Medium: water; 500 mL.

Apparatus 1: 100 rpm.

Time: 30 minutes.

Procedure— Dilute filtered portions of the solutions under test with water to a concentration of about 25 µg per mL. Transfer 5.0-mL portions to suitable tubes. Add 1 mL of a saturated sodium carbonate solution and 2 mL of sodium metaperiodate solution (2 in 100) to each, mix, and allow to stand for 10 minutes. Add 20.0 mL of hexanes, shake for 30 seconds, and allow the phases to separate. Measure the absorbances of the hexanes extract in 1-cm cells at the wavelength of maximum absorbance, at about 242 nm, with a suitable spectrophotometer, using hexanes as the blank. Determine the amount of (C10H15NO)2·H2SO4 dissolved by comparison with a similarly treated Standard solution having a known concentration of USP Ephedrine Sulfate RS in water. Remove the contents of 1 Capsule as completely as possible, with the aid of a current of air, dissolve the empty capsule shell in the Medium, determine the absorbance at the same dilution and in the same manner as for the Capsules, and make any necessary corrections.

Tolerances— Not less than 80% (Q) of the labeled amount of (C10H15NO)2·H2SO4 is dissolved in 30 minutes.

Standard preparation— Weigh accurately about 25 mg of USP Ephedrine Sulfate RS, transfer to a 50-mL volumetric flask with the aid of 10 mL of water, add methanol to volume, and mix. Dilute 5.0 mL of this solution with water to 100.0 mL.

Assay preparation— Weigh accurately the contents of not less than 20 Capsules, and mix. Transfer an accurately weighed portion of the mixture, equivalent to about 25 mg of ephedrine sulfate, to a glass-stoppered conical flask, and add by pipet 50 mL of a 1 in 5 mixture of water in methanol. Shake by mechanical means for 10 minutes, and filter. Dilute 5.0 mL of the filtrate with water to 100.0 mL.

Procedure— Transfer 5-mL portions of the Assay preparation and the Standard preparation to separate glass-stoppered, 50-mL centrifuge tubes. Add 1 mL of saturated sodium carbonate solution and 2 mL of sodium metaperiodate solution (1 in 50) to each tube, mix, and allow to stand for 10 minutes. Pipet 20 mL of n-hexane into each tube, shake for 30 seconds, and allow the phases to separate. Concomitantly determine the absorbances of the n-hexane extracts in 1-cm cells at the wavelength of maximum absorbance at about 242 nm, with a suitable spectrophotometer, using n-hexane as the blank. Calculate the quantity, in mg, of (C10H15NO)2·H2SO4 in the portion of Capsule contents taken by the formula: in which C is the concentration, in µg per mL, of USP Ephedrine Sulfate RS in the Standard preparation, and AU and AS are the absorbances of the hexane extracts of the Assay preparation and the Standard preparation, respectively.