Identification—
The absorption spectrum,obtained between wavelengths of 300nm and 450nm,of the solution employed for measurement of absorbance in the
Assayexhibits 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-mLvolumetric flask an accurately weighed quantity of Gel,equivalent to about 375µg of tretinoin,and dissolve in about 70mLof chloroform,dilute with chloroform to volume,and mix.Dissolve an accurately weighed quantity of
USP Tretinoin RSin chloroform,and dilute quantitatively and stepwise with chloroform to obtain a Standard solution having a known concentration of about 3.75µg per mL.Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 365nm,with a suitable spectrophotometer,using chloroform as the blank.Calculate the quantity,in µg,of C
20H
28O
2in the portion of Gel taken by the formula:
100C(AU/AS),
in which
Cis the concentration,in µg per mL,of
USP Tretinoin RSin the Standard solution,and
AUand
ASare the absorbances of the solution from the Gel and the Standard solution,respectively.