Monobenzone Cream
»Monobenzone Cream contains not less than 94.0percent and not more than 106.0percent of the labeled amount of monobenzone (C13H12O2).
Packaging and storage— Preserve in tight containers,and avoid exposure to temperatures higher than 30.
Identification— Transfer a quantity of Cream,equivalent to about 500mg of monobenzone,to a centrifuge bottle,add 100mLof 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 100mL.Extract with four 25-mLportions of chloroform,filtering the extracts through a pledget of cotton into a 150-mLflask.Evaporate the chloroform in a current of warm air,and add 5mLof pyridine and 3mLof acetic anhydride to the dry residue.Connect the flask to a reflux condenser,reflux for 10minutes,cool,and proceed as directed in Identificationtest Cunder Monobenzone,beginning with “Add 100mLof water.”It meets the requirements of Identificationtest Cunder Monobenzone.
Assay—
Standard preparation— Prepare as directed in the Assayunder Monobenzone.
Assay preparation— Transfer an accurately weighed portion of Cream,equivalent to about 200mg of monobenzone,to a suitable container,add 100mLof methanol,and shake for about 30minutes.Transfer the mixture to a 200-mLvolumetric flask.Rinse the container with two 25-mLportions of methanol,and add the rinsings to the 200-mLvolumetric flask.Dilute with methanol to volume,mix,and filter,discarding the first 20mLof the filtrate.Pipet 4mLof this solution into a 100-mLvolumetric flask,dilute with methanol to volume,and mix.
Procedure— Proceed as directed in the Assayunder Monobenzone,but use the Assay preparationunder Monobenzone Cream.Calculate the quantity,in mg,of monobenzone (C13H12O2)in the portion of Cream taken by the formula:
5000C(AU/AS),
in which Cis the concentration,in mg per mL,of USP Monobenzone RSin the Standard preparationand AUand ASare the absorbances obtained from the Assay preparationand the Standard preparation,respectively.
Auxiliary Information— Staff Liaison:Lawrence Evans,III,Ph.D.,Scientist
Expert Committee:(PA6)Pharmaceutical Analysis 6
USP28–NF23Page 1311
Phone Number:1-301-816-8389
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