A: Pipet 1 mL of Injection into a 125-mL separator containing 10 mL of water and 1 mL of 1 N sodium hydroxide, mix, extract with two 10-mL portions of methylene chloride, and evaporate the extracts on a steam bath just to dryness. Dissolve the residue in methanol, add 1 mL of 1.2 N hydrochloric acid, then add methanol to make 100 mL. Dilute 10 mL of this solution with methanol to 100 mL: the UV absorption spectrum of this solution exhibits a maximum at the same wavelength as that of a similar solution of USP Amitriptyline Hydrochloride RS, concomitantly measured.

B: 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.

C: Pipet a volume of Injection, equivalent to 50 mg of amitriptyline hydrochloride, into a separator containing 25 mL of water. Proceed as directed in the test for Identification—Organic Nitrogenous Bases 181, beginning with “In a second separator,” and using water in place of 0.01 N hydrochloric acid in the Reference Standard solution: the solution of the test specimen so obtained meets the requirements of the test for Identification—Organic Nitrogenous Bases 181.

Phosphate buffer— Dissolve 11.04 g of monobasic sodium phosphate in 900 mL of water, adjust with phosphoric acid to a pH of 2.5 ± 0.5, dilute with water to make 1000 mL, and mix.

Mobile phase— Prepare a filtered and degassed mixture of Phosphate buffer and acetonitrile (58:42). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Amitriptyline Hydrochloride RS in water, and dilute quantitatively with water to obtain a solution having a known concentration of about 0.2 mg per mL.

Assay preparation— Transfer an accurately measured volume of Injection, equivalent to about 50 mg of amitriptyline hydrochloride, to a 250-mL volumetric flask, dilute with water to volume, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4-mm × 30-cm column that contains packing L1. The flow rate is about 2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the tailing factor is not more than 2.0, the column efficiency is not less than 800 theoretical plates, and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20 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 amitriptyline hydrochloride (C20H23N·HCl) in each mL of the Injection taken by the formula: in which C is the concentration, in mg per mL, of USP Amitriptyline Hydrochloride 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.