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Mass Spectroscopy

Mass Spectroscopy. “You can’t make an omelette without breaking eggs” The Joker. What is it?. A device for finding the mass of atoms and groups of atoms. The particles are charged, accelerated into a magnetic field and deflected by their mass/charge ratio.

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Mass Spectroscopy

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  1. Mass Spectroscopy “You can’t make an omelette without breaking eggs” The Joker

  2. What is it? • A device for finding the mass of atoms and groups of atoms. • The particles are charged, accelerated into a magnetic field and deflected by their mass/charge ratio. • The resulting beams of ions are analysed and the identities of the particles discovered.

  3. How it works The sample is first Vapourised. Then it is Ionised by having high energy electrons fired at it. M(g) + e- → M+(g) + 2e- These ions are then Accelerated by a strong electric field V I A

  4. How it works A good vacuum is essential in the whole of the apparatus

  5. How it works The accelerated ions are Deflected by the magnetic field, bigger ions are deflected less. The ion beams can be focussed on the Detector

  6. Aide Memoire • Vapourisation • Ionisation • Acceleration • Deflection • Detection • How did Jordan become famous? • Via DD

  7. Fragmentation • Organic molecules do not hold charge well. • The ions break up or fragment. • They break into smaller ions and neutral fragments. • They do this in regular patterns. • i.e. the same molecule always fragments in the same way. • This allows us to analyse them. • M(g) + e- → M+(g) + 2e- • M+ is called the molecular ion. M+, contain a small amount of excess energy from the bombarding electrons. Also, because M+ has lost an electron, it is less strongly held together than the original molecule. So, some of the molecular ions fall apart (fragment) in the ion source to give fragment ions (F+) and neutral fragments (N),. • M+(g) → F+(g) + N*(g) • Analysis of the charged particles in the mass spectrometer gives the MASS SPECTRUM of the molecule.

  8. Mass Spectrum of ethanol Peaks 46 45 31 29 15 Peaks M+ M+ -1 M+ -15 M+ - 17 M+ - 31

  9. Possible fragments M+-15 M+-1 + + 45 31 M+ 46 M+-17 M+-31 + + + 29 15

  10. Mass Spectrum of propan-1-ol Peaks 60 59 43 31 29 Peaks M+ M+ -1 M+ -17 M+ - 29 M+ - 31

  11. Possible fragments M+-29 M+-1 + + 59 31 M+ 60 M+-17 M+-31 + + + 43 29

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