Waters GCT Premier Operator's Manual page 368

Notes:
• Gain Drop Monitoring only works in DRE mode.
• You must be using a lock mass to use GDM – this is set up in the TDC
settings and can be checked because the lock mass will be flagged in the
spectrum as a blue peak with a star on top of it.
• You must be using a calibration for the lock mass function to work.
• Ion statistics from the stitched weak data will be worse than from the
strong. This means a very weak peak that occurs when the gain has
dropped may not be measured at all.
In order to get an average of the lock mass value the system averages the first
10 scans. In a normal GC run the lock mass intensity can be affected by the
solvent front so errors can occur when trying to use the data when a solvent
delay is used.
Recommendation:
0.1 minutes to 4 minutes as shown in
on page G-14.
Solvent Delay dialog box:
The 4 minute duration can be adjusted to your normal solvent delay for a
Tip:
particular analysis. This allows the system to acquire constant lock mass data
in the first 0.1 minutes before the solvent front elutes and still switches off the
filament when the solvent front causes the large pressure rise in the source
chamber.
Gain drop monitoring successfully produces accurate mass results if the
Note:
gain of the detector is reduced by a large signal. Nevertheless it is useful to
verify the lock mass signal in the data. If a peak elutes from a GC peak with a
G-14 Theory and Principles of Operation
Set the solvent delay in the MS method editor to run from
Figure titled "Solvent Delay dialog box:"