Instrumental
Methods - Mass Spectrometer.
Identifying Elements and Compounds.
A mass spectrometer
can provide a quick and accurate
identification
of a substance from a very small sample.
The instrument works by vapourising
the sample (turning it into gas).
The sample passes through an electron beam which knocks
off some electrons
from the molecules
and turns them into ions.
The charged ions are accelerated
towards a detector.
A strong magnetic
field makes the ions follow a curved
path
instead of moving in a straight line.
Ions with a small
amount of mass curve
the most
and ions with a large
amount of mass curve the least.
A recorder draws a graph
called a mass spectrograph
(usually just called a mass spectrum) which shows a peak for
each ion detected.
The position of the peaks
show the mass to charge
ratio
and this is used to identify the substances which are present in the sample.
The mass to charge
ratio is also used to give
the relative molecular mass
(RMM or RFM) of the
substances in a sample.
A mass spectrometer is
sometimes used with gas chromatography
to identify the different compounds
which
leave the column.
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