Identification—
Transfer a quantity of Cream, equivalent to about 500 mg of monobenzone, to a centrifuge bottle, add 100 mL of water, and shake until the cream is completely dispersed. Centrifuge the suspension, decant the supernatant, wash the residue with water, again centrifuge, and decant the water. Transfer the residue to a separator with the aid of water, and adjust the volume to about 100 mL. Extract with four 25-mL portions of chloroform, filtering the extracts through a pledget of cotton into a 150-mL flask. Evaporate the chloroform in a current of warm air, and add 5 mL of pyridine and 3 mL of acetic anhydride to the dry residue. Connect the flask to a reflux condenser, reflux for 10 minutes, cool, and proceed as directed in
Identification test
C under
Monobenzone, beginning with “Add 100 mL of water.” It meets the requirements of
Identification test
C under
Monobenzone.
Assay—
Standard preparation—
Prepare as directed in the
Assay under
Monobenzone.
Assay preparation—
Transfer an accurately weighed portion of Cream, equivalent to about 200 mg of monobenzone, to a suitable container, add 100 mL of methanol, and shake for about 30 minutes. Transfer the mixture to a 200-mL volumetric flask. Rinse the container with two 25-mL portions of methanol, and add the rinsings to the 200-mL volumetric flask. Dilute with methanol to volume, mix, and filter, discarding the first 20 mL of the filtrate. Pipet 4 mL of this solution into a 100-mL volumetric flask, dilute with methanol to volume, and mix.
Procedure—
Proceed as directed in the
Assay under
Monobenzone, but use the
Assay preparation under
Monobenzone Cream. Calculate the quantity, in mg, of monobenzone (C
13H
12O
2) in the portion of Cream taken by the formula:
5000C(AU / AS),
in which
C is the concentration, in mg per mL, of
USP Monobenzone RS in the
Standard preparation and
AU and
AS are the absorbances obtained from the
Assay preparation and the
Standard preparation, respectively.
.
467
:
meets the requirements.