This method involves the quantitative analysis of ammonium (NH4-N) and nitrate (NO3-N) in water. Ammonium and nitrate are measured by the diffusion-conductivity method based on the gaseous diffusing of ammonia (NH3) across a gas permeable membrane in the presence of excess base (KOH) and subsequent conductivity detection. Samples can be stored for up to three weeks at low temperature (<4°C). For longer term storage, toluene or thymol should be added to the sample to prevent microbial growth. The method has detection limit of approximately 0.05 mg L-1 and is generally reproducible within 7%.
NOTE: In general, SOP 847 is followed for nitrate and ammonium testing. (SOP 845 may be used for difficult matrices.)
Carlson, R. M. 1978. Automated separation and conductimetric determination of ammonia and dissolved carbon dioxide. Anal. Chem. 50:1528-1531.