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95% Mobile A giving sigmoidal UV trace?

Question asked by chembrown2019 on Jan 30, 2020
Latest reply on Feb 3, 2020 by kbusch

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.