I have a problem which is occuring on three different HPLC systems.I am getting very wavevy baselines which makes it difficult to integrate the peaks of interest. When I started my run the baseline was normal for up to 400 minutes but after that the baseline started to get exremlely wavevy.
Once the base line gets wavevy it does not get normal even when you wash the system and start a new run with fresh mobile phase etc. it happened with all three system. the problem has not been corrected yet because cause of the problem is not clear. If anyone experienced similar or same problem and can help, it would be greatly appreciated. Thank you very much in advance.

Dear Anonymus;

Since you have experienced the same problem in three different systems it seems likely that your column and samples are causing the problem. This is of course assuming that your mobile phase components are not introducing some contamination.

What I would do in your case is to try a new column. The likely scenario of your problems is that some of your sample(s) is being retained for a long time in the column and it is slowly coming out after a long time. The symptoms described are typical of such contamination. Another possibility is that the contamination is not in the column but in the autosampler.

A simple test you can perform is to reverse the column, flush it for a long time, and then try it again, in the normal mode using a guard column. Obviously, the guard may need replacement after a few sample injections.

You also mentioned that you have tried cleaning the system. This may or may not be cleaning everything your samples are leaving behind. Without more information is not possible to add more suggestions.

Good Luck

Benjamin

Another thing you may try is to just monitor the baseline with no flow. If it is still cycling, you may have an instrument problem. With three different instruments exhibiting this, it could also be an environmental problem. What type of detection are you using. With RI, you can get this cyclind with temp. flucuations in the room, as when the A/C turns on and off. I have also seen this with UV on some systems.

We have also experienced the same problem in our laboratory. We have seen this cyclic baseline with at least four different methods on three different types of instruments (Waters Alliance, HP 1050, HP 1100), both PDA and UV detectors.

We currently stand as this: after removing the flow cell and having all components off (i.e. no flow) EXCEPT the detector, we still experience this cyclic baseline. Unfortunately, when an attempt to repeat it today was made, no wave was seen. We have cleaned flow cells, replaced flow cells, replaced amplifier boards, installed line conditioners, attached UPS boxes and run off the battery...nothing seems to help.

Any ideas? Thoughts? Suggestions?

David,

I had a problem once with a HP 1050 and a UV detector exhibiting symptoms similar to the ones you have described. In the end the problem was the HPIB cable connection. This connection was not overly loose but after tightening the wavey baseline went away.

Mike M.

David,

Since your problem is affecting multiple instruments and multiple methods I think it is probably an environmental factor.

We had a UV spectrometer that would not pass long term stability. We finally traced the problem down to high frequency noise from halogen corridor lighting that was being both conducted and radiated. High freq. noise and common mode nosie can both be coupled in via the ground conductor and through a UPS.

A transformer based power conditioner is best because it controls noise by isolation and also filters and re-derives the neutral-ground bond.

Also, make sure the data collection computer and the detector are plugged into the same circuit. High frequency ferrite blocking ckokes should be on all data lines. A good laboratory/building power quality assesment is not very expensive www.powercet.com

Anon 1,

What is your MP, column, sample, sample prep, etc.? How are you trying to clean the system?

If this is a reverse phase method, I agree with Benjamin. You probably have strongly retained impurities that finally elute after 400 min. I would monitor at both the analytical wavelength and at 200nm and run a gradient to 100% organic and see what elutes from the column. Becareful to avoid buffer precipitation. If you have a lot of junk eluting from the column and you return to a good basline following the gradient you could just put in a wash step every so many samples to keep the baseline under control. Good luck.

What is your mobile phase? What wavelenght (if you are using UV)? Do you use temperature control? At what temperature?

If your mobile phase is organic and it is not degassed then you may have a noisy baseline (due to bubbles) and pumping failures (check pressure) that can lead to noisy baseline, I have seen it. After some hours the mobile phase may need to be degassed again.