Medium: water;500mL.

Apparatus 2: 50rpm.

Time: 45minutes.

Phosphate buffer-bromothymol blue solution— Dissolve 3.40g of monobasic sodium phosphate in about 50mLof water,add 18mLof 0.1Nsodium hydroxide,dilute with water to 500mL,and mix.Adjust the solution,if necessary,with 1Nsodium hydroxide or 1Nphosphoric acid (Buffer solution)to a pHof 5.8±0.1.Mix 31.2mg of bromothymol blue with 1.0mLof 0.1Nsodium hydroxide,add Buffer solutionto obtain 500mLof solution,and mix.

Standard solution— Dissolve an accurately weighed quantity of USP Hydrocodone Bitartrate RSin water,and dilute quantitatively,and stepwise if necessary,with water to obtain a solution having a known concentration of about 10µg per mL.

Test solution— Pipet into a 125-mLseparator a volume of a filtered portion of the solution under test that is estimated to contain about 0.4mg of hydrocodone bitartrate.Add 2drops of 6Nammonium hydroxide,and extract with three 25-mLportions of chloroform.Filter the extracts through about 3g of anhydrous sodium sulfate supported on filter paper,and combine the filtered extracts in a 100-mLvolumetric flask.Add chloroform through the filter to volume,and mix.

Procedure— Pipet 10mLof the Standard solutioninto a 125-mLseparator,and add 25.0mLof chloroform.Pipet 25mLof the Test solutioninto a second 125-mLseparator,and add 10.0mLof water.Pipet 25mLof chloroform and 10mLof water into a third 125-mLseparator to provide a blank.Treat each mixture as follows.Add 30mLof Phosphate buffer-bromothymol blue solution,and shake vigorously for not less than 15minutes.Allow the layers to separate,and pass the chloroform layer through filter paper,discarding the first 10mLof the filtrate.Determine the absorbances of the clear filtrates in 3-cm cells at the wavelength of maximum absorbance at about 415nm,using the solution from the blank to set the spectrometer.Calculate the amount of C18H21NO3·C4H6O6·2½H2Odissolved by the formula: in which 494.50and 449.46are the molecular weights of the hydrated and anhydrous forms of hydrocodone bitartrate,respectively;CSis the concentration,in µg per mL,of USP Hydrocodone Bitartrate RSin the Standard solution;VUis the volume of the filtered solution under test that is estimated to contain 0.4mg of hydrocodone bitartrate;and AUand ASare the absorbances of the solutions from the Test solutionand the Standard solution,respectively.

Tolerances— Not less than 75%(Q)of the labeled amount of C18H21NO3·C4H6O6·2½H2Ois dissolved in 45minutes.

Procedure for content uniformity— Transfer 1finely powdered Tablet to a 50-mLvolumetric flask,add 0.1Nsulfuric acid to volume,and mix.Filter if necessary,discarding the first 20mLof the filtrate.Concomitantly determine the absorbances of this solution and a solution of USP Hydrocodone Bitartrate RSin the same medium,having a known concentration of about 100µg per mL,in 1-cm cells at the wavelength of maximum absorbance at about 280nm,with a suitable spectrophotometer,using 0.1Nsulfuric acid as the blank.Calculate the quantity,in mg,of C18H21NO3·C4H6O6·2½H2Oin the Tablet taken by the formula: in which 494.49and 449.46are the molecular weights of the hydrated and anhydrous forms of hydrocodone bitartrate,respectively;Tis the labeled quantity,in mg,of hydrocodone bitartrate in the Tablet;Cis the concentration,in µg per mL,of USP Hydrocodone Bitartrate RSin the Standard solution;Dis the concentration,in µg per mL,of the solution from the Tablet,based upon the labeled quantity per Tablet and the extent of dilution;and AUand ASare the absorbances of the solution from the Tablet and the Standard solution,respectively.