Identification—
Transfer a quantity of Lotion, equivalent to about 5 mg of hydrocortisone, to a separator containing 10 mL of methylene chloride, shake for 1 minute, and allow the layers to separate. Filter the methylene chloride extract onto a suitable chromatographic column that has been packed with 2 g of activated magnesium silicate. Wash the column with 25 mL of methylene chloride with the aid of slight air pressure, discarding the washings, and elute the hydrocortisone with 10 mL of methanol. Using
USP Hydrocortisone RS to prepare a Standard solution having a concentration of 500 µg per mL, and using as the solvent system a mixture of 180 volumes of chloroform, 15 volumes of methanol, and 1 volume of water, proceed as directed under
Thin-layer Chromatographic Identification Test 
201
.
Assay—
Mobile phase—
Prepare a filtered and degassed mixture of water, acetonitrile, and methanol (58:21:21). Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard preparation—
Dissolve an accurately weighed quantity of
USP Hydrocortisone RS in alcohol and dilute quantitatively, and stepwise if necessary, with alcohol to obtain a solution having a known concentration of about 0.1 mg per mL. Quantitatively dilute a known volume of the final solution with an equal volume of water to obtain the
Standard preparation.
Assay preparation—
In a tared, 100-mL volumetric flask, weigh 100 mL of Lotion that previously has been shaken to ensure homogeneity, allow to stand until the entrapped air rises, and finally invert carefully just prior to transfer to the volumetric flask. Transfer an accurately weighed quantity of Lotion, freshly mixed but free from air bubbles, equivalent to about 10 mg of hydrocortisone, to a 40-mL beaker, and add about 30 mL of alcohol. Warm gently until the Lotion is dispersed, and cool to room temperature. Quantitatively transfer the mixture, filter through a pledget of cotton previously moistened with alcohol to a 100-mL volumetric flask, rinse the beaker with two 20-mL portions of alcohol, and collect the washings in the same volumetric flask. Dilute with alcohol to volume, and mix. Quantitatively dilute a known volume of this solution with an equal volume of water to obtain the Assay preparation.
System suitability preparation—
Dissolve about 5 mg of propylparaben in 100 mL of alcohol. Dilute 1 mL of this solution with the Standard preparation to 10 mL, 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 the
System suitability preparation, and record the peak responses as directed for
Procedure: the column efficiency determined from the analyte peak is not less than 1000 theoretical plates, the tailing factor for the analyte peak is not more than 1.2, the resolution,
R, between the propylparaben and hydrocortisone peaks is not less than 2.0, and the relative standard deviation for replicate injections of the
Standard preparation is not more than 3.0%.
Procedure—
Separately inject equal volumes (about 20 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 hydrocortisone (C
21H
30O
5) in the portion of Lotion taken by the formula:
200C(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Hydrocortisone RS in the
Standard preparation; and
rU and the
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively. From the observed weight of 100 mL of the Lotion, calculate the quantity of C
21H
30O
5 in each 100 mL.
