Coupling of the phenylisothiocyanate (PITC, Edman reagent) to the alpha-amine of the polypeptide chain under basic conditions to form a phenylthiocarbamyl (PTC) moiety.
Cleavage under mild acidic conditions generate a free amino terminus on the polypeptide and an anilinothiazolinone (ATZ) adducted amino acid.
The latter is extracted and further converted to a more stable phenylthiohydantoin (PTH) derivative.
The resulting PTH residue is analyzed by HPLC and retention times compared to that of standards PTH amino acids.