During the past few years the normal pattern of urinary amino acid excretion, as determined by paper and column chromatography, has been established, and much information has been collected concerning deviations from the normal in an assortment of pathological conditions. Comparable information with respect to keto acid excretion is only now becoming available.
The α-keto-acids are fairly unstable compounds, and, although a few methods have been described for their direct paper chromatography, all these suffer from inaccuracies induced by the decomposition of the acids in the process of extraction or development of the chromatogram. Therefore it has become general usage to convert these compounds to the stabler 2,4-dinitrophenylhydrazone derivatives. These products are then subjected to chromatography.
The 2,4-dinitrophenylhydrazones (DNPH) are intensely yellow-to-orange compounds and can be localized on the filter paper in quantities as low as 2μg.-5μg., by either their intrinsic color or their ultraviolet light absorption. They may be