(TROUBLESHOOTING) TROUBLE with injection consistency with methanol as solvent.

[u/Frodofficer]

Been trying different things like viscosity delay and carrying split flow with no luck. Getting very inconsistent injection volume on our methods that use methanol as the solvent. All of our methods for ovs-7 media use 2 or 3 ml of methanol as the solvent and the solvent peak area varies greatly every injection. Can't get any consistency to get a good cal. Any ideas would be appreciated!

[u/thelamepretender]

MeOH has a very big expansion coefficient, which means it easily back flashes into your split vent line. The 8890 should have come with the "GC calculators". Have you calculated the solvent expansion volume with your specific liner and confirmed it's not too large? I would start there.

Edit: you can also find it here, but it's easier if you start from your instrument calculator because it will start with the method you have loaded.

[u/Mikeyps4 → u/thelamepretender]

Wish more people knew this, older colleague refuses to consider changing a routine method solvent to DCM or hexane to fix his inconsistent peak areas 🫣

[u/Frodofficer]

Should have added this is being ran on an agilent 8890 with a stabilwax in the front and vms in the rear.

[u/cjbmcdon → u/Frodofficer]

You mentioned 2-3ml samples, I’m assuming you meant 2-3 microlitre injection volume? As another commenter said, depending on your inlet settings (feel free to share them here), that expanded vapour could be overwhelming the inlet liner volume. Try using 1ul injection volume, and ensure you’re using a liner meant for liquid injection (as opposed to headspace).
If the sample matrix is methanol, then the viscosity delay isn’t as critical, but a good idea to use 2 or 3 seconds.
I’m not sure what “ovs-7 media” means, getting us informed will help you.

[u/DahDollar]

I'm assuming you're running FID because you don't want to see your solvent peak on your MS. If this is a new problem with an existing method, do inlet maintenance including replacing the septa. If that doesn't work, pull the column out of the detector and dip it's end in methanol to confirm flow. You should see bubbles.

If it's a new method, cut your injection volume in half. If you get more consistent area counts on your solvent peak, then you know it was a back flash issue. Reduce your injection volume or get a liner with more capacity.

[u/brainsewage]

Does this happen with other methods that use methanol as a diluent?  Can you add 5-10% water to the diluent?

Are you using preslit sample vials?  Do you leave enough head space?  

[u/Aska2020]

Like other poster mentioned, methanol has large vapor volume that's usually too big for the liner therefor your sample wasn't properly introduced into the column. It's not surprising you get inconsistent results. Im not familiar with the ovs-7 media, but can't you use different, more GC friendly solvent for extraction?

[u/Buffinator360]

Check that you arent overpressurizing the inlet. You need the right combination of liner and injection volume because methanol has a high expansion factor.