Packaging and storage— Preserve in tight containers, protected from light.

USP Reference standards 11—
USP Tretinoin RS.

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.

Minimum fill 755: meets the requirements.

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 C20H28O2 in the portion of Gel taken by the formula: 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.

Topic/Question	Contact	Expert Committee
Monograph	Feiwen Mao, M.S. Scientist 1-301-816-8320	(MDOOD05) Monograph Development-Ophthalmics Oncologics and Dermatologicals
Reference Standards	Lili Wang, Technical Services Scientist 1-301-816-8129 RSTech@usp.org

USP32–NF27 Page 3780

TRETINOIN GEL

Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.