Ammonia in water is commonly measured by the salicylate colorimetric assay. In this assay, the first reaction step involves the conversion of ammonia to monochloroamine by the addition of chlorine. The monochloroamine then reacts with salicylate to form 5-aminosalicylate. Finally, the 5-aminosalicylate is oxidized in the presence of sodium nitroferricyanide (a catalyst) to form a blue-green colored dye that absorbs light at 650nm.
We have so far tested two salicylate methods for measuring ammonia levels in water samples with the colorimeter:
- Salicylate test - make your own reagents
- API test kit - commercial kit, reagents supplied
Of these two methods tested so far, the API test kit is more convenient for at-home use although we do also like to use the salicylate test as well. Really depends on which is most convenient, and in most cases the API test kit works fine.