A:Infrared Absorption á197Mñ.

B:Thin-Layer Chromatographic Identification Test á201ñ—

Test solution: 10mg per mL,in dioxane.

Test solution: methanol.

Standard solution: methanol.

Application volume: 10µL.

Eluant: a mixture of toluene and isopropyl alcohol (90:10),in a nonequilibrated chamber.

Visualization: 5.

Mobile phase— Prepare a filtered and degassed mixture of water,acetonitrile,and glacial acetic acid (800:700:1.5).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Transfer about 35mg of progesterone to a 50-mLvolumetric flask,add Mobile phaseto volume,and mix.

Standard preparation— Dissolve an accurately weighed quantity of USP Betamethasone Acetate RSin Mobile phase,and quantitatively dilute with Mobile phaseto obtain a solution containing about 0.5mg per mL.Transfer 10.0mLof the resulting solution to a 50-mLvolumetric flask,add 10.0mLof Internal standard solution,dilute with Mobile phaseto volume,and mix to obtain a solution having a known concentration of about 0.1mg of USP Betamethasone Acetate RSper mL.

Assay preparation— Transfer about 50mg of Betamethasone Acetate,accurately weighed,to a 100-mLvolumetric flask,add Mobile phaseto volume,and mix.Transfer 10.0mLof the resulting solution to a 50-mLvolumetric flask,add 10.0mLof Internal standard solution,dilute with Mobile phaseto 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 packing L1.The flow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative retention times are about 3for progesterone and 1.0for betamethasone acetate;the resolution,R,between the analyte and internal standard peaks is not less than 2;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 25µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C24H31FO6in the portion of Betamethasone Acetate taken by the formula: in which Cis the concentration,in mg per mL,of USP Betamethasone Acetate RSin the Standard preparation;and RUand RSare the peak response ratios obtained from the Assay preparationand the Standard preparation,respectively.