Trifluoroacetate counterion (revision 3)
Old revision·21:39, 1 Oct 2024·DiluentDiya
| Trifluoroacetate counterion | |
|---|---|
| Abbreviation | TFA salt |
| Arises from | Trifluoroacetic acid modifier in RP-HPLC |
| Typical content | 5–25% of solid mass, sequence-dependent |
| Alternative | Acetate, hydrochloride, by salt exchange |
| Topic infobox · conventions | |
Trifluoroacetate is the counterion carried by most synthetic peptides purified by reverse-phase chromatography, because trifluoroacetic acid is the standard mobile-phase modifier and the peptide is isolated from that mobile phase by lyophilisation.[1]
The counterion pairs with basic side chains — lysine, arginine, histidine — and with the N-terminal amine, so its mass fraction depends on how many basic residues the sequence carries. For a peptide with several, trifluoroacetate can be a substantial fraction of the solid, commonly cited in the range of 5–25%.[2]
Origin and removal
[edit]Trifluoroacetic acid is used as an ion-pairing modifier because it sharpens peptide peaks considerably; the resulting separation is better than with most alternatives. It is also used in the cleavage step of Fmoc synthesis, so the peptide encounters it twice.[1]
Removal requires salt exchange, most often by repeated lyophilisation from dilute hydrochloric or acetic acid, or by an ion-exchange step. Exchange is not free: it costs a processing step and some yield, and the resulting acetate or hydrochloride salt has its own mass contribution.
References
- ^ a b United States Pharmacopeia, General Chapter <1503>, Quality Attributes of Synthetic Peptide Drug Substances.
- ^ Roux S, Zékri E, Rousseau B, et al. "Elimination and exchange of trifluoroacetate counter-ion from cationic peptides: a critical evaluation of different approaches." Journal of Peptide Science 14(3):354–359 (2008). PMID 17994590.