High-speed liquid chromatographic determination of phenylpyruvic acid

A high-speed liquid chromatographic method has been developed for the determination of urinary phenylpyruvic acid. This acid is converted by treatment with naphthalene-2,3-diamine into 3-benzyl-2-hydroxybenzoquinoxaline, which is extracted into carbon tetrachloride for separation. 2-Mercaptoethanol is a useful stabilizer, and 2-chlorothioxanthone is a suitable internal standard. The method is specific, and the results are not affected by the presence of such 2-oxo-acids as pyruvic acid, 2-oxobutyric acid, 2-oxoglutaric acid, and 4-hydroxphenylpyruvic acid.