in this presentation we learn about the mass spectrometery principal and its mass to charge ratio. components of mass spectrometers . sample inoculation and its processing. i feel these are very good slides.

1. Mass spectrometry
Rabia shehzadi
1730814-012

2. CONTENTS
1. INTRODUCTION
2. HISTORY
3. PRINCIPLE
4. MASS SPECTROMETER
5. COMPONENTS OF MASS SPECTROMETER
6. SAMPLE INTRODUCTION METHODS

3. Introduction
 Mass spectrometry is a powerful analytical technique used to quantify known
materials, to identify unknown compounds within a sample and to elucidate the
structure and chemical properties of different molecules.
 It depends upon chemical reactions in the gas phase in which sample molecules
are consumed during the formation of ionic and neutral species.
 This will be happened by converting the material to charged molecules to
measure their mass to charge ratio.

4. HISTORY
 Mass spectroscopy was first performed at the Cambridge university, in 1912 by
J.J Thomson (1856-1940) when he obtained the mass spectra of O2, N2, CO.
 Mass spectroscopy took off in 1930s and advance technology resulted in the
development of double focusing Mass spectrometers capable of accurate
determination.
 The modern techniques of mass spectrometry were devised by Arthur Jeffrey
Dempster and F.W. Aston in 1918 and 1919 respectively.
 In 2002, the Nobel Prize in Chemistry was awarded to John Bennett Fenn for the
development of electrospray ionization (ESI)

5. MASS SPECTROMETER
 It is an instrument in which the substances in gaseous or vapor state is
bombarded with a beam of electrons, to form positively charged ions (cations)
which are further sorted according to their mass to charge ratio to record their
masses and relative abundances.

6. PRINCIPLE
 In mass spectrometry, organic molecules are bombarded with a beam of energetic electrons
(70 eV) in gaseous state under pressure between 10-7 to 10-5 mm of Hg, using tungsten or
rhenium filament. Molecules are broken up into cations and many other fragments.
 These cations (molecular or parent ion) are formed due to loss of an electron usually from n or
π orbital from a molecule, which can further break up into smaller ions (fragment ions or
daughter ions).
 All these ions are accelerated by an electric field, sorted out according to their mass to charge
ratio by deflection in variable magnetic field and recorded. The output is known as mass
spectrum.
 Each line upon the mass spectrum indicates the presence of atoms or molecules of a particular
mass.

7. principle

8. COMPONENTS OF A MASS SPECTROMETER
 The essential components of a mass spectrometer consist of:
 A sample inlet
 An ionization source
 A mass analyzer
 An ion detector
 Vacuum system

9. MASS ANALYZER
QUADRUPOLE, MAGNETIC
SECTORS, TIME OF FLIGHT, QIT,
FTICR
INLET SYSTEM
FOR SOLIDS, FOR LIQUIDS, FOR
GASES
DETECTOR
ELECTRON MULTIPLIER, FARADAY
CUP, PHOTOMULTIPLIER
CONVERSION DYNODE, ARRAY
IONIZATION MECHANISMS:
PROTONATION, DEPROTONATION,
CATIONIZATION, ELECTRON
EJECTION,
ELECTRON CAPTURE
IONIZATION SOURCE
ESI, MALDI, FAB, FD, PD, APCI, APPI,
EI, CI,
FI.
MASS
SPECTROMETER

10. Mass spectromter

11. SAMPLE INTRODUCTION METHODS
 1. Direct Vapor Inlet
 The simplest sample introduction method.
 The gas phase analyte is introduced directly into the source region of the mass
spectrometer through a needle valve. Pump out lines are usually included to
remove air from the sample.
 This inlet works well for gases, liquids, or solids with a high vapor pressure.
 It only works for some samples.

