Can TFA be used along with a protic acid as an additive

[Mike H.]

I am working on a 17 compound separation using TFA and was wondering if a protic acid be used together with TFA. Reason is there is one compound containing 2--COOH groups that TFA doesn't supress and I know that 0.1% H3PO4 does supress ionization. thx

[Vlad Orlovsky]

Why do you need to suppress these? If you do, why not use sulfuric acid instead of TFA?

[Mike H.]

The separation components consist of -COOH, -NH2 and and -CHO. We have a good separation of all components using the waters flouro phenyl column with 0.05% TFA aq and 0.5% TFA MeOH, but one compound is a di-acid 2(-COOH) and the ionization is not surpressed with TFA. I though maybe adding a protic acid modifier along with the TFA would fix this, but I've never heard of anyone doing this so I ask here.

[Vlad Orlovsky]

I would simply replace TFA with sulfuric acid.

[vmu]

1. TFA is a protic acid.
2. What are the pKa values of the problem compound?