A:Infrared Absorption á197Kñ.

B: Ultraviolet Absorption á197Uñ—

Test solution: 10mg per mL,in dioxane.

Mobile phase— Prepare a filtered and degassed mixture of water and tetrahydrofuran (149:51).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Diluting solution— Prepare a mixture of water,tetrahydrofuran,acetonitrile,and glacial acetic acid (499:250:250:1).

Standard solution— Dissolve an accurately weighed quantity of USP Methylprednisolone Acetate RS,sonicate if necessary,in Diluting solution,and dilute quantitatively,and stepwise if necessary,with Diluting solutionto obtain a solution having a known concentration of about 20µg per mL.

Test solution— Transfer about 20mg of Methylprednisolone Acetate,accurately weighed,to a 20-mLvolumetric flask,dissolve in Diluting solution,sonicate if necessary,dilute with Diluting solutionto 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 L1.The flow rate is about 1mLper minute.Chromatograph the Standard solution,and record the peak responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 5.0%.

Procedure— Inject equal volumes (about 20µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the peak responses.Calculate the percentage of each impurity in the portion of Methylprednisolone Acetate taken by the formula: in which Cis the concentration,in mg per mL,of USP Methylprednisolone Acetate RSin the Standard solution;Wis the weight,in mg,of Methylprednisolone Acetate taken in the Test solution;riis the peak response for each impurity;and rSis the peak response of methylprednisolone in the Standard solution:not more than 1.0%of any individual impurity is found;and not more than 2.0%of total impurities is found.

Mobile phase— Prepare a mixture of n-butyl chloride,water-saturated n-butyl chloride,tetrahydrofuran,methanol,and glacial acetic acid (475:475:70:35:30).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Prepare a solution containing about 6mg per mLof prednisone in a mixture of chloroform and glacial acetic acid (97:3)by first adding the entire amount of glacial acetic acid to the prednisone contained in a 100-mLvolumetric flask,followed by sonication.Then slowly add the chloroform,using sonication and shaking to dissolve the material.Dilute with chloroform to volume,and mix.

Standard preparation— Transfer about 20mg of USP Methylprednisolone Acetate RS,accurately weighed,and 5.0mLof the Internal standard solutionto a 100-mLvolumetric flask.Dilute with chloroform to volume,and shake to dissolve the specimen.

Assay preparation— Prepare a solution of Methylprednisolone Acetate as directed under Standard preparation.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 4-mm ×25-cm column that contains packing L3.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 1.3for prednisone and 1.0for methylprednisolone acetate;the resolution,R,between the analyte and internal standard peaks is not less than 2.5;and the relative standard deviation for replicate injections is not more than 2.0%.

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.Calculate the quantity,in mg,of C24H32O6in the portion of Methylprednisolone Acetate taken by the formula: in which Cis the concentration,in mg per mL,of USP Methylprednisolone Acetate RSin the Standard preparation;and RUand RSare the peak height response ratios of the methylprednisolone acetate peak and the internal standard peak obtained from the Assay preparationand the Standard preparation,respectively.