1. The Mass Spectrometer Honours
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2. You Will learn Parts of the mass spectrometer
The five processes occuring in the mass spectrometer.
The principle of mass spectrometry.
Uses of the mass spectrometer.
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3. F W Aston
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4. Aston’s Mass Spectrometer
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5. SCC Science Dept

6. Mass Spectrometer Working on separating the isotopes of Neon
Invented by F W Aston in 1919
Working on separating the isotopes of Neon
Discovered two types of atom
One type of mass 20
Another type of mass 22
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7. Isotopes [Greek for same place]
Both had 10 protons
The first type had 10 neutrons
Second type had 12 neutrons
Isotopes [Greek for same place]
Atoms of the same element that have the same atomic number but different mass numbers due to different numbers of neutrons
Fredrick Soddy coined phrase working with lead 206,207 and 208 formed when uranium decayed radioactively – Nobel Prize 1921
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8. works on the principal that positive ions are separated by mass
The Mass Spectrometer
works on the principal that
positive ions
are separated
by mass
when moving in a magnetic field
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9. Structure of the Mass Spectrometer
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10. Sample Inlet
Negatively charged plates
Ionisation Chamber
Accelerator
Electron Gun
Separation Unit
Analyser Unit
Variable magnetic field
Lighter particles
Recorder
Intermediate mass particles
Heavier particles
Ion detector
Amplifier
Vacuum Pump
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11. 5 Stages Vaporisation Ionisation Acceleration Separation
Detection, Amplification and Display
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12. 1. Vaporisation Sample must be vaporised
There is a Vacuum in the instrument so liquids vaporise easily
Solids may have to be heated in a special unit
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13. Sample may need to be heated to vaporise it
Vaporisation Chamber
Sample inlet A
Sample in syringe injected into chamber
Sample may need to be heated to vaporise it
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14. 2. Ionisation X + e- = X+ + 2 e-
Turns atoms and molecules into ions
Using an “electron gun”
Fires high energy electrons at atoms
These high energy electrons knock off normal electrons forming positive ions
X + e- = X e-
These ions can then be accelerated and deflected using electric charge and a magnetic field
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15. where atoms are turned into ions+
The positive ions are attracted by the negative charge of the accelerator plates and those which pass through the hole are accelerated to high speeds and fired into the variable magnetic field
These electrons knock other electrons from the atom turning it into a positive ion
A c c e l e r a t o r
This is the
IONISATION CHAMBER
where atoms are turned into ions
Now vaporised atoms are sprayed into ionisation chamber and are hit by the high speed electrons +
Hot wire is negatively charged and boils off electrons which are repelled by negative and attracted to the anode at high speed ▬
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16. 3. Accelerator
Made of a series of Negative plates with a hole in the centre
These attract the positive ions
Some of these ions pass through the holes in the centre of the plates
And as they do so are accelerated to high speeds
This produces a fine beam of positive ions which pass into analyser
Vacuum allows the ions to move [no air molecules to stop or deflect them]
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17. 4. Separation Magnetic field does the separation. In the Analyser
All ions have the same kinetic energy
light particles are deflected most
heavy particles are deflected least
Beam of particles is separated according to their masses
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18. Effect of the magnetic field in the analyser unit on ions of differing Mass
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19. Separator or Analyser Unit
Magnetic Field on
Magnetic Field off
Heavy Ion
Light Ion
No magnetic field
No deflection +
Small deflection
Heavy Ion
Large deflection
Light Ion
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20. Effect of changing the Magnetic Field
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21. Separator or Analyser Unit
Magnetic Field
WEAK
OFF
STRONG
Ion of one mass
No Magnetic Field
No deflection +
Small deflection
Weak Field
Large deflection
Strong Field
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22. 5a. Detector Very sensitive instrument.
Responds to the number of ions hitting it.
The more ions that hit it the bigger the reading
Changing the magnetic field brings particles of different masses to focus on the detector. [Stronger the field the greater the particle mass]
Detector needs to be calibrated
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23. 5b. Amplifier The signal is amplified [made bigger] electronically
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24. 5c. Display On computer screen Trace recorded as a series of peaks
Trace called a Mass Spectrum
When printed called a Mass Specrtrogram
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25. Isotope 2
Abundance
Isotope 1
Isotope 3
Mass
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26. Aston discovered 35Cl and 37Cl
Determined the percentage of each isotope present
Won the Nobel Prize for Chemistry 1922
Discovered 212 of the 287 naturally occurring nuclides
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27. Uses Gases from waste dumps Trace organic pollutants in water
Determinig the Relative molecular mass of atoms [isotopes] till 1970
Determining mass of unknown organic compounds and thus help determine their structures
Gases from waste dumps
Trace organic pollutants in water
Click here for a brief biography of F W Aston
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