by
kate_m » Tue Nov 26, 2019 11:01 am
I'm running an Agilent 1260 with DAD. I have found that my pressure is unstable during my runs - it also isnt reproducible. it seems there is a blockage which moves and then blocks again. A few days ago my LC switched off during the night as it exceeded the max pressure of the method - 300 bar - when i left it running it was around 230 bar. I've disconnected my detector and it does seem there is quite a big pressure drop over the DAD. I've tried back flushing (Water, ACN) and the pressure can be different, but again it is never reporducible. Sometimes i see a pressure drop of 20 bar @ 1mL/min, 40 degC, no column, pure water and then i can disconnect and reconnect and it can be 35 bar or even higher. Sometimes if i reconnect in the opposite direction the pressure drop can even be 10-15 bar different, but again it isn't reproducible.
I've had this problem for a few months where whenever i disconnect and reconnect my detector i get pressure issues. I'm obviously worried about cracking my DAD flow cell, especially if there is a particle in there. But how would i get this out??
I've included a chromatogram of the pressure vs a normal run. It's gradient elution 99% Aq increasing the % of ACN. They're blank water injections.
I've also noticed spikes on the baseline. I know this a symptom of air bubbles right? nothing is leaking and everything has been tightened enough.