Zinc—
Pipet a volume of the well-shaken Injectable Suspension, equivalent to about 6 mg of zinc, into a 125-mL conical flask, and add 2 mL of a buffer mixture containing 5.4 g of ammonium chloride and 26 mL of ammonium hydroxide in each 100 mL. Add 10 mL of water and 2 drops of
eriochrome black TS, and titrate with 0.005
M edetate disodium VS to a clear blue endpoint. Perform a blank titration, and make any necessary correction. Each mL of 0.005
M edetate disodium is equivalent to 0.327 mg of Zn.
Anhydrous dibasic sodium phosphate—
Ammonium molybdate reagent—
Dissolve 6.4 g of ammonium molybdate in 40 mL of water, and add 50 mL of 10 N sulfuric acid. Mix, and dilute with water to 100 mL. This solution is stable for about 2 weeks.
Stannous chloride reagent—
Dissolve 1 g of stannous chloride in 5 mL of hydrochloric acid. Just prior to use, dilute 1 mL of this solution with water to 100 mL.
Standard preparation—
Weigh accurately about 275 mg of anhydrous dibasic sodium phosphate (Na2HPO4) into a 1000-mL volumetric flask. Dissolve in and dilute with water to volume. Dilute 10 mL of this solution with water to 100 mL.
Test preparation—
Pipet 1 mL of the well-shaken Injectable Suspension into a 25-mL volumetric flask, add 0.1 mL of 10 N sulfuric acid, mix, dilute with water to volume, and again mix.
Procedure—
Into separate 100-mL volumetric flasks pipet duplicate 10-mL portions of
Test preparation, duplicate 10-mL portions of
Standard preparation, and 10 mL of water to provide a blank. Treat each flask as follows. Dilute the contents with water to 60 mL, then add 10 mL of 10 N sulfuric acid, and mix. Add 10 mL of
Ammonium molybdate reagent, mix, add 10 mL of water, and again mix. Add slowly, with mixing, 5 mL of
Stannous chloride reagent, dilute with water to volume, and mix. Measure the absorbances of the solutions at 10 minutes, accurately timed, after the first addition of the
Stannous chloride reagent, at a wavelength of 710 nm, with a suitable spectrophotometer, relative to the blank. Calculate the quantity, in µg, of anhydrous dibasic sodium phosphate in the portion of Injectable Suspension taken by the formula:
25C(AU / AS),
in which
C is the concentration, in µg per mL, of Na
2HPO
4 in the
Standard preparation; and
AU and
AS are the absorbances of the solutions from the
Test preparation and the
Standard preparation, respectively.
Assay—
Add sufficient 0.1 N hydrochloric acid to Injectable Suspension to effect complete solution, and using this in making the
Assay preparation, proceed as directed in the
Assay under
Corticotropin Injection.
85
—
It contains not more than 3.1 USP Endotoxin Units per USP Corticotropin Unit.