Ammonium Carbonate
(a moe' nee um kar' bo nate).

Carbonic acid, monoammonium salt mixture with ammonium carbamate;    
Monoammonium carbonate mixture with ammonium carbamate     [8000-73-5].
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).
•  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.
•  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 
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 flask, 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%
•  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%).
•  Heavy Metals, Method I 231
Test preparation:  Reduce to a coarse powder, and volatilize 2 g on a steam bath. Add 1 mL of 3 N hydrochloric acid, and evaporate to dryness. Dissolve the residue in 2 mL of 1 N acetic acid, and add water to make 25 mL.
Acceptance criteria:  NMT 10 ppm
•  Packaging and Storage: Preserve in tight, light-resistant containers, and store at a temperature not above 30.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Robert H. Lafaver, M.S.
Scientific Liaison
(EXC2010) Monographs - Excipients
USP35–NF30 Page 1698