Ichthammol
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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
Ichthammol is obtained by the destructive distillation of certain bituminous schists, sulfonation of the distillate, and neutralization of the product with ammonia. Ichthammol yields NLT 2.5% of ammonia (NH₃) and NLT 10.0% of total sulfur (S).
2 IDENTIFICATION
A.
Sample solution: Ichthammol and water (10:90). Stir for 5 min with a magnetic stirrer.
Analysis: To the Sample solution add hydrochloric acid by 25% of the total volume. A heavy, resinous precipitate is formed. Remove the liquid by decantation, and wash the precipitate with 2 N hydrochloric acid until the last washing is nearly colorless. Transfer the precipitate to absorbent paper, allow it to stand for 10 min, and then transfer 10 mg of the precipitate to a 250-mL conical ask. To the ask add 100 mL of ether, attach an air condenser to the ask, and stir for 30 min with a magnetic stirrer.
Acceptance criteria: The precipitate does not dissolve completely.
B.
Sample solution: 1 in 10
Analysis: To the Sample solution add 1 N sodium hydroxide, and heat to the boiling point.
Acceptance criteria: Ammonia is evolved.
3 ASSAY
Ammonia
Sample solution: 50 mg/mL of Ichthammol in water
Titrimetric system
Mode: Residual titration
Titrant: 0.5 N sulfuric acid VS
Back-titrant: 0.5 N sodium hydroxide VS
Endpoint detection: Visual
Analysis: Transfer 100 mL of the Sample solution to a distillation ask, add 3 g of paran, and then add 20 mL of sodium hydroxide solution (4 in 10). Connect the ask to a condenser by means of a spray trap, and immerse the lower outlet tube of the condenser in 30.0 mL of Titrant. Distill slowly, collect 50 mL of distillate, and then titrate the excess acid with Back-titrant, using methyl red TS as the indicator. Perform a blank determination, and make any necessary correction. Each mL of 0.5 N sulfuric acid is equivalent to 8.515 mg of ammonia (NH₃).
Acceptance criteria: NLT 2.5% of ammonia (NH₃)
Total Sulfur
Sample: 500–800 mg of Ichthammol
Analysis: Transfer the Sample to a Kjeldahl ask with the aid of 20 mL of water. Add 3 g of potassium chlorate, then slowly add 30 mL of nitric acid, and evaporate the mixture on a hot plate to 5 mL. Cool, repeat the oxidation with 3 g of potassium chlorate and 30 mL of nitric acid, and evaporate to 5 mL. Add 25 mL of hydrochloric acid, and again evaporate to 5 mL. Add 100 mL of water, heat to boiling, lter, and wash well. To the hot ltrate add 25 mL of barium chloride TS, and heat on a steam bath for 1 h. Collect the barium sulfate on a previously ignited and tared ltering crucible. Wash, dry, and ignite. Then cool, and weigh. Each g of barium sulfate is equivalent to 137.4 mg of total sulfur (S).
Acceptance criteria: NLT 10.0% of total sulfur (S)
4 IMPURITIES
Residue on Ignition 〈281〉: NMT 0.5%
Limit of Ammonium Sulfate
Sample solution: 40 mg/mL of Ichthammol in alcohol
Analysis: To 25 mL of Sample solution stir, lter, and wash the lter with a mixture of equal volumes of ether and alcohol until the last washing is clear and colorless. Air-dry the lter and residue, and pass 200 mL of warm water, slightly acidied with hydrochloric acid, through the residue on the lter. Heat the ltrate to boiling, add barium chloride TS in excess, and heat for 1 h on a steam bath. Collect the precipitate of barium sulfate on a lter. Wash it well, dry, and ignite to constant weight. Each g of barium sulfate is equivalent to 566.1 mg of ammonium sulfate [(NH₄)₂SO₄].
Acceptance criteria: NMT 8.0% of ammonium sulfate [(NH₄)₂SO₄]
5 SPECIFIC TESTS
Loss on Drying 〈731〉
Analysis: Dry at 80° for 8 h, and continue the drying at 100° for constant weight.
Acceptance criteria: NMT 50.0%
6 ADDITIONAL REQUIREMENTS
Packaging and Storage: Preserve in well-closed containers.
