Standard preparation— Transfer about 45mg of USP Oxymorphone RS,accurately weighed,to a 50-mLvolumetric flask,dissolve in about 10mLof chloroform,dilute with chloroform to volume,and mix.Transfer 15.0mLof this solution to a 100-mLvolumetric flask,dilute with chloroform to volume,and mix.The concentration of USP Oxymorphone RSin the Standard preparationis about 135µg per mL.

Assay preparation— Transfer an accurately measured volume of Injection,equivalent to about 15mg of oxymorphone hydrochloride,to a 125-mLseparator,and add water,if necessary,to bring the volume to 15mL.Adjust by the addition of hydrochloric acid to a pHof less than 2,extract with five 15-mLportions of chloroform,and discard the chloroform extracts.Adjust the aqueous phase with ammonium hydroxide to a pHof 9.5,and extract with four 20-mLportions of chloroform.Filter the chloroform extracts through a chloroform-moistened pledget of cotton into a 100-mLvolumetric flask,dilute with chloroform to volume,and mix.

Procedure— Concomitantly determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 282nm,with a suitable spectrophotometer,using chloroform as the blank.Calculate the quantity,in mg,of C17H19NO4·HCl in each mLof the Injection taken by the formula: in which 337.80and 301.34are the molecular weights of oxymorphone hydrochloride and oxymorphone,respectively;Cis the concentration,in µg per mL,of USP Oxymorphone RSin the Standard preparation;Vis the volume,in mL,of Injection taken;and AUand ASare the absorbances of the Assay preparationand the Standard preparation,respectively.