / [M]+ => n x 0.80%
For 18O: [M+2]+ / [M]+ => n x 0.20%
For 34S: [M+2]+ / [M]+ => n x 4.42%
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39. 
Have seen that for Cl and Br, having two common
isotopes, two radical cation peaks produced. What
about other elements having more than one isotope?
We know what the isotopes are and their natural
occurrence.
For the M+1 peak, one atom must be using an isotope
heavier by one.
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Molecular Peaks, M+1

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We will use isotopic occurrence data for H, C, O for
the M + 1 peak.

41. Technique to obtain molecular formula using intensities of M, M+1, M+2 peaks.
Consider the M+1 peak, nominal mass + 1.
If we know the formula we should be able to calculate the relative intensity of that peak
due to the contributions from each of the atoms present. Here are the major
contributors to M+1.
Example. Given the data.
Peak Intensity
150 (M) 100
151 (M+1) 10.2
152 (M+2) 0.88
Looking at M+2 there is no
Br, Cl or S. There could
be oxygen.
Even mass for M means
there could only be even
number of Nitrogen
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42. Technique to obtain molecular formula using intensities of M, M+1, M+2 peaks.
Example. Given the data.
Peak Intensity
150 (M) 100
151 (M+1) 10.2
152 (M+2) 0.88
Equations
M+1: (1.11% x # of C) +
(0.38 x # of N+ small
contributions from O
M+2: (0.20 x # of O) +
(1.1 x # of C)2/200
We can have 0 or 2 nitrogens. Even number.
We can have 0,1,2,3,4 oxygens. 0.88/0.2 < 5
Can have 0,1,2,3,4,5,6,7,8,9 carbons. 10.2/1.11 <10
Find molecular formulas having reasonable M+1 peaks
M+1 M+2
C7H10N4 9.25 0.38
C8H10N2O 9.61 0.61
C9H10O2 9.96 0.84
C9H14N2 10.71 0.52
Examine reasonable
formulae. Calculate M+1,
M+2 peaks
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43. Example. Identify this molecule
m/e Abundance
1 <0.1
16 1.0
17 21
18 100
19 0.15
20 0.22
Due to heavier isotopes
Molecular radical ion
Ejection of an H
H2O
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44. Example 2
m/e Abundance
12 3.3
13 4.3
14 4.4
15 0.07
16 1.7
28 31
29
30
31
32
100
89
1.3
0.21
Heavier isotopes
parent
H ejection
Oxygen
carbon
CH2O
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45. 
 The “exact mass” feature in ChemDraw will give you a
monoisotopic mass
 Not always correct for complex isotope patterns
 Two freeware apps are available from MSF website
“Links” page
 These can be used to predict the entire isotopic pattern as an
exportable image
 MS-Search program on GC-MS computer can be used
to retrieve mass spectra from NIST’02 library
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Some useful software tools

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Mass spectrometry is very useful technique for identification of
ISOTOPES, through different ionizaion sources for different
molecules
It is observed through study that isotope of some elements are
1unit heavier while others are 2unit heavier than most abundant
isotope hence shown as M+1 and M+2 peaks respectively in
Mass Spectra.
Isotopes 1unit lighter observed as M-1 peak in Mass Spectra.
Observation of poly-isotopes as M+3 and so on.

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REFERENCES
1. MASS SPECTROMETRY BY JURGEN H GROSS, SPRINGER
INTERNATIONAL EDITION
2. NIST WEB BOOK http://webbook.nist.gov
3. LECTURE SLIDES OF DR SHAHABUDDIN MEMON
4. WIKIPEDIA
5. SPECTROMETRIC IDENTIFICATION OF OGANIC COMPOUNDS
BY ROBERT M.SILVERSTEIN 7th EDITION 2005
6. http//www.chemistry.ccsu/glagovich/teaching/316/ms/
7. GOOGLE IMAGES FORM www.google.com
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