Mass spectrometry-1

1. Lecture-1 (Theory)
Ph.D.Ahmed Metwaly
Mass spectrometry
ORCID account
Email: ametwaly@azhar.edu.eg
1
• Associate Professor of Pharmacognosy , faculty of Pharmacy, Al-Azhar University
• Senior research fellow, Liaoning University of Traditional Chinese Medicine, China (20118-2019)
• Visiting scholar, School of Pharmacy, University of Mississippi, USA (2012-2014)

2. Objectives
Definition
Applications
Time line
Theory
Instrument

3. Definition
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio
of charged particles
Applications
This technique is applicable in:
Identifying molecular Wight.
Detecting fragmentation pattern.
Determining the molecular formula (HR-Ms).
Determining the isotopic distribution.
Protein sequence (Ms-Ms)
(Weighs molecules)

9. Theory
The physics behind mass spectrometry is that a charged particle passing through a magnetic field
is deflected along a circular path on a radius that is proportional to the mass to charge ratio, m/e.

10. Different chemicals have different masses.
In the first phase of the mass spectrometry these masses may be vaporized (turned
into gas) and ionized (broken down) into ions.
An electric field accelerates the ions to a high speed.
• The accelerated ions directed into a magnetic field which applies a force to each ion perpendicular to the plane.

11. This force deflects the ions
(makes them curve instead of
traveling in a straight line) to
varying degrees depending on
their masscharge ratio.
Lighter ions get deflected more
than the heavier ions. (due to
Newton's second law of motion.
The acceleration of a particle is
inversely proportional to its mass).
• The detector measures the deflection of each
resulting ion beam.
• Most stable ions appears as higher peaks due to
higher abundance.

16. Instrumentation
Mass spectrometers consist of three basic parts: an ion source, a mass analyzer, and a
detector system.
The stages within the mass spectrometer are:
Production of ions from the sample (ionization).
Separation of ions with different masses (like deflection).
Detection of the number of ions of each mass produced.
Collection of data to generate the mass spectrum.

17. Ion source
The ion source is the part of the mass spectrometer that ionizes the material under
analysis (the analyte), usually to cations by loss of an electron, because ions are
easier to manipulate than neutral molecules. The ions are then transported by
magnetic or electric fields to the mass analyzer.
Electron ionization and chemical ionization are used for gases and vapors. In
chemical ionization sources, the analyte is ionized by chemical ion-molecule
reactions during collisions in the source. Two techniques often used with liquid and
solid biological samples include electrospray ionization, matrix-assisted laser
desorption/ionization (MALDI) and fast atom bombardment (FAB).

18. Mass analyzer
Mass analyzers separate or resolve the ions formed in the ionisation source of the
mass spectrometer according to their mass-to-charge ratio (m/z). All mass
spectrometers are based on dynamics of charged particles in electric and
magnetic fields in vacuum.

19. The mass spectrum calculated according to compounds mass-to-charge ratio (m/z)
because;
The position of peaks on the spectrum depending on;
1. Direct proportional to mass (heavier molecules deflected less and reach
detector first)
2. Inverse proportional to the charge (although most molecules have one charge)
in case of a molecule with 2 charges, it will deflected more (the deflection force
takes place over the charges) .

20. Detection and recording of sample ions
The detector records the charge induced or current produced when an ion passes
by or hits a surface, amplifies it and the signal is then transmitted to the data
system where it is recorded in the form of mass spectra .

21. Summary
Definition
Applications
Time line
Theory
Instrument

22. Ph.D.Ahmed M.Metwaly
Associate professor,Pharmacognosy
department,
Faculty of Pharmacy,Al-Azhar University.
ametwaly@azhar.edu.eg
Email: ametwaly@azhar.edu.eg 22