A: Infrared Absorption 197F.

B: The retention time of the major peak in the chromatogram of the Test solution corresponds to that in the chromatogram of the System suitability solution, as obtained in the test for Limit of methamphetamine.

Test solution: 16 mg per mL, in 1.2 N hydrochloric acid.

Mobile phase— Prepare a filtered and degassed mixture of hexane, isopropyl alcohol, and acetonitrile (98:1.5:0.5). Make adjustments if necessary (see System Suitability under Chromatography 621).

Resolution solution— Mix suitable quantities of a solution of USP Methamphetamine Hydrochloride RS in chloroform and USP Levmetamfetamine RS in chloroform to obtain a solution containing about 0.025 mg per mL and 2.5 mg per mL of methamphetamine hydrochloride and levmetamfetamine, respectively. Transfer 2.0 mL of this solution to a suitable container, add 10 mg of 2-naphthyl chloroformate and 2.0 mL of chloroform, mix with a vortex mixer, and allow to stand for 5 minutes. To this solution, add 2 mL of 1 N sodium hydroxide, mix with a vortex mixer, allow to stand for 5 minutes, and discard the aqueous layer. Wash the organic layer twice with 2 mL of 1 N sodium hydroxide, discarding the aqueous layer. To the organic layer add 2 mL of 1 N hydrochloric acid, mix with a vortex mixer, and discard the aqueous layer. Wash the organic layer twice with 2 mL of 1 N hydrochloric acid, discarding the aqueous layer. To the organic layer add 2 mL of water, mix with a vortex mixer, and discard the aqueous layer. Wash the organic layer twice with 2 mL of water, discarding the aqueous layer. To the organic layer add about 1.0 g of anhydrous sodium sulfate, and mix with a vortex mixer. Transfer 1.0 mL of this solution to a 10-mL volumetric flask, dilute with Mobile phase to volume, mix, and filter.

Test solution— Transfer about 62.5 mg of Levmetamfetamine, accurately weighed, to a 25-mL volumetric flask, dissolve in and dilute with chloroform to volume, and mix. Transfer 2.0 mL of this solution to a suitable container, and proceed as directed in Resolution solution beginning with “add 10 mg of 2-naphthyl chloroformate and 2 mL of chloroform.”

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 274-nm detector and a 4.6-mm × 25-cm column that contains packing L36. The flow rate is about 1.5 mL per minute. Chromatograph the Resolution solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.9 for methamphetamine and 1.0 for levmetamfetamine; and the resolution, R, between methamphetamine and levmetamfetamine is not less than 1.4. Chromatograph the Test solution, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Inject a volume (about 50 µL) of the Test solution into the chromatograph, record the chromatogram, and measure the responses for the major peaks. Calculate the percentage of methamphetamine in the portion of Levmetamfetamine taken by the formula: in which rM is the methamphetamine peak response obtained from the Test solution, and rL is the peak response of levmetamfetamine obtained from the Test solution: not more than 0.1% is found.

Test solution: chloroform.

Standard solution: chloroform.

Eluant: a mixture of chloroform, cyclohexane, and diethylamine (5:4:1).

Visualization: 1.

Limits— No impurity exceeds 0.1%, and the total does not exceed 0.5%.