A photochemical side reaction that interferes with the phenolhypochlorite assay for ammonia1,2

Abstract

Exposure to sunlight of the reaction mixture for the phenolhypochlorite assay for ammonia results in the formation of a compound that absorbs at 640 nm. This compound has been tentatively identified as indophenol, the same compound that is formed in the presence of ammonia. Protection of the reaction mixture from strong light results in low reagent blanks and ammonia standards that display a Beer’s law dependence on concentration.