Colorimetric Methods for the Quantitative Estimation of Indole(3)Acetic Acid

1. Several colorimetric methods were studied to determine their applicability for the quantitative measurement of indoleacetic acid in water solution. These included the reaction between indoleacetic acid and (1) potassium nitrite and nitric acid; (2) ferric chloride and sulphuric acid; and (3) ferric chloride and hydrochloric acid. The nitrite and the ferric chloride-sulphuric acid tests were investigated in detail in order to determine the effect of the different factors involved upon the intensity and stability of the color produced. 2. The nitrite test proved to be applicable for the determination of indoleacetic acid in aqueous solutions having a range of concentrations from 0.01 to 0.15 mg. per cubic centimeter; the ferric chloride-sulphuric acid test was suitable for the estimation of total amounts of from 0.02 to 0.1 mg., under the conditions described. The ferric chloride-hydrochloric acid test was sensitive to essentially the same range of concentrations as that of the nitrite test, but was less suitable as the color produced was not stable.