The working principle of the Ammonia nitrogen water quality online analyzer is mainly based on the chemical reaction between ammonia nitrogen and specific reagents, indirectly calculating the concentration of ammonia nitrogen by measuring the color change or potential value change of the reaction product. Here are several common working principles:
1、 Colorimetric method
Colorimetric method is the most common detection principle, and its specific steps are as follows:
Chemical reaction: In alkaline medium, ammonia nitrogen (in the form of free ammonia or ammonium ions) in water samples reacts with salicylates and hypochlorite ions to form blue compounds (salicylic acid spectrophotometric method), or reacts with Nessler's reagent to form yellow brown complexes (Nessler's reagent spectrophotometric method).
Absorbance measurement: By measuring the absorbance at a specific wavelength (such as 697nm or 420nm), the concentration of ammonia nitrogen in water can be indirectly calculated. The absorbance is directly proportional to the ammonia nitrogen content, and the concentration of ammonia nitrogen can be calculated through a pre established calibration curve.
2、 Electrode method
The electrode method uses a specific composite electrode to directly measure the ammonia nitrogen content in water samples, and its working principle is as follows:
Potential measurement: Electrode methods include ammonia gas sensing electrode method and ammonium ion selective electrode method. The ammonia sensitive electrode method calculates the concentration of ammonia nitrogen by measuring the potential change generated by ammonia on the electrode surface; The ammonium ion selective electrode method is based on the principle of selective adsorption of ammonia nitrogen ions on the electrode. When ammonia nitrogen ions interact with the electrode surface, the potential of the electrode surface will change, resulting in a signal related to the concentration of ammonia nitrogen.
Signal conversion: By measuring the changes in electrode potential values, the concentration of ammonia nitrogen can be calculated. The electrode method has the advantages of fast response speed and wide measurement range, but it requires regular calibration and maintenance of the electrodes to ensure accuracy.
3、 Other methods
In addition to colorimetric and electrode methods, there are also other methods used in ammonia nitrogen water quality online analyzers, such as:
Distillation neutralization titration method: The water sample is heated and distilled in a slightly alkaline eluent, and the released ammonia gas is absorbed by the absorption solution. Then, the ammonium in the absorption solution is titrated with hydrochloric acid standard solution, and the amount of ammonia nitrogen in the water sample is calculated by formula.
Conductivity method: Indirectly calculate the concentration of ammonia nitrogen by using the change in conductivity of the solution after the reaction between ammonia nitrogen and reagents.