Test solution: 50 mg per mL, in 1 N hydrochloric acid.

Adsorbent: 0.25-mm layer of chromatographic silica gel mixture.

Diluted ammonia solution— Transfer 16 mL of concentrated ammonia to a 100-mL volumetric flask, and dilute with water to volume.

Test solution— Transfer about 0.1 g of Tyrosine, accurately weighed, to a 10-mL volumetric flask, dissolve in Diluted ammonia solution, and dilute with water to volume. Apply 5 µL.

Standard solution— In a suitable flask, dissolve an accurately weighed quantity of USP l-Tyrosine RS in 1 mL of Diluted ammonia solution, and dilute with water to volume to obtain a solution having a known concentration of about 0.05 mg per mL. Apply 5 µL. [note—This solution has a concentration equivalent to about 0.5% of that of the Test solution.]

System suitability solution— Dissolve about 10 mg of USP l-Tyrosine RS and about 10 mg of USP l-Phenylalanine RS in 1 mL of Diluted ammonia solution, dilute with water to 25.0 mL, and mix. Apply 5 µL.

Spray reagent— Dissolve 0.2 g of ninhydrin in 100 mL of a mixture of butyl alcohol and 2 N acetic acid (95:5).

Developing solvent system— Prepare a mixture of isopropyl alcohol and ammonium hydroxide (70:30).

Procedure— Proceed as directed for Thin-Layer Chromatography under Chromatography 621. Dry the plate between 100 and 105 until the ammonia disappears completely. Spray with Spray reagent, and heat between 100 and 105 for about 15 minutes. Examine the plate under white light. The chromatogram obtained from the System suitability solution exhibits two clearly separated spots. Any secondary spot in the chromatogram obtained from the Test solution is not larger or more intense than the principal spot in the chromatogram obtained from the Standard solution: not more than 0.5% of any individual impurity is found; and not more than 2.0% of total impurities is found.