Anhydrous dibasic sodium phosphate
Ammonium molybdate reagent
Dissolve 6.4g of ammonium molybdate in 40mLof water,and add 50mLof 10Nsulfuric acid.Mix,and dilute with water to 100mL.This solution is stable for about 2weeks.
Stannous chloride reagent
Dissolve 1g of stannous chloride in 5mLof hydrochloric acid.Just prior to use,dilute 1mLof this solution with water to 100mL.
Standard preparation
Weigh accurately about 275mg of anhydrous dibasic sodium phosphate (Na2HPO4)into a 1000-mLvolumetric flask.Dissolve in and dilute with water to volume.Dilute 10mLof this solution with water to 100mL.
Test preparation
Pipet 1mLof the well-shaken Injectable Suspension into a 25-mLvolumetric flask,add 0.1mLof 10Nsulfuric acid,mix,dilute with water to volume,and again mix.
Procedure
Into separate 100-mLvolumetric flasks pipet duplicate 10-mLportions of
Test preparation,duplicate 10-mLportions of
Standard preparation,and 10mLof water to provide a blank.Treat each flask as follows.Dilute the contents with water to 60mL,then add 10mLof 10Nsulfuric acid,and mix.Add 10mLof
Ammonium molybdate reagent,mix,add 10mLof water,and again mix.Add slowly,with mixing,5mLof
Stannous chloride reagent,dilute with water to volume,and mix.Measure the absorbances of the solutions at 10minutes,accurately timed,after the first addition of the
Stannous chloride reagent,at a wavelength of 710nm,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
Cis the concentration,in µg per mL,of Na
2HPO
4in the
Standard preparation;and
AUand
ASare the absorbances of the solutions from the
Test preparationand the
Standard preparation,respectively.
Assay
Add sufficient 0.1Nhydrochloric acid to Injectable Suspension to effect complete solution,and using this in making the
Assay preparation,proceed as directed in the
Assayunder
Corticotropin Injection.