Spectrophotometric determination of micro amounts of nitrogen as indophenol

Abstract

A critical study has been made of the well known spectrophotometric determination of nitrogen as ammonia, originally based on the reaction of ammonia with hypochlorite and phenol producing a blue coloured indophenol.

This has resulted in a modified method with a gain in sensitivity and reproducibility.

The absorptivity of indophenol found with this method is 0·60 per p.p.m. of nitrogen per cm at a wavelength of 625 nm, which is an improvement on the methods previously reported.

The standard deviation is 0·0013 p.p.m. at the 0·2 p.p.m. level in 50 ml of colour developed solution. The solution obtained after colour development is also suitable for the solvent extraction with isobutyl alcohol. The method described in this paper can be applied to 0·05 to 20 µg of nitrogen.