When should sodium thiosulfate be added to the coliform sample container?

Sodium thiosulfate should be added to the coliform sample container before sterilization because its primary function is to neutralize any residual chlorine in the sample. Chlorine can be used as a disinfectant in water treatment processes, and its presence can inhibit the growth of fecal coliform bacteria, which are key indicators of water quality. By adding sodium thiosulfate prior to sterilization, it ensures that the sample is free from chlorine interference, allowing for accurate detection of bacteria during subsequent testing.

Adding sodium thiosulfate before sterilization helps preserve the true bacterial content of the sample. If added after sterilization, there is a risk that any living organisms may have been affected by residual disinfectants, leading to inaccurate results. Similarly, adding it during collection does not fully protect the integrity of the sample throughout the testing process. Therefore, proper timing of sodium thiosulfate addition is critical for achieving reliable laboratory results in coliform analysis.