Chromatography Forum

Hi All,
When doing RP-HPLC with water and acetonitrile as mobile phases I have seen in the literature people adding 0.1% TFA to the water (phase A) but only 0.08% TFA to the acetonitrile (phase B). Does anyone know the rationale for doing this?
Cheers,
Sat

It gives a better baseline that way, since the absorbance of the mobile phase changes during the gradient.

Good answer Noser222. But to explain with more detail:

Better baseline in the sense of flatter and easier to integrate later eluting peaks.

I discovered this (before I ever saw it published) in work I did in 1985, although I used 1.0% and 0.9%.

Don't know who discovered it first, but it was very helpful in integrating late eluting peaks. Of course it was shared with our peptide suppliers immediately and I saw it everywhere a few years later. I did not completely understand why at the time it worked so well. I have heard explanations of the phenomenon since but I cannot confirm them so I won't go into it.

It has never made a difference in any analysis I ever did, but of course there may be an exception.

best wishes,

Rod

There was a fairly thorough article on this in LC-GC Europe in early 2003:
http://www.lcgceurope.com/lcgceurope/da ... rticle.pdf

Tom

Any chance you could also send links to the other articles in this series (Part II, Part III, etc).

Thanks
Adam

There were only two parts. The second deals with temperature and RI effects:
http://www.lcgceurope.com/lcgceurope/ar ... p?id=75777

Thanks Guy's. I guess I will try 0.08% TFA in my MeCN.
Cheers,
Sat

does anyone know if the same trick will work with methanol mobile phase? i.e., mp A is 0.1% TFA in wter, mp B is 0.08% TFA in methanol? or do we need a different percentage of TFA in methanol to achieve the same results?

does anyone know if the same trick will work with methanol mobile phase?

That specific trick is unique to the interaction between THF and ACN. That's why I posted the link to the Rozing article in LCGC Europe.