We are experiencing fluctuating (long wavy baseline)baseline on our Waters HPLC PDA detectors systems - on all the 4 systems that we have. We have recently installed a new airconditioning system and the humidity was initially very high. Even the fridge was moist up on the outside on the glass door. When the problem was first encountered, there seemed to be a pattern in the fluctuating baseline every ~25 minutes. We were told the cause could be the humidity and temperature fluctuation. However, the humidity has been controlled and now after a month, the baseline is still fluctuating and with no pattern. The fluctuations are not the same for every injection. Some injections may have baselines which fluctuates more than the others. Very few injections have normal baseline.
Please help.

Hi Anon,

*test the baseline over a longer time without any injection ->fluctuations?
*clean up with a strong mobile phase the system-?
*change the flow - is the wavelength of the fluctuations the same or not

You can also try to monitor the baselinw with no flow. Does it still fluctuate? Try isolating the detector, put a box over it or something and see if the fluctuation goes way. Are you using a column heater? Try to make sure the solvents stay at the same temperature. Oh yeah, good luck.

Do you have the same problems over night?