Assay for total NH3
Transfer 10.0 mL to a 250-mL conical flask containing about 50 mL of water. Add 30.0 mL of 0.5 N sulfuric acid VS, and boil until the solution becomes clear. Cool, add
methyl red TS, and titrate the excess acid with 0.5 N sodium hydroxide VS. Perform a blank determination (see
Residual Titrations under
Titrimetry 541). Each mL of 0.5 N sulfuric acid is equivalent to 8.515 mg of NH
3.
Assay for ammonium carbonate
Transfer 10.0 mL to a flask of about 300-mL capacity. Add 30 mL of 0.5 N sodium hydroxide, and boil the mixture, replacing the water lost by evaporation, until the vapors no longer turn moistened red litmus paper blue. Cool, dilute with 100 mL of cold, carbon dioxide-free water, add about 6 drops of
phenolphthalein TS, then add just enough 0.5 N sulfuric acid VS to discharge the color of the phenolphthalein. Add
methyl orange TS, and titrate with 0.5 N sulfuric acid VS. Perform a blank determination (see
Residual Titrations under
Titrimetry 541). Each mL of 0.5 N sulfuric acid consumed in the titration with
methyl orange TS is equivalent to 48.04 mg of (NH
4)
2CO
3.