Identification—
Place about 25 mL of the stock solution, prepared as directed in the
Assay, in a 50-mL beaker, and evaporate on a steam bath with the aid of a current of filtered air to dryness. Dry the residue at 105
for 10 minutes: the IR absorption spectrum of a potassium bromide dispersion of it so obtained exhibits maxima only at the same wavelengths as that of a similar preparation of
USP Miconazole Nitrate RS.
Assay—
Buffer solution—
Transfer 10 mL of triethylamine to a suitable flask, dilute with 1000 mL of water, adjust with phosphoric acid to a pH of 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 Suitablility under
Chromatography 
621
).
Standard preparation—
Dissolve an accurately weighed quantity of
USP Miconazole Nitrate RS and benzoic acid in
Mobile phase, and dilute quantitatively, and stepwise if necessary, with
Mobile phase to obtain a solution having a known concentration of about 0.28 and 0.02 mg per mL for miconazole nitrate and benzoic acid, respectively.
Assay preparation—
Transfer an accurately weighed quantity of Cream, equivalent to about 14 mg of miconazole nitrate, to a 50-mL volumetric flask, dissolve in and dilute with
Mobile phase to volume, and mix. Sonicate in a water bath at 40
to 45
until 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 HPLC vial.
Chromatographic system (see Chromatography 621)—
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 1.0 mL per 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 7500 theoretical 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 10 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 nitrate (C
18H
14Cl
4N
2O·HNO
3) in the portion of Cream taken by the formula:
50C(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Miconazole Nitrate RS in the
Standard preparation; and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