12. Gas Chromatography
 Most common technique for introducing samples into a mass spectrometer.
 Complex mixtures are routinely separated by gas chromatography and mass
spectrometry is used to identify and quantitate the individual components.
 The most significant characteristics of the inlets are the amount of GC carrier gas
that enters the mass spectrometer and the amount of analyte that enters the
mass spectrometer.
 Ideally all the analyte and none of the GC carrier gas would enter the source
region.
 The most common GC/MS interface now uses a capillary GC column

13. Liquid Chromatography
 LC inlets are used to introduce thermally labile compounds not easily separated
by gas chromatography.
 These inlets are used for temperature sensitive compounds.
 The sample is ionized directly from the condensed phase.

14. Direct Insertion Probe
 The Direct Insertion Probe (DIP) is widely used to introduce low vapor pressure
liquids and solids into the mass spectrometer.
 This is important for analyzing temperature sensitive compounds.
 Although the direct insertion probe is more cumbersome than the direct vapor
inlet, it is useful for a wider range of samples.

15. Direct Ionization of Sample
 Some compounds either decompose when heated or have no significant vapor
pressure and can be introduced by direct ionization from the condensed phase.

16. IONIZATION METHODS
 Protonation
 Protonation is a method of ionization by which a proton is added to a
 molecule, producing a net charge of 1+ for every proton added.
 E.g.: More basic residues of the molecule, such as amines; Peptides.
 Can be achieved through MALDI, ESI and APCI.

17. Electron Capture
 With the electron capture ionization method, a net charge of 1- is achieved with
the absorption or capture of and electron.
 E.g.: Molecules with high electron affinity, such as halogenated compound

18. Electron Ejection
 Ionization is achieved through the ejection of an electron to produce a 1+ net
charge, often forming radical cations. It generates significantly fragmented ions.
 E.g.: Non-polar compounds with low molecular weights.
 Most commonly achieved with electron ionization (EI) sources.

19. Cationization
 It produces a charged complex by non-covalently adding a positively charged
cation adduct (e.g. alkali, ammonium) to a neutral molecule.
 E.g.: Carbohydrates are best examples, with Na+ as a common cation adduct.
 Mainly achieved by MALDI, ESI and APCI.

20. Electron Capture
 With the electron capture ionization method, a net charge of 1- is achieved with
 the absorption or capture of and electron.
E.g.: Molecules with high electron affinity, such as halogenated compounds

21. Transfer of a Charged Molecule to the Gas Phase
 The transfer of compounds already charged in solution is achieved through
desorption or ejection of the charged species from the condensed phase into the
gaseous phase.
 Commonly achieved through MALDI or ESI.

22. GENERAL MODES OF FRAGMENTATION
 SIMPLE CLEAVAGE
 REARRANGEMENT REACTIONS ACCOMPANIED BY TRANSFER OF ATOMS
 SKELETAL REARRANGEMENT

23. cleavage
 In this type of cleavage both the electrons of the α bond are taken over by one of
the atoms; the fragments are even electroncation and a radical with the positive
charge residing on the alkyl group.
 It may be noted that the cleavage of C ̶X (X= O,N,S, Cl) bond is more difficult than
that of a C ̶C bond.
 It can be shown by fragmentation of alkyl halide.

24. REARRANGEMENT REACTIONS ACCOMPANIED BY TRANSFER OF
ATOMS
 It involves the migration of γ-hydrogen atom followed by the cleavage of a β-
bond. The rearrangement leads to the elimination of neutral molecules from
aldehydes, ketones, amines, unsaturated compounds etc.
 The rearrangement proceeds through a sterically hindered six membered
transition state.
 The structural requirements for this reaction are a side chain of at least three
carbon atoms bearing a γ-hydrogen and a double bond which could be a carbonyl
group or an olefinic double bond or an aromatic system

25. Conti….

26. SKELETAL REARRANGEMENT
 Induced by radical or charge sites or both may found to have some influence on
rearrangement processes.
 Unsaturated esters and carbonates undergo rearrangements with the loss of
carbon dioxide