The operation of a rapid COD analyzer typically follows a basic procedure of "sample preparation - digestion - measurement".
Turn the analyzer and its digester to power on, allowing the instrument to preheat to a stable state. Select a pre-prepared reagent tube with an appropriate range based on the estimated COD concentration of the water sample. Accurately transfer the specified volume (e.g., 2 mL) of distilled water (as a blank) and the water sample to be tested into their respective reagent tubes, tighten the caps, and shake well. Place the mixed reagent tubes into the preheated digester at the set temperature and start the digestion program. The digestion time depends on the method; for example, the standard method may require heating at 148°C for 2 hours, while the rapid method may require heating at 165°C for 15 minutes. After digestion, remove the reagent tubes and allow them to cool naturally or with water to room temperature. Wipe the outer wall of the cooled reagent tubes clean, ensuring the solution is clear and free of bubbles. Place the blank tube into the analyzer's measurement cell for blank calibration, then place the sample tube in the cell. Select the corresponding preset calibration curve on the instrument; the instrument will directly display or calculate the COD concentration value of the water sample.
The reagents used for digestion (such as potassium dichromate and concentrated sulfuric acid) are highly corrosive and toxic. Protective equipment should be worn during operation, and the process should be carried out in a well-ventilated area. During digestion, the tube cap must be tightly closed and the digester cover must be on to prevent liquid splashing. Digestion colorimetric tubes of specific instrument specifications (e.g., 16mm diameter) must be used. High chloride ion concentrations in the water sample can interfere with the determination; high-concentration samples must be pre-diluted. Do not shake the digestion colorimetric tube during colorimetric analysis to avoid precipitation and deviation. Regularly verify the instrument's accuracy using standard samples. Keep the light-transmitting surface of the colorimetric tube clean and avoid direct contact with your hands. The specific digestion temperature, time, water sample volume, and corresponding calibration curve number must be strictly followed according to the instruction manual and reagent requirements of the instrument model being used.
