Identification—
Shake 50 mL of Oral Solution with 25 mL of chloroform for 5 minutes. Filter the chloroform extract through a pledget of cotton and a layer of anhydrous sodium sulfate, and evaporate on a warm water bath with the aid of a current of air to about 3 mL. Continue the evaporation to dryness at room temperature. Wash the residue with two 10-mL portions of hot solvent hexane, decanting the solvent and discarding it each time. Digest the residue with 25 mL of warm dehydrated alcohol for 15 minutes. Filter the mixture, and evaporate the filtrate to about 3 mL. Add solvent hexane until the mixture becomes slightly cloudy, and chill in a freezer to promote the formation of crystals. Collect the crystals, and dry at 60
for 1 hour: the crystals meet the requirements for
Identification test
A under
Prednisone.
Assay—
Mobile phase—
Dissolve 1.36 g of monobasic potassium phosphate in 600 mL of water, add 400 mL of methanol, pass through a 0.2-µm membrane filter, and degas. Make adjustments if necessary (see
System Suitability under
Chromatography 
621
).
Standard preparation—
Using an accurately weighed quantity of
USP Prednisone RS, prepare a solution in alcohol containing 1 mg per mL. Dilute 4 volumes of this solution quantitatively with 96 volumes of water to obtain a
Standard preparation having a known concentration of about 40 µg per mL.
Assay preparation—
Transfer an accurately measured volume of Oral Solution, equivalent to about 10 mg of prednisone, to a 250-mL volumetric flask. Dilute with water 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 1.5 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the tailing factor for the analyte peak is not more than 2.0; 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 by means of a sampling valve, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of prednisone (C
21H
26O
5) in each mL of the Oral Solution taken by the formula:
(0.25C/V)(rU / rS),
in which
C is the concentration, in µg per mL, of
USP Prednisone RS in the
Standard preparation; V is the volume, in mL, of Oral Solution taken; and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
