Hydrochloric Acid
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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)
1 DEFINITION
Hydrochloric Acid contains NLT 36.5% and NMT 38.0%, by weight, of HCl.
2 IDENTIFICATION
A. Identification Tests—General, Chloride 〈191〉
3 ASSAY
Procedure
Sample: 3 mL
Titrimetric system
(See Titrimetry 〈541〉.)
Mode: Direct titration
Titrant: 1 N sodium hydroxide VS
Blank: 45 mL of water
Endpoint detection: Visual
Analysis:
Place the Sample in a glass-stoppered flask, previously tared while containing about 20 mL of water, and weigh again to obtain the weight of the substance under assay. Dilute with 25 mL of water, and add methyl red TS. Titrate with 1 N sodium hydroxide VS.
Calculate the percentage of hydrochloric acid (HCl) in the Sample taken:
Result = [(Vs − Vb) × N × F] ⁄ W × 100
Vs = volume of Titrant consumed by the Sample (mL)
Vb = volume of Titrant consumed by the Blank (mL)
N = actual normality of the Titrant (mEq/mL)
F = equivalency factor, 36.46 mg/mEq
W = weight of the Sample (mg)
Acceptance criteria: 36.5%–38.0%
4 IMPURITIES
Residue on Ignition 〈281〉
Sample: 20 mL
Analysis:
To the Sample, add 2 drops of sulfuric acid, evaporate to dryness, and ignite.
Acceptance criteria: NMT 2 mg of residue remains (about 0.008%).
5 SPECIFIC TESTS
Bromide or Iodide
Sample solution: 1 part Hydrochloric Acid to 2 parts water
Analysis: Add 1 mL of chloroform to 10 mL of the Sample solution. Cautiously add, dropwise, with constant agitation, chlorine TS that has been diluted with an equal volume of water.
Acceptance criteria: The chloroform remains free from even a transient yellow, orange, or violet color.
Free Bromine or Chlorine
Sample solution: 1 part Hydrochloric Acid to 2 parts water
Analysis: Add 1 mL of potassium iodide TS and 1 mL of chloroform to 10 mL of the Sample solution, and agitate the mixture.
Acceptance criteria: The chloroform remains free from any violet color for at least 1 min.
Sulfate
Sample solution: 1 part Hydrochloric Acid to 2 parts water
Analysis: To a mixture of 3 mL of the Sample solution and 5 mL of water, add 5 drops of barium chloride TS.
Acceptance criteria: Neither turbidity nor precipitate appears within 1 h.
Sulfite
Sample solution: 1 part Hydrochloric Acid to 2 parts water
Analysis: Complete the test for Sulfate, then add to the liquid 2 drops of 0.1 N iodine.
Acceptance criteria: Neither turbidity nor decolorization of the iodine occurs.
6 ADDITIONAL REQUIREMENTS
Packaging and Storage: Preserve in tight containers.
