Analysis principle:

When a strong alkaline solution is added to the water sample to make the pH ≥ 11, the ammonium salt is converted to ammonia. The generated ammonia diffuses through the semi permeable membrane of the ammonia sensitive electrode (water and other ions cannot pass through), causing a change in electrode potential. According to the Nernst equation, at a constant ionic strength, the measured electromotive force has a certain linear relationship with the logarithm of the concentration of ammonia nitrogen in the water sample. Therefore, the content of ammonia nitrogen in the sample can be determined from the measured potential value.