EPA-NERL: 350.1:  Ammonia by Automated Colorimetry

  • Summary
  • Analytes
  • Revisions
  • Data and Sites
Official Method Name
Nitrogen, Ammonia (Colorimetric, Automated Phenate)
Current Revision
Revision 2.0. August 1993
Automated Spectrophotometer
Method Subcategory
Method Source
  Methods for the Determination of Inorganic Substances in Environmental Samples (EPA/600/R-93/100)
Brief Method Summary
Alkaline phenol and hypochlorite react with ammonia to form indophenol blue that is proportional to the ammonia concentration. The blue color is intensified with sodium nitroprusside.
Scope and Application
This method determines ammonia in drinking, surface, and saline waters; domestic and industrial wastes.
Applicable Concentration Range
0.01 - 2.0 mg/L (ammonia as N)
(A) Calcium and Magnesium: Ions of these metals can cause errors by precipitating during analyses. Use EDTA solution (for river and industrial waters) or potassium tartrate solution (for sea water) to reduce this interference.
(B) Turbidity: Sample turbidity should be removed by filtration.
(C) Color: Color absorbing in the range of the indophenol blue complex can interfere.
Quality Control Requirements
Sample Handling
Cool to 4oC, add H2SO4 until sample pH < 2.
Maximum Holding Time
28 days (MCAWW, Table 1).
Relative Cost
Less than $50
Sample Preparation Methods