Why is sodium thiosulfate added to microbiological sample bottles?

Sodium thiosulfate is specifically used in microbiological sample bottles primarily to remove any chlorine residual present in water samples. Chlorine is often used in water treatment processes to disinfect and kill harmful microorganisms. However, if chlorine is still present in the sample when it is analyzed for microbiological content, it could inhibit the growth of bacteria or other microorganisms that need to be cultured for testing. This interference could lead to inaccurate results, as it may appear that fewer microorganisms are present than actually are.

By adding sodium thiosulfate to the sample bottles, the chlorine is effectively neutralized. This ensures that the microorganisms present in the sample can be accurately detected and quantified, thereby preserving the integrity of the microbiological analysis.