Thermo Scientific DSQ II, Hardware Manual

Page: 200 / 242

6
Prefilter and Quadrupole
184 DSQ II Hardware Manual Thermo Scientific
Figure 99. Vacuum Manifold Components
The ratio of the RF and DC voltage determines the range of m/z ions that pass through the
quadrupole mass filter at one time. This determines the width of mass peaks and is called
resolution. Resolution can be adjusted. Higher resolution produces narrower mass peaks but
lower sensitivity.
Ion offset controls the how fast ions fly through the quadrupole mass filter. Lower ion offsets
produce better resolution since ions spend a longer time in the quadrupole mass filter. Higher
ion offsets often produce higher sensitivity because ions are focused better.
Rod DC (A or B) sets the polarity of the DC that is applied to each pair of quadrupole mass
filter rods. The rod DC that works best for your instrument has been selected at the factory.
To ensure the best operation, do not change the rod DC setting.
To improve the performance of the quadrupole mass filter a prefilter is used before the
quadrupole mass filter. The prefilter also has a combination of RF and DC offset voltages
applied to it. The prefilter serves two main purposes. First, the efficiency of the quadrupole
mass filter is impaired after a build up of ions impacting on them, so the prefilter removes
many of the low
m/z ions that would have otherwise struck the quadrupole mass filter rods.
This increases the time needed between routine cleaning of the instrument.
1 Ion Detector 4 Prefilter
2 O-ring 5 Ion Source
3 Quadrupole 6 Transfer Line
5
3
2
6
1
4