Preventing Backflash - Acetonitrile

[ChromatographyDude]

Hoping for suggestions here... I am using a standard splitless liner, 4mm ID x 75mm in length. At the beginning of my GC-MS run, the column head pressure is at 8 psi to generate my 1mL/min constant flow. If I inject acetonitrile into my 250C injector at 8psi, the generated vapor volume is 533uL and my liner volume is only 471uL. Clearly, this poses a problem.

I'd like to know the best way to setup for pulsed splitless injection to get around this issue. If I setup a pulse splitless injection and have the injector pressure at 25psi, the generated vapor volume is now only 305uL, making my choice of liner acceptable. How long do I need to hold the injector pressure at 25psi if my splitless time is 0.75 minutes? Do I need to hold the pressure pulse at 25psi for the entire 0.75 minutes or can I lower it back down to 8psi at say 0.25 minutes? Will lowering it back down to 8psi before the injector vent opens cause backflash or I have already gotten rid of enough solvent vapor during the pulsed 0.25 minutes that I should be "safe"?

Thanks for the advice.

[macgyver]

Is this a straight through glass Agilent/HP splitless liner you're talking about? By my calculation this liner has a volume of 942uL.
You shouldn't have a backflash problem unless you're trying to inject more than 1uL.

I don't have much experience with pulsed splitless injection, but pulse times around 0.25 mins are supposed to work best. Pulse times more than 0.5 mins can result in excessive band broadening. The pressure pulse should be 2 to 3 times the final column pressure.

[ChromatographyDude]

I am pretty sure I've done my calculation correctly, it is a 78.5mm length x 4mm ID Varian 1177 liner with single gooseneck. 500uL should be the max vapor volume it can hold...

[macgyver]

I stand corrected (well sort of)...
Theoretical liner volume is 942uL.
Effective liner volume available for vaporization is approx 1/2 of theoretical - 471uL (due to presence of carrier gas).

I'm still learning too...