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Two methods for determining the forms of ammonia nitrogen in water are described. A univalent cation electrode can be used to detect ionized ammonium if potassium and sodium concentrations of the solution are constant. At pH values less than 7.5 this will correspond to the total ammonia concentration in a water sample. Another approach is to employ a membrane electrode, which is sensitive to unionized ammonia and subject to fewer interferences. It involves an alkalization of a sample to pH 12 and subsequent measurement of liberated unionized ammonia (total ammonia). A direct measurement of free ammonia can be made without alkalization. Suitability of both methods for determination of high ammonia concentrations (above 0.2 to 0.5 mg/liter N) in water samples, mainly fish tanks, is discussed. There is no upper limit of detection, and samples therefore do not require any dilution.
water quality, nitrogen inorganic compounds, ammonia, environmental tests
Research scientist, Freshwater Institute, Winnipeg,