Mass Spectrometry

What is a mass spectrometer

an important analytical instrument which scientists use to identify the mass of elements, ions, isotopes or molecules, and their relative abundances

4 stages of how a mass spectrometer processes a chemical sample

ionisation

acceleration

deflection

detection

ionisation (4)

sample needs to vaporised before put into ionisation chamber

electrically heated metal coil gives off steam of electrons

atoms in sample are bombarded with electrons, collision will knock off electron from particle resulting in positively charged ion

most ions formed will have +1 charge as it is hard to remove a second electron from an already positive ion

Acceleration (2)

positively charged ions are repelled from ionisation chamber (which is positive)
pass through negative charged slits which focus and accelerate this into a beam

Deflection (3)

stream of positive ions are deflected by magnetic field

amount of ions deflected depends on mass of ion (lighter = more deflected), charge of ion (ions with greater charge than +1 are deflected more)

consider these properties as a mass/charge ratio.

Detection (3)

by varying strength of magnetic field, different ion streams can be focused on the ion detector in order of increasing mass/charge ratio

1) ion hits detector.

2) charge is neutralised
3) electrical current is generated (current is proportional to abundance of ion)
4) sent to computer for analysis

mass spectrum is generated, which shows the different m/z values of ions present + relative abundance