Tolnaftate Topical Solution »Tolnaftate Topical Solution contains not less than 90.0percent and not more than 115.0percent of the labeled amount of C19H17NOS. Packaging and storage— Preserve in tight containers. USP Reference standards á11ñ USP Tolnaftate RS. Identification— Evaporate 25mLof the next-to-final chloroform solution prepared in the Assayon a steam bath just to dryness,and dissolve the residue in 1mLof alcohol.Using this as the test solution,proceed as directed in Identificationtest Cunder Tolnaftate:the specified result is observed. Assay— Pipet into a separator a volume of Topical Solution,equivalent to about 10mg of tolnaftate,add 50mLof chloroform,and extract with 50mLof 0.1Nsodium hydroxide.Filter the chloroform layer through a chloroform-washed cotton pledget into a 250-mLvolumetric flask,and extract the aqueous layer with two 45-mLportions of chloroform,filtering each portion into the flask.Add chloroform to volume,and mix.[NOTE—Reserve a 25-mLportion of this solution for the Identificationtest.]Dilute 25.0mLof the solution with chloroform to 100.0mL,and mix.Dissolve an accurately weighed quantity of USP Tolnaftate RSin chloroform,and dilute quantitatively and stepwise with chloroform to obtain a Standard solution having a known concentration of about 10µg per mL.Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 258nm,with a suitable spectrophotometer,using chloroform as the blank.Calculate the quantity,in mg,of C19H17NOSin each mLof Topical Solution taken by the formula: (C/V)(AU/AS), in which Cis the concentration,in µg per mL,of USP Tolnaftate RSin the Standard solution,Vis the volume,in mL,of Topical Solution taken,and AUand ASare the absorbances of the solution from the Topical Solution and the Standard solution,respectively. Auxiliary Information— Staff Liaison:Behnam Davani,Ph.D.,MBA,Senior Scientist Expert Committee:(PA7)Pharmaceutical Analysis 7 USP28–NF23Page 1952 Phone Number:1-301-816-8394