Colorimetric analysis by the salicylate/nitroprusside method. The ammonium reacts with salicylate in the presence of hypochlorite (oxidant) and nitroprusside (catalyst) to form an emerald green color measured colorimetrically on an Lachat 8500 FIA at 660 nm. The reaction takes place in a buffered alkaline medium at a pH of 12.8 – 13.0, thus acidified samples must be neutralized to a pH between 5 and 9.
(See Method Reference No. 39)