6 Determining an Appropriate Solvent Delay

It is very important that the MS not be acquiring data during a GC/MS run while the solvent is eluting from the column. To do so would shorten the life of the filament and/or the Electron Multiplier. When developing a new method or applying an existing method to analyze solutions with a different solvent, it is a good idea to measure the retention of the solvent rather than guessing.

To measure the solvent retention:

1. Edit the MS Parameters (in ChemStation) to set the Solvent Delay to a value greater than the length of the method itself.
2. Being sure the Ion Gauge Controller Multiplier is set to 4, turn ON the Ion Gauge Controller Power and Filament.
3. Run the Method using only Solvent as a sample.
4. Watch the Gauge Meter. When the solvent elutes from the column, the pressure will rise very rapidly.
5. The MINIMUM time you will want to use for the Solvent Delay is that time that the pressure drops back below 1*10 $^{\textrm{-4}}$ torr. Using this time plus 10-20% or so as your solvent delay provides a reasonable margin of safety.
6. Edit the MS Parameters to set the Solvent Delay to the value determined.