Hello my fellow scientists!

I am working with an HPLC-MS/MS Orbitrap Dionex 3000.

I have a very isolated problem on the left nanopump (pump A), but I do not know the part being affected or damaged. I start the chromatography gradient at 2% AcN (on pump B), being the other solvent Water (on pump A).

In the beginning, everything goes the way it should, the slope goes from 2% to 21% in 3 hours time. After that, I put a 90% AcN in order to elute every other compound left on the column and prepare the column for the next injection.

The problem begins with that change. Pump A, water, goes from 79% to 10% of the flow which means a flow change from 237 nl/min to 30 nl/min (because I run at 300 nl/ml flow). The pump is not able to lower down the flow, it goes sooo slowly that when pump B reaches his proper flow, the pressure increases a lot and then a message "Cannot regulate flow. High leaks on the left block" and Dionex stops working.

The picture attached reflects the problem that I talked about. Right after the Dionex switched off automatically, I manually activate the pump and establish a 200 nl/min flow 50%/50%. As you can see, pump B is on 100 nl/min as it should, but pump A is still way higher than that and it would not go down in a minute.

The system itself has a detect leaks test. When I run it, it says that there are no leaks found on any pump, so the leak might be on the capillary between the pump and the flowmeter. I changed the capillary and the problem still going.

The flowmeter was replaced on November '21 so I do not really think that is the problem but could be.

Does anyone know what the problem could be related to or have dealt with the same issue?

Maybe the valve cartridges, the U-shape capillary, pump seals..

Any help is appreciated.