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How Does a Mass Spectrometer Work?
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Principle:
a sample is separated into its constituent parts, such as atoms or molecules,
on the basis of their mass
Objective:
to investigate the relative proportions of molecular, elemental, or isotopic
species in a sample
Did you know?
All parts of a mass spectrometer are
maintained at high vacuum during analysis.
Numerous pumps create a vacuum similar
to that of interstellar space!
A magnetic and/or electric field is
applied to the chamber, which
deflects (curves) the path of the
ions according to their mass.
2 MASS ANALYSER
flight tube
ion beam
magnetic sector
ions that are too heavy
bend too little
only ions of the right mass
can enter the detector
1 ION SOURCE
3 COLLECTOR ASSEMBLY
ions that are too light
bend too much
Ions in gas form are
generated from the sample,
and accelerated and aligned
into a narrow ion beam.
This may consist of a single detector
into which an ion beam may be
focused, two switchable detectors,
or an array of several detectors that
simultaneously collect several ion
beams.
signal out
sample in
plasma source (~7700 C)
o
thermal ionization source
(1200-2500oC)
electric sector
The detector records the charge
induced or current produced when
an ion passes by or hits a surface.
Detection limits:
Today’s mass spectrometers are
capable of measuring abundances in
the parts-per-billion (ppb) range.
One part per billion is roughly
equivalent to one drop of water in an
Olympic-sized swimming pool!
multi-collector arrays:
variable
39.5
From the field...
...to the mass spec...
...to the chem lab...
208 Pb/ 204 Pb
fixed
Indian Pacific
1000
39.0
100
38.5
10
1
38.0
EPR
37.5
17.5
sample / N-MORB
18.0
18.5
206 Pb/ 204 Pb
19.0
19.5
0.1
Cs
Ba U Ta La Pb P Sm Hf Sn Ti Y Lu
Rb Th Nb K Ce Sr Nd Zr Eu Gd Tb Yb
20.0
...to the results!