A: Dissolve a quantity of Ophthalmic Ointment, equivalent to about 1 g of sulfacetamide sodium, in 100 mL of ether in a separator, and extract the mixture with 25 mL of water. Wash the extract with 25 mL of ether, and warm the water extract on a steam bath to remove the last traces of ether. Adjust with 6 N acetic acid to a pH of between 4 and 5, and filter. Wash the precipitate with water, and dry at 105 for 2 hours: the sulfacetamide so obtained melts between 180 and 184, and responds to Identification tests B, D, and E under Sulfacetamide Sodium.

B: To a quantity of Ophthalmic Ointment, equivalent to about 25 mg of prednisolone acetate, add 15 mL of water, extract with two 10-mL portions of peroxide-free ether, discard the ether extracts, and extract with two 10-mL portions of chloroform. Evaporate the combined, clear chloroform extracts, with the aid of a current of air, to dryness: the residue so obtained responds to Identification test A under Prednisolone Acetate.

Standard preparation— Prepare as directed for Standard Preparation under Assay for Steroids 351, using USP Prednisolone Acetate RS.

Assay preparation— Transfer to a suitable flask an accurately weighed quantity of Ophthalmic Ointment, equivalent to about 10 mg of prednisolone acetate, and add 30 mL of alcohol. Heat on a steam bath to melt the ointment base, and mix. Cool to solidify the ointment base, and filter the alcohol solution into a 100-mL volumetric flask. Repeat the extraction with three 20-mL portions of alcohol, add alcohol to volume, and mix. Pipet 10 mL of this solution into a 100-mL volumetric flask, add alcohol to volume, and mix. Pipet 20 mL of the resulting solution into a glass-stoppered, 50-mL conical flask.

Procedure— Proceed as directed for Procedure under Assay for Steroids 351. Calculate the quantity, in mg, of C23H30O6 in the portion of Ophthalmic Ointment taken by the formula: