95% Mobile A giving sigmoidal UV trace?

Question

Has anyone come across this pump issue (see attached trace)? I have an excessive UV sigmoidal trace (214nm) with at 95% Mobile A, but seems to go away at 100% and is limited above 20%. This is a binary pump with an Agilent 1200. Mobile A is 95:5 H20:ACN 0.1%TFA and mobile B is ACN with 0.1%TFA.

I've replaced pump seals, pistons, reseated and pressurized system, passed the leak test, pressure test, and mixer test with 0.1% Acetone (Step Gradient).

Also all of the obvious stuff as well, such as changing mobile phase, column, etc.

kbusch · Accepted Answer

Hey,

Your issue seems similar to the one answered in: Uneven pressure in B pump . It seems like one of the check valves on channel B is sticking. You may need to sonicate the valves to restore the performance. As you see in your pressure signal, Channel A is functioning without ripple and it increases with increased flow from channel B. Therefore, the valves on the Channel B would be the ones to look into.

KB