A: Digest a quantity of finely powdered Tablets, equivalent to about 50 mg of codeine sulfate, with 15 mL of water and 5 mL of 2 N sulfuric acid for 1 hour. Filter, if necessary, and wash any undissolved residue with a few mL of water. Render the filtrate alkaline with 6 N ammonium hydroxide, extract with several small portions of chloroform, and evaporate the chloroform solution on a steam bath to dryness: the resulting residue of codeine responds to Identification test A under Codeine.

B: A filtered solution of Tablets responds to the tests for Sulfate 191.

Medium: water; 500 mL.

Apparatus 1: 100 rpm.

Time: 45 minutes.

Procedure— Determine the amount of (C18H21NO3)2·H2SO4·3H2O dissolved from UV absorbances at the wavelength of maximum absorbance at about 284 nm on filtered portions of the solution under test, suitably diluted with water, if necessary, in comparison with a Standard solution having a known concentration of USP Codeine Sulfate RS in the same Medium.

Tolerances— Not less than 75% (Q) of the labeled amount of (C18H21NO3)2·H2SO4·3H2O is dissolved in 45 minutes.

Procedure for content uniformity— Transfer 1 Tablet to a 50-mL volumetric flask. Add 20 mL of 0.5 N sulfuric acid and 10 mL of water, shake until the Tablet is disintegrated, and allow to stand for 16 hours. Dilute with water to volume, and filter, discarding the first few mL of the filtrate. Dilute a portion of the subsequent filtrate quantitatively and stepwise, if necessary, with 0.2 N sulfuric acid to obtain a solution containing approximately 120 µg of codeine sulfate (trihydrate) per mL. Concomitantly determine the absorbances of this solution and a Standard solution of USP Codeine Sulfate RS in the same medium having a known concentration of about 110 µg per mL, in 1-cm cells, at the wavelength of maximum absorbance at about 284 nm, with a suitable spectrophotometer, using 0.2 N sulfuric acid as the blank. Calculate the quantity, in mg, of (C18H21NO3)2·H2SO4·3H2O in the Tablet taken by the formula: in which 750.87 and 696.82 are the molecular weights of codeine sulfate trihydrate and anhydrous codeine sulfate, respectively; T is the labeled quantity, in mg, of codeine sulfate in the Tablet; C is the concentration, in µg per mL, of USP Codeine Sulfate RS in the Standard solution; D is the concentration, in µg per mL, of codeine sulfate in the test solution, based upon the labeled quantity per Tablet and the extent of dilution; and AU and AS are the absorbances of the test solution and the Standard solution, respectively.