Test solution: 10 mg per mL, in dioxane.

Mobile phase— Prepare a filtered and degassed mixture of water and acetonitrile (55:45). Make adjustments if necessary (see System Suitability under Chromatography 621).

Internal standard solution— Prepare a solution of ethyl benzoate in methanol containing about 2.0 mg per mL.

Standard preparation— Immediately prior to use, dissolve an accurately weighed quantity of USP Hydrocortisone Valerate RS in methanol to obtain a solution having a known concentration of about 0.5 mg per mL. Pipet 2 mL of this solution and 2 mL of Internal standard solution into a 10-mL volumetric flask. Dilute with methanol to volume, and mix to obtain a Standard preparation having a known concentration of about 100 µg of hydrocortisone valerate per mL.

Assay preparation— Transfer about 100 mg of Hydrocortisone Valerate, accurately weighed, to a 100-mL volumetric flask. Dissolve in and dilute with methanol to volume, and mix. Pipet 1 mL of this solution and 2 mL of Internal standard solution into a 10-mL volumetric flask. Dilute with methanol to volume, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm × 30-cm column that contains packing L1. 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 0.8 for ethyl benzoate and 1.0 for hydrocortisone valerate, the resolution, R, between hydrocortisone valerate and ethyl benzoate is not less than 3.0, 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 C26H38O6, in the portion of Hydrocortisone Valerate taken by the formula: in which C is the concentration, in µg per mL, of USP Hydrocortisone Valerate RS in the Standard preparation; and RU and RS are the peak response ratios of the hydrocortisone valerate peak and the internal standard peak obtained from the Assay preparation and the Standard preparation, respectively.