Varian 4000 MS, User Manual

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the imbalance. If the balance is outside the range of 200 to 300 µA, the algorithm
will search the optimal values by changing values of four variables one at a time.
If it fails to find the best voltage setting for lens tuning, auto tune will generate an
error message, and restore the last values in the instrument.
When the Electron Lens Tuning Box is clicked, an additional “Turn on CI gas flow
during tune” option appears. For CI methods in Hybrid mode, the electron
/repeller lens must be tuned with the CI plunger (CI volume) in place and the CI
gas turned on. The user should adjust the CI gas flow in Manual Control before
this tune function is done.
Ion Lens Tuning
The Ion Lens system consists of three lenses (Lens 1, 2 & 3). These lenses are
tuned using Cal Gas ions at m/z 131 and 414. Optimum voltages are determined
based on weighted intensities of the two ions. This is an iterative process in
which transmission of both low and high mass ions is monitored as a function of
lens voltages.
RF Full Scale Adjust
RF Full Scale Adjust sets the full scale adjust potentiometer to give the correct
mass assignment for high mass ions in the calibration gas spectrum. This routine
should always be run before Mass Calibration and Trap Frequency Calibration.
Mass Calibration
Mass Calibration locates and correctly assigns the masses of the PFTBA
calibration gas ions at m/z 69, 131, 264, 414, 464, and 614.
Ion trap temperature changes can shift the mass calibration axis;
do not run this
procedure until the ion trap temperature has stabilized for at least two
hours
. There could also be subtle effects on mass assignments after ion source
temperature are changed. Mass calibration does not have to be performed again
after the auxiliary Helium buffer gas flow rate is changed.
Trap Frequency Calibration
After the mass calibration has been completed, the
Trap Frequency Calibration
must be performed. This calibration determines parameters that are required for
the operation of ion preparation methods such as MS/MS and SIS. These
parameters also help to isolate the range of ions to be acquired in full scan
acquisitions. The routine takes several minutes.
NOTE: Trap Frequency Calibration should always be run
after
Mass Calibration
is done.
Trap DC Offset Voltage
The trap DC offset is adjusted by this routine to optimize the ion signal for m/z
414 in the calibration gas.