Why do we use Sodium Sodium thiosulfate (STS) for raw water analysis?

How chlorine affected the analysis:

The residual chlorine can interface with the microbial analysis of water. These ions are highly active, penetrate the cell wall via lipids, and destroy the enzymes in the cell.

Reason for using sodium thiosulfate:

• Sodium thiosulfate is used to dechlorinate water samples before microbiological testing to ensure the results accurately reflect the water quality at the time of collection.
• It neutralizes any residual chlorine in the sample and prevents the chlorine from killing bacteria while the sample is being transported to the lab.
• Sodium Thiosulphate is added to the bottle before it is sterilized. These ions may be change (inhibit ) the actual results. Sodium Thiosulfate (STS) or Sodium meta bi sulfate (SMBS) can be used to neutralize or remove residual chlorine ions.

Limits of using thiosulfate:

Sodium thiosulfate is usually added to the sample bottle as a white crystal, a drop of liquid, or a powder spot. 2–5% sodium thiosulfate solution can neutralize the chlorine in roughly 170 ml of water; the suggested dosage varies. The thiosulfate should not be taken out or rinsed off once it has been introduced.

Reaction:

It simply reacts and forms sodium hydrogen sulfate or sodium bisulfate, which is an inactive salt.

This neutralization of residual chlorine will help to determine the actual microbial load in the water sample and will not affect the microbial recovery.