Table of Contents
Advertisement
Analyzer
7
Mass filter
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.
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 voltage 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
AMU gain
AMU gain (
) affects the ratio of dc voltage to RF frequency on the mass fil-
AmuGain
ter. This controls the widths of the mass peaks.
• Higher gain yields narrower peaks.
• AMU gain affects peaks at high masses more than peaks at low masses.
223
Advertisement
Table of Contents
