Medium: simulated gastric fluid (without enzyme); 900 mL.

Apparatus 2: 50 rpm.

Time: 30 minutes.

Procedure— Determine the amount of C17H16ClN3O dissolved from UV absorbances at the wavelength of maximum absorbance at about 294 nm of 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 Amoxapine RS in the same Medium.

Tolerances— Not less than 80% (Q) of the labeled amount of C17H16ClN3O is dissolved in 30 minutes.

(Official January 1, 2007)

0.01 M Monobasic sodium phosphate— Dissolve 2.76 g of monobasic sodium phosphate in 2000 mL of water, and mix.

1 M Tetramethylammonium chloride— Dissolve 11.3 g of tetramethylammonium chloride in 100 mL of water, and mix.

Mobile phase— Transfer 40.0 mL of 1 M Tetramethylammonium chloride, 4.0 mL of dilute phosphoric acid (1 in 5), and 720 mL of acetonitrile to a 2000-mL volumetric flask. Dilute with 0.01 M Monobasic sodium phosphate to volume, mix, and filter. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Transfer about 50 mg of USP Amoxapine RS, accurately weighed, to a 50-mL volumetric flask, add 30 mL of acetonitrile, and shake by mechanical means to dissolve. Dilute with acetonitrile to volume, and mix. Quantitatively dilute a portion of this solution with Mobile phase to obtain a solution having a known concentration of about 0.1 mg per mL.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 50 mg of amoxapine, to a 50-mL volumetric flask, add 40 mL of Mobile phase, and shake vigorously by mechanical means for 20 minutes. Dilute with Mobile phase to volume, mix, and filter. Pipet 5.0 mL of the filtrate into a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 25-cm column that contains packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the tailing factor for the analyte peak is not more than 1.8, the column efficiency determined from the analyte peak is not less than 1200 theoretical plates, and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the quantity, in mg, of amoxapine (C17 H16ClN3O) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Amoxapine RS in the Standard preparation; and rU and rS are the amoxapine peak areas obtained from the Assay preparation and the Standard preparation, respectively.