Test solution: 20 mg per mL, in water.

Standard solution and Standard dilutions— Dissolve a suitable quantity of USP Metoprolol Tartrate RS, accurately weighed, in methanol, and dilute quantitatively and stepwise with methanol to obtain solutions having known concentrations of 1.0, 0.5, 0.2, and 0.1 mg per mL, respectively.

Test solution— Dissolve a quantity of Metoprolol Tartrate in methanol to obtain a solution containing 100 mg per mL.

Chromatographic chamber— Line a suitable chamber (see Chromatography 621) with absorbent paper, and pour into the chamber 250 mL of a mixture of chloroform, methanol, and ammonium hydroxide (80:15:2). Saturate the chamber for 1.5 hours before using.

Detecting reagent— Prepare separate solutions of potassium iodide (1 in 100) and soluble starch (prepared by triturating 3 g in 10 mL of cold water and adding the mixture to 90 mL of boiling water with constant stirring). Just prior to use, mix 10 mL of each solution with 3 mL of alcohol.

Procedure— Apply separately 5-µL portions of the Test solution and each of the Standard dilutions to a suitable thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Place the plate in the Chromatographic chamber, seal the chamber, and allow the chromatogram to develop until the solvent front has moved about three-fourths of the length of the plate. Remove the plate, and dry in a current of warm air until the odor of ammonia is no longer perceptible (about 45 minutes). Place a beaker containing 0.5 g of potassium permanganate in a chamber. Add 5 mL of 6 N hydrochloric acid to the beaker, and allow to equilibrate for 5 minutes. Place the plate in the chamber for 5 minutes. Remove the plate from the chamber, allow to stand in a current of cool air for 1 hour, and spray with Detecting reagent. If spots other than the principal spot are observed in the lane of the Test solution, estimate the concentration of each by comparison with the Standard dilutions: the spots from the 1.0, 0.5, 0.2, and 0.1 mg per mL Standard dilutions correspond to 1.0%, 0.5%, 0.2%, and 0.1% of impurities, respectively; and the sum of any observed impurities in the Test solution is not greater than 1.0%.