Ionization Techniques In Mass Spectroscopy

Ionization Techniques In Mass Spectroscopy

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. GasPhaseIonization
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
Inchemicalionization,theionizationoftheanalyteisachievedby
interactionofit'smolecules→withionsofareagentgasinthe
chamberorsource.
CONSTRUCTION & WORKING:
1.Chemicalionizationiscarriedoutinaninstrumentsimilarto
electronimpactionsource.
2.Itisatwopartprocess.
Inthefirststep-
✓AreagentgasisionizedbyElectronImpactionizationinthe
source.
✓Theprimaryionsofreagentgasreactwithadditionalgasto
producestabilizedreagention.

10. Inthesecondstep
The reagent ions interact with sample molecules to form
molecular ions.
Inthistechniquethesampleisdilutedwithalargeexcessof
reagentgassothattheprobabilityofionizingcollisionsbetween
samplemoleculesandtheelectronsisnegligiblysmalland
primaryionsareformedentirelyfrominteractionwithreagent
gasions.

11. ADVANTAGES
✓Usedforhighmolecularweightcompounds.
✓UsedforsampleswhichundergorapidfragmentationinEI.
LIMITATIONS
✓Notsuitableforthermallyunstableandnon-volatilesamples.
✓RelativelesssensitivethenEIionization.

12. DesorptiveIonization
1) Field Desorption
Itisatypeofdesorptionionizationtechniquewhichinvolves
directconversionofSolid/liquidmoleculesintogaseousion
directly.
ThistechniquelowVolatileSampleandusedtoproduce
Stablemolecularions.
SamplesareloadedontheSurfaceoftheCarbonmicroniddle
bydippingintheSampleSolution.
CarbonmicroniddlewillProducehighgradientVoltageon
theirtips.thatiswhysharptipsisused.

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

14. 2)Fastatombombardment[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. Characteristicofthematrix:-
ItShouldbenon-Volatile.
ItShouldlowvapourPressureliquids.
Example:-
Glycerol,Thioglycerol,3-Nitrobenzylalcohol

16. ADVANTAGES
•Usedforionizationofpolarhighmolecularweightsamples.
•Providesrapidheatingofsamplesandreducessample
fragmentation.
•Rapidionization.
DISADVANTAGES
•Difficulttodistinguishbetweenlowmolecularweight
compounds.
•Compoundsmustbesolubleinliquidmatrix.

17. •ItisaSoftionizationtechniqueunderdesorption
ionizationmethods,whichusesPulsedLASER.
•Itisusedtodeterminemolecularweighttheof
peptides,antibodies,Proteinmoleculesetc.
SampleisdissolvedinSolvent→Sol.A
MatrixisdissolvedinSolvent→Sol.B
3)MatrixAssistedLaserDesorptionIonization
(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
EstimationofDNA,RNAandoligosaccharides.
Usedinanalysisoflipids,phosphopeptidesand
syntheticpolymers.

20. EvaporativeIonization
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.