A: Shake a volume of Oral Solution,equivalent to about 5mg of methadone hydrochloride,with 5mLof sodium carbonate TS,and extract with 5mLof chloroform:the extract so obtained responds to the Thin-layer Chromatographic Identification Test á201ñ,a solvent mixture of alcohol,glacial acetic acid,and water (5:3:2)being used for development and iodoplatinate TSbeing used to visualize the spots.

B: It responds to the tests for Chloride á191ñ.

Add the following:

FOR ORAL SOLUTION PACKAGED IN SINGLE-UNIT CONTAINERS: meets the requirements.USP28

Add the following:

FOR ORAL SOLUTION PACKAGED IN MULTIPLE-UNIT CONTAINERS: meets the requirements.USP28

Mobile phase— Prepare a solution containing about 40volumes of acetonitrile and 60volumes of 0.033Mmonobasic potassium phosphate adjusted,dropwise,with phosphoric acid to a pHof 4.0.

Internal standard solution— Prepare a solution of pyrilamine maleate in water containing 250µg per mL.

Standard preparation— Transfer about 20mg of USP Methadone Hydrochloride RS,accurately weighed,to a 25-mLvolumetric flask,add 2.0mLof Internal standard solution,dilute with water to volume,and mix.

Assay preparation— Transfer an accurately measured volume of Oral Solution,equivalent to about 20mg of methadone hydrochloride,to a 125-mLseparator.Extract the specimen with two 50-mLportions of ether,collecting the ether extracts in a second separator.Wash the combined ether extracts with 2mLof water,and discard the ether extract.Transfer the aqueous wash and the aqueous specimen to a 25-mLvolumetric flask,add 2.0mLof Internal standard solution,dilute with water to volume,and mix.Pass the solution through a 5-µm filter.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm ×30-cm column that contains packing L11.The flow rate is about 1.3mLper 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%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph by means of a suitable microsyringe or sampling valve,record the chromatograms,and measure the responses for the major peaks.The relative retention times are about 5.5minutes for the internal standard and 9minutes for methadone hydrochloride.Calculate the quantity,in mg,of methadone hyrdrochloride (C21H27NO·HCl)in each mLof the Oral Solution taken by the formula: in which Cis the concentration,in mg per mL,of USP Methadone Hydrochloride RSin the Standard preparation;Vis the volume,in mL,of Oral Solution taken;and RUand RSare the peak response ratios of the internal standard and methadone hydrochloride peaks obtained from the Assay preparationand the Standard preparation,respectively.