A: Prepare a Standard solution as directed for Standard preparationin the Assay,except to use 1.0mLof pyridine instead of the Internal standard solution,and chromatograph as directed in the Assay:the chromatogram of the Assay preparationobtained in the Assayexhibits 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 25mg of clioquinol,in a 100-mLvolumetric flask,add about 75mLof dilute hydrochloric acid (1in 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 (1in 4)to volume.Filter through paper,and dilute 3mLof the filtrate with dilute hydrochloric acid (1in 4)to 100mL:the UVabsorption spectrum of this solution exhibits maxima and minima at the same wavelengths as that of a similar solution of USP Clioquinol RS,concomitantly measured.

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

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

Procedure— Proceed as directed for Procedurein the Assayunder Clioquinol.Calculate the quantity,in mg,of C9H5ClINOin the portion of Cream taken by the formula: in which Cis the concentration,in mg per mL,of USP Clioquinol RSin the Standard solution used to prepare the Standard preparation,and RUand RSare the ratios of the peak responses of the clioquinol peak to the internal standard peak obtained from the Assay preparationand the Standard preparation,respectively.