Ametek Dycor Dymaxion Mass Spectrometer, Руководство пользователя

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1-4 | Dycor Dymnaxion Mass Spectrometer
Separation
Once the ions reach the quadrupole mass filter, they are filtered according to their
mass-to-charge (m/z) ratio. Each ion has an identifiable mass. The quadrupole
mass filter is constructed of four electrically-conducting, parallel cylindrical rods.
A constant direct current (DC) voltage and an alternating radio-frequency (RF)
voltage is applied along the length of the rods. Through proper electronic tuning,
these voltages set the criteria for the ions that pass through the quadrupole.
As an ion enters the quadrupole mass filter, the RF and DC fields cause it to
undergo oscillations. Depending upon the criteria set for motion through the
quadrupole, an ion passes through the quadrupole where it is neutralized on the
walls of the vacuum housing. Ions meeting the m/z criteria have stable trajecto-
ries and emerge from the mass filter assembly (Figure 1-2). Ions with other m/z
values have unstable trajectories and are neutralized as they strike the walls of the
vacuum housing.
Ions that successfully pass through the quadrupole are again focused towards the
detector using an exit aperture which has an applied negative voltage that attracts
the positively charged ions.
Detection
The simplest detection setup consists of a Faraday cup detector. An electron mul-
tiplier is used for amplified sensitivity.
A Faraday cup detector is a closed structure except for an opening that allows the
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Ionization
Chamber
Focus
Lens
Quadrupole
Exit
Lens
Detector
Figure 1-2.
Quadrupole mass
filter.