A: Shake a volume of Oral Concentrate, equivalent to about 5 mg of methadone hydrochloride, with 5 mL of sodium carbonate TS, and extract with 5 mL of chloroform: the extract so obtained responds to the Thin-layer Chromatographic Identification Test 201, a solvent mixture of alcohol, glacial acetic acid, and water (5:3:2) being used for development and iodoplatinate TS being used to visualize the spots.

B: It responds to the tests for Chloride 191.

(Official January 1, 2007)

Mobile phase— Prepare a suitable mixture of 0.033 M monobasic potassium phosphate and acetonitrile (60:40), adjust with phosphoric acid to a pH of 4.0, filter, and degas. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Methadone Hydrochloride RS in Mobile phase to obtain a solution having a known concentration of about 0.4 mg per mL.

Assay preparation— Transfer an accurately measured volume of Oral Concentrate, equivalent to about 50 mg of methadone hydrochloride, to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix. Transfer 10.0 mL of this solution to a 25-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)—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 2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency determined from the analyte peak is not less than 1500 theoretical plates, the tailing factor for the analyte peak is not more than 2.0, and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of methadone hydrochloride (C21H27NO·HCl) in each mL of the Oral Concentrate taken by the formula: in which C is the concentration, in mg per mL, of USP Methadone Hydrochloride RS in the Standard preparation; V is the volume, in mL, of Oral Concentrate taken; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.