noisy baseline @210nm

[vv]

I have a problem of the Agilent 1100 HPLC. Currently I found the baseline is very noisy at 210nm. Once changed the wavelength to 220nm and above, the baseline was very flat and stable.

To find out the reason, the system was bypassed the column.

No matter what mobile phase is water or AcN, the baseline fluctates about 1mAU.

The Agilent engineer has changed another set of optical unit and flowcell, the problem exists.

But he discovered that the surrounding air flow (from aircon) affects the baseline. When he covered the detector with some paper, the baseline shows not so noisy.

Anyone encountered the similar problem? Why temperature or air flow affect the baseline seriously? Or is there any causes behind?

[HW Mueller]

How did you degas the solvents? How close are you to "blackout" (the point were no light passes your cell)?

[vv]

I degas the solvent by sonication. Do you suspect that air bubbles were traps in the mobile phase?
I don't understand your second question.

[HW Mueller]

The suspicion is that absorbance + scattering is too high, so that you are in a region where too little light goes through your cell.

[Mark Tracy]

Your cell windows may be dirty. I have seen where a UV-absorbing film can develop if you leave the lamp on and the pump off for a long time. I find that 3M nitric removes it; perhaps there are gentler treatments.

[vv]

why the baseline noise is affected at only 210nm only? Once the wavelength is changed to 220nm above, the baseline is flat.

[HW Mueller]

Your absorbance is obviously much less at 220 nm.