0.05 N 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 500 mL of 0.1 N sodium thiosulfate VS to a 1000-mL volumetric flask. Dilute with carbon dioxide-free water to volume.
Standardization
See Volumetric Solutions, 1. Introduction.
See Titrimetry (541).
Standardize by one of the following procedures.
[NOTE-Other standardization procedures may be used. See Volumetric Solutions, 2. Preparation and Standardization, 2.3 Standardization.]
Standardization with visual endpoint: Accurately weigh about 25 mg of primary standard potassium iodate, previously dried according to the label instructions or, if this information is not available, dried at 180° for 1 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 500 mg of potassium iodide and 5 mL of hydrochloric acid. Titrate the liberated iodine with the 0.05 N sodium thiosulfate solution until the solution is pale yellow. Add 3 mL of starch TS, and continue the titration until the blue color disappears. Perform a blank determination.
N = [mgKIO3 x (Assay/100)]/{35.67 x [mL(sample) - mL(blank)] Na2S2O3}
where Assay is the content/potency of potassium iodate.
Standardization with potentiometric endpoint: Accurately weigh about 25 mg of primary standard potassium iodate, previously dried according to the label instructions or, if this information is not available, dried at 180° for 1 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 500 mg of potassium iodide and 5 mL of hydrochloric acid. Titrate the liberated iodine with the 0.05 N sodium thiosulfate solution using a combined platinum electrode. Perform a blank determination.
N = [mgKIO3 x (Assay/100)]/{35.67 x [mL(sample) - mL(blank)] Na2S2O3}
where Assay is the content/potency of potassium iodate.
Restandardize the solution as frequently as supported by laboratory stability data. In the absence of such data, restandardize the solution weekly.
[NOTE-If this volumetric solution is used in a qualitative application such as pH adjustment, dissolution medium, or diluent, its standardization is not required.) (USP 1-DEC-2020)
