Agilent Technologies 5975T LTM GC/MSD, Troubleshooting And Maintenance Manual

Page: 207 / 270

Analyzer
13
Troubleshooting and Maintenance Guide 207
Quadrupole Mass Filter
The mass filter separates ions according to their mass-to-charge
ratio (
m/z ). At a given time, only ions of a selected
mass-to-charge ratio can pass through the filter to the detector.
The mass filter in the MSD is a quadrupole (
Figure 32 ).
The quadrupole is a fused-silica (quartz) tube coated with a thin
layer of gold. The four hyperbolic surfaces create the complex
electric fields necessary for mass selection. Opposing segments
are connected; adjacent segments are electrically isolated. One
pair has positive voltages applied, the other negative.
A combined direct current (DC) and radio frequency (RF) signal
is applied to the two pairs of segments. The magnitude of the RF
voltage determines the mass-to-charge ratio of the ions that
pass through the mass filter and reach the detector. The ratio of
DC-to-RF determines the resolution (widths of the mass peaks).
There are several parameters that control the DC and RF
voltages. All these parameters are set by Autotune, but also can
be manually adjusted in the Edit Parameters window:
• AMU gain (AmuGain)
• AMU offset (AmuOffs)
• 219 width (Wid219)
• DC polarity (DC Pol)
• Mass (axis) gain (MassGain)
• Mass (axis) offset (MassOffs)
Figure 32 Quadrupole mass filter