Chromatography Forum

I have a Waters 2695 LC system that has a very strange problem..

When pumping phase (I am using water but the analysts are using a buffer) we are seeing a drop in the pressure which causes a peak in the baseline.

The strange thing is the pressure drop is not random it happens ~ every 8 minutes. I have changed the check valves which has sorted another pressure problem but am still getting this pressure drop.

Anyone got any ideas?

Sounds like a bubble. I've had a similar problem. Check that your frits don't have air trapped in them and that your degasser is working.

I have the same problem, but it only occurs with some mobile phases. I was using THF:MeOH:H2O:HCOOH (40:15:45:0,1) when the problem presented itself. Then I tried pumping MeOH through coloumn and there was no more pressure drop. The system is brand new (two weeks). I still dont know what is causing this periodical pressure drop.
Any suggestions?

See Noser222´s comment.

The Waters engineer found the problem...

The filters in the solvent bottles were blocked!!

Changed them and the systems are now working fine..

There was a recent discussion about those solvent reservoir "sinker frits".

http://www.sepsci.com/chromforum/viewtopic.php?t=8176

Period cleaning or replacement of those frits is recommended.

Regards,
Dan