A New Method for Measuring Ammonia and TKN in Wastewater

Changing the Paradigm for Water Pollution Monitoring
Oral Presentation

Prepared by I. Lahdesmaki
FIAlab Instruments, Inc., 2151 N. Northlake Way, Suite 100, Seattle, WA, 98103, United States

Contact Information: ilkka@flowinjection.com; 206-258-2290


Ammonia and organic nitrogen are critical pollution parameters monitored in wastewater. As organic nitrogen is evaluated by rendering it to ammonia by the TKN digestion process, the analytical measurement in both cases is centered on ammonia determination. The current Clean Water Act methods for ammonia and TKN are based on the Berthelot chemistry, employing hypochlorite and either alkaline phenol or salicylate for color generation. While functional, the Berthelot reaction is well-known for its lack of specificity, as well as limited reagent stability.

A new method for ammonia determination is presented, based on reacting ammonia with o-phthalaldehyde (OPA) and detecting the product by means of fluorescence. The presentation shows examples demonstrating the enhanced specificity and sensitivity – the former resulting from the use of a different chemical reaction, the latter resulting from the use of fluorescence detection. A discussion of reagent stability is included, comparing the Berthelot and OPA reagents. The new method has undergone an ATP validation process and will be included in the Methods Update Rule currently being processed.