Chromatography Forum

Hello,
we have here the problem that after we changed the solvent of our HPLC, the pressure starts to fluctuate (+/- 10 bar) after about 30 minutes with 1 mL/min.

The HPLC is used with a sodiumphosphate buffer, then the buffer is washed out with water. After washing, the column is stored in 40:60 water:methanol. Then we change the column and change the solvent to 70:30 water:acetonitrile.
After about 30 minutes with 1 mL/min the pressure starts to fluctuate.
Usually it normalize after purging and piston seal washing.

It happend once that it didnt normalize. After keeping the HPLC unused over the weekend, the pressure normalized again.
This time, it seems we cant get a normal pressure again with purging and piston seal washing.

Has anyone an idea why we have this pressure fluctuation always after changing the solvent? Its always only after changing the solvent. We can use the HPLC a week or a month with the same solvent without any problems, but after changing the solvent, pressure starts to fluctuate.

Thank you for your time,
Biwi

Hello

First of all you need to give more details:
-what kind of pump you have? Binary/Quaternary
-methods parameters - are you using prepared mobile phase (70:30 Water-ACN) or you mixing solvents online?
-paste chromatogram with pressure profile - it'd be handy to see how it looks like

I would say you have two possible problems:

1.Air bubble in system (in pump) that can cause pressure fluctuation - you need to make sure you have all line flushed with solvents (even if you don't use other lines it is good practice to flush them)
2.You can have problem with valve/s (inlet or outlet)

I'd recommend to run diagnostic test for pump (leak test) to narrow problem down.

Regards

Tomasz Kubowicz

Thank you for your answer.

Its a binary pump.
We mix the solvents online.

Usually its not before we start a run, so the profile is not saved...i try to find one.

Regards,
Biwi

Hi Biwi

Are you degassing your mobile phase components - if not then you need to.

Peter

We have a degasser unit. The solvents dont get degassed in advance.
If its a degassing problem, i guess the problem would occur not only during solvent change.

Regards,
Biwi

We have a degasser unit. The solvents dont get degassed in advance.
If its a degassing problem, i guess the problem would occur not only during solvent change.

Regards,
Biwi

Some mobile phases are worse than others with respect to problems with bubbles. Acetonitrile is also reputed to make sticky deposits on the seals of check valves.

Peter

pressure fluctuations are usually a check valve issue.
When purging at 5ml/min, compare the "drops" coming out of the purge valve.
It should be consistent fast flowing drops. If not, air is likely not coming out or a faulty part
let me know what model pump, binary agilent G1312B?
Could be active inlet valve cartridge or AIV replaced

What is the volume of your mixing chamber, do you use a dynamic mixing chamber? I would recommend to purge the system with water, maybe also with hot water, without a column connected to the system.
Hope you have already solved your problem.

Thank you for all of the answers.

During purging, the drops are consistent. I would also say, that they are consistent during the pressure fluctuation.

We use a Shimadzu LC 10 ADVP.
We have a manual piston seal washing system, is it normal that the washing water splash out during the pump purge?


We have a 1.7 mL mixingchamber, i dont really know much more about the chamber right now. Why you ask about the mixing chamber?

We already purged the system with acetonitrile, water, warm water and, i guess, 2-propanole. After that, we opened the pumps and cleaned the interior as in the manual described. That helped last time, but this was about two months ago.

Regards,
Biwi