Chromatography Forum

Hi, this is my first post here.
I am pretty new to Agilent HPLCs and we are experiencing some intermittent baseline issues. The ripple is very low (relatively flat baseline). However, it is shaped like many plateaus lined up side by side. The baseline will suddenly drop about 15 mAu, then remain for 10-20 seconds before returning to original position for ~30 seconds. It looks almost like a square wave. This continues throughout the runs. Pump pressure remains constant throughout this which leads me to believe this is possibly a detector issue. However, there is no degasser installed on this model, so I am wondering if that could be an issue as well. Has anything seen this before?

However, there is no degasser installed on this model, so I am wondering if that could be an issue as well.

I would NEVER try to get "decent" results without a degasser. In a pinch, heat/stir pull a vacuum on your mobile phase and let it cool, but that's a band-aid.

So fix first what you know is "bad".

An alternative is to purge the mobile phase with equal volume of He. For example, purge 1 L of mobile phase with 1L He.

... but it's quite hard to see how a degassing issue would create a reliable and regular square-wave. What wavelength is this? Does it happen at all wavelengths, or just some? Does it correlate with pump-rate (i.e. if you pump half the speed, do the plateaus double in length?).

Hi jsciscoe , what is your detector on your HPLC?

Thanks for the replies
The detector is a DAD and the irregular baseline appears both at 214 and 300 nm. Unfortunately, I am unable to consistently duplicate the issue so I have not been able to experiment with pump pressures, flow rates, etc for troubleshooting. This problem will arise for 5 or 6 samples once or twice a week and then disappear.

Hi, if that, i suggest you can do diagnose of the performance of UV lamp, it seems the lamp is going to disable.

Quick update..
I replaced the lamp and so far, so good. Thanks for the help.