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.