Ion suppression with TFA

[Ricardinio]

I would like to understand how does TFA cause ion suppression.
Thanking you for your replies.

[JA]

Assuming electrospray, probably worth Google'ing the ionisation mechanism - it's well understood and longer than anyone should be willing to post here

Then bear in mind that a competitive process is in action for ions wanting to escape from the charged liquid stream. I think that anything which is readily ionised and at relatively high concentration in your mobile phase could lead to ion suppression. TFA evidently forms the trifluoroacetate anion in solution quite happily.

[MG]

TFA is thought to form ion pairs with protonated basic molecules, rendering them neutral.

See:

Journal of the American Society for Mass Spectrometry
Volume 6, Issue 12 , December 1995, Pages 1221-1225

(also that article includes a way to mitigate the problem)

[MG]

Amendment to my previous post: That was applicable to positive ion. I think what JA said is applicable to TFA causing ion suppression in negative ion mode, i.e. it takes all the negative charge for itself. Incidentally TFA is much worse in negative ion mode. In positive mode, you can at least get by.