Solvent mixture— Mix chloroform and methanol (4:1).

Internal standard solution— Prepare a solution of 1-nonyl alcohol in Solvent mixturecontaining about 1.75mg per mL.

Standard preparation— Dilute an accurately weighed quantity of benzyl alcohol,quantitatively and stepwise,with Solvent mixtureto obtain a solution having a known concentration of about 2mg per mL.Transfer 5.0mLof this solution and 5.0mLof Internal standard solutionto a 50-mLvolumetric flask,dilute with Solvent mixtureto volume,and mix.

Test preparation— Transfer 1.0g of Cream to a 50-mLvolumetric flask,add about 30mLof Solvent mixture,and mix.Add 5.0mLof Internal standard solution,dilute with Solvent mixtureto volume,and mix to obtain a clear solution.

Chromatographic system(see Chromatography á621ñ)— The gas chromatograph is equipped with a flame-ionization detector and contains a 2-m ×4-mm glass column packed with 3%phase G3on 100-to 120-mesh support S1AB.The column is maintained at a temperature of about 100,the injection port and detector temperatures are maintained at about 315,and nitrogen is used as the carrier gas at a flow rate of about 45mLper minute.

Procedure— Separately inject equal volumes (about 2µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.In a suitable chromatogram,the resolution,R,between the peaks is not less than 1.6,the tailing factor for the benzyl alcohol peak and the internal standard peak is not greater than 3.5,and the relative standard deviation of the peak response ratios,RS,from replicate injections of the Standard preparationis not more than 3%.[NOTE—After 6injections,raise the column temperature to about 300for about 5minutes,then cool to 100.]Calculate the percentage of benzyl alcohol in the Cream taken by the formula: in which Cis the concentration,in mg per mL,of benzyl alcohol in the Standard preparation;and RUand RSare the peak response ratios of the benzyl alcohol peak to the internal standard peak obtained from the Test preparationand the Standard preparation,respectively:between 90.0%and 110.0%of the claimed amount is present.

Ferrous sulfate solution— Transfer 600mg of ferrous sulfate to a 25-mLvolumetric flask.Add 0.6mLof glacial acetic acid,dilute with water to volume,and mix.

Standard preparation— Dissolve an accurately weighed quantity of USP Ciclopirox Olamine RSin methanol to obtain a solution having a known concentration of about 0.2mg per mL.

Assay preparation— Transfer an accurately weighed quantity of Cream,equivalent to about 10mg of ciclopirox olamine,to a 50-mLvolumetric flask,add 25mLof methanol,and shake by mechanical means for about 10minutes.Dilute with methanol to volume,mix,centrifuge,and use the supernatant.

Procedure— Transfer 4.0mLof the Standard preparation,4.0mLof the Assay preparation,and 4.0mLof methanol to provide a blank,to separate 25-mLvolumetric flasks.Add 15mLof methanol to each flask,and mix.Then to each flask add 1.0mLof Ferrous sulfate solution,mix,dilute with methanol to volume,and mix.Store the flasks in the dark for 1hour.Concomitantly determine the absorbances of the solutions from the Assay preparationand the Standard preparationagainst the blank in 1-cm cells at the wavelength of maximum absorbance at about 440nm,with a suitable spectrophotometer.Calculate the quantity,in mg,of ciclopirox olamine (C12H17NO2·C2H7NO)in each g of the Cream taken by the formula: in which Cis the concentration,in mg per mL,of USP Ciclopirox Olamine RSin the Standard preparation;Wis the weight,in g,of Cream taken;and AUand ASare the absorbances of the solutions from the Assay preparationand the Standard preparation,respectively.