A Salicylate–Hypochlorite Method for Determining Ammonia in Seawater

Total ammonia-nitrogen (NH 4 -N) in artificial seawater was determined spectrophotometrically by a method in which indophenol blue is produced by the reaction of ammonia with salicylate and hypochlorite, in the presence of sodium nitroprusside. Recoveries of 10 to 1000 μg NH 4 -N/L by the salicylate– and phenol–hypochlorite methods compared well (r = 0.99); the coefficient of variation for 25 μg NH 4 -N/L and above was less than 3% for the salicylate–hypochlorite method. The new method is safer than the phenol–hypochlorite method because phenol is not used, but it may not be suitable for field determinations because of photosensitivity. The characteristic colors produced by increasing concentrations of ammonia make the assay useful for the direct, visual estimation of ammonia in culture systems.Key words: ammonia, analytical methods, seawater analysis