Test solution— Transfer a quantity of Oral Solution, equivalent to about 5 mg of dexamethasone, to a 50-mL separator, add 10 mL of water, and extract with two 20-mL portions of chloroform. Filter the lower layers through chloroform-saturated cotton into a 50-mL conical flask, and evaporate to dryness. Dissolve the residue in 10 mL of chloroform.

Developing solvent system: a mixture of methylene chloride and methanol (180:16).

Procedure— Visualize the spots, using a 1 in 5 solution of p-toluenesulfonic acid in a mixture of alcohol and propylene glycol (9:1) followed by heat.

For Oral Solution Packaged In Single-Unit Containers: meets the requirements.

For Oral Solution Packaged In Multiple-Unit Containers: meets the requirements.

(Official January 1, 2007)

Mobile phase— Prepare a filtered and degassed mixture of methanol, water, and glacial acetic acid (55:43:2). Make adjustments if necessary (see System Suitability under Chromatography 621).

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

Standard preparation— Dissolve an accurately weighed quantity of USP Dexamethasone RS in Diluting solution, and dilute quantitatively, and stepwise if necessary, with Diluting solution to obtain a solution having a known concentration of about 0.04 mg per mL.

Assay preparation— Transfer an accurately measured volume of Oral Solution, equivalent to about 4 mg of dexamethasone, to a 100-mL volumetric flask, 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 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 column efficiency is not less than 2000 theoretical plates, the tailing factor 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, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg per mL, of dexamethasone (C22H29FO5) in the portion of Oral Solution taken by the formula: in which L is the labeled quantity, in mg per mL, of dexamethasone in the Oral Solution; D is the concentration, in mg per mL, of dexamethasone in the Assay preparation on the basis of the labeled quantity and the extent of dilution; C is the concentration, in mg per mL, of USP Dexamethasone RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.