Calcium Sulfate
CaSO4 136.14

Sulfuric acid, calcium salt (1:1).
Calcium sulfate (1:1) 136.14 [7778-18-9].

Dihydrate 172.17 [10101-41-4].
» Calcium Sulfate is anhydrous or contains two molecules of water of hydration. It contains not less than 98.0 percent and not more than 101.0 percent of CaSO4, calculated on the dried basis.
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— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Robert H. Lafaver, B.A.
(EM105) Excipient Monographs 1
USP32–NF27 Page 1182
Pharmacopeial Forum: Volume No. 27(6) Page 3337
Chromatographic Column—
Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.