Thermo Scientific Surveyor MSQ Plus, Hardware Manual

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Functional Description
MS Detector
Thermo Scientific Surveyor MSQ Plus Hardware Manual 27
Figure 18. Polarity of the RF and dc voltages applied to the rods of the mass analyzer
Mass Analysis
The mass analyzer in the Surveyor MSQ Plus MS detector is a square array of round rods. The
rods are charged with a variable ratio of RF voltage and dc voltage. These potentials give rise
to an electrostatic field that gives stable oscillations to ions with a specific mass-to-charge ratio
and unstable oscillations to all others. The mass range for the Surveyor MSQ Plus MS
detector is 17 to 2000 u at unit resolution.
At any given instant, one particular set of RF and dc voltage values is being applied to the
mass analyzer rods. Under these conditions, only ions of one mass-to-charge ratio (for
example,
m/z 180) are maintained within bounded oscillations as their velocity carries them
through the mass analyzer. During this same time, all other ions undergo unbounded
oscillations. These ions strike one of the rod surfaces, become neutralized, and are pumped
away by the vacuum system. See
Figure 19 .
Then, at a later time, as the mass analyzer scans to a higher mass, both RF and dc voltages
change, and ions of the next mass-to-charge ratio (for example,
m/z 181) are allowed to pass,
while all other ions (including m/z 180) become unstable and undergo unbounded
oscillations. As the mass analyzer scans over the designated mass range, this process continues
with ions of one mass-to-charge ratio after another being transmitted, as the RF and dc
voltages change in value. At the end of the scan, the RF and dc voltages are discharged to zero,
and the process is repeated.
The Surveyor MSQ Plus MS detector can scan the RF and dc voltages over the full mass range
of the system (for example,
m/z 17 to 2000) in as short a time as 0.2 s. However, under the
conditions usually employed in mass analysis, such a scan should normally be done in about 2
or more seconds to fall within the upper limit of the calibrated scan rate of 1000 u/s.
+ RF voltage
+ dc voltage
– RF voltage
– dc voltage