GC/MS short vacuum drop after injection

[adsfo]

Is it normal to have a short (one second) vacuum drop about 30 sec after injection? My typical vacuum is 3x10-5 and it rops to 3x10-4 about 30s after the injection (splitless) then comes back down to normal within 1s.

[Don_Hilton]

Sounds like the solvent passing from the column and through the mass spectrometer on its way out throgh the pump. Check your linear velocity on the colulmn and the length of the column. This will give you an estimate of the dead time. This spike in pressure will be at or just after the dead time.

[cleh]

Do you have a delay time in your method that keeps the multiplier and filament off until the solvent passes through? If not, it's a good idea to add one to increase the life of the multiplier and filament.

[Rick]

Yes...it is normal (solvent )

[thohry]

It's due to the solvent expansion. If it's too severe, you can inject less and/or use n-hexane instead of MeOH or ACN (just if). Remember to use solvent delay.