This document provides an overview of different ionization techniques used in mass spectrometry. It discusses gas phase ionization methods like electron impact and chemical impact ionization. It also covers desorptive ionization techniques such as field desorption, fast atom bombardment, and matrix-assisted laser desorption ionization. Finally, it summarizes evaporative ionization methods like atmospheric pressure chemical ionization and atmospheric pressure photoionization. The document aims to explain the basic principles, applications, advantages, and limitations of various ionization methods for mass spectrometry analysis.

1. Presented by:
Mr. Akshay. S. Dhole
M. Pharm- I Year
Roll No. 03
Guided by:
Mrs. Jaya Kamble.
(Associate Professor)
Department of Quality Assurance
Vasantidevi Patil Institute of
Pharmacy, Kodoli

2. • Ion Source
•Ionization Techniques
•Methods of Ionization
a) Gas phase
b) Desorption
c) Evaporative

3. The ion source converts molecules into gaseous
ions.
The most involves bombarding the sample with a
beam of energetics from an ion gun.

4.  Ionization Techniques can be categorised into
two parts:-
1) Hard Ionization Techniques:-
High energy will be involved, In that no. of
fragments ion will be Higher and no. of
Molecular ion will be low.
2) Soft Ionization Techniques:-
Low energy, low fragmentation, high
molecule ion.

5. Gas phase
• Electron
impact
• Chemical
impact
Desorptive
• Field
Desorption
• FAB
• MALDI
Evaporative
• Thermo
spray
• ESI
• APCI
• APPI

6. Gas Phase Ionization
The gas phase molecules are bombarded by a beam of
electrons formed by heating a filament at a negative
voltage compared to the source.
1) Electronic Impact Ionization

7. INTRODUCTION
Electron impact (EI) is the classical ionization method in mass
spectrometry.
It is the most widely used and highly developed method.
It is also known as Electron bombardment or Electron Ionization.
CONSTRUCTION & WORKING:
1) Electron impact ionization source consists of a ionizing chamber which
is maintained at a pressure of 0.005 torr and temperature of 200±0.25
degrees.
2) Electron gun is located perpendicular to chamber.
3) Electrons are emitted from a glowing filament (tungsten or rhenium) by
thermionic emission and accelerated by a potential of 70 V applied
between the filament and anode.
4) These electrons are drawn in the ionization chamber through positively
charged slits.
5) The number of electrons is controlled by filament temperature and
energy of energy is controlled by filament potential.

8. ADVANTAGES
Gives molecular mass and also the fragmentation pattern of the
sample.
Extensive fragmentation and consequent large number of
peaks gives structural information.
Gives reproducible mass spectra.
DISADVANTAGES
Sample must be thermally stable and volatile.
A small amount of sample is ionized (1 in 1000 molecules).
Unstable molecular ion fragments are formed so readily that
are absent from mass spectrum.

9. 2) Chemical Impact Ionization
INTRODUCTION
In chemical ionization, the ionization of the analyte is achieved by
interaction of it's molecules →with ions of a reagent gas in the
chamber or source.
CONSTRUCTION & WORKING:
1. Chemical ionization is carried out in an instrument similar to
electron impact ion source.
2. It is a two part process.
In the first step-
✓A reagent gas is ionized by Electron Impact ionization in the
source.
✓ The primary ions of reagent gas react with additional gas to
produce stabilized reagent ion.

10. In the second step
 The reagent ions interact with sample molecules to form
molecular ions.
 In this technique the sample is diluted with a large excess of
reagent gas so that the probability of ionizing collisions between
sample molecules and the electrons is negligibly small and
primary ions are formed entirely from interaction with reagent
gas ions.

11. ADVANTAGES
✓ Used for high molecular weight compounds.
✓ Used for samples which undergo rapid fragmentation in EI.
LIMITATIONS
✓ Not suitable for thermally unstable and non-volatile samples.
✓ Relative less sensitive then EI ionization.

12. Desorptive Ionization
1) Field Desorption
It is a type of desorption ionization technique which involves
direct conversion of Solid / liquid molecules into gaseous ion
directly.
This technique low Volatile Sample and used to produce
Stable molecular ions.
Samples are loaded on the Surface of the Carbon microniddle
by dipping in the Sample Solution.
Carbon microniddle will Produce high gradient Voltage on
their tips. that is why sharp tips is used.

13. Ion formation takes place mainly by two mechanism -
A. Field Ionization
B. Cation attachment

14. 2) Fast atom bombardment [FAB]
•It is a soft ionization method classified under desorption method.
•FAB is used to determine the molecular weight of the
Compound having the Size from 300 to 6000 Daltons-.
•Generally used to determine molecular weight of Peptides.
•Methodology:-

15. Characteristic of the matrix:-
 It Should be non-Volatile.
 It Should low vapour Pressure liquids.
 Example:-
 Glycerol,Thioglycerol, 3-Nitrobenzyl alcohol

16. ADVANTAGES
• Used for ionization of polar high molecular weight samples.
• Provides rapid heating of samples and reduces sample
fragmentation.
• Rapid ionization.
DISADVANTAGES
• Difficult to distinguish between low molecular weight
compounds.
• Compounds must be soluble in liquid matrix.

17. • It is a Soft ionization technique under desorption
ionization methods, which uses Pulsed LASER .
• It is used to determine molecular weight the of
peptides, antibodies, Protein molecules etc.
Sample is dissolved in Solvent →Sol. A
Matrix is dissolved in Solvent →Sol. B
3) Matrix Assisted Laser Desorption Ionization
(MALDI)

18. Matrix
• Matrix is used in MALDI to Absorb the laser energy.
• Prevent analyte agglomeration.(stability, flowability,
dispersability.)
• Protect analyte from being destroyed by direct laser
beam.

19. APPLICATIONS
 Estimation of DNA, RNA and oligosaccharides.
 Used in analysis of lipids, phosphopeptides and
synthetic polymers.

20. Evaporative Ionization
1) Atmospheric Pressure chemical Ionization [APCI]
 It is a type of soft Ionization technique based on the mechanism
of evaporation and Carried out the atmospheric Pressure.
 Actually APCI is Combination of chemical Ionization [CI] and
electrospray Ionization (ESI) with Some deviation.

21. 2) Atmospheric Pressure Photo Ionization [APPI]
• It is a type of soft ionization technique.
• Based on the mechanism of evaporation and Carried
out at atmospheric Pressure.
• APPI is Similar to APCI but ionization is APPI is due
to photons generated by UV.