A: Transfer a quantity of finely powdered Tablets, equivalent to about 10 mg of amitriptyline hydrochloride, to a 100-mL volumetric flask, add 50 mL of methanol, shake well, then add methanol to volume. Filter a portion of this solution, and dilute 10 mL of the filtrate 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.

Medium: 0.1 N hydrochloric acid; 900 mL.

Apparatus 1: 100 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C20H23N·HCl dissolved from UV absorbances at the wavelength of maximum absorbance at about 239 nm on filtered portions of the solution under test, suitably diluted with Medium, if necessary, in comparison with a Standard solution having a known concentration of USP Amitriptyline Hydrochloride RS in the same Medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C20H23N·HCl is dissolved in 45 minutes.

Phosphate buffer, Mobile phase, and Chromatographic system— Prepare as directed in the Assay under Amitriptyline Hydrochloride Injection.

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

Assay preparation— Transfer 20 Tablets to a 500-mL volumetric flask, add 250 mL of Mobile phase, and shake the mixture for 1 hour or until the tablets have disintegrated. Add Mobile phase to volume, mix, and filter. Quantitatively dilute an accurately measured volume (VF mL) of the clear filtrate with Mobile phase to obtain a solution (VA mL) containing about 0.2 mg of amitriptyline hydrochloride per mL.

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 Tablet taken by the formula: in which C is the concentration, in mg per mL, of USP Amitriptyline Hydrochloride RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.