HPLC Analyses of Amino Acids in Plant Materials as DNP‐Derivatives by Use of Methyl Benzoate as the Internal Standard

A liquid chromatographic procedure has been developed for the separation and quantification of amino acids in some vegetables by using methyl benzoate as the internal standard. The DNP‐amino acid derivatives are separated on a reverse phase column (LiChrosorb RP‐18, 5 μm), eluted with a linear gradient of 20–75% v/v acetonitrile in 1% v/v glacial acetic acid in water. The column effluent is monitored at 254 run. A total analysis of DNP‐amino acids was completed in less than 55 min. For 14 amino acids and asparagine plus glutamine, separation and quantification were satisfactory. This technique has been used effectively to analyze amino acids in biological samples by the internal standard method.