A: Ultraviolet Absorption 197U—

B: Place about 1 g in a beaker, warm to melt the cream, add about 25 mL of water, and mix: the solution responds to the tests for Acetate 191.

Standard preparation— Dissolve an accurately weighed quantity of USP Mafenide Acetate RS in 0.01 N hydrochloric acid, and dilute quantitatively and stepwise with the same solvent to obtain a solution having a known concentration of about 200 µg per mL.

Assay preparation— Transfer a quantity of Cream, equivalent to about 100 mg of mafenide acetate and accurately weighed, to a 60-mL separator, and add 20 mL of chloroform to dissolve it. Add 20 mL of water, shake for 2 minutes, allow the layers to separate completely, and discard the lower, chloroform layer. Repeat this washing with two separate 20-mL portions of chloroform, and discard the chloroform washings. Filter the aqueous phase through a dry filter into a 100-mL volumetric flask. Rinse the separator and the filter with water, passing all rinses through the filter, add water to volume, and mix. Centrifuge about 30 mL of the Assay preparation, then pipet 20 mL of the clear, supernatant into a 100-mL volumetric flask, add 1 mL of 1 N hydrochloric acid, add water to volume, and mix.

Procedure— Concomitantly determine the absorbances of the Standard preparation and the Assay preparation in 1-cm cells at the wavelength of maximum absorbance at about 267 nm, with a suitable spectrophotometer, using 0.01 N hydrochloric acid as the blank. Calculate the quantity, in mg, of C7H10N2O2S·C2H4O2 in the portion of Cream taken by the formula: in which C is the concentration, in µg per mL, of USP Mafenide Acetate RS in the Standard preparation, and AU and AS are the absorbances of the solutions from the Assay preparation and the Standard preparation, respectively.