Analyzer 7
5977B Series MSD Troubleshooting and Maintenance Manual 203
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 m/z can pass through the filter to the
detector. The mass filter in the MSD is a quadrupole (See Figure 48 on
page 204).
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 has
negative voltages applied.
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
m/z 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 can be manually adjusted in the Edit Tune
Parameters dialog.
• AMU gain (AmuGain)
• AMU offset (AmuOffs)
• 219 width (Wid219)
• DC polarity (DC Pol)
• Mass (axis) gain (MassGain)
• Mass (axis) offset (MassOffs)
• MS quad temp
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