LCMS pumping air

Discussions about HPLC, CE, TLC, SFC, and other "liquid phase" separation techniques.

4 posts Page 1 of 1
Hi everyone,
this morning I arrived and noticed that the solvent was finished, so the instrument pumped air for a bit. I purged the whole system to remove the air but now the column has a crazy backpressure (while it was okay yesterday). Do you have any suggestions?

thanks!
You've gotten air into your column, which has damaged it. You can try to recharge it by flowing mobile phase through it starting at the lowest flow you are allowed to go and slowly ramp up the flow until you're back at your operating flow rate. Monitor the pressure; I wouldn't increase the flow until the pressure has been stable for awhile at the set flow rate. Definitely check solvent compatibility with your column to determine what should be flowing through it.

If your column allows, an overnight IPA flush of your system and your column can help get out any tiny annoying residual air bubbles left behind.
"Have you tried explaining it to the rubber duck?"
I hate to disagree, but I disagree; it's nothing to do with air. You cannot pump air into a column with a UHPLC pump. The moment the pump head is full of air, all that happens is the pump piston squashes the (compressible) bubble and unsquashes it again, and nothing much moves anywhere. It's really hard to pump air into a column.

But if you've got a binary pump, and one channel runs dry, then you will probably be pumping something from the other channel. So, for example, if your aqueous solvent runs dry, you are now pumping a little bit of pure organic channel, and if you've got anything lingering in the system that can precipitate in 100% acetonitrile, it will.

Similarly, if you didn't have a lower pressure limit set on the pump (presumably you didn't, or it would have stopped pumping; setting a 5-bar lower limit can be a useful technique to guard against empty bottles), then if the bottle ran dry several injections before the end of the batch of samples, you've now made a a number of injections into a possibly unsuitable solvent, or a low/zero flow, meaning you might well have got a load of precipitated sample in the system...

So if you now have a very high back pressure, treat it as a typical blocked column and/or blocked autosampler (easy to check which) and wash with whatever procedures you know help.
I agree with Imh here. Manually prime your lines and pumps with whatever cleaning solution you've got and start cleaning, I wish you luck!
4 posts Page 1 of 1

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