Identification—
Apply 20 µL of a solution prepared as directed for
Assay preparation in the
Assay but without the addition of the
Internal standard solution, and 20 µL of a solution of
USP Triamcinolone Acetonide RS in methanol containing 30 µg per mL, to a line parallel to and about 1.5 cm from the bottom edge of a thin-layer chromatographic plate (see
Chromatography 
621
) coated with a 0.25-mm layer of chromatographic silica gel. Proceed as directed in the
Identification test under
Triamcinolone Acetonide Cream, beginning with “Place the plate in a developing chamber.” The specified result is obtained.
Assay—
Mobile phase—
Prepare a degassed solution of water and acetonitrile (70:30).
Internal standard solution—
Dissolve fluoxymesterone in methanol to obtain a solution having a concentration of about 25 µg per mL.
Standard preparation—
Dissolve an accurately weighed quantity of
USP Triamcinolone Acetonide RS in methanol to obtain a solution having a concentration of about 100 µg per mL. Transfer 15.0 mL of this solution to a 50-mL volumetric flask, add 25.0 mL of
Internal standard solution, dilute with methanol to volume, and mix. This solution has a known concentration of about 30 µg per mL.
Assay preparation—
Fit the valve of a previously weighed Triamcinolone Acetonide Aerosol container with a suitable tube assembly so that the contents can be sprayed directly into the bulb portion of a 100-mL volumetric flask containing 50.0 mL of Internal standard solution and 20 mL of methanol. Spray a portion of the contents, equivalent to about 3 mg of triamcinolone acetonide, into the flask, determining the exact amount sprayed by difference. Place in a sonic bath for about 5 minutes to expel the propellant. Dilute with methanol to volume, and mix. [NOTE—The propellant is extremely flammable. When evaporating, observe proper precautions and work under an explosion-proof hood.]
Procedure—
Introduce equal volumes (between 15 µL and 25 µL) of the
Assay preparation and the
Standard preparation into a chromatograph (see
Chromatography 621) operated at room temperature and fitted with a 3.9-mm × 30-cm column, packed with packing L1, and equipped with a 254-nm detector. Adjust the operating parameters and the
Mobile phase composition such that the separation of triamcinolone acetonide and internal standard is optimized, with a retention time of about 14 minutes for triamcinolone acetonide. In a suitable system, the relative standard deviation for five replicate injections of the
Standard preparation is not more than 3.0%. Measure the responses of the internal standard and triamcinolone acetonide peaks at the same retention times obtained from the
Assay preparation and the
Standard preparation. Calculate the quantity, in µg, of C
24H
31FO
6 in the portion of Topical Aerosol taken by the formula:
100C(RU / RS),
in which
C is the concentration, in µg per mL, of
USP Triamcinolone Acetonide RS in the
Standard preparation, and
RU and
RS are the ratios of the peak responses of triamcinolone acetonide to internal standard obtained from the
Assay preparation and the
Standard preparation, respectively.
