Mass spectroscopy ionization sources by RAJKIRAN REDDY
UNDER THE GUIDANCE
-: PRESENTED BY :R.RAJAKIRAN REDDY,
1ST YEAR M.PHARMACY,
Mass Spectroscopy is an analytical laboratory technique to separate the
components of a sample by their mass by using mass spectrometer.
Also Known As: Mass Spec, mass spectrometry.
In this technique the sample is vaporized into a gas and then
ionized. The ions are then accelerated through a potential difference and focused
into a beam. The ion beam passes through a magnetic field which bends the
charged stream. Lighter components or components with more ionic charge
will deflect in the field more than heavier or less charged components. A detector
counts the number of ions at different deflections and the data can be plotted as a
'spectrum' of different masses.
Mass Spectrometry Ionization Sources
Mass specrtromertry ionization sources are:
1. Electro spray Ionization (ESI)
2. Nano electro spray Ionization (Nano ESI)
3. Atmospheric Pressure Chemical Ionization (APCI)
4. Atmospheric pressure photo ionization (APPI)
5. Matrix-assisted laser desorption ionization mass spectrometry
6. Fast Atom Bombardment (FAB)
7. Electron Ionization (EI)
8. Chemical Ionization (CI)
9. Thermal ionization (TI)
1. Electro spray Ionization (ESI):
The sample solution is sprayed from a region of the
strong electric field at the tip of a metal nozzle maintained at a potential of
anywhere from 700 V to 5000 V. The nozzle (or needle) to which the potential is
applied serves to disperse the solution into a fine spray of charged droplets.
Either dry gas, heat, or both are applied to the droplets
at atmospheric pressure thus causing the solvent to evaporate from
For example: peptides,
2. Nano electrospray Ionization
where the spray needle has been made very small and is
positioned close to the entrance to the mass analyzer.The end result of this rather
simple adjustment is increased efficiency, which includes a reduction in the
amount of sample needed.
Very low flow rates
Very small droplet size (~5µ)
3. Atmospheric Pressure Chemical
The liquid effluent of APCI is introduced directly into the
ionization source. However, the similarity stops there. The droplets are not
charged and the APCI source contains a heated vaporizer, which facilitates rapid
desolvation/vaporization of the droplets. Vaporized sample molecules are carried
through an ion-molecule reaction region at atmospheric pressure.
4. Atmospheric pressure photo
It generates ions directly from solution with relatively
low background and is capable of analyzing relatively non polar compounds.
APPI vaporized sample passes through ultra-violet light.
APPI is much more sensitive than ESI or APCI.
5. Matrix-assisted laser desorption/
ionization mass spectrometry
The analyte is first co-crystallized with a large molar
excess of a matrix compound, usually a UV-absorbing weak organic acid.
Irradiation of this analyte-matrix mixture by a laser results in the vaporization of
the matrix, which carries the analyte with it. The matrix plays a key role in this
The co-crystallized sample molecules also vaporize, but
without having to directly absorb energy from the laser. Molecules sensitive to
the laser light are therefore protected from direct UV laser excitation.
6. Fast Atom Bombardment (FAB):
Immobilized matrix is bombarded with a fast beam of
Argon or Xenon atoms. Charged sample ions are ejected from the matrix and
extracted into the mass analyzers.
Largecompounds with low volatility
(eg peptides, proteins, carbohydrates)
Solid or liquid sample is mixed with a non-volatile matrix
(eg glycerol, crown ethers, nitrobenzyl alcohol)
7. Electron Ionization (EI):
Energetic process a heated filament emits electrons which are
accelerated by a potential difference of usually 70eV into the sample chamber.
Ionization of the sample occurs by removal of an electron from the molecule thus
generating a positively charged ion with one unpaired electron.
Produces M+.radical cation giving molecular weight.
Produces abundant fragment ions.
8. Chemical Ionization (CI):
This process is initiated with a reagent gas such as methane,
isobutane, or ammonia, which is ionized by electron impact.
High gas pressure in the ionization source is required for the reaction between the
reagent gas ions and reagent gas neutrals.
Reagent (R) + e- →R+ + 2eR+ + RH →RH+ + R
RH+ + Analyte (A) → AH+ + R
Biologically important molecules (sugars, amino acids, lipids etc.).
9.Thermal ionization (TI):
In this process samples are deposited on rhenium or tantalum
filament and then carefully evaporated and sent to mass analyzer.
quantify toxic trace elements in foods.
measurement of stable isotope ratio of inorganic elements.
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applications. 1st ed. S. Chand and Company ltd; New Delhi :2008.
2. Chatwal G.R, Anand S.K. Instrumental methods of chemical analysis.
1st ed. Himalaya Publishing house; Mumbai: 2004.
3. S. Ravi Shankar. Text book of pharmaceutical analysis. 3rd ed. Rx
publication; Tirunelveli: 2006.
4. Skoog DA, West DM. principle of instrumental analysis. 2ed edition