Packaging and storage— Preserve in well-closed,light-resistant containers.

USP Reference standards á11ñ— USP Clioquinol RS.

Identification— Place a quantity of Topical Powder,equivalent to about 30mg of clioquinol,in a glass-stoppered,50-mLconical flask,add 20mLof 1Nsulfuric acid,and shake for 5minutes.Filter,transfer 5mLof the filtrate to a glass-stoppered test tube,add 5drops of potassium dichromate TSand 2mLof chloroform,and shake well:a red-violet color develops in the chloroform layer.

Assay— Transfer an accurately weighed quantity of Topical Powder,equivalent to about 50mg of clioquinol,to a 200-mLvolumetric flask,add 100mLof 3Nhydrochloric acid,and shake by mechanical means for 15minutes.Dilute with 3Nhydrochloric acid to volume,and mix.Filter a portion of the solution,dilute 4.0mLof the filtrate with 3Nhydrochloric acid to 200.0mL,and mix.Concomitantly determine the absorbances of this solution and of a Standard solution of USP Clioquinol RSin the same medium having a known concentration of about 5µg per mLin 1-cm cells at the wavelength of maximum absorbance at about 267nm,with a suitable spectrophotometer,using 3Nhydrochloric acid as the blank.Calculate the quantity,in mg,of C9H5ClINOin the portion of Topical Powder taken by the formula: in which Cis the concentration,in µg per mL,of USP Clioquinol RSin the Standard solution,and AUand ASare the absorbances of the solution from the Topical Powder and the Standard solution,respectively.

Expert Committee:(PA7)Pharmaceutical Analysis 7

USP28–NF23Page 500

Phone Number:1-301-816-8394