Mobile phase— Prepare as directed in the Assay under Cortisone Acetate Tablets.

Internal standard solution— Prepare a solution of prednisone in Mobile phase having a concentration of 0.5 mg per mL.

Standard preparation— Transfer about 12 mg of USP Cortisone Acetate RS, accurately weighed, to a stoppered, 50-mL conical flask. Add 20.0 mL of Internal standard solution, and sonicate for 5 minutes. Pass a portion through a polytef syringe filter, then combine 1 mL of the filtrate and 4 mL of Mobile phase to obtain the Standard preparation.

Resolution solution— Dissolve a quantity of hydrocortisone acetate in the Standard preparation to obtain a solution containing about 0.1 mg of hydrocortisone acetate per mL.

Assay preparation— Using a pipet calibrated “to contain,” transfer 2.0 mL of freshly mixed Injectable Suspension to a volumetric flask of a size to give a cortisone acetate concentration of 2 mg per mL when diluted to volume. Rinse the suspension remaining in the pipet into the flask with isopropyl alcohol, dilute with isopropyl alcohol to volume, and sonicate for 3 minutes. Deliver a 3.0-mL aliquot of this solution to a stoppered, 25-mL conical flask, and evaporate on a steam bath with the aid of a current of air to dryness. Add 10.0 mL of Internal standard solution, insert the stopper, and sonicate for 5 minutes. Pass a portion through a polytef syringe filter, then combine approximately 1 mL of the filtrate and 4 mL of Mobile phase to obtain the Assay preparation.

Chromatographic system (see Chromatography 621)—Prepare as directed in the Assay under Cortisone Acetate Tablets. Chromatograph the Resolution solution, and record the peak responses as directed for Procedure: the resolution, R, between cortisone acetate and hydrocortisone acetate is not less than 2.2 (if necessary, add equal parts of n-butyl chloride and water-saturated n-butyl chloride to the Mobile phase to meet this requirement). Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative retention times are 0.6 for cortisone acetate and 1.0 for prednisone; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Proceed as directed in the Assay under Cortisone Acetate Tablets. Calculate the quantity, in mg, of cortisone acetate (C23H30O6) in each mL of the Injectable Suspension taken by the formula: in which V is the capacity, in mL, of the volumetric flask used for the Assay preparation; and the other terms are as defined therein.