Identification—
The absorption spectrum, obtained between wavelengths of 300 nm and 450 nm, 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 Tretinoin RS, concomitantly measured.
Assay—
[NOTE—Avoid exposure to strong light, and use low-actinic glassware in the performance of the following procedure.
] Transfer to a 100-mL volumetric flask an accurately weighed quantity of Gel, equivalent to about 375 µg of tretinoin, and dissolve in about 70 mL of chloroform, dilute with chloroform to volume, and mix. Dissolve an accurately weighed quantity of
USP Tretinoin RS in chloroform, and dilute quantitatively and stepwise with chloroform to obtain a Standard solution having a known concentration of about 3.75 µg per mL. Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 365 nm, with a suitable spectrophotometer, using chloroform as the blank. Calculate the quantity, in µg, of C
20H
28O
2 in the portion of Gel taken by the formula:
100C(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Tretinoin RS in the Standard solution, and
AU and
AS are the absorbances of the solution from the Gel and the Standard solution, respectively.
755
:
meets the requirements.