Identification—
A:
Mix 5 mL of Topical Solution with 5 mL of water: a voluminous yellow precipitate is formed.
B:
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 Topical Solution, equivalent to about 375 µg of tretinoin, dilute with acidified isopropyl alcohol (prepared by mixing 1 mL of 0.01 N hydrochloric acid with isopropyl alcohol to make 1000 mL of solution) to volume, and mix. Dissolve an accurately weighed quantity of
USP Tretinoin RS in the acidified isopropyl alcohol, and dilute quantitatively and stepwise with the same solvent 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 352 nm, with a suitable spectrophotometer, using the acidified isopropyl alcohol as the blank. Calculate the quantity, in µg, of C
20H
28O
2 in the portion of Topical Solution 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 Topical Solution and the Standard solution, respectively.
467
:
meets the requirements.