A: Evaporate 15 mL of a methylene chloride solution of it, prepared as directed under Procedure in the Assay, on a steam bath to dryness, and dissolve the residue in 1 mL of methylene chloride. Proceed as directed in Identification test B under Hydrocortisone Sodium Phosphate Injection, beginning with “Apply 5 µL of this solution.”

B: The residue from the ignition of about 20 mg of it responds to the tests for Phosphate 191 and for Sodium 191.

Standard phosphate solution— Dissolve 143.3 mg of dried monobasic potassium phosphate, KH2PO4, in water to make 1000.0 mL. This solution contains the equivalent of 0.10 mg of phosphate (PO4) in each mL.

Phosphate reagent A— Dissolve 5 g of ammonium molybdate in 1 N sulfuric acid to make 100 mL.

Phosphate reagent B— Dissolve 350 mg of p-methylaminophenol sulfate in 50 mL of water, add 20 g of sodium bisulfite, mix to dissolve, and dilute with water to 100 mL.

Procedure— Dissolve about 50 mg of Hydrocortisone Sodium Phosphate, accurately weighed, in a mixture of 10 mL of water and 5 mL of 2 N sulfuric acid contained in a 25-mL volumetric flask, by warming if necessary. Add 1 mL each of Phosphate reagent A and Phosphate reagent B, dilute with water to 25 mL, mix, and allow to stand at room temperature for 30 minutes. Similarly and concomitantly, prepare a standard solution, using 5.0 mL of Standard phosphate solution instead of the 50 mg of the substance under test. Concomitantly determine the absorbances of both solutions in 1-cm cells at 730 nm, with a suitable spectrophotometer, using water as the blank. The absorbance of the test solution is not more than that of the standard solution. The limit is 1.0% of phosphate (PO4).

1000WU (1 L / 100) / WS

Specific rotation 781S : between +121 and +129, determined in a solution prepared by weighing accurately 5.0 mL of Test preparation and diluting with pH 7.0 phosphate buffer (see Buffer Solutions in the section Reagents, Indicators, and Solutions) to 50.0 mL.

pH 791 : between 7.5 and 10.5, in a solution prepared by diluting a portion of Test preparation with 9 volumes of carbon dioxide-free water.

Free hydrocortisone— Dilute 1 mL of Test preparation with carbon dioxide-free water to 100 mL. Pipet 5 mL of this solution into a glass-stoppered, 50-mL tube, add 25.0 mL of methylene chloride, insert the stopper, and mix by gentle shaking. Prepare a 1 in 500,000 solution of USP Hydrocortisone RS in methylene chloride. Similarly, shake 25 mL of this solution with 5 mL of water. Allow to stand until the methylene chloride layers are clear (about 5 minutes). Determine the absorbances of the methylene chloride solutions in 1-cm cells at 239 nm, with a suitable spectrophotometer, using methylene chloride as the blank. The absorbance of the Test preparation does not exceed that of the Standard solution (1.0%).

pH 9 buffer with magnesium— Mix 3.1 g of boric acid and 500 mL of water in a 1-liter volumetric flask, add 21 mL of 1 N sodium hydroxide and 10 mL of 0.1 M magnesium chloride, dilute with water to volume, and mix.

Alkaline phosphatase solution— Transfer 250 mg of alkaline phosphatase enzyme to a 25-mL volumetric flask, and dissolve by diluting with pH 9 buffer with magnesium to volume. Prepare this solution fresh daily.

Standard preparation— Dissolve about 50 mg of USP Hydrocortisone Phosphate Triethylamine RS, accurately weighed, in carbon dioxide-free water to make 25.0 mL.

Assay preparation— Weigh accurately, in g, 2.0 mL of the Test preparation, prepared as directed under Specific rotation, pH, and Free hydrocortisone, into a tared 100-mL volumetric flask, and dilute with carbon dioxide-free water that has been saturated with methylene chloride to volume. Pipet 10 mL of this solution into a 125-mL separator, and extract with two 25-mL portions of water-washed methylene chloride, discarding the washings.

Procedure— Weigh accurately 1.0 mL each of the Standard preparation (WS) and the Assay preparation (WA) into separate tared 100-mL volumetric flasks. To each flask, and to a similar flask containing 1.0 mL of water to provide a blank, add 1.0 mL of Alkaline phosphatase solution and then 50 mL of methylene chloride, and insert the stopper. Allow the flasks to stand at room temperature (not below 25) for 2 hours with gentle mixing about every 15 minutes. Add 1 mL of dilute hydrochloric acid (1 in 10) to each flask, and mix gently. Add methylene chloride to each flask until the interfaces are at the 100-mL marks, and mix gently. Remove the aqueous layers by aspiration. Determine the absorbances of the methylene chloride solutions obtained from the Standard preparation and the Assay preparation at 239 nm, with a suitable spectrophotometer, using the methylene chloride solution blank to set the instrument. Calculate the percentage of C21H29Na2O8P, on the dried basis, taken by the formula: in which AU and AS are the absorbances of the solutions from the Assay preparation and the Standard preparation, respectively; CA and CS are the corresponding concentrations, in mg per mL, of those preparations; and 0.895 is the ratio of the molecular weight of hydrocortisone sodium phosphate to that of hydrocortisone phosphate triethylamine.