Peptides purified by reverse-phase HPLC with trifluoroacetic acid usually end up as TFA salts. Basic residues such as Lys and Arg pair with counterions, which add mass to the powder.
Net peptide content vs purity
HPLC purity describes how much of the peptide material is the correct sequence. Net peptide content describes how much of the total powder weight is peptide rather than counterions and residual water. Both numbers matter for accurate concentrations.
When TFA can be a problem
- Sensitive cell-proliferation assays
- Studies with very high peptide concentrations
- Spectroscopy where TFA absorbs
Options
Acetate or hydrochloride salt exchange reduces residual TFA. For most binding and analytical work the standard salt form is suitable, provided concentrations are corrected for net content.
