Re: How to get rid of TFA?

Rod Levine (rlevine@nih.gov)
Mon, 20 Jul 1998 14:22:11 -0400

At 09:52 AM 7/20/1998 -0400, Leo Benoiton wrote:
>
>
>TFA is a strong acid. It will protonate (create the TFA salt) any amino
>group. The same goes for HCl.
>Acetic acid is a weak acid. It will only protonate more-basic amino groups
>such as that on the side chain of lysine and of course the guanidino group
>of arginine. As such, AcOH cannot displace TFA from a salt...
>
>
>The only way to remove the TFA is to displace it (evaporate in the presence
>of) with a stronger acid - Hydrochloric acid will displace TFA ...

On an equimolar basis I'm sure you're right. But I wonder if things are a
bit different if one has first dried the peptide to remove excess TFA, then
redisolved/resuspended in acetic acid?

This principle (mass action) is the basis of the "TFA fix" introduced by
Alex Apffel and his colleagues for dealing with the suppresion caused by
TFA when introducing an LC eluate into an electrospray mass spec. The
eluant (with the usual 0.05-0.10% TFA) is mixed with half its volume of a
mixture consisting of 1:1 acetic acid:acetonitrile. It is impressively
good in displacing TFA and improving the signal in the mass spec.

See: Apffel A, Fischer S, Goldberg G, et al: Enhanced sensitivity for
peptide mapping with electrospray liquid chromatography-mass spectrometry
in the presence of signal suppression due to trifluoroacetic
acid-containing mobile phases. J.Chromatogr.A. 1995; 712:177-190.

Rod Levine

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