0.05 M Sodium Arsenite 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)
Dissolve 6.496 g of sodium arsenite in water to make 1000 mL.
1 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.]
1.1 Standardization with visual endpoint
Transfer 20.0 mL of the sodium arsenite solution to a 250-mL flask, add 5 mL of water and about 5 g of sodium bicarbonate, shake well until the sodium bicarbonate is completely dissolved. Stir, preferably with a magnetic stirrer, and titrate with the 0.1 N iodine VS adding 3 mL of the starch TS as the endpoint is approached.
M = (N/2 iodine x mL iodine)/20.0 mL
1.2 Standardization with potentiometric endpoint
Transfer 10.0 mL of the sodium arsenite solution to a 250-mL flask, add 60 mL of water and about 5 g of sodium bicarbonate, shake well until the sodium bicarbonate is completely dissolved. The amount of water can be adjusted to immerse an electrode properly. Stir, preferably with a magnetic stirrer, and titrate with the 0.1 N iodine VS using a combined platinum electrode.
M = (N/2 iodine x mL iodine)/10.0 mL
[NOTE-If this volumetric solution is used in a qualitative application suc Mas pH adjustment, dissolution medium, or diluent, its standardization is not required.) (USP 1-AUG-2023)
