Identification—
Transfer a portion of Topical Powder, equivalent to about 100 mg of miconazole nitrate to a 50-mL beaker, disperse in 40 mL of methanol, and mix for a minimum of 5 minutes. Allow to settle for 5 to 10 minutes, and filter into a 100-mL beaker. Evaporate on a steam bath to dryness. Dry the residue at 105
for 10 minutes: the IR absorption spectrum of a potassium bromide dispersion of the residue so obtained exhibits maxima only at the same wavelengths as that of a similar preparation of
USP Miconazole Nitrate RS.
Assay—
Internal standard solution—
Dissolve cholestane in chloroform to obtain a solution having a concentration of about 0.5 mg per mL.
Standard preparation—
Dissolve an accurately weighed quantity of
USP Miconazole Nitrate RS in a mixture of chloroform and methanol (1:1) to obtain a solution having a known concentration of about 0.8 mg per mL. Transfer 5.0 mL of this solution to a test tube, add 2.0 mL of
Internal standard solution, and evaporate at a temperature not higher than 40
with the aid of a current of nitrogen to dryness. Dissolve the residue in 2.0 mL of a mixture of chloroform and methanol (1:1), and mix to obtain a
Standard preparation having a known miconazole nitrate concentration of about 2 mg per mL.
Assay preparation—
Transfer an accurately weighed portion of Topical Powder, equivalent to about 20 mg of miconazole nitrate, to a stoppered 50-mL centrifuge tube. Add 25.0 mL of methanol, and shake by mechanical means for 30 minutes to dissolve the miconazole nitrate. Centrifuge to obtain a clear supernatant. Transfer 5.0 mL of this solution to a test tube, add 2.0 mL of
Internal standard solution, and evaporate at a temperature not higher than 40
with the aid of a current of nitrogen to dryness. Dissolve the residue in 2.0 mL of a mixture of chloroform and methanol (1:1).
Chromatographic system
(see
Chromatography 
621
)—The gas chromatograph is equipped with a flame-ionization detector and a 1.2-m × 2-mm glass column containing 3 percent phase G32 on support S1A. The injection port, detector, and column are maintained at temperatures of about 250
, 300
, and 250
, respectively. Helium is used as the carrier gas, at a flow rate of about 50 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed under
Procedure: the resolution,
R, between the cholestane and miconazole nitrate peaks is not less than 2.0, and the relative standard deviation for replicate injections is not more than 3.0%.
Procedure—
Separately inject equal volumes (about 5 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times for cholestane and miconazole nitrate are about 0.5 and 1.0, respectively. Calculate the quantity, in mg, of miconazole nitrate (C
18H
14Cl
4N
2O·HNO
3) in the portion of Topical Powder taken by the formula:
10C(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 response ratios of the miconazole nitrate peak to the cholestane peak obtained from the
Assay preparation and the
Standard preparation, respectively.
