A: Prepare a Standard solution as directed for Standard preparation in the Assay, except to use 1.0 mL of pyridine instead of the Internal standard solution, and chromatograph as directed in the Assay: the chromatogram of the Assay preparation obtained in the Assay exhibits a peak for clioquinol, the retention time of which corresponds with that exhibited by the Standard solution.

B: Place a quantity of Cream, equivalent to about 25 mg of clioquinol, in a 100-mL volumetric flask, add about 75 mL of dilute hydrochloric acid (1 in 4), and heat on a steam bath to melt the cream, shaking vigorously to extract the clioquinol. Cool under running water, and add dilute hydrochloric acid (1 in 4) to volume. Filter through paper, and dilute 3 mL of the filtrate with dilute hydrochloric acid (1 in 4) to 100 mL: the UV absorption spectrum of this solution exhibits maxima and minima at the same wavelengths as that of a similar solution of USP Clioquinol RS, concomitantly measured.

(Official January 1, 2007)

Internal standard solution, Standard preparation, and Chromatographic system— Proceed as directed in the Assay under Clioquinol.

Assay preparation— Transfer an accurately weighed portion of Cream, equivalent to about 150 mg of clioquinol, to a 60-mL separator. Place the separator on its side in a vacuum oven at a pressure of about 10 mm of mercury at 45 for 4 hours. Remove the separator from the oven, allow to cool, add 15 mL of a mixture of pyridine and n-hexane (4:1), insert a polytef stopper, and mix. Transfer the mixture to a 50-mL volumetric flask, and rinse the separator with two 15-mL portions of the same solvent, shaking each time for 30 seconds. Transfer both rinsings to the volumetric flask, dilute with the same solvent to volume, and mix. Transfer 1.0 mL to a screw-capped glass vial fitted with a septum, add 1.0 mL of bis(trimethylsilyl)acetamide and 1.0 mL of Internal standard solution, attach the cap, and mix.

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