Most peptides contain the basic functionalities: the guanidino group of Arg, the ε-amino group of Lys, the free N-terminus, and the imidazole moiety of His. These basic functionalities can form salts with acids. All our peptides are provided as trifluoroacetate salts unless specified otherwise. During cleavage from the carrier resin and purification, the peptide will react to the trifluoroacetic acid (a strong acid). Additional ion-exchange steps are needed to make the acetate salt or HCL salt form peptides. Some acidic peptides, containing Asp, Glu, phosphor group, or sulfotyrosine, can form salts with bases and may be provided as ammonium salts.