We are having baseline problems with two 1260 systems. Both systems have quaternary pumps (G711B) with VWD (G7114A) detectors. At a detection wavelength 254 nm with the pump flowing at 1 mL/min 90% A (H2O) and 10% B (acetonitrile), there is considerable waviness in the baseline. I am using a restriction capillary to eliminate any column effects. The height of the peaks is around 0.03 mAU. If I switch to 100% channel A the waves are not observed and the peak-to-peak noise is about 0.005 mAU.
By contrast, if I perform the same separation on one of my 1100s, the waviness is not observed, and the peak-to-peak noise is about 0.015 mAU.
What is causing this problem and how do I resolve it?
Examples are in the attached file.