Assay
Transfer an accurately measured volume of previously well-mixed Injectable Suspension, equivalent to about 100 mg of testosterone, to a fine-porosity, sintered-glass filtering crucible, previously dried at 105
for 1 hour, and filter with suction. If the filtrate is not clear, again pass it through the same filter into a second receiver. Wash the residue in the filter with several 5-mL portions of water until 2 mL of the last washing, when evaporated on a steam bath, leaves a negligible residue.
[NOTEIf the Injectable Suspension is passed through the filter twice, rinse the first receiver with the portions of water before passing them through the filter.
] Dry the crucible and the collected testosterone at 105
for 1 hour. Completely dissolve the testosterone with five 25-mL portions of methanol, passing each portion through the crucible under gentle suction, and transfer the combined methanol solution to a 200-mL volumetric flask. Rinse the crucible and receiver with two 25-mL portions of methanol, add the rinsings to the main solution, dilute with methanol to volume, and mix. Transfer 5.0 mL of this solution to a 250-mL volumetric flask, dilute with methanol to volume, and mix. Concomitantly determine the absorbances of this solution and a Standard solution of
USP Testosterone RS, in the same medium having a known concentration of about 10 µg per mL in 1-cm cells at the wavelength of maximum absorbance at about 241 nm, with a suitable spectrophotometer, using methanol as the blank. Calculate the quantity, in mg, of C
19H
28O
2 in each mL of the Injectable Suspension taken by the formula:
(10C / V)(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Testosterone RS in the Standard solution,
V is the volume, in mL, of Injectable Suspension taken, and
AU and
AS are the absorbances of the solution from the Injectable Suspension and the Standard solution, respectively.