Buffer solution— Transfer 10mLof triethylamine to a suitable flask,dilute with 1000mLof water,adjust with phosphoric acid to a pHof about 2.5,and mix.

Mobile phase— Prepare a filtered and degassed mixture of Buffer solution,methanol,acetonitrile,and tetrahydrofuran (8:5:4:3).Make adjustments if necessary (see System Suitablilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Miconazole Nitrate RSand benzoic acid in Mobile phase,and dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having a known concentration of about 0.28and 0.02mg per mLfor miconazole nitrate and benzoic acid,respectively.

Assay preparation— Transfer an accurately weighed quantity of Cream,equivalent to about 14mg of miconazole nitrate,to a 50-mLvolumetric flask,dissolve in and dilute with Mobile phaseto volume,and mix.Sonicate in a water bath at 40to 45until the sample is completely dispersed,and mix.Cool the solution to below room temperature,mix,and pass a portion of the solution through a 0.45-µm teflon filter into an HPLCvial.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 225-nm detector and 4.6-mm ×25-cm column that contains packing L11.The flow rate is about 1.0mLper minute.The column temperature is maintained at 45.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the column efficiency for miconazole nitrate peak is not less than 7500theoretical plates;the tailing factor for miconazole nitrate peak is not more than 2.0;and the relative standard deviation for replicate injections of miconazole nitrate is not more than 2.0%.The resolution between miconazole nitrate and benzoic acid is not less than 13.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of miconazole nitrate (C18H14Cl4N2O·HNO3)in the portion of Cream taken by the formula: in which Cis the concentration,in mg per mL,of USP Miconazole Nitrate RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.