» Hydrous Benzoyl Peroxide contains not less than 65.0 percent and not more than 82.0 percent of C14H10O4. It contains about 26 percent of water for the purpose of reducing flammability and shock sensitivity.
Caution—Hydrous Benzoyl Peroxide may explode at temperatures higher than 60 or cause fires in the presence of reducing substances. Store it in the original container, treated to reduce static charges.
A: Prepare a solution in methanol to contain 10 mg of benzoyl peroxide per mL. Apply 5 µL of this solution and 5 µL of a freshly prepared Standard solution of Hydrous Benzoyl Peroxide, previously subjected to the Assay, in methanol containing 10 mg per mL on a line parallel to and about 2.5 cm from the bottom of a thin-layer chromatographic plate (see Chromatography 621 ) coated with a 0.25-mm layer of chromatographic silica gel mixture. Place the plate in a developing chamber containing, and equilibrated with, a mixture of toluene, dichloromethane, and glacial acetic acid (50:2:1). Develop the chromatogram until the solvent front has moved about three-fourths of the length of the plate. Remove the plate, and allow the solvent to evaporate. Observe the plate under short-wavelength UV light: the RF value of the principal spot obtained from the solution under test corresponds to that obtained from the Standard solution.
B: Dissolve an accurately weighed quantity in acetonitrile to obtain a solution containing 0.32 mg of benzoyl peroxide per mL. Chromatograph this test solution and a freshly prepared Standard solution of Hydrous Benzoyl Peroxide, previously subjected to the Assay, in acetonitrile containing 0.32 mg per mL as directed in the test for Related compounds under Benzoyl Peroxide Gel: the solution under test exhibits a major peak for benzoyl peroxide, the retention time of which corresponds to that exhibited by the Standard solution.
Chromatographic purity— Calculate the area percentage of each peak in the chromatogram of the test solution prepared as directed in Identification test B: the sum of the areas of all peaks other than the principal peak does not exceed 2.0% of the total area, and the area of any individual peak other than the principal peak does not exceed 1.5% of the total area.
Assay— Place about 300 mg of previously mixed Hydrous Benzoyl Peroxide in an accurately weighed conical flask fitted with a ground-glass stopper, and weigh again to obtain the weight of the test specimen. Add 30 mL of glacial acetic acid, previously sparged with carbon dioxide for not less than 2 minutes just before use, and swirl the flask gently to effect solution. Add 5 mL of potassium iodide solution (1 in 2), and mix. Allow the solution to stand for 1 minute. Titrate the liberated iodine with 0.1 N sodium thiosulfate VS. As the endpoint is approached add 1 drop of starch iodide paste TS, or equivalent, and continue the titration to the discharge of the blue color. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N sodium thiosulfate is equivalent to 12.11 mg of C14H10O4.