Simple determination of high urinary excretion of 5-hydroxyindole-3-acetic acid with ferric chloride.

Abstract

We describe a method for determination of urinary 5-hydroxyindole-3-acetic acid, a metabolite of serotonin and tryptophan and a useful indicator of metastasizing carcinoid tumor. The analysis is based on the color development with ferric chloride added to the residue obtained on evaporating a diethyl ether extract of the sample that has been acidified with sulfuric acid and saturated with sodium chloride. The color is measured by 510 nm. The reaction was made highly specific by the acidification so that nonspecific reactions with catecholamines and with other phenolic compounds such as salicylic acid could be eliminated.