Glossary
TFA (trifluoroacetate) salt
A peptide paired with trifluoroacetate counterions, a common salt form left by standard reverse-phase purification.
Trifluoroacetic acid (TFA) is widely used as an additive in reverse-phase HPLC purification, so many peptides are isolated as their TFA salt unless a salt-exchange step is performed. The trifluoroacetate counterion is heavier than acetate and adds proportionally more to the gross powder weight, so salt form affects how much of the vial's mass is peptide versus counterion. A certificate should state the salt form, and residual TFA is sometimes reported as a residual-solvent figure.
Covered in depth in Purity versus net peptide content.
Related terms
- Acetate salt
- A peptide paired with acetate counterions, the most common and lower-toxicity salt form produced during purification.
- Residual solvent
- Traces of the organic solvents used during synthesis and purification that remain in the finished powder.
- Gross peptide weight
- The total mass of powder in a vial, including salt, residual water and any excipient — not the mass of peptide alone.
- Net peptide content
- The actual mass of peptide in a sample, excluding salt, residual water and excipients — measured by amino acid analysis, not HPLC.