Abstract. To solve the problems that the traditional ammonia detection methods were complex, not easy to maintenance and difficult to realize quick measurement in situ, an intelligent ammonia sensor has been designed in this paper. The intelligent ammonia sensor integrates ammonia electrode, pH electrode and Ammonium ion electrode together to realize the In situ detection of ammonia. Because the output signal of ammonia electrode is weak and easy to be disturbed by external interference, a low-pass filter circuit has been designed, this kind of circuit have a good effect. The test results have shown that the sensor is easy operation, low cost and no pollution.

1 Introduction

Our country is a big agricultural country. Aquatic production has been 15 consecutive years ranked first in the world. However, most farmers rely on their own experience, with color, smell, water taste or observed other aquatic animal‘s abnormal behavior to evaluation aquaculture water quality. For aquaculture, dissolved oxygen, ammonia nitrogen, PH is one of the important water quality parameters need to be monitoring.

Ammonia existing in water has certain toxicity for aquaculture products. It influents the quality of aquatic products, restrict the sustainable development of aquaculture, especially with the promotion of high density factory farming technology, ammonia pollution control demand is increasingly prominent. Ammonia harm the aquatic organisms mainly refers to the dangers of non-ionic ammonia, after non-ionic ammonia entering aquatic organisms. It has a significant impact on enzyme hydrolysis  reaction and membrane stability. Demonstrated difficulty in breathing, not feeding, decreased immunity, convulsions, coma and other phenomena, affect the growth and reproduction of aquatic organisms, even lead to aquatic organisms decimated, even causing loss to the economy.

There are different ways to determine the content of ammonia nitrogen in the water

. The existing method of ammonia nitrogen determination has some shortcomings

. Such as titration’s sensitivity is not high enough. Spectrophotometry needs a large amount of chemical reagent and complicated steps

. Ammonium ion

electrode method is easily affected by other monovalent cations. Optical fluorescence

technology is not mature. Spectrometry instruments are expensive. These methods are difficult to meet the needs of the scene in situ detection with high frequency. With ammonia sensitive probe we can realize quick measurement in situ. The sensor has some good features, such as simple operation, low cost, pollution-free, and don’t need to pretreatment the water. Based on the above analysis, an compound ammonia sensors which integrated ammonia sensitive probe and PH probe has been designed in this paper. A low cost ammonia nitrogen on-line monitoring method will be the main research content, and find a solution of electrochemical intelligent ammonia sensor. 

2 Measurement principle

Ammonia nitrogen content in the water is in the form of free ammonia NH3 and ammonium ion NH4+ chemical combination of the existence of the amount of nitrogen. It is an important index of water pollution. When free ammonia NH3 reaches a certain concentration is harmful to aquatic organisms. For example, it will be able to cause toxic effects on some kind of fish when free ammonia over 0.2mg/L .The solubility of ammonia in water at different temperatures and PH is different, when the PH content is high, it will have a higher proportion of free ammonia, on the contrary, a higher proportion of the ammonium ions. Under a certain condition, the ammonia and the ammonium ion has the following balance equation: NH3 + H2O↔NH4++ OHIn this study, Ammonia electrode  was elected to measure ammonia content in water. The ammonia electrode is a composite electrode, PH glass electrode as indicator electrode, silver - silver chloride electrode as the reference electrode. Put the electrodes inside a plastic sleeve which containing 0.1mol/L ammonium chloride liquid-filled, and equipped with gas-sensitive film. Add ionic strength to the aqueous sample solution, PH may be raised to 11 or more, and ammonium salts are converted to ammonia, because of diffusion, ammonia gas will pass through the membrane (water and other ions can pass the gas membrane). After ammonia gas into the inner filling, will present the following balance:

4 -3  H2O  NH  OH  NH

Ammonia leads the balance equation shift to the right, then the value of PH increased with the entry of ammonia. Finally PH glass electrode measured value changes. At constant ionic strength, temperature, nature and electrode parameters, the measured electromotive force and the ammonia concentration in water samples meet the Nernst equation. We can determine the nitrogen content of the sample from the measured potential value. Finally draw a standard curve by measured voltage signal to determine the concentrations of the unknown samples.