A: Infrared Absorption 197K.

B: Ultraviolet Absorption 197U—

Solution: 5 µg per mL.

Medium: methanol.

Standard solutions— Dissolve USP Dapsone RS in methanol and mix to obtain Standard solution A having a known concentration of 12.5 mg per mL. Dilute quantitatively with methanol to obtain Standard solution B, containing 125 µg of the USP Reference Standard per mL, and Standard solution C, containing 62.5 µg of the USP Reference Standard per mL.

Test solution— Dissolve an accurately weighed quantity of Dapsone in methanol to obtain a solution containing 12.5 mg per mL.

Procedure— [note—Prepare the solvent system fresh daily. Equilibrate the chromatographic chamber with the solvent system for 30 minutes prior to development of the chromatographic plate.] Separately apply 4 µL of the Test solution and each of the Standard solutions to a suitable high-performance thin-layer chromatographic plate (see Chromatography 621) coated with a 150- to 200-µm layer of chromatographic silica gel. Dry the applications with the aid of a stream of nitrogen. Position the plate in a chromatographic chamber, and develop the chromatograms in a solvent system consisting of a mixture of chloroform, acetone, n-butyl alcohol, and formic acid (60:15:15:10) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber and air-dry. Spray the plate lightly with a 0.1% (w/v) solution of 4-dimethylaminocinnamaldehyde in a mixture of equal volumes of glacial acetic acid and water. Examine the spots that are developed immediately, and compare the intensities of any secondary spots observed in the chromatogram of the Test solution with those of the principal spots in the chromatogram of the Standard solutions: no secondary spot from the chromatogram of the Test solution is larger or more intense than the principal spot obtained from Standard solution C (0.5%), and the sum of the intensities of all the secondary spots obtained from the Test solution corresponds to not more than 1.0%.

Mobile phase— Transfer 100 mL of isopropyl alcohol, 100 mL of acetonitrile, and 100 mL of ethyl acetate to a 1000-mL volumetric flask. Add hexane to volume without mixing, then mix, and allow the mixture to cool to room temperature.

Standard preparation— Dissolve an accurately weighed quantity of USP Dapsone RS in Mobile phase to obtain a solution having a known concentration of about 250 µg per mL. Pipet 5 mL of this solution into a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix to obtain a Standard preparation having a known concentration of about 25 µg per mL.

Assay preparation— Transfer about 50 mg of Dapsone, accurately weighed, to a 200-mL volumetric flask. Dissolve in and dilute with Mobile phase to volume, and mix. Pipet 5 mL of this solution into a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)— The chromatograph is equipped with a 254-nm detector and a 4-mm × 30-cm column that contains 10-µm diameter packing L3. Chromatograph a sufficient number of injections of the Standard preparation as directed for Procedure: the relative standard deviation is not more than 2%.

Procedure— Separately introduce equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph by means of a suitable microsyringe or sampling valve, adjusting the specimen size and other operating parameters to obtain satisfactory chromatograms. Measure the responses for the major peaks obtained at corresponding retention times with the Assay preparation and the Standard preparation. Calculate the quantity, in mg, of C12H12N2O2S in the portion of Dapsone taken by the formula: in which C is the concentration, in µg per mL, of USP Dapsone RS in the Standard preparation; and PU and PS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.