PRINCIPLE, INSTRUMENTATION, SPECTRAL CHARACTERIZATION OF MASS SPECTROMETER

1. Mass
Spectrometry
T.Y.B.Pharm
2018

2. Mass spectrometer is measurement of
atomic mass of molecules and atoms and
detection of then on the basis of mass to
charge ratio.
Mass number(A) – it is total number of
protons and neutrons in atom. it is different
for different atoms and molecules.
E.g.. carbon atom have 6 proton +6 neutrons
in nucleus hence its mass number is 12

3. What is it mass spectrometery?
It is instrumental technique in which sample is
converted to positive charged ions by electron
bombardment and the particles are separated
according to their mass, finally they are detected
by detector
What is mass spectrum?
It is plot of relative abundance against ratio of
mass/charge(m/e)

6. The first step in the mass spectrometric analysis of
compounds is the production of gas phase ions of the
compound, basically by electron ionization.
This molecular ion undergoes fragmentation.
Each primary product ion derived from the molecular
ion, in turn, undergoes fragmentation, and so on.
 The ions are separated in the mass spectrometer
according to their mass-to-charge ratio, and are detected
in proportion to their abundance.
 A mass spectrum of the molecule is thus produced.
 It displays the result in the form of a plot of ion
abundance versus mass-to-charge ratio.
Ions provide information concerning the nature and the
structure of their precursor molecule.

7. In the spectrum of a pure compound, the molecular
ion, if present, appears at the highest value of m/z
(followed by ions containing heavier isotopes) and gives
the molecular mass of the compound.
Components
The instrument consists of three major components:
Ion Source: For producing gaseous ions from the
substance being studied.
Analyzer: For resolving the ions into their characteristics
mass components according to their mass-to-charge
ratio.
Detector System: For detecting the ions and recording
the relative abundance of each of the resolved ionic
species.

9. Stage 1 Ionisation-
Electro Ionisation is the most common type of ionisation.
The sample is bombarded by electrons which come from a heated
filament.
The electrons run in a stream between the cathode and anode.
When the sample passes through the electron stream, the high energy
electrons in the stream knock electrons out of the sample to form ions.
Stage 2 Acceleration
Acceleration is a simple step where the ions are placed between a set of
charges parallel plates.
The ions will then be repelled by one plate and attracted to the other.
There is a slit cut in the plate which the ions are attracted to. the force
of attraction and repulsion forces the ions through the slit at an
accelerated rate.
The speed of acceleration can be adjusted by changing the charge on
the plates.

11. Stage 3 Deflection
ions are deflected by the magnetic field surrounding the
instrument.
The amount of deflection depends on the mass and charge of the
ions.
The heavier ions and ions with a positive charge of 2 or more, are
deflected the least (Ion stream C)
The lightest ions and ions with 1 positive charge are deflected the
most (Ion Stream A)
The ions at the correct mass and charge travel to the detector. (Ion
Stream B)
The mass to charge ratio (m/z) is determined from the ion that hits
the detector.

13. Step 4 Detection
When the ion stream reached the detector the hit
a wire. On hitting the wire they become
neutralised by an electron jumping from the metal
wire to the ion.
The amplifier picks up on this current being
created between the wire and the ion and
amplifies the signal being detected.
The computer picks up on this and converts it to
mass/charge ratio and a spectrum is produced.

21. Applications of Mass Spectrometry
Mass Spectrometry as a technique can be
coupled with other techniques such as HPLC
and GC.
As it is used in the identification of
compounds it is used in all areas of science.
Some of its uses are : Trace Gas Analysis,
Pharmaceutical Industry, Space Exploration,
Forensic Toxicology, Archaeological Dating.