Na2SO4·10H2O 322.20

Sulfuric acid disodium salt, decahydrate.
Disodium sulfate decahydrate [7727-73-3].

Anhydrous 142.04 [7757-82-6].

Packaging and storage— Preserve in tight containers, preferably at a temperature not exceeding 30.

Labeling— Label it to indicate whether it is the decahydrate or is anhydrous.

Identification— A solution (1 in 20) responds to the tests for Sodium 191 and for Sulfate 191.

Acidity or alkalinity— To 10 mL of a solution, containing the equivalent of 1.0 g of Na2SO4·10H2O in 20 mL of water, add 1 drop of bromothymol blue TS: not more than 0.50 mL of either 0.010 N hydrochloric acid or 0.010 N sodium hydroxide is required to change the color of the solution.

Loss on drying 731— Dry at 105 for 4 hours: the decahydrate loses between 51.0% and 57.0% of its weight, and the anhydrous form loses not more than 0.5% of its weight.

Chloride 221— A portion equivalent to 1.0 g of Na2SO4·10H2O shows no more chloride than corresponds to 0.30 mL of 0.020 N hydrochloric acid (0.02%).

Heavy metals 231— Dissolve a portion containing the equivalent of 2.0 g of Na2SO4·10H2O in 10 mL of water, add 2 mL of 0.1 N hydrochloric acid, then add water to make 25 mL: the limit is 0.001%.

Assay— Weigh accurately a portion of Sodium Sulfate, equivalent to about 400 mg of anhydrous sodium sulfate, dissolve in 200 mL of water, and add 1 mL of hydrochloric acid. Heat to boiling, and gradually add, in small portions and while constantly stirring, an excess of hot barium chloride TS (about 8 mL). Heat the mixture on a steam bath for 1 hour, collect the precipitate of barium sulfate on a tared filtering crucible, wash until free from chloride, dry, ignite, and weigh. The weight of the barium sulfate so obtained, multiplied by 0.6086, represents its equivalent of Na2SO4.

Topic/Question	Contact	Expert Committee
Monograph	Elena Gonikberg, Ph.D. Senior Scientist 1-301-816-8251	(MDGRE05) Monograph Development-Gastrointestinal Renal and Endocrine

USP32–NF27 Page 3585