Peptides have charged groups: the N-terminus and side chains such as those of lysine or arginine. For the material to be stable and solid, those charges are neutralised by oppositely charged ions. The peptide is therefore obtained as a salt.
TFA appears because it is used in solid-phase synthesis to release the peptide from the resin and in HPLC purification. That is why, unless an extra step is done, the peptide ends up as a TFA salt. Through ion exchange it can be converted into an acetate salt or a hydrochloride, which is common for pharmaceutical-grade peptides.
The counter-ion adds weight without being peptide, so it lowers the peptide content of the powder. In some sensitive cell assays, residual TFA can also interfere with the results.
Two batches of the same peptide, one as TFA and the other as acetate, have a different salt molecular weight and different peptide content. The certificate should state which form is supplied.
Related terms
Learn it in depth at the Peptide University
- Related impurities and counterions · Module 7
- Peptide content, water, counterion and reading the COA · Module 7
- Lyophilization and excipients · Module 11
Definition for educational and scientific purposes. It is not medical advice or a recommendation for use. NeoPeptidos products are sold labelled for research use only (RUO).