0.1 N Ferric Ammonium Sulfate 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 50 g of ferric ammonium sulfate in a mixture of 300 mL of water and 6 mL of sulfuric acid, dilute with water to 1000 mL, and mix. Store in tight containers, protected from light.
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 measure about 40 mL of the solution into a glass-stoppered flask, add 5 mL of hydrochloric acid, mix, and add a solution of 3 g of potassium iodide in 10 mL of water. Insert the stopper, allow to stand for 10 min, and titrate the liberated iodine with the sodium thiosulfate solution until the solution is yellowish-green in color. Add 3 mL of starch TS, and continue the titration until the blue color disappears. Perform a blank determination. (USP 1-Dec-2022)
N = ((mL Na2S2O3sample − mL Na2S2O3 blank) × N Na2S2O3) / (mL FeNH4(SO4)2)
Standardization with potentiometric endpoint: Accurately measure about 10 mL of the solution into a glass-stoppered flask, add 1.25 mL of hydrochloric acid, mix, and add a solution of 0.75 g of potassium iodide in 50 mL of water. Insert the stopper, allow to stand for 10 min, and then titrate the liberated iodine with 0.1 N sodium thiosulfate VS potentiometrically using a combined platinum (Pt) electrode. Perform a blank determination.
N = ((mL Na2S2O3sample − mL Na2S2O3 blank) × N Na2S2O3) / (mL FeNH4(SO4)2)
[Note - If this volumetric solution is used in a qualitative application such as pH adjustment, dissolution medium, or diluent, its standardization is not required.]
