Automatic analytical methods for environmental monitoring and control

III.4.1.2.Ammonia

Ammonia is a principal excretion product of fishes, resulting from the metabolism of nitrogenous (nitrogen containing) compounds in their food. Ammonia is also formed from the bacterial degradation of nitrogen containing organic materials.

1. 
   The first reaction is the addition of chlorine to convert ammonia to monochloroamine.
   
2. 
   The second step follows with the reaction of monochloroamine with salicylate to form 5-aminosalicylate.
   
3. 
   Finally the 5-aminosalicylate is oxidized by sodium nitroprussiate to form a blue-green colored compound that can be monitored over the wavelength range from 650 nm to 710 nm.
   

Several components interfere with the determination of ammonia. First is a usual interferent, the turbidity of the sample. Sulfide, hydrazine and glycine will intensify the final blue-green color; they should be previously eliminated. Other interfering are the metallic ions iron, calcium and magnesium; and the inorganic anions sulfate, phosphate, nitrate and nitrite. The usual method of preparing doped standard solutions for the calibration or using the standard addition procedure can minimize or eliminate the influence of the interferents.

Analytical figures of merit are: linear dynamic range 10 to 1000 mg NH₃ L^-1 [0.59 m mol L^-1 – 58.8 m mol L^-1 NH₃; deviation: 10 to 1000 mg range: 3%. Sample throughput: 112 samples per hour.

The following figures depicted the schematic flow assembly in which ammonia analysis is performed in the Z flow cell above using a stop flow procedure (Figure III.4.3); and, the visible spectrum of the resulting complex (Figure III.4.4.).