Problems with the unstable baseline

[vicou_chen]

Hi,everybody!I have encountered a troublesome question:My hplc system is Agilent 1100 system equipped with a DAD detector,the mobile phase was 100% methanol ,detection wavelength was 254 nm ,reference wavelength was set to off ,when I turn on the detector the baseline ran from zero level to -120mAU in 10 minutes ,-156mAU in 15 minutes...the system pressure was stable and the new deuterium lamp has changed the ole one .But The situation was occurring in several different days ,I don't know why?who can help me?

[JA]

It's a little hard to deduce your procedure from the information you have given.

I'm assuming you have your mobile phase flowing through the column before you turn on the detector lamp? Do you switch it off at the end of every sample batch?

Agilent suggest a warm up time of at least 30 minutes for a deuterium lamp* - how long in total did you monitor your baseline for? If the column backpressure is steady and the detector output stabilises within this timescale then I would assume it was ready to run and begin my analyses.

If the analysis method is one which has been run in the past I would simply compare the retention time, height and area to some historical data.

* http://www.chem.agilent.com/Library/Sup ... f01002.pdf

[mbicking]

Make sure that you have high purity methanol and that you have the proper flow coming out of the detector line. Make sure that the purge valve is completely closed.

What pressure is reported by the instrument? Is it 20 bar, 50 bar, 100 bar?

Zero (balance) the detector and see if you still have the same problem.