Paraformaldehyde
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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)
(CH2O)n CAS RN: 30525-89-4.-Fine, white powder.
1 Assay
Transfer about 1 g, accurately weighed, to a 250-mL conical flask containing 50.0 mL of 1 N sodium hydroxide VS, and mix by swirling. Immediately, and slowly, add 50 mL of Hydrogen peroxide TS, previously neutralized to bromothymol blue, through a small funnel placed in the neck of the flask. After the reaction moderates, rinse the funnel and inner wall of the flask with water, allow the solution to stand for 30 minutes, add bromothymol blue TS, and titrate the excess alkali with 1 N sulfuric acid VS. Each mL of 1 N sodium hydroxide is equivalent to 30.03 mg of
HCHO: not less than 95% is found.
2 Residue on Ignition
not more than 0.1%.
3 Solubility in Ammonia
Dissolve 5 g in 50 mL of ammonia TS: a practically clear, colorless solution results.
4 Reaction
Shake 1 g with 20 mL of water for about 1 minute, and filter: the filtrate is neutral to litmus.
