Baseline shift causing extraneous peaks - not reproducible!

[rakhi202]

What could be reason for a big baseline shift on only one sample in a sample set? I have one chromatogram with extraneous peaks and for the peak of interest the baseline also shifted below in the end valley. Several "extraneous peaks" were integrated, however, it appears to me that the extraneous peaks are not really peaks but the baseline shifting up and down. The peaks were not reproducbile. One note to be made is that the baseline shifted down slightly (from "0" to "-0.2") for the next chromatogramonly. After that, it went back to "0" and remained "0". Not a carryover from the previous injections either. The HPLC system was used everyday and the baseline was consistently stable for days after. What could be a reason for this? Please HELP!

[tristanewalters]

Could you provide a chromatogram so that we can see what these "peaks" look like? Also, a little bit more information about the method could be useful.

[rakhi202]

Thank you for your attention. Could you please tell me how to include the chromatogram? I do not see any option to upload any images.

[tristanewalters]

Go to this topic which explains how you can do it.

viewtopic.php?f=1&t=2617

[rakhi202]

Here is the Chromatogram. Thank you!

[tristanewalters]

Alright great. Now that we have that, could you tell us more about the method. I.e. isocratic or gradient, mobile phases, etc.

[rakhi202]

sorry...this is my first time using a discussion forum. I am also not so experienced in chromatography! It was an isocratic run with mobile phase 70:30 Phosphate Buffer:ACN / Wavelength 280 / Ambient Column Temp.

At this point, I am thinking it was an air bubble passing through causing the baseline shift.

[tristanewalters]

That could be. Always check for air bubbles before running. A good indicator that there is an air bubble in the system is a drastic cyclic pressure change. What it also might be is carryover from a previous injection. One important way to tell the difference between an isocratic and gradient method is that isocratic method peaks will get wider as time goes on whereas gradient method peaks will have the same peak width, assuming that there is a constant change in %B per minute

[rakhi202]

Thank you very much. That was a great help in moving towards the right direction.

[Jia Xin]

Maybe some debris washed off from the column frit.