Edexcel AS Chemistry - Mass Spectrometry

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  • Created by: Booga
  • Created on: 02-01-11 20:37

MASS SPECTROMETRY

MASS SPECTROMETER:

(http://www.chemguide.co.uk/analysis/masspec/masspec.GIF)

First the sample must be vapourised and injected into the first chamber, as a mass spectrometer only works with gaseous samples

IONISATION: The heated metal coil gives of electrons which are attracted to the positively charged plate above. The beam of electrons bombards the sample with electrons. These electrons knock off electrons from the sample turning the sample into a positive ion

ACCELERATION: Positive ions are repelled from the ion chamber. The sample passes through 3 plates (with decreasing voltages between them) this creates a finely focused beam which then accelerates the ions

Here the velocity selector ensures that the ions travel at equal velocity

DEFLECTION: A magnetic field is placed in order to deflect the ions. Deflection depends on mass (more mass = less deflection) and charge (larger charge = more deflection). These 2 factors create the mass/charge ratio (m/z or m/e)

{m/z = mass / charge}

DETECTION: Here the detector records the ion stream which reaches the end. The rest of the streams will hit the walls of the machine and gain electrons, this makes them neutral- these

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