Chromatography Forum

Hello everyone

During instrument qualification I ran into trouble with gradient mixing between channels C and D (A vs. B works perfectly).
A picture says more than words: here is my problem:
[img]IMAGE%20HACKED[/img]
See the problem at 99 % D? I have seen this even more pronounced during pre-tests, I thought this might be a problem of insufficiently equilibrated solvent line D or so, but after > 200 ml the line should be equilibrated.
Any idea?

Thanks a lot in advance
Jörg

Did you purge ALL FOUR channels well before this?

Yes. Lines A and C are in water, lines B and D are in 0.1 % acetone/water.

OK, it gets worse and worse after more purging:



I suspect some serious error in the gradient proportioning valve. However, channels A and B are (still?) OK. Does anyone have experience with the GPV, can it be cleaned other than by purging the lines?

Thanks for your help
Jörg

Have you tested Line A + D and B + C too?

When the proportioning valve is the problem I think the problem must occour then too.

I would suggest that you first replace the Active Inlet Valves respectively the Cartridges to ensure that they are not the problem.

I had recently a problem with a cartridge. (see: viewtopic.php?p=114311#p114311)

Maybe that could help you.

To test the proportioning valve try this:

http://www.sepscience.com/Techniques/LC ... e-GPV-Test

You may try replacing the solvent inlet filters too. These are often forgotten items that may severely interfere gradient composition.

OK, it gets worse and worse after more purging...

Humor me and pull off the waste tubing from the purge valve, and run the pump with the purge valve closed, maybe at flow to produce 200 bar pressure. See if any droplets come out the purge valve exit when in the closed position.

Hi everybody

Sorry for the late update, but I have been very busy the last days.
I searched and found a step-by-step instruction on how to clean the valves of the gradient module (click), but the situation did not improve.

You may try replacing the solvent inlet filters too. These are often forgotten items that may severely interfere gradient composition.

This is the first thing I did

Humor me and pull off the waste tubing from the purge valve, and run the pump with the purge valve closed, maybe at flow to produce 200 bar pressure. See if any droplets come out the purge valve exit when in the closed position.

No leak over here. However, I don't understand how this should affect channels C/D but not A/B.

Next update will take some longer, the instrument is in use by a colleague.

Jörg