0.5 N Hydrochloric Acid 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)
(USP 1-May-2021)
To a 1000-mL volumetric flask containing 40 mL of water slowly add 43 mL of hydrochloric acid. Cool, and add water to volume.
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. Preparations and Standardization, 2.3 Standardization.]
Standardization with visual endpoint: (USP 1-May-2021) Accurately weigh about 2.5 g of tromethamine, dried according to the label instructions or, if this information is not available, dried at 105° for 3 h. Dissolve in 50 mL of water, and add 2 drops of bromocresol green TS. Titrate with the hydrochloric acid solution to a pale yellow endpoint. Each 60.57 mg of tromethamine is equivalent to 1 mL of 0.5 N hydrochloric acid.
N = [mg tromethamine x (Assay/100)] / (121.14 x mL HCI)
Standardization with potentiometric endpoint: Accurately weigh about 0.5 g of tromethamine, dried according to the label instructions or, if this information is not available, dried at 105° for 3 h. Dissolve in 50 mL of water. Titrate potentiometrically with the hydrochloric acid solution using a combined pH electrode. Each 60.57 mg of tromethamine is equivalent to 1 mL of 0.5 N hydrochloric acid.
N= [mg tromethamine x (Assay/100)] / (121.14 x mL HCI) (USP 1-May-2021)
[NOTE-If this volumetric solution is used in a qualitative application such as pH adjustment, dissolution medium, or diluent, its standardization is not required.]
