A: The chromatogram of the Assay preparation obtained as directed in the Assay for clioquinol exhibits a peak for clioquinol, the retention time of which corresponds to that exhibited by the Standard preparation.

B: The chromatogram of the Assay preparation obtained as directed in the Assay for hydrocortisone exhibits a peak for hydrocortisone, the retention time of which corresponds to that exhibited by the Standard preparation.

(Official January 1, 2007)

Internal standard solution , Standard solution, Standard preparation, and Chromatographic system—Prepare as directed in the Assay for clioquinol under Clioquinol and Hydrocortisone Cream.

Assay preparation— Transfer an accurately weighed quantity of Ointment, equivalent to about 150 mg of clioquinol, to a 125-mL separator. Add 75 mL of n-hexane, insert the stopper in the separator, and mix until the specimen is completely dispersed. Extract with 25 mL of dimethylformamide, collecting the extract in a 50-mL volumetric flask. Repeat the extraction with two 10-mL portions of dimethylformamide, collecting the extracts in the 50-mL volumetric flask, dilute with dimethylformamide to volume, and mix. Transfer 1.0 mL of this solution to a suitable size screw-capped vial, and evaporate the solution with the aid of nitrogen at about 60 to dryness. Dissolve the residue in 1.0 mL of a mixture of pyridine and hexane (4:1), and pipet 1.0 mL of N,O-bis(trimethylsilyl)acetamide and 1.0 mL of Internal standard solution into the glass vial, fitted with a polytef-lined septum, securely close, and mix. Heat the vial on a water bath at 50 for 15 minutes, and cool to room temperature.

Procedure— Proceed as directed for Procedure in the Assay for clioquinol under Clioquinol and Hydrocortisone Cream. Calculate the quantity, in mg, of C9H5ClINO in the portion of Ointment taken by the formula: in which C is the concentration, in mg per mL, of USP Clioquinol RS in the Standard preparation; and RU and RS are the peak response ratios obtained from the Assay preparation and the Standard preparation, respectively.

Mobile phase, Standard preparation, Resolution solution, and Chromatographic system— Prepare as directed in the Assay for hydrocortisone under Clioquinol and Hydrocortisone Cream.

Assay preparation— Transfer an accurately weighed quantity of Ointment, equivalent to about 10 mg of hydrocortisone, to a 50-mL centrifuge tube. Add 30 mL of alcohol and heat on a steam bath just to boiling. Shake for 15 minutes, and centrifuge. Quantitatively transfer the supernatant extract to a 100-mL volumetric flask. Repeat the extraction with two 20-mL portions of alcohol, combining the extracts in the 100-mL volumetric flask. Add alcohol to volume, mix, and filter.

Procedure— Proceed as directed for Procedure in the Assay for hydrocortisone under Clioquinol and Hydrocortisone Cream. Calculate the quantity, in mg, of C21H30O5 in the portion of Ointment taken by the formula: in which C is the concentration, in µg per mL, of USP Hydrocortisone RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.