Trifluoroacetic acid (TFA, CF3COOH, 114.02 g/mol) is used twice in a typical synthesis: at high concentration to cleave the finished peptide from its solid-phase resin, and at about 0.1% in HPLC mobile phases as an ion-pairing agent that sharpens peptide peaks. Peptides isolated from those conditions carry trifluoroacetate as their counter-ion.
Residual trifluoroacetate is a known variable in cell-based in vitro work, so some studies call for an acetate or hydrochloride salt instead. Exchange is done by ion-exchange chromatography or by repeated lyophilisation from a dilute acid of the desired counter-ion.
See also
For in vitro laboratory research only. Not for human or veterinary use. This library describes chemistry, analytical methods and published laboratory research; it gives no guidance on use in people or animals.