The instrument collects water samples through an automatic sampling device and adds specific reducing agents and indicators to the samples. Under alkaline conditions, nitrates in water samples are reduced to nitrites, which then react with indicators to form colored compounds. The color depth of this colored compound is proportional to the concentration of nitrate ions in the water sample. The instrument's built-in photoelectric sensor monitors the color changes of the reaction solution in real time and converts them into electrical signals. By measuring this electrical signal and comparing it with a preset standard curve, the instrument can accurately calculate the concentration of nitrate ions in the water sample. This method offers advantages such as easy operation, intuitive results, and high accuracy, and is widely used in water quality and environmental monitoring.