During the detn. of minute amts. of amino acids by the method of Sanger (C.A. 40, 5399.4), polymers (usually up to the tetramer) were identified by their Rf values. Fluorodinitrobenzene, amino acids, and dinitrophenol amino acids must be present to produce polymerization. The proportion of dinitrophenyl amino acid dimer under equal reaction conditions is in the order glycine .mchlt. b-alanine <e-aminocaproic acid .apprx. w-aminoheptanoic acid .apprx. w-aminoundecanoic acid. Certain losses in quant. dinitrophenylation may be due to polymerization.