This refers to a condition where the absolute abundance at the upper end of the mass range is poor. Absolute abundance should not be confused with the relative abundance (percentage) of m/z 502 to m/z 69. Sensitivity at high masses can be excellent even if the relative abundance of m/z 502 is low.
If your MSD's relative abundance is incorrect for the tune program used, refer to the symptom Relative abundance of m/z 502 is less than 3. If the relative abundance is correct but absolute abundance at high masses is poor, check the following:
Tune programs other than autotune have different relative abundance targets. The DFTPP and BFB target tune programs adjust the MSD to achieve about a 0.8% ratio of m/z 502/69. Check which tune program was used. If the relative abundance you observe is not appropriate for the tune program used, refer to the other possible causes.
Make sure the tune file specified in the current method is appropriate for the samples being analyzed.
Contaminants that interfere with the relative abundance of m/z 502 may still be present in the instrument. Wait until the MSD has been on with the heated zones at their normal setpoints at least 2 hours, then try autotune again.
On MSDs equipped with a diffusion pump, column (carrier gas) flow should not exceed 2.0 ml/minute. On MSDs equipped with a turbomolecular pump, column (carrier gas) flow should not exceed 4.0 ml/minute. Reduce the column flow and retune the MSD.
Select the
other filament and when prompted to autotune click YES.
If sensitivity improves, use the new filament.
Replace the original filament when convenient.
See the MSD maintenance documentation for instructions for replacing a filament.
Switch the dc polarity on the quadrupole mass filter (quad). Retune the MSD. If performance improves, continue to use the new dc polarity.