By Michael Getsie on Friday, October 11, 2002 - 06:27 am:
Over the past month, we have been experiencing a "wavy" baseline ("sine wave")in some of our LC's. It seems to happen periodically, with no flow. The LC's are from different manufacturers, so it is not brand dependent. We have changed lamps and flow cells but this phenomena still occurs. Not all of our LC's have experienced this. Any ideas?
By Anonymous on Friday, October 11, 2002 - 06:34 am:
Try checking for some type of environmental cause. Depending on your location, it could be either the heat cycling on and off, or the Air conditioning. You may check the fan filters on the units to make sure they are getting good air flow which would lead to thermal stability of the optics bench. I have seen some labs try to troubleshoot this by putting a box over the detector to see if that changes the problem. Good luck.
By Anonymous on Friday, October 11, 2002 - 08:33 am:
I have seen this effect using some mobile phase combinations at low wavelengths (observing wave length above the UV utoff of the MP). In my case the periodic cycle could be directly liked to the A/C cycle in the lab which we belive was causing slight absorbance shifts in this particular mobile phase wavelength combo. Some added insulation on the tubing exiting the column to the detector significantly helped. This wave may not be fully be related to temperature, humidity can also play a role. The acutal distance between each groove in the diffraction grating in the detector can change slightly with changes in humidity which could also have an impact. I have seen this demonstrated by flooding an optics bench with dry nitrogen.
By Anonymous on Monday, October 14, 2002 - 04:17 am:
See 'Wavevy Baseline' discussion from 03 Oct.
By Anonymous on Friday, October 18, 2002 - 09:02 am:
what is the frequency of the sine wave. Is it due to pump noise / check valve noise i.e quite a fast sine wave? or a slow frequency i.e drift in base line due to environmental effects / temperature etc.???
By Mel on Friday, October 18, 2002 - 12:20 pm:
Michael -
Did you find the source of your problem?
I am always curious as to the outcome of these types of situations.
By Michael on Wednesday, January 22, 2003 - 01:21 pm:
We had the local electric company and and electricity expert assess the problem and they determinined that it was in an electrical "switching unit" in the laboratory. This unit was shut down, and the problem disappeared. The reason why this "switching unit" began doing this is still not known.
By Anonymous on Thursday, January 30, 2003 - 03:52 pm:
Thanks for getting back to us! Another problem cause to be filed in the mental folder...