» Clotrimazole Lotion contains not less than 90.0 percent and not more than 110.0 percent of the labeled amount of clotrimazole (C22H17ClN2).
Packaging and storage Preserve in tight containers, and store at a temperature between 2 and 30.
USP Reference standards 11
USP Clotrimazole Related Compound A RS
Identification The retention time of the major peak for clotrimazole in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.
pH 791: between 5.0 and 7.0.
Microbial enumeration tests 61 and Tests for specified microorganisms 62 It meets the requirements of the tests for absence of Staphylococcus aureus and Pseudomonas aeruginosa.
Limit of clotrimazole related compound A Using the chromatograms of the Assay preparation and the Standard preparation obtained as directed in the Assay, calculate the percentage of clotrimazole related compound A in the portion of Lotion taken by the formula:
2000(C / Q)(RU / RS)in which C is the concentration, in mg per mL, of USP Clotrimazole Related Compound A RS in the Standard preparation; Q is the quantity, in mg, of clotrimazole (C22H17ClN2) in the portion of Lotion taken; and RU and RS are the peak response ratios of clotrimazole related compound A to testosterone propionate obtained from the Assay preparation and the Standard preparation, respectively: not more than 5% is found.
Dibasic potassium phosphate solution Dissolve 4.35 g of dibasic potassium phosphate in water to make 1000 mL.
Mobile phase Prepare a mixture of methanol and Dibasic Potassium phosphate solution (3:1), pass through a membrane filter having a 0.5-µm or finer porosity, and degas.
Internal standard solution Prepare a solution of testosterone propionate in dehydrated alcohol having a concentration of about 0.07 mg per mL.
Clotrimazole standard stock solution Transfer about 50 mg of USP Clotrimazole RS, accurately weighed, to a 25-mL volumetric flask, add dehydrated alcohol to volume, and mix.
Clotrimazole related compound A standard stock solution Prepare a solution of USP Clotrimazole Related Compound A RS in dehydrated alcohol having a known concentration of about 0.1 mg per mL.
Standard preparation Mix 5.0 mL of Clotrimazole standard stock solution, 5.0 mL of Clotrimazole related compound A standard stock solution, and 10.0 mL of Internal standard solution.
Assay preparation Accurately weigh a portion of freshly mixed Lotion, equivalent to about 10 mg of clotrimazole, and transfer to a screw-capped, 50-mL centrifuge tube. Add 10.0 mL of Internal standard solution, place the cap on the tube, and heat at 50 in a water bath for 5 minutes, with occasional shaking. Remove the tube from the bath, and shake vigorously for 5 minutes. Cool in a methanol-ice bath for 15 minutes, and promptly centrifuge. Transfer the supernatant to a test tube. Add 10.0 mL of dehydrated alcohol to the residue in the centrifuge tube, and repeat the extraction as directed above, beginning with place the cap on the tube. Transfer the supernatant to the test tube containing the supernatant from the first extraction, mix, and use this solution as the Assay preparation.
Chromatographic system (see Chromatography 621) The liquid chromatograph is equipped with a 254-nm detector and a 2.1-mm × 6-cm guard column that contains 10-µm packing L2 and a 3.9-mm × 30-cm analytical column that contains 10-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 retention times are about 0.9 for clotrimazole related compound A, 1.0 for clotrimazole, and 1.5 for testosterone propionate; the resolution, R, between clotrimazole related compound A and clotrimazole is not less than 1.2; the resolution, R, between clotrimazole and testosterone propionate is not less than 1.9; and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure Separately inject equal volumes (about 20 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 clotrimazole (C22H17ClN2) in each g of Lotion taken by the formula:
20(C / W)(RU / RS)in which C is the concentration, in mg per mL, of USP Clotrimazole RS in the Standard preparation; W is the weight, in g, of Lotion taken; and RU and RS are the peak response ratios of clotrimazole to testosterone propionate obtained from the Assay preparation and the Standard preparation, respectively.
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USP35NF30 Page 2742Pharmacopeial Forum: Volume No. 30(2) Page 474