Mobile phase— Prepare a filtered and degassed mixture of water and isopropyl alcohol (72:28).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ.)

Diluent— Prepare a mixture of alcohol and water (85in 100).

Internal standard solution— Dissolve an accurately weighed quantity of USP Methyltestosterone RSin Diluentto obtain a solution containing about 6.6mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Progesterone RSin Diluent,and dilute quantitatively,and stepwise if necessary,with Diluentto obtain a solution having a known concentration of about 2.5mg per mL.

Standard curve— To four separate polytef-lined,screw-capped centrifuge tubes,pipet 3-,4-,5-,and 6-mLportions,respectively,of the Standard preparation.Add Diluentto each tube to make about 8mLof solution.Transfer 1.0mLof Internal standard solutionto each tube,and mix.

Assay preparation— Transfer an accurately measured volume of Injectable Suspension,equivalent to about 25mg progesterone,to a polytef-lined,screw-capped,25mLtest tube.Add 16mLof Diluent,and shake until clear.Add 2.0mLof Internal standard solution,and mix.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 2.1-mm ×1-m column that contains packing L2.The chromatographic conditions are such that retention times of the internal standard and progesterone are between 3and 6minutes and 7and 11minutes,respectively.Chromatograph any solution of the Standard curve,and record the peak areas as directed for Procedure:the resolution,R,between progesterone and methyltestosterone is not less than 3.5;and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (5.0µL)of each solution of the Standard curveand the Assay preparationinto the chromatograph,record the chromatograms,and measure the peak areas.Plot the progesterone to methyltestosterone peak ratio versus the concentration,in mg per mL,of progesterone in the Standard curvesolutions.Extrapolate the progesterone to methyltestosterone peak ratio of the Assay preparationin the Standard curveso obtained,and determine the progesterone concentration,C,in mg per mL,in the Assay preparation.Calculate the amount,in mg,of progesterone (C21H30O2)in each mLof the Injectable Suspension taken by the formula: in which Vis the total volume of the Assay preparation;Ais the volume in mLof Injectable Suspension taken;and Cis the concentration of progesterone in the Assay preparationcalculated above.