pH 
791
:
between 5.5 and 7.5, in a solution, constituted as directed in the labeling, containing 10 mg of thiotepa per mL.
Assay—
Remove, as completely as possible, the contents of not less than 20 containers of Thiotepa for Injection, weigh, and mix. Transfer an accurately weighed portion of the powder, equivalent to about 75 mg of thiotepa, to a suitable container, extract with three 5-mL portions of carbon disulfide, and filter the carbon disulfide extract with the aid of vacuum. Concentrate the combined filtrates under vacuum to approximately 5 mL. Transfer the carbon disulfide solution to a 10-mL volumetric flask with the aid of a few mL of carbon disulfide, and dilute with carbon disulfide to volume (
Assay solution). Concomitantly determine the absorbances of this solution and a Standard solution of
USP Thiotepa RS in the same medium having a known concentration of about 7.5 mg per mL
(Standard solution), in 0.1-mm cells, at the wavelength of maximum absorbance at about 10.75 µm, with a suitable IR spectrophotometer, using carbon disulfide as the blank. Calculate the quantity, in mg, of thiotepa (C
6H
12N
3PS) in the portion of Thiotepa for Injection taken by the formula:
10C(AU / AS),
in which
C is the concentration, in mg per mL, of
USP Thiotepa RS in the Standard solution; and
AU and
AS are the absorbances of the
Assay solution and the
Standard solution, respectively.
