Standard solutions— Dissolve an accurately weighed quantity of USP Amoxapine RS in chloroform, and mix to obtain Standard preparation A having a known concentration of 0.50 mg per mL. Quantitatively dilute a portion of Standard solution A with chloroform to obtain Standard solution B having a known concentration of 0.25 mg per mL.

Test solution— Dissolve an accurately weighed quantity of Amoxapine in chloroform to obtain a solution containing 50 mg per mL.

Procedure— Separately apply 5 µL of the Test solution and each of the two Standard solutions to a suitable thin-layer chromatographic plate (see Chromatography 621), coated with a 0.2-mm layer of chromatographic silica gel mixture. Allow the spots to dry, and develop the chromatogram in a solvent system consisting of a mixture of chloroform, methanol, and ammonium hydroxide (18:2:0.1) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, air-dry, examine the plate under short-wavelength UV light, and compare the intensities of any secondary spots observed in the chromatogram of the Test solution with those of the principal spots in the chromatograms of the Standard solutions: no secondary spot from the chromatogram of the Test solution is larger or more intense than the principal spot obtained from Standard solution B (0.5%), and the sum of the intensities of the secondary spots obtained from the Test solution corresponds to not more than 1.0%.