How should the retrieved water samples be stored?

Environmental protection companies and third-party testing companies must go to the customer's site to take water samples in the process of sewage and wastewater testing, and then take them back to the company's professional laboratory for testing and report. Since sewage and wastewater contain many microorganisms and bacteria, combined with factors such as temperature, time, and environment, the COD, ammonia, nitrogen, total phosphorus, and total nitrogen values in water samples will change to varying degrees. How can we avoid and reduce changes in water samples? Today we will talk about how to control the change of COD ammonia nitrogen and total phosphorus concentration in water samples.

There are several ways to store water samples:

1. The function of refrigeration or freezing is to inhibit microbial activity and slow down the rate of physical volatilization and chemical reaction, but this method is greatly affected by temperature, time, and water sample pollution concentration, and is not suitable for storage for more than 12 hours.

2. Adding chemical reagents for preservation

Adding biological inhibitors: For example, adding HgCI2 to the water samples for the determination of ammonia nitrogen, nitrate nitrogen and chemical oxygen demand (COD) can inhibit the biological redox; for the water samples for the determination of phenol, adjust the pH to 4 with H3PO4, adding an appropriate amount of CuSO4 can inhibit the decomposition activity of phenol bacteria.

Adjust pH: The water sample for measuring metal ions is usually acidified to pH 1-2 with an HN03 solution, which can not only prevent the hydrolysis and precipitation of heavy metal ions but also prevent the metal from being adsorbed by the wall; add NaOH solution to the water sample for measuring cyanide or volatile phenol Adjust the pH to 12 to generate stable phenates, etc.

Add oxidant or reducing agent: if the water sample for mercury determination needs to add HNO3 (to pH)