Mobile phase, Diluting solvent, System suitability preparation, and Chromatographic system— Prepare as directed in the Assay.

Ferric chloride solution— Transfer 4 mL of ferric chloride TS to a 100-mL volumetric flask, dilute with water to volume, and mix.

Identification solution— Dissolve 10 mg of naloxone in 100 mL of 0.1 N hydrochloric acid. Transfer 10.0 mL of this solution to a 100-mL volumetric flask, and add 0.5 mL of Ferric chloride solution. Heat on a steam bath for 10 minutes, cool, dilute with water to volume, and mix.

Standard solution— Transfer 2.0 mL of the Standard preparation prepared as directed in the Assay to a 100-mL volumetric flask, dilute with Diluting solvent to volume, and mix.

Test solution— Use the Assay preparation.

Procedure— Separately inject equal volumes (about 100 µL) of the Identification solution, the Standard solution, and the Test solution into the chromatograph, record the chromatograms, and measure the areas of the peak responses for naloxone and 2,2¢-bisnaloxone. The relative retention times are about 2.8 for the naloxone dimer and 1.0 for naloxone. Calculate the percentage of 2,2¢-bisnaloxone in the volume of Injection taken by the formula: in which L is the labeled quantity, in µg per mL, of naloxone hydrochloride (C19H21NO4·HCl) in the Injection taken, 363.84 and 327.38 are the molecular weights of anhydrous naloxone hydrochloride and naloxone, respectively, C is the concentration, in µg per mL, of USP Naloxone RS in the Standard solution, 1.8 is the ratio of UV absorptivity of 2,2¢-bisnaloxone to that of naloxone hydrochloride, Vb is the volume, in mL, of the Test solution, V is the volume, in mL, of Injection taken, rU is the peak response for 2,2¢-bisnaloxone obtained from the Test solution, and rS is the peak response for naloxone obtained from the Standard solution. Not more than 4.0% is found.

Mobile phase— Prepare a filtered and degassed mixture of 1.36 g of sodium 1-octanesulfonate, 1.0 g of sodium chloride, 580 mL of water, 420 mL of methanol, and 1.0 mL of phosphoric acid. Make adjustments if necessary (see System Suitability under Chromatography 621).

Diluting solvent— Transfer 150 mg of edetate disodium to a 2000-mL volumetric flask, and add 0.9 mL of hydrochloric acid. Dilute with water to volume, and mix.

Standard preparation— Dissolve an accurately weighed quantity of USP Naloxone RS in Diluting solvent, and dilute quantitatively, and stepwise if necessary, with Diluting solvent to obtain a solution having a known concentration of about 10 µg per mL.

Assay preparation 1 (for Injection labeled to contain not more than 100 µg of naloxone hydrochloride per mL)—Transfer an accurately measured volume of Injection, equivalent to about 100 µg of naloxone hydrochloride, to a 10-mL volumetric flask, add Diluting solvent to volume, and mix.

Assay preparation 2 (for Injection labeled to contain more than 100 µg of naloxone hydrochloride per mL)—Transfer an accurately measured volume of Injection, equivalent to about 2000 µg of naloxone hydrochloride, to a 200-mL volumetric flask, add Diluting solvent to volume, and mix.

System suitability preparation— Prepare a solution in Diluting solvent containing about 20 µg of USP Naloxone RS and about 2.5 µg of acetaminophen per mL.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 229-nm detector and a 4.6-mm × 25-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation (about 100 µL) and the System suitability preparation (about 20 µL), and record the peak responses as directed under Procedure: the resolution, R, between the acetaminophen and naloxone peaks is not less than 8, and the relative standard deviation for replicate injections of the Standard preparation is not more than 1.5%.

Procedure— [note—Use peak areas where peak responses are indicated.] Separately inject equal volumes (about 100 µL) of the Standard preparation and the appropriate Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are about 0.5 for acetaminophen and 1.0 for naloxone. Calculate the quantity, in µg, of C19H21NO4·HCl in each mL of the Injection taken by the formula: in which 363.84 and 327.38 are the molecular weights of anhydrous naloxone hydrochloride and naloxone, respectively; Va is the volume, in mL, of the Assay preparation; C is the concentration, in µg per mL, of USP Naloxone RS in the Standard preparation; V is the volume, in mL, of Injection taken; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.