ISQ User Guide - Write Frame of Mind

7 Optimizing Your Method
Modifying an Automatic Tune
– Repeller—Select this option to control how the repeller pushes the ions out of
the ionization region. The voltage applied to this component will have a very
strong effect on the energy of the ion beam, which will have a strong effect on the
resolution and the intensity. The lower the voltage, the better the resolution.
However, higher voltages will prevent ions from striking the repeller surface,
which leads to better robustness. Typical values are 0 to 5 V, although a dirty
system may have the repeller climb as high as 12.5 V. We do not recommend
setting the repeller any higher.
– Lens 1—Select this option to control Lens 1, which is the first of three lenses
that the ions see as they leave the ionization region. These three lenses act as a
focusing element to maximize the ion beam intensity that is entering the ion
guide. This field is typically set between -35 and -50 V.
– Lens 2—Select this option to control Lens 2, which is the second of three lenses
that the ions see as they leave the ionization region. These three lenses act as a
focusing element to maximize the ion beam intensity that is entering the ion
guide. This field is typically set between 0 and -15 V in EI mode. In CI, the
optimal voltage may be between 0 and -30 V.
– Lens 3—Select this option to control Lens 3, which is the last of three lenses that
the ions see as they leave the ionization region. These three lenses act as a
focusing element to maximize the ion beam intensity that is entering the ion
guide. This field is typically set near the same voltage as lens 1.
– Ion Guide DC—Select this option to control the ion guide’s DC offset voltage.
It can potentially help focus the ions into the quadrupole while ensuring that
neutral noise is eliminated. The voltage on this component is mass dependant
and should be set at several different masses. This field is typically set between +1
and -15 V, depending on the mass of the ion.
– Ion Guide RF—Select this option to control the ion guide’s RF voltage. It can
potentially help focus the ions into the quadrupole while ensuring that neutral
noise is eliminated. The voltage on this component is mass dependant and
should be set at several different masses. This field is typically set between 0 and
+5 V, depending on the mass of the ion.
– Q1—Select this option to control the voltage that pulls the ions into the
quadrupole. The voltage applied to this component will have a very strong effect
on the energy of the ion beam, which will have a strong effect on the resolution
and the intensity. The lower the voltage, the better the resolution. However,
higher voltages will pull more ions into the quads, which leads to better signal.
This field is typically set between 0 and -5 V.
– Resolution—Select this option to adjust the ratio of the quadrupole DC and RF
voltages to create the resolution required for your analysis. You can set the desired
peak width at a given mass and whether you measure the width at 10% or 50%
of the peak height. Because there is no static DC voltage involved, the start, stop,
and step values are not used.
• Mass—Use this pull-down menu to select the ion to be used for tuning.
Thermo Scientific ISQ User Guide 83