Test specimen— Dissolve about 150mg in 25mLof water in a small separator,add a few drops of 6Nammonium hydroxide slowly until no more white precipitate is formed.Extract with three 5-mLportions of chloroform,filter the extracts through a dry filter,collecting the filtrate in a small flask.Evaporate the filtrate on a steam bath to dryness,and dry the residue at 105for one hour.

Test solution: 25mg per mL,in water.

Internal standard stock solution— Prepare a solution of isopropyl alcohol,which has been tested and found to be free of methanol and alcohol,having a concentration of about 0.12mg per mL.

Internal standard solution— Transfer 5.0mLof theInternal standard stock solution to a 100-mLvolumetric flask,dilute with water to volume,and mix.

Standard solution— Transfer 2.0mLof anhydrous methanol and 2.0mLof alcohol to a 100-mLvolumetric flask,dilute with water to volume,and mix.Transfer 3.0mLof this solution and 5.0mLofInternal standard stock solution to a 100-mLvolumetric flask,dilute with water to volume,and mix.

Test solution— Transfer about 75mg of Naltrexone Hydrochloride,accurately weighed,to a suitable container,add 5.0mLofInternal standard solution,and shake to dissolve.

Chromatographic system(see Chromatography á621ñ)— The gas chromatograph is equipped with a flame-ionization detector and a 4-mm ×1.8-m glass column packed with 80-to 100-mesh support S3.The column temperature is maintained at 150,and the injection port and detector temperature are maintained at 170.Chromatograph theStandard solution,and record the peak responses as directed forProcedure:the relative retention times are about 0.24for methanol,0.53for alcohol,and 1.0for isopropyl alcohol.

Procedure— Separately inject equal volumes (about 5µL)of theStandard solution and theTest solution into the gas chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the percentages of methanol and alcohol in the portion of Naltrexone Hydrochloride taken by the formula: in whichWis the weight,in mg,of Naltrexone Hydrochloride in theTest solution;andRUandRSare the peak response ratios of methanol or alcohol to isopropyl alcohol obtained from theTest solution and theStandard solution,respectively.To these added percentages,add the percentage of water determined in the test forWater:the sum of water and alcoholic solvents is not more than 5.0%for the anhydrous form and not more than 11.0%for the dihydrate form.

10F(C/W)(rU/rS),

Solution A— Dissolve about 1.08g of sodium 1-octanesulfonate and about 23.8g of sodium acetate in 800mLof water.Add 1.0mLof triethylamine and 200mLof methanol,and mix.Adjust with glacial acetic acid to a pHof 6.5±0.1.Filter and degas prior to use.

Solution B— Dissolve about 1.08g sodium 1-octanesulfonate and about 23.8g sodium acetate in 400mLof water.Add 1.0mLtriethylamine and 600mLof methanol,and mix.Adjust with glacial acetic acid to a pHof 6.5±0.1.Filter and degas prior to use.

Mobile phase— Use variable mixtures ofSolution AandSolution Bas directed forChromatographic system.

Standard preparation— Transfer an accurately weighed quantity of about 22.5mg of USP Naltrexone RSto a 10-mLvolumetric flask.Add 1.5mLof methanol and 0.6mLof 0.1Nhydrochloric acid.Dissolve by swirling the flask,and dilute with 0.1Mphosphoric acid to volume.

Resolution solution— Transfer about 3.0mg,accurately weighed,of USP Naltrexone Related Compound A RSto a 10-mLvolumetric flask.Add 3.0mLof methanol,and dissolve by swirling.Dilute with 0.1Mphosphoric acid to volume,and mix.Transfer 0.5mLof this solution to a 10-mLvolumetric flask,add 5.0mLofStandard preparation,dilute with 0.1Mphosphoric acid to volume,and mix.

Assay preparation— Transfer an accurately weighed quantity of about 25mg of Naltrexone Hydrochloride to a 10-mLvolumetric flask.Dissolve in and dilute with 0.1Mphosphoric acid to volume,and mix.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 280-nm detector and a 3.9-mm ×15-cm column that contains packing L1and is programmed to provide,at a flow rate of about 1mLper minute,a variable mixture ofSolution AandSolution B.At the time the specimen is injected into the chromatograph,the percentage ofSolution Ais 100%;over the next 35minutes,the proportion ofSolution Bis increased linearly to 100%,and then over the next minute,decreased linearly to 100%ofSolution A.Allow the system to equilibrate until the late eluting peak has been observed,approximately 17minutes later.Chromatograph about 20µLof theResolution solution,and record the peak responses as directed underProcedure:the relative retention times are about 0.55for noroxymorphone,0.70for 10-hydroxynaltrexone,1.0for naltrexone,1.26for naltrexone related compound A,1.80for 2,2¢-bisnaltrexone,and 1.99for 10-ketonaltrexone;the resolution,R,between naltrexone and naltrexone related compound Ais not less than 2.0;the tailing factor for the naltrexone peak is not greater than 1.4;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20µL)of theStandard preparation andAssay preparation into the chromatograph,record the chromatograms,and measure the responses for all the peaks.Calculate the quantity,in mg,of C20H23NO4·HCl in the portion of Naltrexone Hydrochloride taken by the formula: in which 377.86and 341.41are the molecular weights of naltrexone hydrochloride and naltrexone,respectively;Cis the concentration,in mg per mL,of USP Naltrexone RSin theStandard preparation,andrUandrSare the peak responses of naltrexone obtained from theAssay preparation and theStandard preparation,respectively.