A: Infrared Absorption 197K.

B: Ultraviolet Absorption 197U—

Test solution: 10 mg per mL, in dioxane.

Mobile phase— Prepare a filtered and degassed mixture of water and tetrahydrofuran (149:51). Make adjustments if necessary (see System Suitability under Chromatography 621).

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 solution to obtain a solution having a known concentration of about 20 µg per mL.

Test solution— Transfer about 20 mg of Methylprednisolone Acetate, accurately weighed, to a 20-mL volumetric flask, dissolve in Diluting solution, sonicate if necessary, dilute with Diluting solution to volume, and mix.

Chromatographic system (see Chromatography 621)— 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 1 mL per 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 20 µL) of the Standard solution and the Test solution into 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 C is the concentration, in mg per mL, of USP Methylprednisolone Acetate RS in the Standard solution; W is the weight, in mg, of Methylprednisolone Acetate taken in the Test solution; ri is the peak response for each impurity; and rS is 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 Suitability under Chromatography 621).

Internal standard solution— Prepare a solution containing about 6 mg per mL of 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-mL volumetric 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 20 mg of USP Methylprednisolone Acetate RS, accurately weighed, and 5.0 mL of the Internal standard solution to a 100-mL volumetric 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 621)— 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 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative retention times are about 1.3 for prednisone and 1.0 for 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 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C24H32O6 in the portion of Methylprednisolone Acetate taken by the formula: in which C is the concentration, in mg per mL, of USP Methylprednisolone Acetate RS in the Standard preparation; and RU and RS are the peak height response ratios of the methylprednisolone acetate peak and the internal standard peak obtained from the Assay preparation and the Standard preparation, respectively.