Inconsistent peak widths are most apparent in the tune report. Do not acquire data if the MSD cannot pass tune. Possible causes include:
Make sure the tune file specified in the method is a valid file. Make sure it is appropriate for the analytical technique and for the type of sample you are analyzing. Do not acquire data if the MSD cannot pass tune.
It takes at least 2 hours after all of the heated zones have reached their setpoint for the MSD to reach thermal equilibrium.
Changes in MSD temperature can cause small shifts in mass assignments. A large shift in the temperature in the laboratory is sometimes enough to change the MSD temperature and affect mass assignments.
If the calibration vial is empty, you should see the error message: Not enough signal to begin tune or possibly No peaks found. If the vial is almost empty, you may instead see symtoms such as inconsistent peak widths.
Remove the upper MSD cover.
Check the PFTBA level in the calibration vial. If necessary, add PFTBA.
See the MSD maintenance documentation for instructions for refilling the calibration vial.
The calibration valve may be partially plugged or otherwise malfunctioning. Check the other possible causes. If they are not responsible for the problem, try replacing the calibration valve.
See the MSD maintenance documentation for instructions for replacing the calibration valve.
The horn on the electron multiplier may be nearing the end of its useful lifetime. If autotune consistently sets the electron multiplier voltage at or near its limit of 3000 V, this is probably the case. Replace the electron multiplier horn.
See the MSD maintenance documentation for instructions for replacing the electron multiplier horn.
The grounds for the detector and GC power sources may be at different potentials. This creates a current path (ground loop) through the detector interface and analyzer. Make sure the grounds for the power sources are at the same potential.
WARNING! Checking for a ground loop should be done by a qualified electrician.