Interference with ammonium determination by the indophenol-type reaction of salicylate and dichloroisocyanurate

Two widely accepted indophenol-type reactions with ammonium, which use phenol/hypochlorite and salicylate/dichloroisocyanurate as reagents, were compared for possible interferences with other naturally occurring nitrogen-containing compounds. Unlike the first method, the second showed strong interference from all amino acids and peptides tested. As much as 57 mole % of threonine and 49 mole % of serine were degraded to ammonium. Pyrimidines, purines, nucleosides and urea were negative in both reactions. The wide distribution and importance of free and combined amino acids in naturally occurring waters favours the application of the classical phenol/ hypochlorite reaction with ammonium rather than the modified salicylate/dichloroisocyanurate reaction.