Chromatography Forum

Hi all,
I've got a problem with our HPSEC column. I think there is air trapped inside it, because when I run through eluent the pressure gradually increases and the system cuts out because the max pressure is reached. Is there a way I can fix this or am I looking at buying a new column?
Thanks
Tim

It would be nice to have more details:
column dimensions, particle size,type of packing, flow rate, pressure, and the amount of time it takes to overpressure.

In the absence of data, my guess is that air, per se, is unlikely to cause overpressure. Liquids are somewhat compressible, and an HPLC system doesn't pressurize instantaneously, so a partial blockage can result in a gradual pressure rise. Check with the manufacturer to find out if you can back-flush the column. If so, try that (may get rid of junk on the inlet frit).

Some columns with polymer-based packings have maximum flow rate limits. If the flow rate is exceeded, the particles presumably start to deform and the pressure rises in the manner you describe.

Hi, thanks for the reply. Here are a few more details:
It is a Bio-Sil SEC 125-5 column, 300 x 7.8 mm, particle size 5 uM. Packing is highly porous silica beads. Typical pressure when it was operating ok was 8 MPa (at 1.0mL/min flow rate), but now it rises from 0 to 55 (maximum) in about an hour after it is switched on, and then cuts out.
The problem seemed to arise after I performed a column wash. This involved reversing the column and running eluent and then HPLC grade water through (which was fine), but then after I performed the wash with NaH2PO4, to remove hydrophilically adsorbed material, the problem has arisen.
I have tried running eluent and water backflushes since the problem has started but no luck.
Hope this info helps.
Thanks.

That happens without injecting anything?

Yes, thats right. And the flow rate is only 0.1 mL/min.

Some more info...
Just noticed that because the pressure is so high some eluent is flowing out of the injector valve! This is slightly worse when the valve is in the load position rather than the inject position.

I'd vote for salt precipitated in the column. Try a long (24 hours?) water wash at low flow rate (obviously!) and moderately high temperature (40-50 deg C). If that doesn't fix the problem, then it's time for a new column.

I vote for the salt precipitation too. It sounded like a problem I had almost one year ago.

Ok...I've tried a water wash for 24 hours with the column in normal and reverse direction but the pressure is still high. I noticed that when I reverse the column and start the pump the pressure is low for a while and then goes up to max, almost as if there is a blockage inside the column which takes a while to transfer to the other side of the column.
Would an HCl acid wash be something to try next?
Thanks.

It will strip any remaining bonded phase from the column, but since the column is dead anyway, you won't be any worse off.

At this point, I'd say the chances are your column is dead. Unless you volunteer your time, the most cost-effective route would be to replace it.