Chromatography Forum

Hi there - I didn't find anything similar to this, so I'll open up a new discussion.

We're running an Agilent 1260 System with a quat pump (G1311B) and noticed strange pressure drops last week when my colleague made some clean-up runs (we're using it semiprep most of the time).
The flow rate will always show 1mL/min and the pressure stays stable at 200bar and suddenly drops to ~1-3 bar, and will then ripple from there to 30 bars and will eventually go up again. We measured the actual flow and it is as expected less than 1mL/min.
I then exchanged the frit and gold seal (and later on also the whole purge valve, which isn't very old btw) and it seemed that the problem has been solved. At least for ~10 runs and the problem occured again, even with the new PV. I took a look under the microscope with our "old" PV but didn't notice anything broken.
I took a look at the pistons (seemed good I think..) and exchanged all the seals in the pump head. I also connected water directly to the inlet valve (passive inlet valve) and put a restriction capillary to the other end to exclude a problem with the column. Still nothing.
The Agilent technician was here 3 times now and just left and left the pump running at 1mL/min with 50/50 MeOH/H2O and this is what the pressure-meter is telling me:

The picture attached continues with a short time period of 70 bar, after that 10 minutes of rippling 0-30bar, then again it goes up to 70 bar for 10 mins and then 200 bar.
He also exchanged the MCGV and degassing unit, also the inlet and outlet valves; he also changed the eluent-inlet-filters and also tried it without any filters.
Did anyone ever had this kind of problem? I'd be glad to hear some cheering words before we must buy a new pump or something

Best regards

What solvent your colleague used for the cleaning runs?
No leak can be detected??? I had a similar case many years ago and it was a leak on the column inlet connection. I would use a white filter paper and go from connection to connection to check for leakages.
Did you check flow rate from each channel? Did you check the injection system? Any air bubbles in the system. Flush with Isopropanol and than again with MeOH/water 50:50
Good luck

She used PBS (Phosphate buffered saline) but nevertheless, it occurs with every channel.
I didn't find any leaks. I checked everything, opened up every connection. Maybe the eluents are running somehow backwards but that would be a problem with the seals which have been all replaced. The system has been flushed by the Agilent technician beforehand. Air bubbles were also my first suggestion but I purged like a world champion...
The injecion system (manual injector) is fine and can be excluded because I did this test with the solvent directly let into the pump and the outlet connected to the waste.
At the moment (last 30 mins) it's running fine at 200 bars but I expect a drop again ...

Viele Grüße

Did you change the pistons ?

Do you have a second system? If so, can you just swap in the pump head complete, to try?

Either air is leaking in (before the pump), or liquid is leaking out like between a piston and the seal, or through a valve.

If mine, I'd use the Agilent little fitting which bypasses the MCGV, and concentrate on just using one channel and the pump, that way you don't have to worry about whether ALL channels in the MCGV were fully purged. Good that the inlet filters were taken off to try, clogged ones can cause issues. I agree that maybe new pistons might be a good idea, they can get little scratches on them. We've also seen leakage underneath by the springs, even a broken spring there.

I'm not that familiar with Agilent systems but got similar issues on Waters Alliance.
My thought would be an issue with check valves, maybe stucked or air trapped there, coming from mixing.
Even with quite new check valves.

? did you premix the MeOH/H2O 50/50 or online mix?
? is your deagasser working properly? (got told that this was somehow a weak part in Agilent systems in the past)

Either way, try ultrasonic and He degassing the liquids before seting up on the system.
If needed I also sonicate the CV cartridges in HNO3 6mol/L and then wash with pure water.

Agilent degassers have worked well for us, but I did cut off a broken end of rubber vacuum tubing and re-insert a few months ago - guess I forgot to read the sticker about "no user serviceable parts inside"!!

But I doubt that the degasser is involved here, unless there's a leakage of air into the HPLC tubing, as that pressure change is a whopper. But one could de-gas by ultrasonic mixing or vacuum externally, then go from there directly into the pump to temporarily get the degasser out of the system.

Somehow forgot this topic here. At the moment the System seems to be working fine. Made some semiprep-runs with a gradient at 5mL/min. The pressure was stable all along (around 100 bar).

To answer some of your questions:
I also think the degasser was not a problem because I directly put a solvent line onto the pump head and the problem persisted.
@Hollow: I online mix it (MCGV, low pressure mixing), this was also exchanged. They also changed the degasser.
My guess, since everything now was exchanged was that it could be the pistons got scratched maybe and solvend ran back into the MCGV or a combination of this, worn seals and everything. We'll monitor the machine closely and if anything changes, I'll be right here