Identification—
Evaporate the 5-mL portion of the methanol solution, reserved from the
Assay preparation, on a steam bath just to dryness, and dissolve the residue in 1 mL of alcohol. Using this as the test solution, proceed as directed in
Identification test
C under
Tolnaftate: the specified result is observed.
Assay—
Mobile phase—
Prepare a filtered and degassed mixture of acetonitrile and water (2:1). Make adjustments if necessary (see
System Suitability under
Chromatography 
621
).
Internal standard solution—
Dissolve progesterone in methanol to obtain a solution containing about 1 mg per mL.
Standard preparation—
Dissolve an accurately weighed quantity of
USP Tolnaftate RS in methanol to obtain a solution having a known concentration of about 0.22 mg per mL. Transfer 20.0 mL of this solution to a 50-mL volumetric flask, add 5.0 mL of
Internal standard solution, dilute with methanol to volume, and mix to obtain a solution having a known concentration of about 0.088 mg of
USP Tolnaftate RS per mL.
Assay preparation—
Transfer an accurately weighed quantity of Topical Powder, equivalent to about 5 mg of tolnaftate, to a screw-capped, 50-mL centrifuge tube. Add 25.0 mL of methanol, place the cap on the tube, rotate on a rotating device for 10 minutes, and centrifuge at about 2000 rpm for 5 minutes. Pass the supernatant through a 0.45-µm porosity filter, and transfer 20.0 mL of the filtrate to a 50-mL volumetric flask, retaining the remaining portion of the filtrate (about 5 mL) for the
Identification test. Add 5.0 mL of
Internal standard solution to the volumetric flask, dilute with methanol to volume, and mix.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4-mm × 30-cm column that contains 10-µm packing L1. The flow rate is about 1 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the resolution,
R, between the analyte and internal standard peaks is not less than 3.0, and the relative standard deviation for replicate injections is not more than 3.0%.
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. The relative retention times are about 0.7 for progesterone and 1.0 for tolnaftate. Calculate the quantity, in mg, of C
19H
17NOS in the portion of Powder taken by the formula:
62.5C(RU / RS),
in which
C is the concentration, in mg per mL, of
USP Tolnaftate RS in the
Standard preparation, and
RU and
RS are the peak response ratios obtained from the
Assay preparation and the
Standard preparation, respectively.
