Separation - Ametek FlarePro User Manual

Figure 1-2.
Mass Filter.
1-4 | FlarePro Process 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 trajectories 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
toward the detector using an exit aperture which has an applied negative
voltage that attracts the positively charged ions.
Focus
Lens
Ionization
Chamber
Quadrupole
-
+
+
+
+
+ +
+
+
-
+
+ dc
Exit
Detector
Lens
+
- dc