A: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

B: Transfer 2 mL of Injection to a test tube, add 5 mL of 1 N hydrochloric acid and a few drops of ammonium reineckate TS: a red-violet precipitate is produced.

(Official January 1, 2007)

0.05 M Phosphate buffer— Dissolve 6.805 g of monobasic potassium phosphate in 1000 mL of water.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile and 0.05 M Phosphate buffer (65:35). Adjust with phosphoric acid to a pH of 4.7, and mix. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Levocarnitine RS in water to obtain a solution having a known concentration of about 10 mg per mL.

System suitability solution— Dissolve accurately weighed quantities of USP Levocarnitine RS and USP Levocarnitine Related Compound A RS in water to obtain a solution having concentrations of about 5.0 mg per mL and 0.024 mg per mL, respectively.

Assay preparation— Pool the contents of ten containers, and dilute an accurately measured volume of Injection quantitatively with water to obtain a solution having a concentration of about 10 mg of levocarnitine per mL.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 205-nm detector and a 3.9-mm × 30-cm column that contains packing L8. The flow rate is maintained at about 1 mL per minute. The system is programmed to provide variable mixtures of acetonitrile, Mobile phase, and water. Initially elute 50 mL of acetonitrile, then change the composition linearly over the next 20 minutes to a mixture of 65% acetonitrile and 35% water. Elute 100 mL of this mixture, then change the composition linearly over the following 20 minutes to 100% Mobile phase, and allow the chromatograph to proceed for about 3 hours. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the resolution, R, between levocarnitine related compound A and levocarnitine is not less than 1.0; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 5 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 levocarnitine (C7H15NO3) in the portion of Injection taken by the formula: in which C is the concentration, in mg per mL, of USP Levocarnitine RS in the Standard preparation; L is the labeled quantity, in mg, of levocarnitine in each container; D is the concentration, in mg per mL, of levocarnitine in the Assay preparation, based on the labeled quantity per container and the extent of dilution; and rU and rS are the levocarnitine peak responses obtained from the Assay preparation and the Standard preparation, respectively.