[EN] COMPOUND FOR DERIVATIZING POLYPEPTIDES AND METHOD FOR SEQUENCING AND QUANTIFIFYING AMINO ACIDS IN POLYPEPTIDES USING THE SAME [FR] COMPOSE PERMETTANT DE DERIVER DES POLYPEPTIDES, ET PROCEDE DE SEQUENÇAGE ET DE QUANTIFICATION D'ACIDES AMINES DANS DES POLYPEPTIDES FAISANT APPEL AUDIT COMPOSE