Determination of Free and Total Indole-3-acetic Acid and of the Indole Index.

A new method is described for measurement of the urinary excretion of free and total indole-3-acetic acid and for obtaining the chromogenic value of the total indoles. The color reaction employed is Fischl’s (1) tryptophan reaction. Hydrolysis and extractions were done by Weissbach’s (2) procedure. The ratio of the various fractions is expressed by a new term: “indole index” (1.1.). By the evaluation of the data obtained under various conditions, many abnormalities of tryptophan metabolism may be detected.