Ammonium Carbonate - Definition, Identification, Impurities - USP 2025
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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
Ammonium Carbonate consists of ammonium bicarbonate (NH4HCO3) and ammonium carbamate (NH2COONH4) in varying proportions. It
yields NLT 30.0% and NMT 34.0% of ammonia (NH3).
2 IDENTIFICATION
A. When heated, it is volatilized without charring, and the vapor is alkaline to moistened litmus paper. A solution (1 in 20) effervesces with acids.
3 ASSAY
Procedure
Sample solution: Place 10 mL of water in a weighing bottle, tare the bottle and its contents, add 2 g of Ammonium Carbonate, and weigh. Titrimetric system
(See Titrimetry 〈541〉.)
Mode: Residual titration
Titrant: 1 N sulfuric acid VS
Back-titrant: 1 N sodium hydroxide VS
Blank: 50.0 mL of 1 N sulfuric acid VS, accurately measured
Endpoint detection: Colorimetric
Analysis: Transfer the Sample solution to a 250-mL ask, add 50.0 mL of 1 N sulfuric acid VS, and when the solution has been effected, add methyl orange TS. Titrate the excess acid with 1 N sodium hydroxide VS. Perform a blank determination. Calculate the percentage of ammonia (NH3) in the sample taken.
Result = [(B − V) × N × F × 100]/W
B = 1 N sodium hydroxide VS consumed by the Blank (mL)
V = 1 N sodium hydroxide VS consumed by the sample (mL)
N = actual normality of the Back-tritrant (mEq/mL)
F = equivalency factor, 17.03 mg/mEq
W = weight of the sample (mg)
Acceptance criteria: 30.0%–34.0%
4 IMPURITIES
Residue on Ignition 〈281〉: NMT 0.1%
Chloride and Sulfate, Chloride 〈221〉: A 2.0-g portion shows no more chloride than corresponds to 0.10 mL of 0.020 N hydrochloric acid (0.0035%).
Chloride and Sulfate, Sulfate 〈221〉: A 2.0-g portion shows no more sulfate than corresponds to 0.10 mL of 0.020 N sulfuric acid (0.005%).
ADDITIONAL REQUIREMENTS
Packaging and Storage: Preserve in tight, light-resistant containers, and store at a temperature not above 30°.
