Unless requested, our peptides are generally provided as TFA salts. This is because we use trifluoroacetic acid (TFA) to cleave the peptide from the resin. We also add small amounts of TFA during the reversed-phase HPLC purification of peptides to help improve their solubility and HPLC separation. Although lyophilisation can remove most free TFA, it also binds to basic amino acids and to the N-termini of peptides, resulting in peptides typically being isolated as TFA salts. TFA counterions can be toxic and adversely affect biological assays. To mitigate this, we offer the option to substitute TFA counterions with other alternatives such as acetate or hydrochloride (HCl) when you opt for our TFA salt exchange service.