Standardization of the thiosulphate solution

The known amount of liberated iodine then is titrated with thiosulphate solution. The standardization of the thiosulphate solution is exactly the same as the last step in the determination of oxygen and thus any subjective error in recognizing the endpoint of the titration or any other bias affecting the indication of the endpoint is compensated for. 

Including the standardization of the thiosulphate solution the sample concentration of oxygen is calculated as ... 

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