Mass Spectroscopy

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Introduction ofMass Spectrometry
salmanzafar27_at_yahoo.com

• PRESENTED BY
• SALMAN ZAFAR
• 163 INORGANIC CHEMISTRY

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CONTENT

• DEFINATION
• INTRODUCTION
• HISTORY
• MASS SPECTROMETER
• PRINCIPLE
• STRUCTURE ANALYSIS
• FRAGMENTATION
• EXSAMPLES

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DEFINATION

• Mass spectrometry is the most accurate technique
  to determine the molecular mass and molecular
  composition of organic and inorganic compounds.
  It provides both qualitative and quantitative
  information about the molecular composition of
  organic and in organic compounds. It is also
  called positive ion spectra or line spectra.

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INTRODUCTION

• Powerful analytical technique
• Smallest scale
• Destructive technique
• Useful for identification of species

According to the IUPAC (International Union of
Pure and Applied Chemistry), it is the branch of
science dealing with all aspects of mass
spectrometers and results obtained with these
instruments.
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INTRODUCTION

• Why we say mass spectrometry not mas
  spectroscopy?
• In mass spectrometry there is no absorption of
  electromagnetic radiations. It is just a
  measurement of molecular weights of different
  molecules in a compound according to their m/z
  ratio.

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HISTORY
Brief History of Mass Spectrometry
J.J. Thomson. Discovered electrons by cathode
rays experiment. Nobel prize in 1906.
Francis Aston recognized 1st mass spectrometer
and measure z/m of ionic compounds.
First double focusing magnetic analyzer was
invented by Johnson and Neil.
Munson and Field described chemical ionization.
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HISTORY
Electrospray Ionization was invented by Dole,
Mack and friends.
Atmospheric Pressure Chemical Ionization (APCI)
was developed by Carroll and others.
F. Hillenkamp, M.Karas and co-workers describe
and coin the term matrix assisted laser
desorption ionization (MALDI).
w. Paul discovered the ion trap technique.
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HISTORY
Nobel prize pioneers

Joseph John Thomson1906 Nobel Prize for Physics(theoretical and experimental investigations on the conduction of electricity by gases) Francis William Aston1922 Nobel Prize for Chemistry (mass spectrograph, of isotopes, in a large number of non-radioactive elements) Wolfgang Paul1989 Nobel Prize for Physics(for the development of the ion trap technique) John Bennet Fenn2002 Nobel Prize for Chemistry (for the development of Soft Desorption ionization Method) Koichi Tanaka2002 Nobel Prize for Chemistry (mass spectrometric analyses of biological macromolecules)
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PRINCIPLE
Mass spectrometer
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PRINCIPLE
Mass spectrometer is similar to a prism.
In the prism, light is separated into its
component wavelengths which are then detected
with an optical receptor, such as visualization.
Similarly, in a mass spectrometer the generated
ions are separated in the mass analyzer,
digitized and detected by an ion detector.
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PRINCIPLE
Basic Components of Mass Spectrometer

• Four basic components
• Sample inlet
• Ionization source
• Mass analyzer
• Ion detector

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PRINCIPLE
Understanding Mass Spectrometry
In a mass spectrometer, the same thing is
happening, except it's atoms and molecules that
are being deflected, and it's electric or
magnetic fields causing the deflection. It's also
happening in a cabinet that can be as small as a
microwave or as large as a chest freezer.
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PRINCIPLE

• First of all sample is bombarded with high
  electron beam produce the positive ions.
• They travel in a straight path.
• When a magnetic field or electric field is
  applied they travel in curved path.
• The fragments of different masses are separated
  based on the radius of curvature.
• m/z a r²
• These are then detected on detector.

