» Tretinoin Cream contains not less than 90.0 percent and not more than 120.0 percent of the labeled amount of tretinoin.
Packaging and storage Preserve in collapsible tubes or in tight, light-resistant containers.
USP Reference standards 11
Identification The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation obtained as directed in the Assay.
Minimum fill 755: meets the requirements.
Assay [noteAvoid exposure to strong light, and use low-actinic glassware in the performance of the following procedure. Use stabilized tetrahydrofuran in the preparation of the Standard preparation and the Assay preparation. ]
Dilute phosphoric acid Dilute 10 mL of phosphoric acid with water to 100 mL.
Phosphate buffer Dissolve 1.38 g of monobasic sodium phosphate in 1000 mL of water, adjust with Dilute phosphoric acid to a pH of 3.0, and mix.
Diluting solution Prepare a mixture of water and Dilute phosphoric acid (9:1).
Mobile phase [notePhosphate buffer and tetrahydrofuran may be filtered and degassed separately before mixing. ] Prepare a filtered and degassed mixture of Phosphate buffer and tetrahydrofuran (58:42). Make adjustments if necessary (see System Suitability under Chromatography 621).
Standard preparation Dissolve an accurately weighed quantity of USP Tretinoin RS in tetrahydrofuran to obtain a solution having a known concentration of about 0.4 mg per mL. Dilute a known volume of this solution, quantitatively and stepwise if necessary, with a mixture of tetrahydrofuran and Diluting solution (3:2) to obtain a solution having a known concentration of about 4 µg per mL.
Assay preparation Transfer an accurately weighed quantity of Cream, equivalent to 1.0 mg of tretinoin, to a 50-mL volumetric flask, and add 20.0 mL of tetrahydrofuran. Shake the flask to disperse the cream, dilute with tetrahydrofuran to volume, mix, and filter, if necessary. Transfer 5.0 mL of this solution to a 25-mL volumetric flask, dilute with a mixture of tetrahydrofuran and Diluting solution (3:2) to volume, mix, and filter.
Chromatographic system (see Chromatography 621)The liquid chromatograph is equipped with a 365-nm detector and a 3.9-mm × 15-cm column that contains 4-µm packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 2.0%.
Procedure Separately inject equal volumes (about 25 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of tretinoin (C20H28O2) in the portion of Cream taken by the formula:
0.250C(rU / rS)in which C is the concentration, in µg per mL, of USP Tretinoin RS in the Standard preparation, and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.
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USP35NF30 Page 4921