Identification—
Place a number of Suppositories, equivalent to 5 mg of oxymorphone hydrochloride, in a 125-mL separator. Add 25 mL of 0.1 N hydrochloric acid, and shake without heating until the specimen is dissolved. Wash the solution with five 25-mL portions of chloroform, shaking the separator gently to avoid forming emulsions, and discard the chloroform washings. Adjust with 6 N ammonium hydroxide to a pH of about 9.5, using short-range pH indicator paper, and extract with three 25-mL portions of chloroform, filtering the extracts through chloroform-moistened glass wool into a 200-mL round-bottom flask. Evaporate the combined extracts to dryness, using a rotary evaporator. Add 25 mL of 0.1 N hydrochloric acid, insert the stopper, and swirl to dissolve the residue: the UV absorption spectrum of the solution so obtained exhibits maxima and minima at the same wavelengths as that of a similar solution of
USP Oxymorphone RS, concomitantly measured.
Assay—
Mobile phase—
0.05 M Sodium borate adjusted to a pH of about 9.1.
Internal standard solution—
Prepare a solution of procaine hydrochloride in 0.01 N hydrochloric acid having a concentration of about 3 mg per mL.
Standard preparation—
Using an accurately weighed quantity of
USP Oxymorphone RS, prepare a solution in 0.01 N hydrochloric acid having a known concentration of about 4.5 mg per mL, sonicating, if necessary, to effect solution. Transfer 10.0 mL of this solution, 10.0 mL of the
Internal standard solution, and 5.0 mL of 0.01 N hydrochloric acid to a 125-mL separator. Extract with four 25-mL portions of chloroform, discarding the chloroform layer each time. Transfer the aqueous layer to a suitable flask, and bubble filtered air through the solution for 10 minutes to remove final traces of chloroform. The concentration of
USP Oxymorphone RS in the
Standard preparation is about 1.8 mg per mL.
Assay preparation—
Transfer a number of Suppositories, accurately counted and equivalent to about 50 mg of oxymorphone hydrochloride, to a 125-mL separator. Add 15.0 mL of 0.01 N hydrochloric acid, 10.0 mL of Internal standard solution, and 25 mL of chloroform. Shake until the suppositories dissolve. Discard the chloroform layer. Extract the aqueous layer with three 25-mL portions of chloroform, discarding the chloroform each time. Transfer the aqueous layer to a suitable flask and bubble filtered air through the solution for 10 minutes to remove final traces of chloroform.
Chromatographic system
(see
Chromatography 
621
)—The liquid chromatograph is equipped with a 254-nm detector and a 2.1-mm × 100-cm column that contains packing L12. The flow rate is about 1 mL per minute. Chromatograph five replicate injections of the
Standard preparation, and record the peak responses as directed for
Procedure: the relative standard deviation is not more than 2.0%, and the resolution factor between oxymorphone hydrochloride and procaine hydrochloride is not less than 1.5.
Procedure—
Separately inject equal volumes (about 15 µL) of the
Standard preparation and the
Assay preparation into the chromatograph by means of a suitable microsyringe or sampling valve, record the chromatograms, and measure the responses for the major peaks. The retention times are about 5 and 7.5 minutes for oxymorphone hydrochloride and procaine hydrochloride, respectively. Calculate the quantity, in mg, of C
17H
19NO
4·HCl in each Suppository taken by the formula:
(337.80 / 301.34)(25C/N)(RU / RS),
in which 337.80 and 301.34 are the molecular weights of oxymorphone hydrochloride and oxymorphone, respectively;
C is the concentration, in mg per mL, of
USP Oxymorphone RS in the
Standard preparation; N is the number of Suppositories taken; and
RU and
RS are the ratios of the peak responses of oxymorphone hydrochloride and procaine hydrochloride obtained from the
Assay preparation and the
Standard preparation, respectively.