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VIDEO
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VIDEO
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STRUCTURE ANALYSIS

• Structural analysis and Fragmentation Patterns
• Mass spectrum
• Graph of ion intensity (relative abundance) along
  x-axis versus mass-to-charge ratio (m/z) (units
• daltons, Da) along Y-axis
• Molecular ion (Parent ion)
• Fragmentation peaks
• Base peak
• Isotopic peaks

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MOLECULAR ION PEAK
Molecular ion (Parent ion)
the peak corresponding to the mol. wt.of the
compound
The peak of an ion formed from the original
molecule by electron ionization, by the loss of
an electron, or by addition or removal of an
anion or cation and also known as parent peak,
radical peak.
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ISOTOPIC PEAKS
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NATURAL ABUNDANCE
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NATURAL ABUNDANCE
M M1 M2
Silicon 28Si 100 29Si 5. 2
30Si 3.35
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ISOTOPIC PEAKS
79Br
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BASE PEAK
Base peak
The most intense (tallest) peak in a mass
spectrum, due to the most abundant ion. Not to be
confused with molecular ion base peaks are not
always molecular ion and molecular ion are not
always base peaks.
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FRAGMENTATION

• The process of breaking molecules/ions into
  fragments is known as fragmentation.
• This can be seen in the form of peaks in mas
  spectra. Methanol can be divided into four
  fragments. e.g.
• CH3OH ? CH3OH e
• CH3OH ? CH3 OH
• CH30H ? CH2OH H
• CH30H ? CHO H2

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FRAGMENTATION PEAKS
.
120 100 80 60 40 20 0
120 100 80 60 40 20 0

CHO?
CH3OH? CH3?

CH2OH?
5 10 15 20 25
30 35
m/e
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RULES OF FRAGMENTATION

• Intensity of M is larger for linear chain than
  for branched compounds.
• Intensity of M decrease with increasing
  molecular weight. (exception of fatty acids)
• Cleavage is favored at branching.
• Aromatic rings, Double bond, Cyclic structure
  stabilize M

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RULES OF FRAGMENTATION

• 1.Hydrocarbons
• Hydrocarbons give clusters of peaks.
• Molecular ion peaks of very low abundance are
  observed for linear hydrocarbons.
• For branched hydrocarbons give a low intensity at
  M.
• Intensity of (CnH2n1) peaks decreases with
  increasing mass.

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STRUCTURE ANALYSIS

• DBR Calculations
• Nitrogen Rule

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STRUCTURE ANALYSIS
DBR Calculations
Double bond or ring calculations tell us about
how many rings or double bonds are present in a
compound. DBR C-H/2N/21 C number of carbon
atoms H number of hydrogen atoms N number of
nitrogen atoms
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STRUCTURE ANALYSIS
Nitrogen Rule
If a compound contains an even number of nitrogen
atoms (or no nitrogen atoms), its molecular ion
will appear at an even mass number. If,
however, a compound contains an odd number of
nitrogen atoms, then its molecular ion will
appear at an odd mass value. This rule is very
useful for determining the nitrogen content of an
unknown compound.
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EXAMPLE
Mass spectra (examples)
Alkanes
Strong M (but intensity decreases with an
increase of branches. Carbon-carbon bond
cleavage loss of CH units in series M-14, M-28,
M-42 etc
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EXAMPLE
Alkanes
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EXAMPLE
Alkenes
Strong M Fragmentation ion has formula CnH2n
and CnH2n-1 -Cleavage A series of peaks M-15,
M-29, M-43, M-57 etc
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EXAMPLE
Alkynes
Strong M Strong base peak at M-1 peak due to the
loss of terminal hydrogen Alpha cleavage
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EXAMPLE
Aromatic Hydrocarbons
Strong M Loss of hydrogen gives base
peak McLafferty rearrangement Formation of
benzyl cation or tropylium ion
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EXAMPLE
Alcohols
M weak or absent Loss of alkyl group via
a-cleavage Dehydration (loss of water) gives peak
at M-18
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Thank You !
Mass Spectrometry

• salmanzafar27_at_yahoo.com