Sodium Thio Sulfate (STS)

Dechlorinating Agent:

·  Water containing residual chlorine disinfectant should be sampled in a bottle containing dechlorinating agent (sodium thiosulphate). Sodium thiosulphate neutralizes the chlorine, thus preventing further bactericidal effects on organisms in the water during transit. (ie. results of analysis will be representative of sample at time of sampling.)

·     Add validated (2mL of a 3%) solution of sodium thiosulphate, Na2S2O3, per 250mL sample.

·    Sodium thiosulphate ‘pills’ are available commercially and can be used in place of the solution.

·    Raw water chlorinated by add the Sodium Hypochlorite        (NaClO) Concentration 2-4 PPM

·         Chlorite water done to remove of microbial load.

·      It is an inorganic compound  that is typically available as the pentahydrate. Na2S2O3.5H₂0

·       Dissolves well in water.

·       It is also called Sodium hyposulfate.

Mechanism Action:

·        When Sodium hypochlorite dissolve in the water it produces hypochlorous acid and Hypochlorite ions.

·         Hypochlorite ions are known as “free chlorine”.

·         All the free chlorine is not consumed is the chlorination.

·      This means chlorite is known as “ residual Chlorine” which can interfere with the microbial analysis of water.

·      Sodium thio Sulfate (Na2 S2O3) can be used to the neutralization this residual Chlorine.

·       It simply reacts and forms Sodium Hydrogen Sulfate or Sodium bi sulfate whis is an inactive salt.

             Na2S2O3 + 4HoCl + H2O -------------------------  2 NaHSo4 + 4Hcl

Add validated  (2 ml of 3 % ) Na2S2O3 is added to the water sample bottle before sterilization.

3 % Na2S2O3   Preparation:

		30 g of Na2S2O3 Crystals in 1000 ml of water make up .
	·         This solution can be stored under (2 to 80C) refrigeration.
	·         This neutralization of residual chlorine will help to determine the actual

  microbial load. water sample and will not affect the microbial recovery.

10 % Na2S2O3   Preparation:

·         add 0.1 ml of 10% Sodium thiosulphate is added to the water sampling bottle before sterilization.

·         100 gms N₂S₂O₃ dissolved -1000 ml of water.

·         This solution can be stored under refrigerated (2 to 8⁰C) for 3 months.