Mass Spectroscopy (Instrumentation & Spectral analysis )

1. Mass Spectroscopy
(Instrumentation & Spectral
analysis )
Presented by- Aquib Rehanullah Siddiqui
Ph.D. Scholar (Pharmaceutical Chemistry)
Integral university

2. Mass Spectrometry (MS) Definition
• Mass Spectrometry (MS) is an analytical chemistry technique that
helps to identify the amount and type of chemicals present in a sample
by measuring the mass-to-charge ratio and abundance of gas-phase
ions.
• In this instrumental technique, the sample is converted to rapidly
moving positive ions by electron bombardment and charged particles
are separated according to their masses.
• A mass spectrum is a plot of relative abundance against the ratio of
mass/charge (m/q).
• These spectra are used to determine the elemental or isotopic
signature of a sample, the masses of particles and of molecules, and to
elucidate the chemical structures of molecules and other chemical
compounds.

3. Principle of Mass Spectrometry (MS)
• In this technique, molecules are
bombarded with a beam of
energetic electrons.
• The molecules are ionized and
broken up into many fragments,
some of which are positive ions.
Each kind of ion has a particular
ratio of mass to charge, i.e. m/q
ratio (value).
• For most ions, the charge is one,
and thus, the m/q ratio is simply the
molecular mass of the ion.
• The ions pass through magnetic and
electric fields to reach the detector
where they are detected and signals
are recorded to give mass spectra.

4. Steps of Mass Spectrometry (MS)
A. Sample Inlet
• A sample stored in the large reservoir from which molecules reach the
ionization chamber at low pressure in a steady stream by a pinhole
called “Molecular leak”.

5. Contd..
B. Ionization
• Atoms are ionized by knocking one or more electrons off to give
positive ions by bombardment with a stream of electrons. Most of the
positive ions formed will carry a charge of +1.
• Ionization can be achieved by :
• Electron Ionization (EI-MS)
• Chemical Ionization (CI-MS)
• Desorption Technique (FAB)

6. Different Kind Of Ionization Technique
Are Used For Different Kind Of Samples

7. Contd..
C. Acceleration
• Ions are accelerated so that they all have the same kinetic energy.
• Positive ions pass through 3rd slits with voltage in decreasing order.
• Middle slit carries intermediate and finals at zero volts.
D. Deflection
• Ions are deflected by a magnetic field due to differences in their masses.
• The lighter the mass, the more they are deflected.
• It also depends upon the no. of +ve charge an ion is carrying; the more +ve
charge, the more it will be deflected.

8. Contd..
E. Detection
• The beam of ions passing through the mass analyzer is detected by a
detector on the basis of the m/e ratio.
• When an ion hits the metal box, the charge is neutralized by an electron
jumping from the metal onto the ion.
• Types of analyzers:
• Magnetic sector mass analyzers
• Double focusing analyzers
• Quadruple mass analyzers
• Time of Flight analyzers (TOF)
• Ion trap analyzer
• Ion cyclotron analyzer.

9. Instrumentation and Working of
Positive Potential

10. Working of Mass Spectrometry (MS)
• In a typical procedure, a sample, which may be solid, liquid, or gas, is
ionized, for example by bombarding it with electrons.
• This may cause some of the sample’s molecules to break into charged
fragments. These ions are then separated according to their mass-to-charge
ratio, typically by accelerating them and subjecting them to an electric or
magnetic field:
• Ions of the same mass-to-charge ratio will undergo the same amount of
deflection.
• The ions are detected by a mechanism capable of detecting charged
particles, such as an electron multiplier. Results are displayed as spectra of
the relative abundance of detected ions as a function of the mass-to-charge
ratio.
• The atoms or molecules in the sample can be identified by correlating
known masses (e.g. an entire molecule) to the identified masses or through a
characteristic fragmentation pattern

11. BASIC PRINCIPLES IN
INTERPRETATION OF MASS
SPECTRA

12. General approach for acquiring
information about a sample
• Degree of unsaturation.
• Structures and functional groups, Connectivity of
structures.
• Reference spectra and comparison to possible structures
where unique identification is not possible.

13. GENERAL RULES FOR INTERPRETATION OF
MASS SPECTRA
• In order to interpret the mass spectrum , one should attain an
understanding of the ionization process.
• To observe fragmentation pattern.
1.The exact molecular weight: The molecular weight of a pure
compound from the identification of the parent peak. The molecular
weight one can determine from molecular formula.
2.The isotope effects : Heavy isotopes will exhibit peaks in a mass
spectrum at m/e one or more units higher than normal. i.e., there will be
small peaks at M+1 and M+2.

14. The nitrogen rule
• In organic compounds there is a relationship between the valance and the
mass of the most common isotope for most elements.
• Even elements have an even valance.
• Odd elements have an odd valance.
• This leads to the ‘nitrogen rule.’ It assumes that we are limiting our
elements to C, H, halogens, O and N.
• A compound containing only C, H, O or X will have an even molecular
weight.
• A compound with an odd number of nitrogens will have an odd molecular
weight.
• A compound with an even number of nitrogens will have an even
molecular weight.

21. What is base peak?
• 100% abundance is called as base peak.
• M- is parent ion peak . It is all so called as molecular ion peak.
• Molecular peak of M produced when an electron is ejected from the
molecule

22. Background of fragmentation
• The impact of a stream of high energy electrons causes the molecule to
lose an electron forming a radical cation.