CaSO4 136.14

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

Dihydrate 172.17 [10101-41-4].

Packaging and storage— Preserve in well-closed containers.

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

Identification— Dissolve about 200mg by warming in a mixture of 4mLof 3Nhydrochloric acid and 16mLof water.This solution responds to the tests forCalcium á191ñand forSulfate á191ñ.

Loss on drying á731ñ— Dry it at a temperature not lower than 250to 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 á241ñ— Dissolve 100mg in 8mLof 3Nhydrochloric acid,and dilute with water to 47mL:the limit is 0.01%.

Heavy metals,Method Iá231ñ— Mix 2.0g with 20mLof water,add 25mLof 3Nhydrochloric acid,and heat to boiling to dissolve the test specimen.Cool,and add ammonium hydroxide to a pHof 7.Filter,evaporate to a volume of about 25mL,and refilter,if necessary,to obtain a clear solution:the limit is 0.001%.

Assay— Dissolve about 300mg of Calcium Sulfate,accurately weighed,in 100mLof water and 4mLof 3Nhydrochloric acid.Boil,if necessary,to dissolve,and cool before titrating.While stirring,preferably with a magnetic stirrer,add,in the order named,0.5mLof triethanolamine,300mg of hydroxy naphthol blue,and,from a 50-mLburet,about 30mLof 0.05Medetate disodium VS.Add sodium hydroxide solution (45in 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 0.5mL.The pHis between 12.3and 12.5.Continue the titration dropwise with 0.05Medetate disodium VSto the appearance of a clear-blue endpoint that persists for not less than 60seconds.Each mLof 0.05Medetate disodium is equivalent to 6.807mg of CaSO4.

Expert Committee:(EMC)Excipients:Monograph Content

USP28–NF23Page 2971

Phone Number:1-301-816-8262