Sodium Sulfide Topical Gel
» Sodium Sulfide Topical Gel contains not less than 90.0 percent and not more than 120.0 percent of the labeled amount of sodium sulfide (Na2S·9H2O) in a suitable gel base.
Packaging and storage Preserve in tight containers at controlled room temperature or in a cool place.
Identification Proceed as directed for the Identification test under Sodium Sulfide.
pH 791: between 11.5 and 13.5.
Diluent Transfer 500.0 mL of a 4.0 M sodium hydroxide solution to a 1000-mL volumetric flask, and add about 67.0 g of edetate disodium and 36.0 g of ascorbic acid, each accurately weighed. Dilute with water to volume, and mix.
Assay preparation Transfer an accurately weighed portion of the Topical Gel, equivalent to about 30 mg of sodium sulfide, to a 100-mL volumetric flask, add 50 mL of Diluent, and shake by mechanical means until the Topical Gel is dispersed. Dilute with Diluent to volume, and mix.
Procedure Transfer 30.0 mL of the Assay preparation to a suitable beaker, and titrate with 0.01 M lead perchlorate VS, determining the endpoint potentiometrically. Perform a blank determination, and make any necessary correction. Each mL of 0.01 M lead perchlorate is equivalent to 2.4018 mg of sodium sulfide (Na2S·9H2O).
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USP32NF27 Page 3586Pharmacopeial Forum: Volume No. 28(2) Page 366