Dragendorff's reagent— Dissolve 0.85 g of bismuth subnitrate in a mixture of 40 mL of water and 10 mL of glacial acetic acid (Solution A). Dissolve 8 g of potassium iodide in 20 mL of water (Solution B). Transfer 5 mL of Solution A, 5 mL of Solution B, and 20 mL of glacial acetic acid to a 100-mL volumetric flask, dilute with water to volume, and mix.

Procedure— Transfer a volume of Injection, equivalent to about 50 mg of miconazole, to a 10-mL volumetric flask, dilute with methanol to volume, and mix. Dissolve a suitable quantity of USP Miconazole RS in methanol to obtain a Standard solution having a known concentration of about 5 mg per mL. Apply separate 5-µL portions of the two solutions to the starting line of a suitable thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Develop the chromatogram in a suitable chamber with a freshly prepared solvent system consisting of a mixture of n-hexane, chloroform, methanol, and ammonium hydroxide (60:30:10:1) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the chamber, and allow the solvent to evaporate. Locate the spots on the plate by spraying with Dragendorff's reagent: the RF value of one of the principal spots obtained from the test solution corresponds to that obtained from the Standard solution.

Mobile phase— Dissolve 5.0 g of ammonium acetate in 200 mL of water, add 300 mL of acetonitrile and 500 mL of methanol, mix, filter, and degas. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Miconazole RS in Mobile phase and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.5 mg per mL. Transfer 10.0 mL of this solution to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix to obtain a Standard preparation having a known concentration of about 50 µg per mL.

Resolution solution— Dissolve suitable quantities of USP Miconazole RS and dibutyl phthalate in Mobile phase to obtain a solution containing about 50 µg of each per mL.

Assay preparation— Transfer an accurately measured volume of Injection, equivalent to about 50 mg of miconazole, to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix. Transfer 10.0 mL of this solution to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 230-nm detector and a 4.6-mm × 30-cm column that contains packing L7. The flow rate is about 2 mL per minute. Chromatograph the Resolution solution and the Standard preparation, and record the peak responses as directed under Procedure: the resolution, R, between the dibutyl phthalate and miconazole peaks is not less than 5.0, the tailing factor for the miconazole peak is not more than 1.3, and the relative standard deviation for replicate injections of the Standard preparation is not more than 2.0%. The relative retention times are about 0.7 for dibutyl phthalate and 1.0 for miconazole.

Procedure— [note—Allow the chromatograph to run for at least 16 to 18 minutes between injections to allow for elution of all components associated with the Injection vehicle.] Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of miconazole (C18H14Cl4N2O) in each mL of the Injection taken by the formula: in which C is the concentration, in µg per mL, of USP Miconazole RS in the Standard preparation, V is the volume, in mL, of Injection taken, and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.