Mobile phase— Prepare a filtered and degassed mixture of acetonitrile and water (2:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Dissolve progesterone in methanol to obtain a solution containing about 1mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Tolnaftate RSin methanol to obtain a solution having a known concentration of about 0.22mg per mL.Transfer 20.0mLof this solution to a 50-mLvolumetric flask,add 5.0mLof Internal standard solution,dilute with methanol to volume,and mix to obtain a solution having a known concentration of about 0.088mg of USP Tolnaftate RSper mL.

Assay preparation— Transfer an accurately weighed quantity of Topical Powder,equivalent to about 5mg of tolnaftate,to a screw-capped,50-mLcentrifuge tube.Add 25.0mLof methanol,place the cap on the tube,rotate on a rotating device for 10minutes,and centrifuge at about 2000rpm for 5minutes.Pass the supernatant through a 0.45-µm porosity filter,and transfer 20.0mLof the filtrate to a 50-mLvolumetric flask,retaining the remaining portion of the filtrate (about 5mL)for the Identificationtest.Add 5.0mLof Internal standard solutionto the volumetric flask,dilute with methanol to volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4-mm ×30-cm column that contains 10-µm packing L1.The flow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the resolution,R,between the analyte and internal standard peaks is not less than 3.0,and the relative standard deviation for replicate injections is not more than 3.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.The relative retention times are about 0.7for progesterone and 1.0for tolnaftate.Calculate the quantity,in mg,of C19H17NOSin the portion of Powder taken by the formula: in which Cis the concentration,in mg per mL,of USP Tolnaftate RSin the Standard preparation,and RUand RSare the peak response ratios obtained from the Assay preparationand the Standard preparation,respectively.