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

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

Topic/Question	Contact	Expert Committee
Monograph	Rick G. Schnatz Manager, Compounding Pharmacy Expert Committee 1-301-816-8526	(CRX05) Compounding Pharmacy05

USP32–NF27 Page 3637