» Hydroquinone Cream contains not less than 94.0 percent and not more than 106.0 percent of the labeled amount of hydroquinone (C6H6O2).
Packaging and storage Preserve in well-closed, light-resistant containers.
USP Reference standards 11
Identification Dissolve a portion of Cream equivalent to about 50 mg of hydroquinone, in a mixture of equal volumes of methanol and chloroform to make 50 mL: a 5-µL portion of this solution responds to Identification test B under Hydroquinone.
Minimum fill 755: meets the requirements.
Standard preparation Dissolve a suitable quantity of USP Hydroquinone RS in methanol, and dilute quantitatively and stepwise with methanol to obtain a solution having a known concentration of about 10 µg per mL.
Assay preparation Transfer an accurately weighed portion of Cream, equivalent to about 20 mg of hydroquinone, to a 100-mL beaker. Triturate the Cream with 50 mL of methanol, and pass the liquid through folded filter paper, previously washed with methanol, into a 500-mL volumetric flask. Repeat the trituration and filtration. Dilute, by washing the contents of the filter paper with methanol through the paper into the volumetric flask, to volume, and mix. Pipet 25 mL of this solution into a 100-mL volumetric flask, add methanol 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 293 nm, with a suitable spectrophotometer, using methanol as the blank. Calculate the quantity, in mg, of hydroquinone (C6H6O2) in each g of the Cream taken by the formula:
2000(C / W)(AU / AS)in which C is the concentration, in mg per mL, of USP Hydroquinone RS in the Standard preparation; W is the weight, in g, of Cream taken; and AU and AS are the absorbances of the Assay preparation and the Standard preparation, respectively.
Auxiliary Information Please check for your question in the FAQs before contacting USP.
USP35NF30 Page 3451Pharmacopeial Forum: Volume No. 27(1) Page 1790