0.01 M Sodium Thiosulfate VS
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
Transfer 100 mL of 0.1 N sodium thiosulfate VS to a 1000-mL volumetric flask. Dilute with carbon dioxide-free water to volume.
Standardization: Accurately weigh about 21.0 mg of primary standard potassium dichromate, previously pulverized and dried according to the label instructions or, if this information is not available, dried at 120° for 4 h, and dissolve in 100 mL of water in a glass-stoppered, 500-mL flask. Swirl to dissolve the solid, remove the stopper, and quickly add 1 g of potassium iodide, 2 g of sodium bicarbonate, and 5 mL of hydrochloric acid. Insert the stopper gently in the flask, swirl to mix, and allow to stand in the dark for exactly 10 min. Rinse the stopper and the inner walls of the flask with water, and titrate the liberated iodine with 0.01 M sodium thiosulfate VS until the solution is yellowish green in color. Add 3 mL of starch TS, and continue the titration until the blue color is discharged. Perform a blank determination. Restandardize the solution as frequently as supported by laboratory stability data. In the absence of such data, restandardize the solution weekly.
M = (mg K2Cr2O7)/(49.04 x mL Na2S2O3) (ERR 1-May-2018)
[NOTE-If this volumetric solution is used in a qualitative application such as pH adjustment, dissolution medium, or diluent, its standardization is not required.]
