Medium: water;900mL.

Apparatus 2: 50rpm.

Time: 60minutes.

0.05M Buffer solution— Dissolve 7.0g of monobasic sodium phosphate in 1Lof water.

Mobile phase— Prepare a mixture of 600mLof 0.05M Buffer solution,1.1g of sodium 1-octane sulfonate monohydrate and 400mLof methanol.Adjust with dilute sodium hydroxide to a pHof 6.7±0.05,if necessary,filter,and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

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 heated to 45.The flow rate is about 1mLper minute.Chromatograph replicate injections of the Standard solution,and record the peak responses as directed for Procedure:the relative standard deviation is not more than 2.0%.

Procedure— Inject a volume (about 100µL)of a filtered portion of the solution under test into the chromatograph,record the chromatogram,and measure the response for the major peak.Calculate the amount of C20H23NO4·HCl dissolved in comparison with a Standard solution having a known concentration of USP Naltrexone RSin the same Mediumand similarly chromatographed.

Tolerances— Not less than 80%(Q)of the labeled amount of C20H23NO4·HCl is dissolved in 60minutes.

Solution A,Solution B,Mobile phase,Resolution solution,Standard preparation,and Chromatographic system— Proceed as directed in the Assayunder Naltrexone Hydrochloride.

Assay preparation— Transfer not fewer than 20Tablets to a tared container,and determine the average Tablet weight.Grind the Tablets to a homogeneous mixture.Transfer an accurately weighed portion,equivalent to about 250mg of naltrexone hydrochloride,to a 100-mLvolumetric flask.Add about 80mLof 0.1Mphosphoric acid,and shake or sonicate for at least 30minutes.Dilute with 0.1Mphosphoric acid to volume,mix,and filter.

Procedure— Proceed as directed for Procedurein the Assayunder Naltrexone Hydrochloride.Calculate the quantity,in mg,of naltrexone hydrochloride (C20H23NO4·HCl)in the portion of Tablets taken by the formula: in which the terms are defined therein.