Baseline problems Waters UPLC

[JM]

Hi Mattias,
you are in right direction!!
Yes a dirty flowcell or air bubble can cause high noise when the flow is off. It is evident that your mobile phase and pump systems are OK.
The most likly culprit is your detector . You can clean the flow cell by flushing it with dil.nitric acid using a syringe.

JM

[Uwe Neue]

Well, it seems that things are going fairly much as what I thought would happen. You reduced the path length, and your noise decreased about 4 times (in principle, it should have been 2.5x, but at least we are going into the right direction). When comparing different detectors, you still need to have the same sampling rate/time constant settings. However, since you are within a factor of 2 within the range of the analytical system without even adressing this second issue, I think we are on a good path, and the "problem" may have disappeared, or at least diminished.

[danko]

Hi Mattias,

Yes dirty cell will cause more noise, as less light reaches the sensors and thus more amplification is needed.

Regarding the lower noise level with the 10 mm cell: It is not any surprise at all, the absorbance decreases due to the shorter pathlength. But it also means that your peaks’ absorbance will be reduced equally. So it is not quite certain that S/N will be different from the one with the 25 mm cell. Unless the 25 mm cell actually was dirty. But it should have influenced the noise with pure water in the cell too.

Best Regards