2000 MS Hardware Maintenance
134
Troubleshooting
3. Adjust the RF ramp by turning the RF tuning screw on the front panel. Adjust
to minimize the highest reading.
Check the RF Storage Level
Check whether the RF storage level is incompatible with the scan range,
proceeding as follows:
1. Open the Method Editor.
2. Select EI-AGC segment, and click on Ionization Mode. Note Ionization
Storage Level. Confirm values are appropriate for mass range. Refer to
Method Editor manual or help for details on appropriate rf storage values.
Check the Trap Temperature
Check whether the trap temperature is too high to permit you to observe all cal
gas ions, proceeding as follows:
If the trap temperature is too high, the height of the mass 614 peak may be
reduced, and the mass 502 peak may disappear entirely (above 200 °C).
Reduce trap oven temperature to 150 °C and wait 2 hours for thermal
equilibration.
NOTE: If, after performing these tests, you are still unable to isolate the cause of
the problem, contact your Varian Customer Support Representative.
What To Do If the Resolution is Poor But the Air and Water
Levels are Acceptable
If the peaks are broader than you would have expected, you should investigate
the following possible causes:
•
There are too many ions in the trap (i.e., contamination or high column
bleed).
•
The axial modulation value is too high or too low.
•
Axial modulation is not functioning properly.
Before you begin troubleshooting, however, be sure that Saturn has baked out
for at least 2 hours. If you have done this, and the problem persists, continue as
follows.
Check the Ion Content of the Trap
With the trap turned on, note the TIC (total ion current) value. If the TIC value
exceeds 20,000 counts in full-scan mode, or a few thousand counts in MS/MS,
reduce the number of stored ions.
To reduce the number of ions in the trap, do one or more of the following:
1. Make sure that the electron multiplier is set for a gain of 10
5
. In the Method
Editor, check that the Multiplier Offset is equal to 0 in the Method. Reduce
the trap filament current and/or ion time settings (AGC OFF).
2. Reduce the AGC target value to 10,000 (AGC ON).
