Packaging and storage— Preserve in well-closed containers,and avoid prolonged exposure to excessive heat.

Assay— Transfer about 500mg of Ointment,accurately weighed,to a suitable conical flask,add 5mLof nitric acid and 3mLof bromine,warm slightly,and allow to stand overnight.Heat gently on a steam bath until the excess bromine has been dissipated.Add 30mLof water and then 30mLof ether,and swirl to dissolve most of the ointment base.Transfer the mixture to a separator,with the aid of a 20-mLand a 10-mLportion of ether,followed by two 10-mLportions of water.Shake the mixture,and draw off the water layer into a suitable beaker or flask.Extract the ether layer with two 40-mLportions of water each containing 1mLof hydrochloric acid.Heat the combined water extracts on a steam bath to remove all traces of ether.Dilute the solution with water to about 200mL,heat to boiling,and add slowly,with constant stirring,about 20mLof hot barium chloride TS.Heat on a steam bath for 1hour,then collect the precipitate on a filter,wash it well with hot water,dry,and ignite to constant weight.The weight of the barium sulfate so obtained,multiplied by 0.1374,represents the weight of S.

Expert Committee:(PA7)Pharmaceutical Analysis 7

USP28–NF23Page 1838

Phone Number:1-301-816-8394