A:Infrared Absorption á197Kñ.

B:Ultraviolet Absorption á197Uñ—

Test solution: 10mg per mL,in dioxane.

Mobile phase— Prepare a filtered and degassed mixture of methanol and water (4:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Transfer about 100mg of desoxycorticosterone acetate to a 50-mLvolumetric flask,add methanol to volume,and mix.

Standard preparation— Transfer about 12.5mg of USP Desoxycorticosterone Pivalate RS,accurately weighed,to a 25-mLvolumetric flask,add 20mLof methanol,and mix.Add 2.5mLof Internal standard solution,dilute with methanol to volume,and mix to obtain a solution having a known concentration of about 0.5mg of USP Desoxycorticosterone Pivalate RSper mL.

Assay preparation— Transfer about 50mg of Desoxycorticosterone Pivalate,accurately weighed,to a 100-mLvolumetric flask,add 80mLof methanol,and mix.Add 10.0mLof Internal standard solution,dilute with methanol to volume,and mix.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×25-cm column that contains packing L7.The flow rate is about 1.5mLper 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 2.0;and the relative standard deviation for replicate injections is not more than 1.5%.

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.The relative retention times are about 0.5for desoxycorticosterone acetate and 1.0for desoxycorticosterone pivalate.Calculate the quantity,in mg,of C26H38O4in the portion of Desoxycorticosterone Pivalate taken by the formula: in which Cis the concentration,in mg per mL,of USP Desoxycorticosterone Pivalate RSin the Standard preparation;and RUand RSare the peak response ratios obtained from the Assay preparationand the Standard preparation,respectively.