Sodium Ammonium Phosphate Tetrahydrate
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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)
(Microcosmic Salt), NaNH4HPO4· 4H2O 209.07—Colorless crystals or white granules. Freely soluble in water; insoluble in alcohol.
Effloresces in air and loses ammonia.
Insoluble Matter and Ammonium Hydroxide Precipitate
Analysis: Dissolve 10 g in 100 mL of water, add 10 mL of ammonia TS, and heat on a steam bath for 1 hr. If any precipitate is formed, lter,
wash well with water, and ignite.
Acceptance criteria: NMT 1 mg (0.01%)
Chloride (Reagent test): One g shows NMT 0.02 mg of Cl (0.002%).
Heavy Metals
Analysis: Dissolve 3 g in 25 mL of water, add 15 mL of 1 N sulfuric acid, then add 10 mL of hydrogen sulde TS.
Acceptance criteria: Any brown color developed in 1 min is not darker than that of a control containing 3 mL of Standard lead solution TS and
0.5 mL of 1 N sulfuric acid (0.001%).
Nitrate
Analysis: Dissolve 1 g in 10 mL of water, add 0.1 mL of indigo carmine TS, then add, with stirring, 10 mL of sulfuric acid.
Acceptance criteria: Blue color persists for 10 min (about 0.005%).
Sulfate (Reagent test, Method II)
Analysis: Dissolve 10 g in 100 mL of water, add 5 mL of hydrochloric acid, and lter if necessary.
Acceptance criteria: NMT 5 mg (0.02%)
