A COLORIMETRIC METHOD FOR THE ESTIMATION OF CERTAIN INDOLES

Abstract

The Ehrich reaction can, under standardized conditions, form the basis of a sensitive method of estimating certain indoles down to 1–2 μg/5 ml. An appropriate concentration of HCl in the Ehrich's reagent is essential. The concentration of trichloroacetic acid to give maximum sensitivity compatible with linearity between concentration of indole and absorbance must be experimentally determined. Absorbance should be measured between 530 and 580 mμ after a precisely measured time for colour development. Specificity can be increased by extraction of the colour complex into chloroform. The method has proved satisfactory for estimating the recovery of indoles from paper and thin‐layer chromatograms and from silica gel columns. Copyright © 1970, Wiley Blackwell. All rights reserved