Chromatography Forum

While trying to clean a C18 HPLC column, I encountered something I haven't seen before. The backpressure is significantly different depending on whether I'm running the column forward or in reverse. Running 50% ACN in reverse, I have a stable backpressure of 2.3 kpsi. When I turn the column back around, the pressure steadily climbs to at least 4 kpsi. Flushing the column backward with stronger solvents hasn't yet seemed to help. In each case, the column is disconnected from the detector. Has anyone else seen this?

Thanks!

I have seen that with something stuck in the high pressure side inlet hole. When you go in the low pressure direction try connecting a piece of tubing to the outlet end and see if it goes up again.

I have seen that with something stuck in the high pressure side inlet hole. When you go in the low pressure direction try connecting a piece of tubing to the outlet end and see if it goes up again.

That solution sounded so elegant that I ran to the lab to try it out. But it didn't work--attaching tubing (SS or PEEK) to the outlet didn't change the pressure. Thanks though!

Well, another thought is that there may be some fines at the bottom of the column. If they packed at too high a velocity they could crush the particles at the end which would then clog the frit in the forward direction but perhaps not in the reverse. Was the column like this when you recieved or it happened after it was working for some period of time?

The column has been working fine for the last few months. In fact, it was working fine last week. When I started up again today, the pressure problem started, even before making any injections.

really sounds like something stuck in that inlet hole to your column.
I would try running it backwards with no tubing attached to the inlet and tap (or bang) on the inlet end as you push solvent through. Or, depending on the column hardware you might even be able to remove the inlet fitting without disturbing the inlet frit or packing and then sonicate the fitting in IPA/water.

some columns have different pore size for two frits in the two ends.

I have had the same problem after injecting too much dirt on the column, I changed the inlet frit and the problem was solved.