(Official January 1, 2007)

Citrate buffer— Prepare a 0.0033 M solution of citric acid in water, adjust with 1 N sodium hydroxide to a pH of 6.2, and mix.

Diluting solution: a mixture of methanol and water (1:1).

Mobile phase— Prepare a filtered and degassed mixture of Citrate buffer and methanol (31:19). Make adjustments if necessary (see System Suitability under Chromatography 621).

System suitability solution— Dissolve suitable quantities of prednisolone and hydrocortisone in a mixture of methanol and water (1:1) to obtain a solution containing about 100 µg per mL and 90 µg per mL, respectively.

Standard preparation— Dissolve an accurately weighed quantity of USP Prednisolone RS in Diluting solution, and dilute quantitatively, and stepwise if necessary, with Diluting solution to obtain a solution having a known concentration of about 0.1 mg per mL.

Assay preparation— Transfer an accurately measured volume of Oral Solution, equivalent to about 5.0 mg of prednisolone, to a 50-mL volumetric flask, dissolve in Diluting solution, shake by mechanical means for 15 minutes, 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 × 15-cm column that contains packing L10. The flow rate is about 1 mL per minute. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.8 for hydrocortisone and 1.0 for prednisolone; the resolution, R, between hydrocortisone and prednisolone 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 prednisolone (C21H28O5) in the volume of Oral Solution taken by the formula: in which C is the concentration, in mg per mL, of USP Prednisolone RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.