TFA salt means the peptide is supplied with trifluoroacetate as its counter-ion, paired with the positively charged basic residues in the sequence. It is the default because trifluoroacetic acid is used both to cleave the peptide from the resin at the end of SPPS and as the ion-pairing agent in preparative reversed-phase HPLC, so it is present at every downstream step unless deliberately exchanged.
Why TFA salt form matters in peptide research
Two consequences. Mass accounting comes first: TFA content commonly runs from about 10% to 25% of gross weight depending on how many basic residues the sequence carries, so a labelled 5 mg vial may hold appreciably less than 5 mg of peptide. Any molarity calculation should therefore start from net peptide content on the certificate of analysis, not from the label.
The second is assay interference. Residual TFA is reported to be cytotoxic to some cell lines and to affect cell proliferation readouts at concentrations well below those that harm the peptide, so cell-based work often calls for the acetate salt instead. TFA also produces a characteristic infrared band that can confound spectroscopic work. See reading a COA.