Packaging and storage—
Preserve in well-closed containers.
Labeling—
Label it to indicate whether it is anhydrous or the dihydrate.
Identification—
Dissolve about 200 mg by warming in a mixture of 4 mL of 3 N hydrochloric acid and 16 mL of water. This solution responds to the tests for
Calcium 
191
and for
Sulfate 191.
Loss on drying 731—
Dry it at a temperature not lower than 250
to constant weight: the anhydrous form loses not more than 1.5% of its weight, and the dihydrate loses between 19.0% and 23.0% of its weight.
Iron 241—
Dissolve 100 mg in 8 mL of 3 N hydrochloric acid, and dilute with water to 47 mL: the limit is 0.01%.
Heavy metals, Method I 231—
Mix 2.0 g with 20 mL of water, add 25 mL of 3 N hydrochloric acid, and heat to boiling to dissolve the test specimen. Cool, and add ammonium hydroxide to a pH of 7. Filter, evaporate to a volume of about 25 mL, and refilter, if necessary, to obtain a clear solution: the limit is 0.001%.
Assay—
Dissolve about 300 mg of Calcium Sulfate, accurately weighed, in 100 mL of water and 4 mL of 3 N hydrochloric acid. Boil, if necessary, to dissolve, and cool before titrating. While stirring, preferably with a magnetic stirrer, add, in the order named, 0.5 mL of triethanolamine, 300 mg of hydroxy naphthol blue, and, from a 50-mL buret, about 30 mL of 0.05 M edetate disodium VS. Add sodium hydroxide solution (45 in 100) until the initial red color changes to clear blue. Continue to add it dropwise until the color changes to violet, and add an additional 0.5 mL. The pH is between 12.3 and 12.5. Continue the titration dropwise with 0.05 M edetate disodium VS to the appearance of a clear-blue endpoint that persists for not less than 60 seconds. Each mL of 0.05 M edetate disodium is equivalent to 6.807 mg of CaSO4.
Auxiliary Information—
Staff Liaison :
Catherine Sheehan, B.Sc., Scientist
Expert Committee : (EM105) Excipient Monographs 1
USP29–NF24 Page 3290
Pharmacopeial Forum : Volume No. 27(6) Page 3337
Phone Number : 1-301-816-8262
