A sensitive and accurate method for amino acid analysis using isotopic double labeling with fluorodinitrobenzene

A double-labeling procedure for amino acid analysis using ³H-labeled 1-fluoro-2,4-dinitrobenzene and ¹⁴C-labeled amino acids as internal standards is described. The procedure was tested by analyzing lysozyme and insulin B chain, and the results obtained were in good agreement with their accepted amino acid compositions. Analysis of samples containing from 100 pmol of each amino acid can be achieved at an accuracy comparable to that obtained by conventional automated amino acid analysis methods, many of which require considerably more material. An important advantage is that amino acids present in low molar proportions can be separated and measured more readily than by column chromatography.