phosphate buffer gives a peak

[agomulcz]

Hello,
When I was analyzing impurities on a SEC column, I've noticed that the phosphate buffer which I use as the solvent has a peak in the impurities range. The intensity of that peak is strictly dependent on the molarity of the buffer. I don't think that my solution is contaminated and I wonder for what reason the phosphate should have a peak on a SEC column. The peak comes out at app. 25 min. on the TSK gel G4000SW column.
Thanks in advance for your help.

[Gerhard Kratz]

That is unusual for this specific column. But it is possible that a compound is absorbed and depending on the molarity of your phosphat buffer is eluted. First to do is to follow the column cleaning procedure as stated on your Operation Conditions Sheet delivered together with the column. After cleaning the column it should be gone. One question, do you have Tween 80 in your sample?

[danko]

Just inject the the same volume of the buffer several times and watch the peak.
If the peak gets smaller then something is eluting from the column. If the peak remains at the same level, then your buffer is containing the stuff that causes the peak.

Best Regards

[Ting Wu]

Do you have Tween 80/20 in your sample？

[carlos.teixeira]

It is a good question:
1) What is the wavelenght of your method?
2) Can you change your mobile-phase "bad" component (brand of lot)?
All the best,

Carlos Teixeira
teixeiracs@yahoo.com
Chromatography Specialist

[ym3142]

I do not see what kind detector you have.

If RI, an peak merely indicates that the sample and mobile phase have slightly difference.

If UV, it can be UV detector refractive effect related to sample concentration.

If CAD or ELSD and you are running isocractic the peak probably real; and suddenly mobile phase change could cause CAD or ELSD peak too.