The UV absorption spectrum of the solution employed for measurement of absorbance in the Assay
exhibits maxima and minima at the same wavelengths as that of a similar solution of USP Tolnaftate RS
, concomitantly measured.
Prepare a test solution by dissolving 10 mg in 10 mL of alcohol. Apply 10 µL of this test solution and 10 µL of a Standard solution of USP Tolnaftate RS
in alcohol having a concentration of 1.0 mg per mL to a thin-layer chromatographic plate (see Chromatography 621
) coated with a 0.25-mm layer of chromatographic silica gel mixture. Allow the spots to dry, and develop the chromatogram, using toluene as the solvent system, until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, allow the solvent to evaporate, and view under short-wavelength UV light: the RF
value of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.
Dissolve about 50 mg of Tolnaftate, accurately weighed, in methanol, and dilute the solution quantitatively and stepwise with methanol to obtain a concentration of about 10 µg per mL. Dissolve an accurately weighed quantity of USP Tolnaftate RS
in methanol, and dilute quantitatively and stepwise with methanol to obtain a Standard solution having a known concentration of about 10 µg per mL. Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 258 nm, with a suitable spectrophotometer, using methanol as the blank. Calculate the quantity, in mg, of C19
NOS in the portion of Tolnaftate taken by the formula:
5C(AU / AS),
in which C
is the concentration, in µg per mL, of USP Tolnaftate RS
in the Standard solution, and AU
are the absorbances of the solution of Tolnaftate and the Standard solution, respectively.