HPLC unstable baseline

[Maulwurf]

Hi there,

i am experiencing a strange baseline phenomenon i don't know how to solve. When i am running just the mobile phase (e.g. pure MeOH (HPLC quality) and MeOH/water mixtures), i observe these huge jumps in the baseline (see graph). The example was recorded at 530 nm, but i observe it also with over wavelengths. It appeared after i installed a new column ( a replacement for same worn-out one) and it's the first time something like this happened after a change of columns. I purged a lot and flushed the tubing for half a day. The HPLC is equipped with a degassing device for the solvents. Also I checked the flowcell visually and it seemed ok. No leakage in the system. My impression is that i have air in my system, but i have no idea how i get rid of it. Or could be the column defective? Has anyone an idea?

Thanks!

[elsico]

First try to add backpressure (5-10 bar) on waste line from detector. Any idex or other brand will be useful.
If you say which brand detector you use it will be better.

[uzman]

You may connect a ZDV ( Zero dead volüme ) union in place of column and pump the mobile phase at 3 ml / minute.
Check the signal , this will remove any bubbles in the flow cell .

But it looks like detector fault , since all the signals nearly have equal heights , may be a bad electrical connection inside the detector.

It may also because of a bad deuterium lamp trying to strike again and again.
The wavelenght is out of the range of deuterium lamp ( 530nm - visible ) but some detectors use deuterium lamp up to 600nm .

[Gerhard Kratz]

I agree and vote for lamp problem.
If you are not sure about air in the system flush with Isopropanol (disconnect column first).
Good luck

[Maulwurf]

Thanks guys for the help!
I flushed everything with acetonitrile at a very high flow rate and after some hours (!) it brought me back my stable baseline. There must have been a lot of air in it. D2 and W-Lamp etc. are working fine ( it's a relatively new ChromElite System ~ 4 years old). Seems like my systems works now.

[uzman]

If you flushed the system some hours to get rid of air bubbles , it is not normal.
A bubble in the flow cell can be flushed away in seconds.

May be your mobile phase filter is clogged and producing bubbles , so may face it again.

[chrsdrake]

I suspect your new column had dried out during storage and the bubbles you were seeing were from the column. Now you have them all flushed out the problem should not reappear. If it does come back then you need to check the system components again, particularly the degasser.

Good luck

Chris